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NBME Micro > Microbiology: Clinial Bacteriology > Flashcards

Microbiology: Clinial Bacteriology Flashcards

1
Q

How would you differentiate Pseudomonas from other nonlactose fermenters?

A

It is oxidase positive, other nonlactose fermenters are oxidase ⊖

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2
Q

What differentiates Q fever from the diseases of the Rickettsia genus, to which it is closely related?

A

Coxiella burnetii, the causative agent of Q fever, can survive outside in endospore form; there is no rash or vector

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3
Q

What 2 mycobacterial species are usually resistant to multiple drugs?

A

M tuberculosis and M avium–intracellulare

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4
Q

A patient has a Haemophilus infection. By what route was it likely acquired?

A

Respiratory tract

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5
Q

A young woman presents with nonpainful, gray vaginal discharge. You suspect Gardnerella. What outcome do you expect on an amine whiff test?

A

A strong fishy odor; mixing the discharge with 10% potassium hydroxide (KOH) solution in an amine whiff test for G vaginalis enhances its odor

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6
Q

Antibodies to which virulent component of Streptococcus pyogenes can give rise to rheumatic fever?

A

M protein (antibodies enhance host defense, but can give rise to rheumatic fever)

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7
Q

What cutaneous manifestations are likely if a patient has a history of syphilis?

A

A maculopapular rash on palms and soles, condylomata lata (smooth, painless, wart-like lesions on genitalia), and patchy hair loss (features of secondary syphilis)

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8
Q

What 2 outcomes could be expected after a primary tuberculosis infection?

A

90%: recovery (fibrous healing/calcification, PPD test ⊕); <10%: progressive primary TB (seen in patients with AIDS or malnutrition)

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9
Q

What organism is the 2nd most common cause of uncomplicated urinary tract infection (UTI) in young women?

A

Staphylococcus saprophyticus

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10
Q

What vaccinations could have prevented a 12-year-old boy’s infection with a gram ⊖ aerobic coccobacillus?

A

The Tdap or DTaP vaccines would have protected against Bordetella pertussis infection

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11
Q

What are the virulence factors produced by Pseudomonas aeruginosa?

A

Phospholipase C; Endotoxin; Exotoxin A; Pigments: pyoverdine and pyocyanin (blue-green pigment; generates reactive oxygen species); produces PEEP

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12
Q

You visualize a spirochete using light microscopy with an aniline dye (Wright or Giemsa stain). What is it?

A

Borrelia (Borrelia is Big); due to size, this is the only spirochete visible on light microscopy

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13
Q

What type of hemolysis is induced by Enterococcus species?

A

Enterococcus species exhibit variable hemolysis

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14
Q

Is a VDRL test better for screening or confirmation of syphilis?

A

Screening; VDRL is considered sensitive but not specific; often used for initial screening and is widely available

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15
Q

Name an aerobic, gram ⊕, acid-fast branching filament.

A

Nocardia

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16
Q

What pyogenic illnesses are caused by Streptococcus pyogenes?

A

Pharyngitis, erysipelas, impetigo (“honey-crusted” lesions), cellulitis

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17
Q

What types of bacteria grow pink colonies on MacConkey agar?

A

Lactose-fermenting enteric: Citrobacter, Klebsiella, E coli, Enterobacter, Serratia (Lactose is key; test with MacConKEE’S agar)

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18
Q

What immunologic diseases result from Streptococcus pyogenes pharyngitis?

A

Rheumatic fever, glomerulonephritis (“Phyogenes pharyngitis can result in rheumatic “phever” and glomerulonephritis)

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19
Q

Reptiles and poultry are the animal hosts of what pathogen that causes a diarrheal illness?

A

Salmonella spp (exception: S typhi)

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20
Q

How is Campylobacter jejuni transmitted?

A

Fecal-oral transmission (eg, pet feces, contaminated food, contact with hands of infected persons)

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21
Q

What do patients with Salmonella and Shigella have in common with their clinical presentation?

A

Both Salmonella and Shigella often cause bloody diarrhea (note that S typhi diarrhea is often preceded by constipation)

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22
Q

What are the symptoms of Q fever?

A

Headache, cough, flu-like symptoms, pneumonia, possibly with hepatitis; may also present as culture ⊖ endocarditis

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23
Q

A patient is diagnosed with bacterial vaginosis secondary to Gardnerella vaginalis. What do you expect to see on wet prep?

A

Clue cells or vaginal epithelial cells covered with bacteria (stippled appearance along outer margins)

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24
Q

How would a patient with Weil disease (icterohemorrhagic leptospirosis) present?

A

Severe form of leptospirosis that presents with elevated bilirubin and creatinine levels, fever, hemorrhage, and low hemoglobin level

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25
Q

Which form of leprosy presents with intact T-cell response (cell-mediated immunity) and only a few hypoesthetic, hairless skin nodules?

A

Tuberculoid leprosy

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26
Q

In a patient with Mycoplasma pneumoniae, why are you unable to observe bacteria on a Gram stain?

A

M pneumoniae lack cell walls, so are not seen on a Gram stain

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27
Q

Pseudomonas aeruginosa exotoxin A shares a mechanism with which pseudomembrane-forming pathogen?

A

Pseudomonas aeruginosa’s exotoxin A and Corynebacterium diphtheriae’s diphtheria toxin both inhibit EF-2

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28
Q

Which optochin-resistant bacteria, part of the normal oropharyngeal flora, cause dental caries?

A

Streptococcus mutans and Streptococcus mitis; Viridans group strep live in the mouth; they are not afraid of-the-chin (op-to-chin resistant)

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29
Q

A woman has a positive VDRL test, but she is negative for syphilis on FTA-ABS testing. Which conditions can result in a false positive VDRL test?

A

False-Positive VDRL results due to Pregnancy, Viral infection (eg, EBV, hepatitis), Drugs, Rheumatic fever, Lupus or leprosy

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30
Q

What are the virulence factors of Shigella species?

A

Endotoxin; Shiga toxin (enterotoxin). Organisms that produce little toxin can cause disease by M cell invasion (key to pathogenicity)

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31
Q

A patient is diagnosed with peptic ulcer disease secondary to infection with Helicobacter pylori. The organism is found to be resistant to macrolides. Treatment?

A

Bismuth-based quadruple therapy

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32
Q

What 3 possible colors do colonies of lactose-fermenting bacteria exhibit on EMB agar?

A

Purple and black; E coli grows with a green sheen

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33
Q

What 2 risk factors are associated with staphylococcal toxic shock syndrome?

A

Prolonged use of vaginal tampons or nasal packing

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34
Q

A patient is told that she has traveler’s diarrhea. What type of diarrhea does it cause?

A

Watery diarrhea

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35
Q

You are told that a patient has diarrhea from an enteropathogenic Escherichia coli (EPEC) infection. What population typically gets this type of infection?

A

Children (EPEC = Pediatrics)

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36
Q

You culture 2 different α-hemolytic species. What might catalase and optochin sensitivity testing reveal?

A

Streptococcus pneumoniae is optochin sensitive, viridans streptococci are resistant; all are catalase ⊖

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37
Q

What are the key signs and symptoms of Lyme disease? (Hint: Lyme [lime] pie to the FACE)

A

Facial nerve palsy (usually bilateral), Arthritis, Cardiac block, Erythema migrans

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38
Q

A 30-year-old man has a Clostridium difficile infection. What cellular changes are caused by toxin B (cytotoxin) in his gut?

A

Destruction of cytoskeletal organization by means of actin depolymerization; causes pseudomembranous colitis and diarrhea

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39
Q

Where, geographically, are Chlamydia trachomatis serotypes A, B, and C found, and what diseases do they cause?

A

Africa; cause Blindness and result in Chronic infection; (ABC)

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40
Q

Of α-hemolytic cocci, which are bile soluble and insoluble?

A

Streptococcus pneumoniae is bile soluble; viridans streptococci are bile insoluble

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41
Q

How can the leukocyte differential help you determine if a patient’s bloody diarrhea is due to a Salmonella or Shigella species?

A

Both Salmonella and Shigella primarily have a PMN response, but S typhi has a monocytic response

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42
Q

Name the toxins produced by Staphylococcus aureus and their associated effects.

A

TSST-1 causes toxic shock syndrome; exfoliative toxin causes scalded skin syndrome; enterotoxin causes rapid-onset food poisoning

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43
Q

What characteristic finding can you see while examining L monocytogenes under the microscope in broth?

A

Tumbling motility (L monocytogenes is also the only gram-positive organism that produces lipopolysaccharide)

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44
Q

What 2 characteristics differentiate Actinomyces from Nocardia?

A

Actinomyces are anaerobes and acid fast ⊖; Nocardia are weakly acid-fast aerobes. Both are gram ⊕ and form long, branching filaments resembling fungi

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45
Q

A boy is bitten by a human body louse and develops a rash that spreads from his trunk outward. Will it reach his palms and soles?

A

No; this is epidemic typhus, which spares the palms and soles (think Typhus on the Trunk), caused by Rickettsia prowazekii

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46
Q

How are Chlamydophila pneumoniae and C psittaci transmitted?

A

Aerosol transmission

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47
Q

A boy with a new pet turtle has gastroenteritis and bloody diarrhea. What is the most likely cause, and what are possible sources?

