Microbiology: Clinial Bacteriology Flashcards
How would you differentiate Pseudomonas from other nonlactose fermenters?
It is oxidase positive, other nonlactose fermenters are oxidase ⊖
What differentiates Q fever from the diseases of the Rickettsia genus, to which it is closely related?
Coxiella burnetii, the causative agent of Q fever, can survive outside in endospore form; there is no rash or vector
What 2 mycobacterial species are usually resistant to multiple drugs?
M tuberculosis and M avium–intracellulare
A patient has a Haemophilus infection. By what route was it likely acquired?
Respiratory tract
A young woman presents with nonpainful, gray vaginal discharge. You suspect Gardnerella. What outcome do you expect on an amine whiff test?
A strong fishy odor; mixing the discharge with 10% potassium hydroxide (KOH) solution in an amine whiff test for G vaginalis enhances its odor
Antibodies to which virulent component of Streptococcus pyogenes can give rise to rheumatic fever?
M protein (antibodies enhance host defense, but can give rise to rheumatic fever)
What cutaneous manifestations are likely if a patient has a history of syphilis?
A maculopapular rash on palms and soles, condylomata lata (smooth, painless, wart-like lesions on genitalia), and patchy hair loss (features of secondary syphilis)
What 2 outcomes could be expected after a primary tuberculosis infection?
90%: recovery (fibrous healing/calcification, PPD test ⊕); <10%: progressive primary TB (seen in patients with AIDS or malnutrition)
What organism is the 2nd most common cause of uncomplicated urinary tract infection (UTI) in young women?
Staphylococcus saprophyticus
What vaccinations could have prevented a 12-year-old boy’s infection with a gram ⊖ aerobic coccobacillus?
The Tdap or DTaP vaccines would have protected against Bordetella pertussis infection
What are the virulence factors produced by Pseudomonas aeruginosa?
Phospholipase C; Endotoxin; Exotoxin A; Pigments: pyoverdine and pyocyanin (blue-green pigment; generates reactive oxygen species); produces PEEP
You visualize a spirochete using light microscopy with an aniline dye (Wright or Giemsa stain). What is it?
Borrelia (Borrelia is Big); due to size, this is the only spirochete visible on light microscopy
What type of hemolysis is induced by Enterococcus species?
Enterococcus species exhibit variable hemolysis
Is a VDRL test better for screening or confirmation of syphilis?
Screening; VDRL is considered sensitive but not specific; often used for initial screening and is widely available
Name an aerobic, gram ⊕, acid-fast branching filament.
Nocardia
What pyogenic illnesses are caused by Streptococcus pyogenes?
Pharyngitis, erysipelas, impetigo (“honey-crusted” lesions), cellulitis
What types of bacteria grow pink colonies on MacConkey agar?
Lactose-fermenting enteric: Citrobacter, Klebsiella, E coli, Enterobacter, Serratia (Lactose is key; test with MacConKEE’S agar)
What immunologic diseases result from Streptococcus pyogenes pharyngitis?
Rheumatic fever, glomerulonephritis (“Phyogenes pharyngitis can result in rheumatic “phever” and glomerulonephritis)
Reptiles and poultry are the animal hosts of what pathogen that causes a diarrheal illness?
Salmonella spp (exception: S typhi)
How is Campylobacter jejuni transmitted?
Fecal-oral transmission (eg, pet feces, contaminated food, contact with hands of infected persons)
What do patients with Salmonella and Shigella have in common with their clinical presentation?
Both Salmonella and Shigella often cause bloody diarrhea (note that S typhi diarrhea is often preceded by constipation)
What are the symptoms of Q fever?
Headache, cough, flu-like symptoms, pneumonia, possibly with hepatitis; may also present as culture ⊖ endocarditis
A patient is diagnosed with bacterial vaginosis secondary to Gardnerella vaginalis. What do you expect to see on wet prep?
Clue cells or vaginal epithelial cells covered with bacteria (stippled appearance along outer margins)
How would a patient with Weil disease (icterohemorrhagic leptospirosis) present?
Severe form of leptospirosis that presents with elevated bilirubin and creatinine levels, fever, hemorrhage, and low hemoglobin level
Which form of leprosy presents with intact T-cell response (cell-mediated immunity) and only a few hypoesthetic, hairless skin nodules?
Tuberculoid leprosy
In a patient with Mycoplasma pneumoniae, why are you unable to observe bacteria on a Gram stain?