A

Salmonella spp; eggs, poultry, turtles (reptiles), and other pets are sources

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48
Q

Which 2 chlamydial species cause atypical pneumonia?

A

Chlamydophila pneumoniae and C psittaci

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49
Q

In a patient with peptic ulcers caused by Helicobacter pylori, how are the bacteria able to thrive in the stomach?

A

These organisms create an alkaline environment from the ammonia produced by urease

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50
Q

In a nonimmune host (eg, a child), what kind of infection occurs after exposure to M tuberculosis?

A

Primary tuberculosis

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51
Q

During its life cycle, which form of chlamydia replicates by fission in the cell?

A

The Reticulate body Replicates by means of fission and Reorganizes into elementary bodies

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52
Q

Name 3 types of infections caused by nontypeable strains of Haemophilus influenzae.

A

Otitis media, conjunctivitis, and bronchitis (all mucosal infections)

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53
Q

Name the common treatment for the following conditions: focal dystonia, achalasia, and muscle spasm.

A

Local botulinum toxin injections

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54
Q

Name 4 Clostridium species that produce exotoxins.

A

Clostridium perfringens, C botulinum, C tetani, and C difficile

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55
Q

What drugs are used to treat a patient with leprosy, low bacterial load, and a largely Th1-type immune response?

A

Dapsone and rifampin (diagnosis: tuberculoid leprosy)

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56
Q

Describe the gram staining, hemolysis, and unique antibiotic resistance pattern(s) of viridans group streptococci.

A

Gram ⊕, α-hemolytic cocci, resistant to optochin (unlike S pneumoniae)

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57
Q

Where do Pasteurella infections often originate from?

A

Various animals via bites, particularly dogs and cats

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58
Q

A 10-year-old boy who is not up to date on vaccinations presents with low-grade fevers and coryza. What clinical symptoms do you expect next?

A

Intense coughing followed by inspiratory “whoop” and vomiting (paroxysmal stage); diagnosis: Bordetella pertussis

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59
Q

Compare and contrast the infectivity of Salmonella and Shigella. Hint: ID50.

A

Salmonella’s is low (large inoculum needed due to high ID50; bug is inactivated by gastric acid); Shigella’s is high (due to low ID50; resistant to gastric acid)

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60
Q

In the lab, you grow normal skin bacteria that are Gram ⊕, catalase ⊕, coagulase ⊖, urease ⊕ cocci in clusters, sensitive to novobiocin. What organism was isolated?

A

Staphylococcus epidermidis

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61
Q

What 3 clinical conditions usually follow Neisseria meningitidis infection?

A

Meningococcemia, meningitis, and Waterhouse-Friderichsen syndrome

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62
Q

What 3 spirochete species most commonly infect humans?

A

Borrelia, Leptospira, and Treponema (BLT)

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63
Q

Which Mycobacterium species presents with hand infection, and how is it acquired?

A

Mycobacterium marinum; acquired through aquatic exposure, likely through aquarium handling

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64
Q

You perform a Gram stain on Listeria in the lab. What are your results?

A

Listeria is a gram ⊕ rod

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65
Q

Does Staphylococcus epidermidis ferment mannitol?

A

No; S epidermidis cannot ferment mannitol (unlike S aureus)

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66
Q

Which serotype of Haemophilus influenzae causes the most invasive disease?

A

Capsular type B

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67
Q

What organism is the likely pathogen if osteomyelitis develops following a puncture wound, especially in patients with diabetes?

A

Pseudomonas aeruginosa (a common cause of osteomyelitis after a puncture wound)

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68
Q

A young woman presents with a urinary tract infection caused by Enterococcus faecalis. What antibiotic are these bacteria normally resistant to?

A

Penicillin G

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69
Q

What are the various treatment options for Pseudomonas aeruginosa infection? (Hint: CAMPFIRE)

A

Carbapenems, Aminoglycosides, Monobactams, Polymyxins, Fluoroquinolones, thIRd/fourth-generation cephalosporins, Extended-spectrum penicillins

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70
Q

What are spirochetes?

A

Spiral-shaped bacteria with axial filaments

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71
Q

A patient contracts an infection by gram ⊕ bacteria that are notably resistant to vancomycin therapy. Most likely causative organism?

A

Vancomycin-resistant enterococci (VRE), a major cause of nosocomial infections

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72
Q

Tabes dorsalis with general paresis may present in which stage of syphilis?

A

Tertiary syphilis; this is neurosyphilis

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73
Q

Your patient has recurring Clostridium difficile infections. What treatment would you recommend that could prevent relapse?

A

Repeat courses of metronidazole, oral vancomycin, or fidaxomicin; for refractory cases, a fecal transplant can be performed

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74
Q

A 7-year-old boy eats an undercooked hamburger and then experiences diarrhea and oliguria. What lab abnormalities do you see?

A

Low RBC/platelet counts (schistocytes on blood smear), acute kidney injury; diagnosis: Hemolytic-uremic syndrome due to enteroHemorrhagic Escherichia coli (EHEC) from Hamburgers

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75
Q

Typically, what part of the body does the gram ⊕ cocci Streptococcus bovis colonize?

A

The Gut

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76
Q

What animal reservoirs are the source of disease in those afflicted with plague?

A

Rats and prairie dogs; transmit Yersinia pestis

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77
Q

A 26-year-old woman has vaginosis caused by Gardnerella vaginalis. What kind of vaginal discharge will you note on physical exam?

A

Gray discharge with a fishy odor

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78
Q

A complication caused by lipopolysaccharide (LPS) endotoxin develops in a man with Escherichia coli infection. What complication is it?

A

Septic Shock

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79
Q

In the lab, gram ⊕ bacteria form “medusa head” colonies. What is the capsule made of?

A

Bacillus anthracis synthesizes a polypeptide capsule (contains poly D-glutamate)

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80
Q

A 75-year-old smoker has mild flu-like symptoms. Labs show hyponatremia. The antigen of the causative bacteria is detected in the urine. Treatment?

A

Macrolides or quinolones. Diagnosis: likely Pontiac fever caused by L pneumophila

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81
Q

What structural changes might result from local tissue destruction by secondary tuberculosis?

A

Cavitation, caseation, and scar formation

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82
Q

A patient with trismus, risus sardonicus, and opisthotonos comes to your office. He asks, “What could I have done to prevent this?”

A

Received a tetanus vaccine

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83
Q

A patient is bitten by a louse and subsequently develops recurring fevers. What bacterium is likely responsible?

A

Borrelia recurrentis (B recurrentis: relapsing fever)

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84
Q

Name 7 common sites of extrapulmonary tuberculosis.

A

Meninges, lymph nodes, liver, spleen, adrenal glands, joints/long bones, vertebral bodies

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85
Q

Why does infection with Yersinia enterocolitica often present in a manner similar to Crohn disease or appendicitis?

A

The bacterium causes mesenteric adenitis and/or terminal ileitis, producing right lower quadrant abdominal pain

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86
Q

What type of Pseudomonas toxin produces symptoms of sepsis?

A

Endotoxin

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87
Q

What organism causes Hansen disease?

A

Also known as leprosy, it is caused by Mycobacterium leprae, an acid-fast bacillus

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88
Q

A patient with Helicobacter pylori has an ↑ risk for which 2 cancers?

A

Gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma

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89
Q

What population groups are at risk of Legionella pneumophila infection?

A

Smokers, patients with chronic lung disease, and people using old air conditioning systems

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90
Q

How is the screening sample to test for group B streptococci collected in a pregnant woman?

A

Rectal and vaginal swabs

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91
Q

How would you treat a patient with profuse rice-water diarrhea caused by gram ⊖ flagellated bacteria?

A

Prompt oral rehydration therapy (this is Vibrio cholerae)

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92
Q

Which organism may be either α-hemolytic or γ-hemolytic?

A

Enterococcus

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93
Q

A urine culture from a 20-year-old sexually active woman is growing a catalase ⊕ organism. Diagnosis?

A

Staphylococcus saprophyticus (common cause of urinary tract infections in sexually active women)

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94
Q

A woman is 37 weeks pregnant with positive cultures for Streptococcus agalactiae. What medication should be used as prophylaxis?

A

Prophylactic intrapartum penicillin administration for Streptococcus agalactiae infection

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95
Q

Neisseria diplococci are isolated from a patient experiencing a severe inflammatory response. What virulence factor is causing these symptoms?

A

Lipooligosaccharides, which have potent endotoxin activity

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96
Q

What are the reservoirs for Shigella and Salmonella?

A

All strains of Salmonella except S typhi have animal reservoirs; humans are the only reservoirs for S typhi and Shigella

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97
Q

Describe the appearance of α, β, and γ hemolysis on agar.

A

α: partial (green); β: complete (clear); γ: absent

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98
Q

Your culture of gram ⊕, catalase ⊖ cocci exhibits no hemolysis. How will you further identify the species?

A

Nonenterococci species (eg, Streptococcus bovis) cannot grow in 6.5% NaCl; enterococci (Enterococcus faecium and Enterococcus faecalis) can grow in 6.5% NaCl

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99
Q

What vaccination options are available to prevent Salmonella typhi infection?

A

Oral vaccine with live S typhi or an intramuscular vaccine with Vi capsular polysaccharide

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100
Q

A patient has an enterococcal biliary tract infection. What lab test can differentiate these bacteria from nonenterococcal group D bacteria?

A

Enterococci grow in 6.5% sodium chloride and bile; nonenterococcal group D bacteria cannot

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101
Q

Many patients come to the emergency department after ingesting spinach salad at a picnic. They have dysentery, anemia, and low platelet counts. Responsible toxin?

A

Shiga-like toxin; the patients likely have infection by enterohemorrhagic Escherichia coli (EHEC) from the raw leafy vegetable

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102
Q

Which form of Staphylococcus aureus is an important cause of serious nosocomial and community-acquired infections?

A

Methicillin-resistant Staphylococcus aureus (MRSA)

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103
Q

A patient is diagnosed with duodenal ulcers caused by a curved gram ⊖ rod. This bacterium is positive for what 3 enzymes?

A

Catalase, oxidase, and urease; the bacterium is Helicobacter pylori

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104
Q

What drug could prevent disseminated M avium-intracellulare infection in a patient with AIDS?

A

Azithromycin, which is used for prophylaxis, particularly in patients with AIDS when the CD4+ count is <50 cells/mm3

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105
Q

What tests are used to screen for and confirm a case of secondary syphilis?

A

To screen, use VDRL/RPR; to confirm, use FTA-ABS

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106
Q

In a patient with virulent Mycobacterium tuberculosis infection, what activates macrophages?

A

Cord factor, which causes a “serpentine cord” appearance in virulent strains and activates macrophages

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107
Q

A newborn is found to have neonatal chlamydia. How was this disease acquired?

A

As the infant passed through an infected birth canal

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108
Q

Is Staphylococcus saprophyticus novobiocin sensitive or resistant?

A

Novobiocin resistant

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109
Q

What diseases are caused by Chlamydia trachomatis?

A

Conjunctivitis (neonatal and follicular adult), urethritis, pelvic inflammatory disease, and reactive arthritis

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110
Q

A patient has a positive result on urea breath testing. What 2 pathologic conditions in the gastrointestinal (GI) tract are caused by the urease ⊕ organism?

A

Gastritis and peptic ulcers (especially duodenal); diagnosis: Helicobacter pylori

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111
Q

Name 4 clinically important mycobacteria that cause Tuberculosis-like illness

A

M tuberculosis, M scrofulaceum, M avium–intracellulare, and M marinum

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112
Q

What product of Pseudomonas aeruginosa causes degradation of cell membranes?

A

Phospholipase C

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113
Q

Why are Chlamydia species obligate intracellular organisms?

A

Because they cannot make their own ATP

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114
Q

Which Chlamydia trachomatis serotypes cause urethritis, pelvic inflammatory disease (PID), ectopic pregnancy, neonatal pneumonia with eosinophilia, and neonatal conjunctivitis?

A

Types D-K

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115
Q

A newborn comes to the NICU with a staccato cough and eye discharge. You notice significant eosinophilia on lab studies. What is the cause?

A

Chlamydia trachomatis, types D-K

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116
Q

You identify a fast lactose-fermenting gram ⊖ bacillus growing in culture medium. What are the 3 possibilities?

A

Klebsiella, Escherichia coli, and Enterobacter

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117
Q

What are the modes of transmission of Neisseria meningitidis?

A

Respiratory and oral secretions

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118
Q

You perform a Gram stain on Serratia in the lab. What are your results?

A

Serratia is a gram ⊖ bacillus

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119
Q

A patient presents with Escherichia coli-induced dysentery. No toxins are detected. How does the responsible pathogen cause bloody diarrhea?

A

EnteroInvasive E coli (EIEC) Invades the mucosa of the intestine, causing necrosis and inflammation, which results in dysentery

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120
Q

In the microbiology lab, you identify a slow lactose-fermenting, gram ⊖ bacillus. What are the 2 possibilities?

A

Citrobacter and Serratia

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121
Q

What is the Gram stain and morphology of Yersinia enterocolitica?

A

Gram ⊖ rod

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122
Q

What pathogen is found in unpasteurized dairy products and can cause recurrent rising and falling fevers?

A

Brucella spp (brucellosis), which causes undulating fevers from unpasturized dairy products

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123
Q

What are the common sources of infection for Pseudomonas aeruginosa?

A

Water from sources such as swimming pools and hot tubs (P aeruginosa causes swimmer’s ear and hot tub folliculitis)

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124
Q

Name 11 conditions/properties associated with Pseudomonas infection using the PSEUDOMONAS mnemonic

A

Pneumonia, Sepsis, Ecthyma gangrenosum, UTIs, Diabetes, Osteomyelitis, Mucoid polysaccharide capsule, Otitis externa, Nosocomial infections, Addicts (drug abusers), Skin infections

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125
Q

Under the microscope, you observe gram ⊕, spore-forming, obligate anaerobic bacilli. Diagnosis?

A

Clostridium spp

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126
Q

What abnormal values will you see on labs in a patient with Staphylococcal toxic shock syndrome?

A

↑ AST, ↑ ALT, ↑ bilirubin levels

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127
Q

A patient has lymphogranuloma venereum. Which Chlamydia trachomatis serotypes may be the cause?

A

Types L1, L2, and L3 cause Lymphogranuloma venereum

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128
Q

In the lab, you identify a streptococcal species resistant to bacitracin. Which strain is this?

A

Bacitracin: group B streptococci are Resistant; group A streptococci are Sensitive (B-BRAS)

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129
Q

What is a pupil called that constricts with accommodation but does not react to light?

A

Argyll Robertson pupil or “prostitute’s pupil”

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130
Q

What novobiocin-sensitive bacterium found in normal skin flora commonly contaminates blood cultures?

A

Staphylococcus epidermidis

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131
Q

How would you prevent disease transmission of N gonorrhoeae?

A

Condoms decrease sexual transmission; erythromycin ointment prevents neonatal blindness

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132
Q

In which 2 populations can Listeria monocytogenes infection lead to meningitis, and what is the empiric treatment of meningitis for them?

A

Neonates and the immunocompromised; ampicillin

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133
Q

Subacute endocarditis develops after a patient undergoes gastric bypass surgery. What is the likely causative organism?

A

Enterococci; patients are prone to such infections after gastrointestinal and genitourinary procedures

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134
Q

Do Salmonella and Shigella produce H2S gas?

A

Salmonella spp. (including S typhi) produce H2S; Shigella do not

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135
Q

What is the pathologic significance of flagella in Salmonella typhi?

A

Flagella enable hematogenous dissemination

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136
Q

You suspect that a patient has a Haemophilus influenzae infection. What medium should you use to grow the bacteria?

A

Chocolate agar with factors V (NAD+) and X (hematin); can also be grown with Staphylococcus aureus (providing factor V by way of RBC hemolysis)

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137
Q

An 8-year-old boy presents with whooping cough. What are the virulence factors that facilitate this infection?

A

Tracheal cytotoxin and pertussis toxin (which disables Gi), and adenylate cyclase toxin (↑ cAMP); diagnosis: Bordetella pertussis infection

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138
Q

How does staphylococcal food poisoning present?

A

Usually presents with nonbloody diarrhea and emesis 2-6 hours after ingestion of food with preformed toxin

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139
Q

A concerned parent at your doctor’s office is asking how vaccines work. Describe the vaccine used against Haemophilus influenzae.

A

It consists of a type b capsular polysaccharide (polyribosylribitol phosphate [PRP]) conjugated to diphtheria toxoid or another protein

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140
Q

How can you differentiate between Streptococcus pyogenes and Streptococcus agalactiae on blood agar?

A

By testing its sensitivity to bacitracin (Streptococcus pyogenes is sensitive and S agalactiae is resistant)

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141
Q

For which Neisseria species is a vaccine available?

A

N meningitidis (type B vaccine, not widely available); available for individuals at risk

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142
Q

How would you describe the lesions generated by Actinomyces?

A

Oral/facial abscesses that drain through sinus tracts; drainage contains yellow “sulfur granules”

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143
Q

What form of leprosy (also known as Hansen disease) presents with diffuse, communicable skin lesions and leonine facies?

A

Lepromatous (it has a high bacterial load)

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144
Q

What kind of illness does Yersinia enterocolitica typically cause?

A

Acute diarrhea or pseudoappendicitis

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145
Q

A patient with dental caries has an abscess with sinus drainage that contains yellow “sulfur granules.” Where is this organism normally found?

A

The normal oral, reproductive, and GI flora; this is Actinomyces

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146
Q

In which host cell type do bacterial microcolonies form when a patient is infected with ehrlichiosis?

A

Monocytes; Monocytes for Ehrlichiosis; Granulocytes for Anaplasma (MEGA berry)

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147
Q

What are the common routes of transmission of Listeria monocytogenes to a newborn?

A

Transplacental transmission and vaginal transmission during delivery

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148
Q

The rickettsiae genus are transmitted by way of what vector?

A

Arthropods (eg, ticks), except Coxiella, which is transmitted in aerosols

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149
Q

What 2 clinical syndromes are caused by Legionella?

A

Legionnaires’ disease and Pontiac fever

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150
Q

What organism causes Q fever, and how is it transmitted?