M pneumoniae lack cell walls, so are not seen on a Gram stain
Pseudomonas aeruginosa exotoxin A shares a mechanism with which pseudomembrane-forming pathogen?
Pseudomonas aeruginosa’s exotoxin A and Corynebacterium diphtheriae’s diphtheria toxin both inhibit EF-2
Which optochin-resistant bacteria, part of the normal oropharyngeal flora, cause dental caries?
Streptococcus mutans and Streptococcus mitis; Viridans group strep live in the mouth; they are not afraid of-the-chin (op-to-chin resistant)
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?
False-Positive VDRL results due to Pregnancy, Viral infection (eg, EBV, hepatitis), Drugs, Rheumatic fever, Lupus or leprosy
What are the virulence factors of Shigella species?
Endotoxin; Shiga toxin (enterotoxin). Organisms that produce little toxin can cause disease by M cell invasion (key to pathogenicity)
A patient is diagnosed with peptic ulcer disease secondary to infection with Helicobacter pylori. The organism is found to be resistant to macrolides. Treatment?
Bismuth-based quadruple therapy
What 3 possible colors do colonies of lactose-fermenting bacteria exhibit on EMB agar?
Purple and black; E coli grows with a green sheen
What 2 risk factors are associated with staphylococcal toxic shock syndrome?
Prolonged use of vaginal tampons or nasal packing
A patient is told that she has traveler’s diarrhea. What type of diarrhea does it cause?
Watery diarrhea
You are told that a patient has diarrhea from an enteropathogenic Escherichia coli (EPEC) infection. What population typically gets this type of infection?
Children (EPEC = Pediatrics)
You culture 2 different α-hemolytic species. What might catalase and optochin sensitivity testing reveal?
Streptococcus pneumoniae is optochin sensitive, viridans streptococci are resistant; all are catalase ⊖
What are the key signs and symptoms of Lyme disease? (Hint: Lyme [lime] pie to the FACE)
Facial nerve palsy (usually bilateral), Arthritis, Cardiac block, Erythema migrans
A 30-year-old man has a Clostridium difficile infection. What cellular changes are caused by toxin B (cytotoxin) in his gut?
Destruction of cytoskeletal organization by means of actin depolymerization; causes pseudomembranous colitis and diarrhea
Where, geographically, are Chlamydia trachomatis serotypes A, B, and C found, and what diseases do they cause?
Africa; cause Blindness and result in Chronic infection; (ABC)
Of α-hemolytic cocci, which are bile soluble and insoluble?
Streptococcus pneumoniae is bile soluble; viridans streptococci are bile insoluble
How can the leukocyte differential help you determine if a patient’s bloody diarrhea is due to a Salmonella or Shigella species?
Both Salmonella and Shigella primarily have a PMN response, but S typhi has a monocytic response
Name the toxins produced by Staphylococcus aureus and their associated effects.
TSST-1 causes toxic shock syndrome; exfoliative toxin causes scalded skin syndrome; enterotoxin causes rapid-onset food poisoning
What characteristic finding can you see while examining L monocytogenes under the microscope in broth?
Tumbling motility (L monocytogenes is also the only gram-positive organism that produces lipopolysaccharide)
What 2 characteristics differentiate Actinomyces from Nocardia?
Actinomyces are anaerobes and acid fast ⊖; Nocardia are weakly acid-fast aerobes. Both are gram ⊕ and form long, branching filaments resembling fungi
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?
No; this is epidemic typhus, which spares the palms and soles (think Typhus on the Trunk), caused by Rickettsia prowazekii
How are Chlamydophila pneumoniae and C psittaci transmitted?
Aerosol transmission
A boy with a new pet turtle has gastroenteritis and bloody diarrhea. What is the most likely cause, and what are possible sources?
Salmonella spp; eggs, poultry, turtles (reptiles), and other pets are sources
Which 2 chlamydial species cause atypical pneumonia?
Chlamydophila pneumoniae and C psittaci
In a patient with peptic ulcers caused by Helicobacter pylori, how are the bacteria able to thrive in the stomach?
These organisms create an alkaline environment from the ammonia produced by urease
In a nonimmune host (eg, a child), what kind of infection occurs after exposure to M tuberculosis?
Primary tuberculosis
During its life cycle, which form of chlamydia replicates by fission in the cell?
The Reticulate body Replicates by means of fission and Reorganizes into elementary bodies
Name 3 types of infections caused by nontypeable strains of Haemophilus influenzae.
Otitis media, conjunctivitis, and bronchitis (all mucosal infections)
Name the common treatment for the following conditions: focal dystonia, achalasia, and muscle spasm.