A

Coxiella burnetii; transmitted by spores from bovine/ovine amniotic fluid inhaled as aerosols (no arthropod vector)

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151
Q

A man has gram ⊕ cocci that grow normally in the colon and are penicillin G resistant. What do PYR and catalase testing yield?

A

Enterococci are catalase ⊖ and PYR ⊕

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152
Q

Why does Neisseria gonorrhoeae not have a vaccine?

A

Due to antigenic variation of pilus proteins

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153
Q

How do antibiotics affect fecal excretion of bugs in patients with Salmonella and Shigella infections?

A

Antibiotics prolong the duration of fecal excretion for patients with Salmonella; they shorten duration in patients with Shigella

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154
Q

What component of virulent M tuberculosis induces release of TNF-α?

A

Cord factor

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155
Q

A boy who ate food from a poorly sealed container comes to the office with diplopia and ↓ tone in his arms. Diagnosis?

A

Clostridium botulinum

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156
Q

Name 3 possible conditions that may give a ⊕ PPD test result.

A

Current tuberculosis infection, previous exposure, and bacille Calmette-Guérin (BCG) vaccination

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157
Q

A child is infected with gram ⊕ rods with metachromatic granules and a positive Elek test. How is this infection transmitted?

A

Corynebacterium diphtheriae is transmitted via respiratory droplets

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158
Q

A child has gray-white membranes adhering to his pharynx and diffuse lymphadenopathy. How do you culture the suspected infectious agent?

A

Use cystine-tellurite agar, on which Corynebacterium diphtheriae will grow black colonies (gray-white membranes indicate pseudomembranous pharyngitis)

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159
Q

A farm girl develops bloody diarrhea, abdominal cramps, nausea, vomiting, and fever. From which animal populations might she have contracted her illness?

A

Poultry or reptiles (this is a Salmonella spp infection, excluding S typhi)

160
Q

A patient has a Bacillus anthracis infection. What are the 2 modes of transmission of this infection?

A

Cutaneous exposure and inhalation

161
Q

How does the rash caused by Rickettsia rickettsii spread on the body?

A

Rash usually starts at ankles and wrists, and then spreads to trunk, palms, and soles

162
Q

How is anaplasmosis transmitted?

A

The Ixodes tick transmits Anaplasma spp from deer and mice

163
Q

What is the characteristic fever that Brucella causes?

A

Unduluating fever (undulating fever from unpasteurized milk)

164
Q

How is tularemia contracted?

A

From rabbits, deer flies, and ticks containing Francisella tularensis

165
Q

What specific finding on chest x-ray confirms primary tuberculosis?

A

Ghon complex (Ghon focus, typically in mid/lower lobes of the lung, with hilar node involvement)

166
Q

What stabilizes the membrane of Mycoplasma pneumoniae?

A

Sterols in the bacterial membranes; M pneumoniae lack cell walls

167
Q

What subtype of Streptococcus bovis is most strongly associated with colon cancer?

A

Streptococcus gallolyticus, biotype 1 of S bovis (Bovis in the blood = cancer in the colon)

168
Q

Name organisms that are gram ⊖ coccobacilli.

A

Haemophilus influenzae, Bordetella pertussis, Francisella tularensis, Pasteurella, and Brucella

169
Q

What pathogen is responsible for Rocky Mountain spotted fever?

A

Rickettsia rickettsii, transmitted via tick

170
Q

Why is a patient at higher risk for V cholerae infection at low inoculum if he is under PPI therapy when visiting a developing country?

A

PPIs ↓ gastric acidity; V cholerae typically requires a large inoculum (ID50) because it is sensitive to stomach acid

171
Q

Which bacteria are responsible for endemic typhus and epidemic typhus, and how are they transmitted?

A

Endemic: Rickettsia typhi, transmitted via fleas
Epidemic: Rickettsia prowazekii, transmitted via human body louse

172
Q

What bacterium is transmitted by fleas and causes plague in humans?

A

Yersinia pestis

173
Q

In a partially immune, hypersensitized host, what kind of infection occurs after exposure to M tuberculosis?

A

Secondary tuberculosis

174
Q

Lobar pneumonia with “currant jelly” sputum develops in a patient who aspirated his own vomit. What is the most likely pathogen?

A

Klebsiella (5 As = Aspiration pneumonia, Abscess in lungs and liver, Alcoholics, diAbetics, “currAnt jelly” sputum)

175
Q

The mnemonic ABCDEFG is useful for remembering key information about Corynebacterium diphtheriae. Explain this mnemonic.

A

Adenosine diphosphate - (ADP) ribosylation; β-prophage; Corynebacterium Diphtheriae; Elongation Factor 2; Granules

176
Q

What is responsible for the recurrent nature of the fever in Borrelia recurrentis infections?

A

Variation in bacterial surface antigens

177
Q

What is the source of the spirochete Leptospira interrogans?

A

Water contaminated with animal urine; the disease is particularly prevalent in the tropics (eg, Hawaii) and among surfers

178
Q

Which bacteria that frequently causes atypical pneumonia can cause an atypical variant of Stevens-Johnson syndrome in children and adolescents?

A

Mycoplasma pneumoniae

179
Q

What form of visualization, other than a dark-field microscope, can you use to test for Treponema?

A

Direct fluorescent antibody (DFA) microscopy

180
Q

Pneumonia and meningitis develop in a neonate as a result of infection with Escherichia coli. What virulence factor is responsible?

A

K capsule

181
Q

A patient comes in with food poisoning caused by Staphylococcus aureus despite eating properly cooked food. What is the reason for the illness?

A

Enterotoxin is heat stable and not destroyed by cooking

182
Q

A lab tech notes brownish-greenish rings around colonies on blood agar. Which 2 gram ⊕ cocci might these be?

A

Streptococcus pneumoniae and viridans streptococci

183
Q

Which form of leprosy causes cell-mediated immunity to fail and tends to have a poor prognosis?

A

Lepromatous form can be lethal; causes a Th2 response

184
Q

A 42-year-old man presents with a broad-based gait, the Romberg sign, and Argyll Robertson pupils. What tests can confirm the most likely diagnosis?

A

VDRL and FTA-ABS tests and PCR of spinal fluid (diagnosis: neurosyphilis)

185
Q

How are gonococcal and meningococcal infections diagnosed?

A

Gonococcus: nucleic acid amplification test (NAAT)
Meningococcus: culture-based tests or PCR

186
Q

A child presents with acid-fast organisms in his blood and cervical lymphadenitis. If tuberculosis is ruled out, what is the likely cause?

A

Mycobacterium scrofulaceum infection

187
Q

What hematologic finding may help confirm Mycoplasma pneumoniae infection?

A

A high titer of cold agglutinins (IgM); they can agglutinate or lyse red blood cells (Mycoplasma gets cold without a coat)

188
Q

A Streptococcus culture exhibits partial (α, green) hemolysis. How will you further categorize the species?

A

Viridans streptococci: no capsule, optochin resistant, bile insoluble; Streptococcus pneumoniae: capsule present, optochin sensitive, bile soluble

189
Q

What lab findings are expected when Staphylococcus saprophyticus is grown in a culture?

A

Gram ⊕, catalase ⊕, coagulase ⊖, urease ⊕ cocci in clusters

190
Q

What is the treatment for a patient infected with Brucella?

A

Doxycycline and rifampin or streptomycin

191
Q

What is the causative organism and vector of ehrlichiosis?

A

Ehrlichia chaffeensis, which is carried by the Lone Star tick (Amblyomma)

192
Q

How does Staphylococcus aureus infection cause toxic shock syndrome?

A

Toxic shock syndrome is caused by superantigen TSST-1 that binds MHC II and T-cell receptors, results in polyclonal T-cell activation

193
Q

Which animal acts as a reservoir of Mycobacterium leprae in the United States?

A

Armadillos

194
Q

You find oxidase ⊖, gram ⊖, lactose-nonfermenting bacilli. Which agar can be used to differentiate bacteria based on H2S production?

A

Triple sugar iron (TSI) agar

195
Q

Why is drug sensitivity testing important when a patient has an infection caused by Klebsiella?

A

Klebsiella is associated with multidrug resistance

196
Q

In the lab, you see a strain of Streptococcus with partial hemolysis. If the bacteria are optochin sensitive, what is the specific strain?

A

Optochin: Viridans is Resistant, Pneumoniae is Sensitive (OVRPS [overpass])

197
Q

What symptoms are seen in the catarrhal phase of Bordetella pertussis infection?

A

Low grade fevers, coryza (catarrhal)

198
Q

What are the classical symptoms of tuberculosis?

A

Night sweats, weight loss, fever, hemoptysis, cough (productive or nonproductive)

199
Q

In patients with Chlamydia infection, why is azithromycin the favored treatment?

A

It is a one-time treatment (in contrast to doxycycline, which requires several doses)

200
Q

What is the definition of zoonosis?

A

The transmission of an infectious disease between animals and humans

201
Q

In what stage of syphilis would a patient note lymphadenopathy and patchy hair loss?

A

Secondary

202
Q

What symptoms characterize the first stage (early localized) of Lyme disease?

A

Erythema migrans (expanding red “bull’s-eye” rash) and flu-like symptoms

203
Q

You add Streptococcus agalactiae to a culture of Staphylococcus aureus, which enlarges the area of hemolysis. What bacterial substance causes this finding?

A

CAMP factor made by S agalactiae (CAMP denotes the authors of the test, not cyclic AMP)

204
Q

What symptoms would you observe in a patient in the third (late disseminated) stage of Lyme disease?

A

Encephalopathy, chronic arthritis

205
Q

In the lab, you observe a group of lactose-nonfermenting, gram ⊖ bacilli that are also oxidase positive. Likely bacteria?

A

Pseudomonas

206
Q

Cystitis and pyelonephritis develop in a 73-year-old woman as a result of infection with Eshcerichia coli. What virulence factor is responsible?

A

Fimbriae (P pili for pyelonephritis)

207
Q

What gives the mucoid appearance of Klebsiella pneumoniae colonies?

A

Its polysaccharide capsule

208
Q

Why is penicillin ineffective as a therapy option for Mycoplasma pneumoniae?

A

M pneumoniae, lacking cell walls, is resistant to penicillin; infection is treated with macrolides, doxycycline, or fluoroquinolones

209
Q

How does enteropathogenic Escherichia coli (EPEC) cause damage to enterocytes?

A

It adheres to the apical surface and flattens villi, decreasing absorption (EPEC does not produce a toxin)

210
Q

What medications would be used to treat the lepromatous form of leprosy (Hansen disease)?

A

Dapsone, rifampin, and clofazimine

211
Q

A pregnant woman has vaginal colonies of Streptococcus agalactiae. What 3 diseases is her baby at risk of developing if the mother isn’t treated?

A

Group B streptococcal infection, which causes pneumonia, meningitis, and sepsis in Babies

212
Q

In a patient with virulent M tuberculosis infection, what inhibits phagolysosome fusion?

A

Sulfatides (surface glycolipids)

213
Q

A man has an ulcerating lesion with black eschar. A culture shows gram ⊕ spore-forming organisms. What are the organisms?

A

Bacillus anthracis (gram ⊕ spore-forming rods)

214
Q

What type of laboratory sample is tested to diagnose Legionella infection?

A

Urine is used to detect presence of antigen

215
Q

What kind of virulence factor is produced by Haemophilus influenzae?

A

Immunoglobulin A (IgA) protease

216
Q

What is latent syphilis, and when does it occur?

A

Latent syphilis is characterized by positive serology but no symptoms; it follows secondary syphilis

217
Q

You culture a cellulitis sample, which yields catalase ⊕ cocci. How can you differentiate the 3 main species in this group?

A

Staphylococcus aureus is coagulase ⊕; coagulase ⊖ species: Staphylococcus epidermidis is novobiocin sensitive and Staphylococcus saprophyticus is resistant

218
Q

You want to grow Helicobacter pylori to study in the lab. What part of a patient’s stomach should you take a sample from?

A

The antrum; H pylori mainly colonizes the antrum

219
Q

Dysarthria, dysphagia, and diplopia develop after a man eats food from a poorly sealed can. What is the mechanism of the causative toxin?

A

Inhibition of acetylcholine release at the neuromuscular junction, causing botulism (this heat-labile toxin is produced by Clostridium botulinum)

220
Q

An unvaccinated boy has epiglottitis. A neck x-ray shows the “thumb sign.” How is the most likely causative agent transmitted?

A

Aerosol; diagnosis: Haemophilus influenzae

221
Q

In which host cell type do bacterial microcolonies form when a patient is infected with anaplasmosis?

A

Granulocytes; Monocytes for Ehrlichiosis; Granulocytes for Anaplasma (MEGA berry)

222
Q

A febrile patient with jaundice complains of RUQ tenderness after an endoscopic retrograde cholangiopancreatography (ERCP) procedure. What is the causative organism?

A

Enterococci; diagnosis is ascending cholangitis (enterococci are a common cause of biliary tract infection after gastrointestinal/genitourinary [GI/GU] procedures)

223
Q

In the lab you see a strain of Streptococcus showing partial hemolysis. If the bacteria are optochin resistant, what is the strain?

A

Optochin: Viridans is Resistant, but Pneumoniae is Sensitive (OVRPS [overpass])

224
Q

You are concerned that a patient has enterohemorrhagic Escherichia coli (EHEC). How can you distinguish EHEC from other types of E coli using a culture?

A

EHEC does not ferment sorbitol

225
Q

Which gram ⊕ filamentous and weakly acid fast bacteria spread to the CNS?

A

Nocardia

226
Q

Following severe bacteremia caused by tuberculosis, what might be seen on examination of histopathology slides from various organs?

A

Small, widespread granulomas in multiple organs; diagnosis: miliary tuberculosis

227
Q

Where can treponemes be found during primary and secondary syphilis, and what do you use to visualize them?

A

Primary syphilis: in chancres; secondary syphilis: in condylomata lata; use fluorescent or dark-field microscopy to see treponemes

228
Q

How do you confirm a Mycobacterium leprae infection?

A

M leprae is diagnosed by tissue PCR or skin biopsy; it cannot be grown in vitro

229
Q

What are the possible modes of transmission of Yersinia enterocolitica?

A

Pet feces (eg, from puppies), contaminated milk, or pork

230
Q

What are the modes of transmission of Neisseria gonorrhoeae?

A

N gonorrhoeae is transmitted during sex or birth

231
Q

A patient with suspected syphilis has a positive VDRL test result. Why do you confirm the result with an FTA-ABS test?

A

An FTA-ABS test is more specific for syphilis; a VDRL test is more sensitive and more likely to yield a false-positive result

232
Q

What are the drugs used to treat a gonococcal infection?

A

Ceftriaxone (plus azithromycin or doxycycline for concurrent chlamydial coinfection)

233
Q

As a medical student, you are told a culture grows gram ⊖ diplococci. What are the 2 strains that may be growing?

A

Neisseria species and Moraxella species

234
Q

A sexually active woman has pelvic inflammatory disease (PID) due to Chlamydia trachomatis. How do you treat her?

A

Azithromycin (single dose) or doxycycline, plus ceftriaxone to empirically treat for gonorrhea

235
Q

An patient who is immunocompromised has a pulmonary infection with an acid-fast bacteria. PPD test is negative; he has unusual skin lesions. Treatment of choice?

A

TMP-SMX; he may have a severe Nocardia infection, which can mimic TB but with negative PPD findings; can cause cutaneous infections after trauma

236
Q

A scientist working on MRSA knocks out the bacteria’s penicillinases but finds that the bug is still resistant to several penicillins. Why?

A

MRSA alters its penicillin-binding proteins to resist killing by penicillinase-stable penicillins (eg, methicillin, oxacillin, nafcillin)

237
Q

A 35-year-old man complains of pain and swelling along the inguinal lymph nodes, which have begun to ulcerate, forming buboes. Treatment?

A

Treat with doxycycline (Chlamydia trachomatis types L1, L2, and L3 cause Lymphogranuloma venereum)

238
Q

Which part of the body does Helicobacter pylori typically colonize?

A

Antrum of the stomach

239
Q

What is the vector for the pathogen causing Rocky Mountain spotted fever?

A

Dermacentor (dog tick); bites transmit Rickettsia rickettsii

240
Q

A chest x-ray of a 70-year-old man with a cough shows left lower lobe pneumonia. What hemolysis pattern does the most likely pathogen exhibit?

A

Green, partial hemolysis (α-hemolysis); Streptococcus pneumoniae is the most common cause of pneumonia in older patients

241
Q

What prophylaxis should be offered to a health care worker who may have been exposed to N meningitidis?

A

Rifampin, ciprofloxacin, or ceftriaxone

242
Q

In the lab, you grow gram ⊖ aerobic diplococci. They do not use maltose. Polymerase chain reaction (PCR) for Neisseria DNA is negative. Organism isolated?

A

Moraxella

243
Q

What are the symptoms of Mycoplasma pneumoniae pneumonia?

A

Atypical “walking pneumonia”; insidious onset with nonproductive cough, headache, and patchy or diffuse interstitial infiltrates on chest x-ray

244
Q

A patient is told that she has traveler’s diarrhea. What toxins are responsible for this diarrhea?

A

Labile and stable enteroToxins of enterotoxic Escherichia coli (ETEC) cause Traveler’s diarrhea

245
Q

What is the mechanism of action of Staphylococcus aureus protein A (virulence factor)?

A

It binds the Fc region of IgG (Fc-IgG), inhibiting complement activation and phagocytosis

246
Q

A bird trader who experiences fever and dyspnea is found to have an atypical pneumonia. What pathogen is the most likely cause?

A

Chlamydophila psittaci, which has an avian reservoir (parrots) and causes atypical pneumonia

247
Q

A pregnant woman and her husband both have a rickettsial infection. How do you treat them?

A

Chloramphenicol for the pregnant woman; doxycycline for her husband

248
Q

What 3 types of Escherichia coli do not invade the intestinal mucosa?

A

Enterohemorrhagic (EHEC), enterotoxigenic (ETEC), and enteropathogenic (EPEC); only the enteroinvasive (EIEC) type invades intestinal mucosa

249
Q

A patient with cystic fibrosis presents with cough productive of blue-green sputum. Which drugs of the penicillin class are appropriate for treatment?