Local botulinum toxin injections
Name 4 Clostridium species that produce exotoxins.
Clostridium perfringens, C botulinum, C tetani, and C difficile
What drugs are used to treat a patient with leprosy, low bacterial load, and a largely Th1-type immune response?
Dapsone and rifampin (diagnosis: tuberculoid leprosy)
Describe the gram staining, hemolysis, and unique antibiotic resistance pattern(s) of viridans group streptococci.
Gram ⊕, α-hemolytic cocci, resistant to optochin (unlike S pneumoniae)
Where do Pasteurella infections often originate from?
Various animals via bites, particularly dogs and cats
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?
Intense coughing followed by inspiratory “whoop” and vomiting (paroxysmal stage); diagnosis: Bordetella pertussis
Compare and contrast the infectivity of Salmonella and Shigella. Hint: ID50.
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)
In the lab, you grow normal skin bacteria that are Gram ⊕, catalase ⊕, coagulase ⊖, urease ⊕ cocci in clusters, sensitive to novobiocin. What organism was isolated?
Staphylococcus epidermidis
What 3 clinical conditions usually follow Neisseria meningitidis infection?
Meningococcemia, meningitis, and Waterhouse-Friderichsen syndrome
What 3 spirochete species most commonly infect humans?
Borrelia, Leptospira, and Treponema (BLT)
Which Mycobacterium species presents with hand infection, and how is it acquired?
Mycobacterium marinum; acquired through aquatic exposure, likely through aquarium handling
You perform a Gram stain on Listeria in the lab. What are your results?
Listeria is a gram ⊕ rod
Does Staphylococcus epidermidis ferment mannitol?
No; S epidermidis cannot ferment mannitol (unlike S aureus)
Which serotype of Haemophilus influenzae causes the most invasive disease?
Capsular type B
What organism is the likely pathogen if osteomyelitis develops following a puncture wound, especially in patients with diabetes?
Pseudomonas aeruginosa (a common cause of osteomyelitis after a puncture wound)
A young woman presents with a urinary tract infection caused by Enterococcus faecalis. What antibiotic are these bacteria normally resistant to?
Penicillin G
What are the various treatment options for Pseudomonas aeruginosa infection? (Hint: CAMPFIRE)
Carbapenems, Aminoglycosides, Monobactams, Polymyxins, Fluoroquinolones, thIRd/fourth-generation cephalosporins, Extended-spectrum penicillins
What are spirochetes?
Spiral-shaped bacteria with axial filaments
A patient contracts an infection by gram ⊕ bacteria that are notably resistant to vancomycin therapy. Most likely causative organism?
Vancomycin-resistant enterococci (VRE), a major cause of nosocomial infections
Tabes dorsalis with general paresis may present in which stage of syphilis?
Tertiary syphilis; this is neurosyphilis
Your patient has recurring Clostridium difficile infections. What treatment would you recommend that could prevent relapse?
Repeat courses of metronidazole, oral vancomycin, or fidaxomicin; for refractory cases, a fecal transplant can be performed
A 7-year-old boy eats an undercooked hamburger and then experiences diarrhea and oliguria. What lab abnormalities do you see?
Low RBC/platelet counts (schistocytes on blood smear), acute kidney injury; diagnosis: Hemolytic-uremic syndrome due to enteroHemorrhagic Escherichia coli (EHEC) from Hamburgers
Typically, what part of the body does the gram ⊕ cocci Streptococcus bovis colonize?
The Gut
What animal reservoirs are the source of disease in those afflicted with plague?
Rats and prairie dogs; transmit Yersinia pestis
A 26-year-old woman has vaginosis caused by Gardnerella vaginalis. What kind of vaginal discharge will you note on physical exam?
Gray discharge with a fishy odor
A complication caused by lipopolysaccharide (LPS) endotoxin develops in a man with Escherichia coli infection. What complication is it?
Septic Shock
In the lab, gram ⊕ bacteria form “medusa head” colonies. What is the capsule made of?
Bacillus anthracis synthesizes a polypeptide capsule (contains poly D-glutamate)
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?
Macrolides or quinolones. Diagnosis: likely Pontiac fever caused by L pneumophila
What structural changes might result from local tissue destruction by secondary tuberculosis?
Cavitation, caseation, and scar formation
A patient with trismus, risus sardonicus, and opisthotonos comes to your office. He asks, “What could I have done to prevent this?”