A

Extended-spectrum penicillins (eg, piperacillin, ticarcillin) can be used to treat his likely Pseudomonas aeruginosa infection

250
Q

A patient who has had the bacille Calmette-Guérin (BCG) vaccine is being evaluated for tuberculosis. What is the most appropriate test to order?

A

Interferon-γ release assay (IGRA), a more specific test that yields fewer false ⊕ results than PPD yields from BCG vaccination

251
Q

What areas of the body are likely to be infected by Mycobacterium leprae?

A

The skin and superficial nerves, causing “glove and stocking” loss of sensation; M leprae likes cool temperatures

252
Q

In what population infected with tuberculosis is progressive lung disease most likely to occur?

A

Individuals who are malnourished and/or HIV ⊕

253
Q

A man with a chronic peptic ulcer has a positive result on urease breath testing. What is the first-line treatment?

A

Triple therapy: Amoxicillin (metronidazole if allergic to penicillin), Clarithromycin, Proton pump inhibitor (Antibiotics Cure Pylori)

254
Q

You are given a group of gram ⊖ bacilli. They are differentiated by their ability to ferment what substance?

A

Lactose

255
Q

What are the laboratory characteristics of Pseudomonas aeruginosa?

A

It is an aerobic, motile, catalase ⊕, oxidase ⊕, gram ⊖ rod; is a nonlactose fermenter with a grape-like odor

256
Q

What spirochete causes destruction of the vasa vasorum of the aorta?

A

Treponema pallidum, which causes syphilis; diagnosis: aortitis

257
Q

What 2 diseases are associated with Bartonella infections in patients who are immunocompromised?

A

Bacillary angiomatosis and cat scratch disease

258
Q

Name 2 polymyxin antibiotics that can be used to treat P aeruginosa infection.

A

Polymyxin B, colistin

259
Q

A bacteria is identified to be hippurate test ⊕, PYR ⊖, bacitracin resistant, and β-hemolytic. Name the bacteria.

A

Streptococcus agalactiae

260
Q

A 9-year-old boy has ascending weakness. If this is related to an infection, what did he most likely eat to cause it?

A

Poultry, meat, or unpasteurized milk, which can harbor Campylobacter jejuni, and which can cause Guillain-Barré syndrome

261
Q

What spirochete is responsible for causing syphilis?

A

Treponema pallidum

262
Q

Differentiate Legionnaires’ disease from Pontiac fever.

A

Legionnaires’ disease is marked by severe pneumonia (unilateral, lobar) with fever, CNS and GI symptoms; Pontiac fever is a mild, flu-like syndrome

263
Q

A colleague tells you that your next patient has confirmed tetanus toxin in his system. What symptoms do you expect this patient to exhibit?

A

Spastic paralysis, risus sardonicus (open grin and raised eyebrows), trismus (lockjaw), and opisthotonos (spinal extensor spasms)

264
Q

A positive Venereal Disease Research Laboratory (VDRL) test indicates that antibodies have formed against what molecule?

A

Beef cardiolipin

265
Q

In what 4 ways can Shigella be transmitted between humans?

A

The Four Fs = Fingers, Flies, Food, and Feces

266
Q

In what states is Rocky Mountain spotted fever commonly found?

A

South Atlantic states, especially North Carolina (despite its name)

267
Q

What are the 2 virulence factors of Streptococcus pneumoniae?

A

IgA protease and its capsule

268
Q

What pathogen causes leprosy, and from where do humans acquire it?

A

Mycobacterium leprae; mainly from infected humans (rarely, armadillos)

269
Q

How do you counsel a pregnant woman to prevent transmission of Listeria monocytogenes?

A

Avoid ingestion of unpasteurized dairy products and cold deli meats; L monocytogenes grows well at 4°-10°​​​​​​​C, refrigeration temperatures

270
Q

What type of lesion is seen on an x-ray of the lung fields of a patient with secondary tuberculosis?

A

A fibrocaseous cavitary lesion in the upper lobe

271
Q

In the lab, you identify a streptococcal species sensitive to bacitracin. Which strain is this?

A

Bacitracin: group B streptococci are Resistant; group A streptococci are Sensitive (B-BRAS)

272
Q

An unvaccinated boy contracts meningitis. Bacteria grow on chocolate agar containing factors V and X. Treatment plan?

A

Treat with ceftriaxone for Haemophilus influenzae meningitis; close contacts should receive rifampin prophylaxis

273
Q

Name the enzyme produced by E coli that breaks down lactose into glucose and galactose.

A

β-galactosidase

274
Q

Blood agar grows a β-hemolytic organism. How would you differentiate both Streptococcus pyogenes and Streptococcus agalactiae from Staphylococcus aureus?

A

Both are catalase ⊖, unlike S aureus, which is catalase ⊕

275
Q

In the lab, you have a coagulase ⊖ Staphylococcus bacterium. You notice that it is novobiocin sensitive. Identify it.

A

NOvobiocin: Saprophyticus is Resistant; Epidermidis is Sensitive (NO StRESs on the office “staph” retreat)

276
Q

How would the presentation be different if a patient had Staphylococcus aureus toxic shock syndrome (TSS) versus Streptococcus pyogenes TSS?

A

S aureus TSS: fever, vomiting, shock, desquamation, rash, and end-organ failure; S pyogenes TSS: painful skin infection

277
Q

You culture a sputum sample, suspecting either Staphylococcus or Streptococcus. How can you differentiate the bacteria?

A

Staphylococcus is catalase ⊕ and grows in clusters; Streptococcus is catalase ⊖ and grows in pairs or chains (both are gram ⊕ cocci)

278
Q

Name 6 inflammatory diseases that can result from infection with Staphylococcus aureus.

A

Skin infection, endocarditis, pneumonia (often following influenza virus infection), organ abscess, septic arthritis, and osteomyelitis

279
Q

A hospitalized patient develops severe diarrhea with a foul odor. Which toxin produced by the causative bacteria binds the gut’s brush border?

A

Toxin A, which is an enterotoxin produced by Clostridium difficile that alters fluid secretions

280
Q

A 5-year-old boy eats raw beef and then has bloody diarrhea. Two weeks later, he cannot move his legs and has hyporeflexia. What happened?

A

He likely has Guillain-Barré syndrome triggered by Campylobacter jejuni infection (bloody diarrhea)

281
Q

How do levels of Shiga toxin compare between S boydii, S sonnei, S dysenteriae and S flexneri?

A

From most to least: S dysenteriae, S flexneri, S boydii, and S sonnei

282
Q

A man has watery, nonbloody diarrhea after eating reheated rice 9 hours earlier. Explain how the causative organisms likely survived heating.

A

This is likely a Bacillus cereus infection; spores survive cooking; rewarming the rice promotes spore germination and enterotoxin formation

283
Q

A medical student finds gram ⊕ spherical bacteria appearing in clusters. What is the most likely strain?

A

Staphylococcus

284
Q

Chlamydia trachomatis can cause conjunctivitis in which age group?

A

Neonates as well as adults

285
Q

In the lab, you discover an oxidase ⊕, comma-shaped, gram ⊖ organism that grows in alkaline media. Identify this bacterium.

A

Vibrio cholerae

286
Q

What 5 disease states might Neisseria gonorrhoeae present as?

A

Gonorrhea, pelvic inflammatory disease (PID), septic arthritis, Fitz-Hugh–Curtis syndrome, and neonatal conjunctivitis (2-5 days after birth)

287
Q

What are the laboratory characteristics of Vibrio cholerae?

A

Gram ⊖, comma-shaped, flagellated, oxidase ⊕ bacteria that grow in alkaline media and is sensitive to stomach acid (acid labile)

288
Q

In a patient with Mycoplasma pneumoniae pneumonia, how does the chest x-ray finding compare to the severity of clinical illness?

A

X-ray usually looks worse than the patient

289
Q

What antibiotics are used to treat infection with Salmonella typhi and other Salmonella species?

A

Salmonella typhi: ceftriaxone or fluoroquinolone

Salmonella spp. (except S typhi): antibiotics not indicated

290
Q

Name the aerobic gram ⊕ bacilli.

A

Corynebacterium, Listeria, and Bacillus

291
Q

Name the 4 illnesses most commonly caused by infection with Streptococcus pneumoniae.

A

Meningitis, otitis media (in children), pneumonia, sinusitis

292
Q

A sexually active woman has pelvic inflammatory disease (PID). If it is caused by Chlamydia trachomatis, what do you see on microscopy?

A

Cytoplasmic inclusions (reticulate bodies) on Giemsa or fluorescent antibody staining

293
Q

What property of S epidermidis allows it to easily infect prosthetic devices (eg, hip implants, heart valves) and intravenous catheters?

A

Production of an adherent biofilm

294
Q

In the lab, you have a coagulase ⊖ Staphylococcus bacterium. You notice that it is novobiocin resistant. Identify it.

A

NOvobiocin: Saprophyticus is Resistant; Epidermidis is Sensitive (NO StRESs on the office “staph” retreat)

295
Q

What 2 patient populations are susceptible to Streptococcus pneumoniae sepsis?

A

Patients with sickle cell disease and asplenia

296
Q

What is the classic triad of symptoms of Rocky Mountain spotted fever?