Received a tetanus vaccine
A patient is bitten by a louse and subsequently develops recurring fevers. What bacterium is likely responsible?
Borrelia recurrentis (B recurrentis: relapsing fever)
Name 7 common sites of extrapulmonary tuberculosis.
Meninges, lymph nodes, liver, spleen, adrenal glands, joints/long bones, vertebral bodies
Why does infection with Yersinia enterocolitica often present in a manner similar to Crohn disease or appendicitis?
The bacterium causes mesenteric adenitis and/or terminal ileitis, producing right lower quadrant abdominal pain
What type of Pseudomonas toxin produces symptoms of sepsis?
Endotoxin
What organism causes Hansen disease?
Also known as leprosy, it is caused by Mycobacterium leprae, an acid-fast bacillus
A patient with Helicobacter pylori has an ↑ risk for which 2 cancers?
Gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma
What population groups are at risk of Legionella pneumophila infection?
Smokers, patients with chronic lung disease, and people using old air conditioning systems
How is the screening sample to test for group B streptococci collected in a pregnant woman?
Rectal and vaginal swabs
How would you treat a patient with profuse rice-water diarrhea caused by gram ⊖ flagellated bacteria?
Prompt oral rehydration therapy (this is Vibrio cholerae)
Which organism may be either α-hemolytic or γ-hemolytic?
Enterococcus
A urine culture from a 20-year-old sexually active woman is growing a catalase ⊕ organism. Diagnosis?
Staphylococcus saprophyticus (common cause of urinary tract infections in sexually active women)
A woman is 37 weeks pregnant with positive cultures for Streptococcus agalactiae. What medication should be used as prophylaxis?
Prophylactic intrapartum penicillin administration for Streptococcus agalactiae infection
Neisseria diplococci are isolated from a patient experiencing a severe inflammatory response. What virulence factor is causing these symptoms?
Lipooligosaccharides, which have potent endotoxin activity
What are the reservoirs for Shigella and Salmonella?
All strains of Salmonella except S typhi have animal reservoirs; humans are the only reservoirs for S typhi and Shigella
Describe the appearance of α, β, and γ hemolysis on agar.
α: partial (green); β: complete (clear); γ: absent
Your culture of gram ⊕, catalase ⊖ cocci exhibits no hemolysis. How will you further identify the species?
Nonenterococci species (eg, Streptococcus bovis) cannot grow in 6.5% NaCl; enterococci (Enterococcus faecium and Enterococcus faecalis) can grow in 6.5% NaCl
What vaccination options are available to prevent Salmonella typhi infection?
Oral vaccine with live S typhi or an intramuscular vaccine with Vi capsular polysaccharide
A patient has an enterococcal biliary tract infection. What lab test can differentiate these bacteria from nonenterococcal group D bacteria?
Enterococci grow in 6.5% sodium chloride and bile; nonenterococcal group D bacteria cannot
Many patients come to the emergency department after ingesting spinach salad at a picnic. They have dysentery, anemia, and low platelet counts. Responsible toxin?
Shiga-like toxin; the patients likely have infection by enterohemorrhagic Escherichia coli (EHEC) from the raw leafy vegetable
Which form of Staphylococcus aureus is an important cause of serious nosocomial and community-acquired infections?
Methicillin-resistant Staphylococcus aureus (MRSA)
A patient is diagnosed with duodenal ulcers caused by a curved gram ⊖ rod. This bacterium is positive for what 3 enzymes?
Catalase, oxidase, and urease; the bacterium is Helicobacter pylori
What drug could prevent disseminated M avium-intracellulare infection in a patient with AIDS?
Azithromycin, which is used for prophylaxis, particularly in patients with AIDS when the CD4+ count is <50 cells/mm3
What tests are used to screen for and confirm a case of secondary syphilis?
To screen, use VDRL/RPR; to confirm, use FTA-ABS
In a patient with virulent Mycobacterium tuberculosis infection, what activates macrophages?
Cord factor, which causes a “serpentine cord” appearance in virulent strains and activates macrophages
A newborn is found to have neonatal chlamydia. How was this disease acquired?
As the infant passed through an infected birth canal
Is Staphylococcus saprophyticus novobiocin sensitive or resistant?
Novobiocin resistant
What diseases are caused by Chlamydia trachomatis?
Conjunctivitis (neonatal and follicular adult), urethritis, pelvic inflammatory disease, and reactive arthritis
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?