A

Fever, headache, and rash (vasculitis)

297
Q

What features help in isolating Streptococcus pneumoniae from a culture medium?

A

It is a gram ⊕, α-hemolytic, lancet-shaped diplococci, which is sensitive to optochin

298
Q

What are the Gram stain characteristics of Legionella?

A

Legionella is a gram-⊖ bacillus but does not react well to Gram stain; use silver stain

299
Q

A patient tells you that he started vomiting about an hour after eating reheated rice. What is the most likely causative toxin?

A

Cereulide, the preformed toxin in Bacillus cereus (patient has reheated rice syndrome)

300
Q

A sexually active patient develops Gardnerella vaginalis infection but her partner does not. What is the reason?

A

It is not sexually transmitted but, it is associated with sexual activity

301
Q

What are the 2 forms of Hansen disease?

A

Lepromatous and tuberculoid (Hansen disease is also known as leprosy)

302
Q

What staining property do all mycobacteria have in common?

A

All are gram ⊕, acid-fast rods

303
Q

What is the vector for the pathogen causing endemic typhus?

A

Fleas; transmit Rickettsia typhi

304
Q

One patient has an Actinomyces infection; another has a Nocardia infection. How do you treat each patient?

A

Sulfonamides can treat Nocardia; Actinomyces is treated with Penicillin (Treatment is a SNAP)

305
Q

N meningitidis and N gonorrhoeae both ferment what type of sugar and produce which type of immunoglobulin protease?

A

Both ferment glucose and produce IgA protease

306
Q

Where do viridans group streptococci commonly colonize in the human body?

A

The oropharynx

307
Q

A patient has severe diarrhea; exam reveals pseudomembranous colitis, and culture shows gram ⊕ spore-forming bacilli. Treatment?

A

Metronidazole or oral vancomycin (this is infection with Clostridium difficile [Difficile causes diarrhea])

308
Q

A man who swims in a cove has fever, fatigue, body aches, photophobia, and conjunctival suffusion. What is the water contaminated with?

A

Animal urine containing Leptospira interrogans; diagnosis: leptospirosis

309
Q

A 7-year-old girl has had a cough with whooping on inspiration for 2 months. What is the Gram stain reaction and shape of the causative organism?

A

Bordetella, a gram ⊖ coccobacillus

310
Q

Explain the mechanism through which viridans group streptococci cause subacute bacterial endocarditis.

A

Streptococcus sanguinis makes dextrans, which bind to fibrin-platelet aggregates on damaged heart valves (sanguinis = blood, in the heart)

311
Q

Where does Staphylococcus saprophyticus normally inhabit the human body?

A

The female genital tract and perineum

312
Q

A patient with pseudomembranous pharyngitis and arrhythmias has diphtheria. What is the toxin, and how does it inhibit protein synthesis?

A

Exotoxin (encoded on a β-prophage); it inhibits protein synthesis by adenosine diphosphate- (ADP) ribosylation of elongation factor 2 (EF-2)

313
Q

An infant who is fed breast milk mixed with honey and jaggery, presents with ↓ tone in all limbs. How would you treat the condition?

A

Treat with human botulinum immunoglobulin

314
Q

What abnormalities may present in a case of congenital syphilis?

A

Saber shins, saddle nose, cranial nerve VIII deafness, Hutchinson (notched) teeth, mulberry molars, rhagades, snuffles, short maxilla

315
Q

A 27-year-old man has spastic paralysis. Renshaw cell neurotransmitter release is inhibited. Name the toxin and explain how it works.

A

Tetanospasmin exotoxin (from Clostridium tetani); cleaves SNARE proteins, thus blocking release of glycine and γ-aminobutyric acid (GABA), which are inhibitory neurotransmitters

316
Q

How is Vibrio cholerae transmitted?

A

By consumption of contaminated water or uncooked food (eg, raw shellfish)

317
Q

What 3 illnesses can Klebsiella cause?

A

Aspiration pneumonia, abscesses in lungs and liver, and nosocomial UTIs

318
Q

A girl presents with a strawberry tongue, circumoral pallor, sore throat, fever, and sandpaper-like body rash. Causative agent?

A

Streptococcus pyogenes (Diagnosis: scarlet fever caused by the erythrogenic toxin)

319
Q

What 2 pigments are produced by Pseudomonas aeruginosa?

A

Pyoverdine and pyocyanin (blue-green pigment, generates reactive oxygen species)

320
Q

What property of Pseudomonas may contribute to the chronic pneumonia in patients with cystic fibrosis?

A

The mucoid polysaccharide capsule causes chronic pneumonia in patients with cystic fibrosis as a result of biofilm formation

321
Q

What are 2 common modes of transmission for Campylobacter jejuni?

A

Fecal-oral (for person-to-person contact) or via ingestion

322
Q

How does Salmonella spread through the body compared with Shigella?

A

Salmonella spreads hematogenously, whereas Shigella spreads from cell to cell without hematogenous spread

323
Q

What populations are most likely to experience a Mycoplasma pneumoniae outbreak?

A

Individuals <30 years of age, military recruits, and inmates

324
Q

In the lab, you discover an oxidase ⊕, comma-shaped, gram ⊖ bacterium that grows at 42°C. Identify it.

A

Campylobacter jejuni

325
Q

How does coagulase positivity contribute to the pathogenicity of Staphylococcus aureus?

A

It allows the organism to form a fibrin clot around itself, permitting abscess formation

326
Q

In what medium is Legionella pneumophila grown in vitro?

A

Charcoal yeast extract (iron & cysteine); French legionnaire (soldier) with his silver helmet, sitting around a campfire (charcoal) with his iron dagger; he is no sissy (cysteine)

327
Q

How long does Staphylococcus aureus toxin take to cause nonbloody diarrhea and emesis?

A

Preformed Staphylococcal enterotoxins causing food poisoning have a short incubation period of 2-6 hours

328
Q

A farmer has cycling fevers, night sweats, and arthralgias after drinking unpasteurized milk. What is the causative organism?

A

Brucella (the farmer likely has brucellosis)

329
Q

What culture medium could you use to grow Mycoplasma pneumoniae?

A

Eaton agar; this is not routinely done for diagnosis because culture takes 2-3 weeks to grow

330
Q

What symptoms would you observe in a patient in the second (early disseminated) stage of Lyme disease?

A

Secondary lesions, atrioventricular block, facial nerve (Bell) palsy, migratory myalgias/transient arthritis, carditis

331
Q

A sheep farmer inhales Bacillus anthracis spores. What sort of symptoms do you expect to arise?

A

Flu-like symptoms, rapidly progressing to fever, mediastinitis, pulmonary hemorrhage, and shock

332
Q

You have a culture of gram ⊕, catalase ⊖ cocci that are γ-hemolytic and fail to grow in 6.5% NaCl. Do they grow in bile?

A

Yes; these are nonenterococcus bacteria (eg, Streptococcus bovis), which will grow in bile

333
Q

What rickettsial organism is commonly responsible for culture ⊖ endocarditis?

A

Coxiella burnetii

334
Q

What is the vector for the pathogen that causes Lyme disease?

A

Ixodes ticks that dwell on deer and mice

335
Q

A culture is growing a nonlactose-fermenting, gram ⊖ rod that is commonly associated with wound infection in burn victims. Name the bacteria

A

Pseudomonas aeruginosa

336
Q

A shepherd presents with hemoptysis. A chest x-ray shows mediastinal widening. Diagnosis?

A

Bacillus anthracis infection (also called woolsorter’s disease; mediastinal widening is due to mediastinitis)

337
Q

A woman is 36 weeks pregnant. What bacterium should you screen for?

A

Streptococcus agalactiae colonizes the vagina and is screened for at 35-37 weeks of gestation

338
Q

What 3 diseases start with a rash on the palms and soles?

A

Coxsackievirus A infection, Rocky Mountain spotted fever, and secondary syphilis (you drive CARS using your palms and soles)

339
Q

In the microbiology lab, you identify a β-hemolytic organism that is both catalase and coagulase ⊕. What organism did you find?

A

Staphylococcus aureus

340
Q

What agar, other than EMB, can be used to diagnose a possible Klebsiella infection?

A

MacConkey agar; you will observe pink colonies

341
Q

Overgrowth of what type of bacteria occurs in the vagina of a patient with bacterial vaginosis?

A

Anaerobic bacteria including Gardnerella vaginalis

342
Q

What 2 immediate complications are possible if a patient contracts an infection with Streptococcus bovis?

A

Bacteremia and subacute endocarditis

343
Q

What laboratory tests can be done that indicate a recent Streptococcus pyogenes infection?

A

ASO titer and anti-DNase B antibodies

344
Q

What similarities are there in laboratory characteristics and pathogenicity of Salmonella and Shigella?

A

Both are gram ⊖ rods, oxidase ⊖, nonlactose fermenters, and able to invade the GI tract via M cells of Peyer patches

345
Q

You are administering vaccines at the pediatrician’s office. Typically, the Haemophilus influenzae vaccine is given to which age group?

A

Infants 2-18 months of age

346
Q

How is the bacteria Legionella pneumophila transmitted?