Gastritis and peptic ulcers (especially duodenal); diagnosis: Helicobacter pylori
Name 4 clinically important mycobacteria that cause Tuberculosis-like illness
M tuberculosis, M scrofulaceum, M avium–intracellulare, and M marinum
What product of Pseudomonas aeruginosa causes degradation of cell membranes?
Phospholipase C
Why are Chlamydia species obligate intracellular organisms?
Because they cannot make their own ATP
Which Chlamydia trachomatis serotypes cause urethritis, pelvic inflammatory disease (PID), ectopic pregnancy, neonatal pneumonia with eosinophilia, and neonatal conjunctivitis?
Types D-K
A newborn comes to the NICU with a staccato cough and eye discharge. You notice significant eosinophilia on lab studies. What is the cause?
Chlamydia trachomatis, types D-K
You identify a fast lactose-fermenting gram ⊖ bacillus growing in culture medium. What are the 3 possibilities?
Klebsiella, Escherichia coli, and Enterobacter
What are the modes of transmission of Neisseria meningitidis?
Respiratory and oral secretions
You perform a Gram stain on Serratia in the lab. What are your results?
Serratia is a gram ⊖ bacillus
A patient presents with Escherichia coli-induced dysentery. No toxins are detected. How does the responsible pathogen cause bloody diarrhea?
EnteroInvasive E coli (EIEC) Invades the mucosa of the intestine, causing necrosis and inflammation, which results in dysentery
In the microbiology lab, you identify a slow lactose-fermenting, gram ⊖ bacillus. What are the 2 possibilities?
Citrobacter and Serratia
What is the Gram stain and morphology of Yersinia enterocolitica?
Gram ⊖ rod
What pathogen is found in unpasteurized dairy products and can cause recurrent rising and falling fevers?
Brucella spp (brucellosis), which causes undulating fevers from unpasturized dairy products
What are the common sources of infection for Pseudomonas aeruginosa?
Water from sources such as swimming pools and hot tubs (P aeruginosa causes swimmer’s ear and hot tub folliculitis)
Name 11 conditions/properties associated with Pseudomonas infection using the PSEUDOMONAS mnemonic
Pneumonia, Sepsis, Ecthyma gangrenosum, UTIs, Diabetes, Osteomyelitis, Mucoid polysaccharide capsule, Otitis externa, Nosocomial infections, Addicts (drug abusers), Skin infections
Under the microscope, you observe gram ⊕, spore-forming, obligate anaerobic bacilli. Diagnosis?
Clostridium spp
What abnormal values will you see on labs in a patient with Staphylococcal toxic shock syndrome?
↑ AST, ↑ ALT, ↑ bilirubin levels
A patient has lymphogranuloma venereum. Which Chlamydia trachomatis serotypes may be the cause?
Types L1, L2, and L3 cause Lymphogranuloma venereum
In the lab, you identify a streptococcal species resistant to bacitracin. Which strain is this?
Bacitracin: group B streptococci are Resistant; group A streptococci are Sensitive (B-BRAS)
What is a pupil called that constricts with accommodation but does not react to light?
Argyll Robertson pupil or “prostitute’s pupil”
What novobiocin-sensitive bacterium found in normal skin flora commonly contaminates blood cultures?
Staphylococcus epidermidis
How would you prevent disease transmission of N gonorrhoeae?
Condoms decrease sexual transmission; erythromycin ointment prevents neonatal blindness
In which 2 populations can Listeria monocytogenes infection lead to meningitis, and what is the empiric treatment of meningitis for them?
Neonates and the immunocompromised; ampicillin
Subacute endocarditis develops after a patient undergoes gastric bypass surgery. What is the likely causative organism?
Enterococci; patients are prone to such infections after gastrointestinal and genitourinary procedures
Do Salmonella and Shigella produce H2S gas?
Salmonella spp. (including S typhi) produce H2S; Shigella do not
What is the pathologic significance of flagella in Salmonella typhi?
Flagella enable hematogenous dissemination
You suspect that a patient has a Haemophilus influenzae infection. What medium should you use to grow the bacteria?
Chocolate agar with factors V (NAD+) and X (hematin); can also be grown with Staphylococcus aureus (providing factor V by way of RBC hemolysis)
An 8-year-old boy presents with whooping cough. What are the virulence factors that facilitate this infection?
Tracheal cytotoxin and pertussis toxin (which disables Gi), and adenylate cyclase toxin (↑ cAMP); diagnosis: Bordetella pertussis infection
How does staphylococcal food poisoning present?