A

Aerosol transmission from an environmental water source such as an air conditioner or hot water tank (no person-to-person transmission)

347
Q

How do you diagnose disease in a patient with suspected Clostridium difficile infection (marked by diarrhea after antibiotic use)?

A

On the basis of the presence of toxin A (enterotoxin) and/or toxin B (cytotoxin) in stool, via polymerase chain reaction (PCR) or antigen detection

348
Q

What are the virulence factors of Salmonella typhi?

A

Endotoxin and Vi capsule

349
Q

A woman diagnosed wih bacterial vaginosis is prescribed metronidazole but cannot tolerate it. What second medication may be given instead?

A

Clindamycin is a reasonable second-line treatment (overgrowth of vaginal anaerobic bacteria characterize bacterial vaginosis)

350
Q

A traveler is ill with typhoid fever and goes untreated. In which organ does the causative agent colonize?

A

Gallbladder (this is Salmonella typhi)

351
Q

What toxigenic diseases result from infection with Streptococcus pyogenes?

A

Scarlet fever, necrotizing fasciitis, toxic shock-like syndrome

352
Q

What unique property of chlamydial cell walls makes β-lactam antibiotics ineffective?

A

The cell walls lack classic peptidoglycans because there is less muramic acid

353
Q

Among lactose nonfermenters, which gram ⊖ bacilli are oxidase negative?

A

Shigella, Salmonella, Proteus, and Yersinia

354
Q

You identify 2 distinct Neisseria species in the lab. How can you distinguish between these 2 species based on their metabolism?

A

N meningitidis ferments maltose; N gonorrhoeae does not ferment maltose

355
Q

A 2-year-old boy, unvaccinated against Haemophilus influenzae, has the flu. Which organism could be the cause?

A

Influenza virus causes the flu, not H influenzae

356
Q

What vector is responsible for the transmission of Ehrlichiosis and Anaplasmosis?

A

Tick

357
Q

What 2 conditions may bring about a false negative PPD test result?

A

Sarcoidosis or HIV (with low CD4+ counts) may show a ⊖ PPD test result despite active infection

358
Q

To what condition is a female with an intrauterine device at risk if she has a confirmed Actinomyces infection?

A

Pelvic inflammatory disease (PID), which can be caused by Actinomyces in women with IUDs

359
Q

Which bacteria is a gram ⊕, filamentous, weakly acid-fast aerobe usually found in soil and mostly affects immunocompromised hosts?

A

Nocardia

360
Q

A man receives intramuscular penicillin for treatment of spirochetes and later has fever, chills, headache, and myalgia. What caused these symptoms?

A

The Jarisch-Herxheimer reaction, a flu-like syndrome due to release of toxins by bacteria (in this case, spirochetes) killed by antibiotics

361
Q

Why might bacterial infection in a patient with whooping cough be mistaken for a viral infection?

A

Bordetella pertussis can be mistaken for a viral infection because the immune response generates a lymphocytic infiltrate

362
Q

What histologic finding is characteristic of the lesions associated with Brucella infection?

A

Noncaseating granulomas

363
Q

A baby who was recently fed honey now shows signs of floppy baby syndrome. Ingestion of what substance caused the symptoms?

A

Clostridium botulinum spores, classically found in honey, cause floppy baby syndrome

364
Q

You find gram ⊕ bacilli in a specimen that are able to survive without oxygen. Which bacteria are they?

A

Cutibacterium (formerly known as Propionibacterium) and Clostridium

365
Q

Which gene from the staphylococcal chromosomal cassette is involved in penicillin resistance?

A

mecA gene

366
Q

What 2 factors help Streptococcus pyogenes impair host phagocytosis?

A

The hyaluronic acid capsule and M protein inhibit phagocytosis

367
Q

In what region of the United States is Lyme disease common?

A

The northeastern United States

368
Q

Evidence of what recent skin infection is noted on examination of a boy presenting with a puffy face and tea-colored urine?

A

Impetigo (“honey-crusted” lesions), which is caused by Streptococcus pyogenes & more commonly precedes glomerulonephritis than pharyngitis

369
Q

Into what 4 shapes can gram ⊖ organisms be classified?

A

Diplococci, coccobacilli, bacilli, and comma-shaped rods

370
Q

A man presents with lockjaw and spasms. A few days ago, he suffered a wound while playing football in the mud. How would you treat him?

A

Treat a Clostridium tetani infection with antitoxin ± vaccine booster, diazepam (for muscle spasms), antibiotics, and wound debridement

371
Q

Staphylococcus aureus most commonly colonizes which parts of the body?

A

The nares, axilla, ears, and groin

372
Q

During its life cycle, which form of chlamydia is infectious?

A

The Elementary body (small and dense), which is “Enfectious” and Enters the cell by means of Endocytosis

373
Q

How does enteropathogenic Escherichia coli (EPEC) cause diarrhea?

A

It adheres to the apical surface and flattens villi, decreasing absorption

374
Q

What 2 features differentiate gonococcus from meningococcus?

A

N gonorrhoeae lacks polysaccharide capsule, produces acid via glucose; N meningitidis has a polysaccharide capsule and ferments maltose and glucose

375
Q

In the lab you find an oxidase ⊕, comma-shaped, gram ⊖ bacterium that is able to produce urease. What is the likely culprit?

A

Helicobacter pylori

376
Q

A 20-year-old pig farmer has bloody diarrhea. He later complains of dysuria and sore red knees. What happened? How did he get infected?

A

He has reactive arthritis from Campylobacter jejuni infection, most likely contracted from infected pigs (can also be acquired from dogs and cats)

377
Q

Compare the pathogenic mechanism of dysentery caused by enterohemorrhagic Escherichia coli (EHEC) and by enteroinvasive E coli (EIEC).

A

EHEC produces a Shiga-like toxin, causing necrosis and inflammation; EIEC directly invades the mucosa, causing necrosis and inflammation

378
Q

How does Listeria monocytogenes infection commonly present in a healthy individual?

A

As mild, self-limited gastroenteritis

379
Q

You isolate a gram ⊕ rod from a patient with nausea and vomiting 2 hours after eating. What foods did the patient likely ingest?

A

Rice or pasta contaminated with Bacillus cereus; preformed toxin can cause an emetic-type infection (nausea and vomiting within 1 to 5 hours)

380
Q

What disease does Rickettsia prowazekii cause, and what is its vector?

A

Epidemic typhus; body lice

381
Q

What symptoms and incubation period are associated with the diarrheal type of Bacillus cereus infection?

A

Nonbloody, watery diarrhea and gastrointestinal pain that arises 8-18 hours after ingestion of contaminated foods

382
Q

What are the 2 different types of presentations with Bacillus cereus infection?

A

Emetic and diarrheal types

383
Q

What bacteria is found in animal urine and often contaminates public recreational water supplies?

A

Leptospira spp

384
Q

A patient has confirmed Haemophilus influenzae infection. Name 4 diseases that can be caused by this pathogen.

A

Epiglottitis, Meningitis, Otitis media, and Pneumonia (caused by HaEMOPhilus)

385
Q

What bug is responsible for corneal ulcers in contact lens wearers?

A

Pseudomonas aeruginosa; causes corneal ulcers/keratitis and minor eye trauma

386
Q

What findings (eg, lab results, morphology, growth temperature) help identify Campylobacter jejuni as a cause of infection?

A

It is comma or S shaped, has polar flagella, is oxidase ⊕, and grows at 42°C

387
Q

Which cephalosporins can be used to treat a Pseudomonas aeruginosa infection?

A

Third- and fourth-generation cephalosporins (eg, ceftazidime, cefepime)

388
Q

Which β-hemolytic bacteria is a catalase-negative, bacitracin-resistant, gram-positive cocci?

A

Streptococcus agalactiae (group B strep)

389
Q

What two tests can be used to diagnose infection with Helicobacter pylori?

A

Urea breath test and fecal antigen test

390
Q

What bacterium causes Lyme disease?

A

Borrelia burgdorferi

391
Q

What symptoms are seen in the paroxysmal phase of Bordetella pertussis infection?

A

Paroxysms of intense cough preceding an inspiratory “whooP”

392
Q

A 10-year-old boy with Escherichia coli serotype O157:H7 has thrombocytopenia, anemia, and acute renal failure. What causes these symptoms?

A

Shiga-like toxin, which damages endothelium; microthrombi form, → hemolysis, ↓ renal blood flow, and platelet consumption (hemolytic-uremic syndrome)

393
Q

The Ixodes tick, which causes Lyme disease, relies on what animal as part of its life cycle?

A

The mouse, which serves as a natural reservoir

394
Q

Your ill patient’s blood cultures are now growing coagulase ⊖ Staphylococcus. What are the possible pathogens?

A

Staphylococcus saprophyticus or Staphylococcus epidermidis (coagulase ⊖ strains are common contaminants in blood cultures)

395
Q

An aerobic catalase ⊖ culture of cocci in chains exhibits complete hemolysis. How will you further categorize the species?

A

These are streptococci exhibiting β-hemolysis: Streptococcus pyogenes is bacitracin sensitive and Streptococcus agalactiae is resistant

396
Q

A patient presents with fever, diarrhea, and rose-colored spots on his abdomen. What is the causative agent?

A

Salmonella typhi

NBME Micro (36 decks)

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