Usually presents with nonbloody diarrhea and emesis 2-6 hours after ingestion of food with preformed toxin
A concerned parent at your doctor’s office is asking how vaccines work. Describe the vaccine used against Haemophilus influenzae.
It consists of a type b capsular polysaccharide (polyribosylribitol phosphate [PRP]) conjugated to diphtheria toxoid or another protein
How can you differentiate between Streptococcus pyogenes and Streptococcus agalactiae on blood agar?
By testing its sensitivity to bacitracin (Streptococcus pyogenes is sensitive and S agalactiae is resistant)
For which Neisseria species is a vaccine available?
N meningitidis (type B vaccine, not widely available); available for individuals at risk
How would you describe the lesions generated by Actinomyces?
Oral/facial abscesses that drain through sinus tracts; drainage contains yellow “sulfur granules”
What form of leprosy (also known as Hansen disease) presents with diffuse, communicable skin lesions and leonine facies?
Lepromatous (it has a high bacterial load)
What kind of illness does Yersinia enterocolitica typically cause?
Acute diarrhea or pseudoappendicitis
A patient with dental caries has an abscess with sinus drainage that contains yellow “sulfur granules.” Where is this organism normally found?
The normal oral, reproductive, and GI flora; this is Actinomyces
In which host cell type do bacterial microcolonies form when a patient is infected with ehrlichiosis?
Monocytes; Monocytes for Ehrlichiosis; Granulocytes for Anaplasma (MEGA berry)
What are the common routes of transmission of Listeria monocytogenes to a newborn?
Transplacental transmission and vaginal transmission during delivery
The rickettsiae genus are transmitted by way of what vector?
Arthropods (eg, ticks), except Coxiella, which is transmitted in aerosols
What 2 clinical syndromes are caused by Legionella?
Legionnaires’ disease and Pontiac fever
What organism causes Q fever, and how is it transmitted?
Coxiella burnetii; transmitted by spores from bovine/ovine amniotic fluid inhaled as aerosols (no arthropod vector)
A man has gram ⊕ cocci that grow normally in the colon and are penicillin G resistant. What do PYR and catalase testing yield?
Enterococci are catalase ⊖ and PYR ⊕
Why does Neisseria gonorrhoeae not have a vaccine?
Due to antigenic variation of pilus proteins
How do antibiotics affect fecal excretion of bugs in patients with Salmonella and Shigella infections?
Antibiotics prolong the duration of fecal excretion for patients with Salmonella; they shorten duration in patients with Shigella
What component of virulent M tuberculosis induces release of TNF-α?
Cord factor
A boy who ate food from a poorly sealed container comes to the office with diplopia and ↓ tone in his arms. Diagnosis?
Clostridium botulinum
Name 3 possible conditions that may give a ⊕ PPD test result.
Current tuberculosis infection, previous exposure, and bacille Calmette-Guérin (BCG) vaccination
A child is infected with gram ⊕ rods with metachromatic granules and a positive Elek test. How is this infection transmitted?
Corynebacterium diphtheriae is transmitted via respiratory droplets
A child has gray-white membranes adhering to his pharynx and diffuse lymphadenopathy. How do you culture the suspected infectious agent?
Use cystine-tellurite agar, on which Corynebacterium diphtheriae will grow black colonies (gray-white membranes indicate pseudomembranous pharyngitis)
A farm girl develops bloody diarrhea, abdominal cramps, nausea, vomiting, and fever. From which animal populations might she have contracted her illness?
Poultry or reptiles (this is a Salmonella spp infection, excluding S typhi)
A patient has a Bacillus anthracis infection. What are the 2 modes of transmission of this infection?
Cutaneous exposure and inhalation
How does the rash caused by Rickettsia rickettsii spread on the body?
Rash usually starts at ankles and wrists, and then spreads to trunk, palms, and soles
How is anaplasmosis transmitted?
The Ixodes tick transmits Anaplasma spp from deer and mice
What is the characteristic fever that Brucella causes?
Unduluating fever (undulating fever from unpasteurized milk)
How is tularemia contracted?
From rabbits, deer flies, and ticks containing Francisella tularensis
What specific finding on chest x-ray confirms primary tuberculosis?
Ghon complex (Ghon focus, typically in mid/lower lobes of the lung, with hilar node involvement)
What stabilizes the membrane of Mycoplasma pneumoniae?
Sterols in the bacterial membranes; M pneumoniae lack cell walls
What subtype of Streptococcus bovis is most strongly associated with colon cancer?
Streptococcus gallolyticus, biotype 1 of S bovis (Bovis in the blood = cancer in the colon)
Name organisms that are gram ⊖ coccobacilli.
Haemophilus influenzae, Bordetella pertussis, Francisella tularensis, Pasteurella, and Brucella
What pathogen is responsible for Rocky Mountain spotted fever?
Rickettsia rickettsii, transmitted via tick
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?
PPIs ↓ gastric acidity; V cholerae typically requires a large inoculum (ID50) because it is sensitive to stomach acid
Which bacteria are responsible for endemic typhus and epidemic typhus, and how are they transmitted?
Endemic: Rickettsia typhi, transmitted via fleas
Epidemic: Rickettsia prowazekii, transmitted via human body louse
What bacterium is transmitted by fleas and causes plague in humans?
Yersinia pestis
In a partially immune, hypersensitized host, what kind of infection occurs after exposure to M tuberculosis?
Secondary tuberculosis
Lobar pneumonia with “currant jelly” sputum develops in a patient who aspirated his own vomit. What is the most likely pathogen?
Klebsiella (5 As = Aspiration pneumonia, Abscess in lungs and liver, Alcoholics, diAbetics, “currAnt jelly” sputum)
The mnemonic ABCDEFG is useful for remembering key information about Corynebacterium diphtheriae. Explain this mnemonic.
Adenosine diphosphate - (ADP) ribosylation; β-prophage; Corynebacterium Diphtheriae; Elongation Factor 2; Granules
What is responsible for the recurrent nature of the fever in Borrelia recurrentis infections?
Variation in bacterial surface antigens
What is the source of the spirochete Leptospira interrogans?
Water contaminated with animal urine; the disease is particularly prevalent in the tropics (eg, Hawaii) and among surfers
Which bacteria that frequently causes atypical pneumonia can cause an atypical variant of Stevens-Johnson syndrome in children and adolescents?
Mycoplasma pneumoniae
What form of visualization, other than a dark-field microscope, can you use to test for Treponema?
Direct fluorescent antibody (DFA) microscopy
Pneumonia and meningitis develop in a neonate as a result of infection with Escherichia coli. What virulence factor is responsible?
K capsule
A patient comes in with food poisoning caused by Staphylococcus aureus despite eating properly cooked food. What is the reason for the illness?
Enterotoxin is heat stable and not destroyed by cooking
A lab tech notes brownish-greenish rings around colonies on blood agar. Which 2 gram ⊕ cocci might these be?
Streptococcus pneumoniae and viridans streptococci
Which form of leprosy causes cell-mediated immunity to fail and tends to have a poor prognosis?
Lepromatous form can be lethal; causes a Th2 response
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?
VDRL and FTA-ABS tests and PCR of spinal fluid (diagnosis: neurosyphilis)
How are gonococcal and meningococcal infections diagnosed?
Gonococcus: nucleic acid amplification test (NAAT)
Meningococcus: culture-based tests or PCR
A child presents with acid-fast organisms in his blood and cervical lymphadenitis. If tuberculosis is ruled out, what is the likely cause?
Mycobacterium scrofulaceum infection
What hematologic finding may help confirm Mycoplasma pneumoniae infection?
A high titer of cold agglutinins (IgM); they can agglutinate or lyse red blood cells (Mycoplasma gets cold without a coat)
A Streptococcus culture exhibits partial (α, green) hemolysis. How will you further categorize the species?
Viridans streptococci: no capsule, optochin resistant, bile insoluble; Streptococcus pneumoniae: capsule present, optochin sensitive, bile soluble
What lab findings are expected when Staphylococcus saprophyticus is grown in a culture?
Gram ⊕, catalase ⊕, coagulase ⊖, urease ⊕ cocci in clusters
What is the treatment for a patient infected with Brucella?
Doxycycline and rifampin or streptomycin
What is the causative organism and vector of ehrlichiosis?
Ehrlichia chaffeensis, which is carried by the Lone Star tick (Amblyomma)
How does Staphylococcus aureus infection cause toxic shock syndrome?
Toxic shock syndrome is caused by superantigen TSST-1 that binds MHC II and T-cell receptors, results in polyclonal T-cell activation
Which animal acts as a reservoir of Mycobacterium leprae in the United States?
Armadillos
You find oxidase ⊖, gram ⊖, lactose-nonfermenting bacilli. Which agar can be used to differentiate bacteria based on H2S production?
Triple sugar iron (TSI) agar
Why is drug sensitivity testing important when a patient has an infection caused by Klebsiella?
Klebsiella is associated with multidrug resistance
In the lab, you see a strain of Streptococcus with partial hemolysis. If the bacteria are optochin sensitive, what is the specific strain?
Optochin: Viridans is Resistant, Pneumoniae is Sensitive (OVRPS [overpass])
What symptoms are seen in the catarrhal phase of Bordetella pertussis infection?
Low grade fevers, coryza (catarrhal)
What are the classical symptoms of tuberculosis?
Night sweats, weight loss, fever, hemoptysis, cough (productive or nonproductive)
In patients with Chlamydia infection, why is azithromycin the favored treatment?
It is a one-time treatment (in contrast to doxycycline, which requires several doses)
What is the definition of zoonosis?
The transmission of an infectious disease between animals and humans
In what stage of syphilis would a patient note lymphadenopathy and patchy hair loss?
Secondary
What symptoms characterize the first stage (early localized) of Lyme disease?
Erythema migrans (expanding red “bull’s-eye” rash) and flu-like symptoms
You add Streptococcus agalactiae to a culture of Staphylococcus aureus, which enlarges the area of hemolysis. What bacterial substance causes this finding?
CAMP factor made by S agalactiae (CAMP denotes the authors of the test, not cyclic AMP)
What symptoms would you observe in a patient in the third (late disseminated) stage of Lyme disease?
Encephalopathy, chronic arthritis
In the lab, you observe a group of lactose-nonfermenting, gram ⊖ bacilli that are also oxidase positive. Likely bacteria?
Pseudomonas
Cystitis and pyelonephritis develop in a 73-year-old woman as a result of infection with Eshcerichia coli. What virulence factor is responsible?
Fimbriae (P pili for pyelonephritis)
What gives the mucoid appearance of Klebsiella pneumoniae colonies?
Its polysaccharide capsule
Why is penicillin ineffective as a therapy option for Mycoplasma pneumoniae?
M pneumoniae, lacking cell walls, is resistant to penicillin; infection is treated with macrolides, doxycycline, or fluoroquinolones
How does enteropathogenic Escherichia coli (EPEC) cause damage to enterocytes?
It adheres to the apical surface and flattens villi, decreasing absorption (EPEC does not produce a toxin)
What medications would be used to treat the lepromatous form of leprosy (Hansen disease)?
Dapsone, rifampin, and clofazimine
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?
Group B streptococcal infection, which causes pneumonia, meningitis, and sepsis in Babies
In a patient with virulent M tuberculosis infection, what inhibits phagolysosome fusion?
Sulfatides (surface glycolipids)
A man has an ulcerating lesion with black eschar. A culture shows gram ⊕ spore-forming organisms. What are the organisms?
Bacillus anthracis (gram ⊕ spore-forming rods)
What type of laboratory sample is tested to diagnose Legionella infection?
Urine is used to detect presence of antigen
What kind of virulence factor is produced by Haemophilus influenzae?
Immunoglobulin A (IgA) protease
What is latent syphilis, and when does it occur?
Latent syphilis is characterized by positive serology but no symptoms; it follows secondary syphilis
You culture a cellulitis sample, which yields catalase ⊕ cocci. How can you differentiate the 3 main species in this group?
Staphylococcus aureus is coagulase ⊕; coagulase ⊖ species: Staphylococcus epidermidis is novobiocin sensitive and Staphylococcus saprophyticus is resistant
You want to grow Helicobacter pylori to study in the lab. What part of a patient’s stomach should you take a sample from?
The antrum; H pylori mainly colonizes the antrum
Dysarthria, dysphagia, and diplopia develop after a man eats food from a poorly sealed can. What is the mechanism of the causative toxin?
Inhibition of acetylcholine release at the neuromuscular junction, causing botulism (this heat-labile toxin is produced by Clostridium botulinum)
An unvaccinated boy has epiglottitis. A neck x-ray shows the “thumb sign.” How is the most likely causative agent transmitted?
Aerosol; diagnosis: Haemophilus influenzae
In which host cell type do bacterial microcolonies form when a patient is infected with anaplasmosis?
Granulocytes; Monocytes for Ehrlichiosis; Granulocytes for Anaplasma (MEGA berry)
A febrile patient with jaundice complains of RUQ tenderness after an endoscopic retrograde cholangiopancreatography (ERCP) procedure. What is the causative organism?
Enterococci; diagnosis is ascending cholangitis (enterococci are a common cause of biliary tract infection after gastrointestinal/genitourinary [GI/GU] procedures)
In the lab you see a strain of Streptococcus showing partial hemolysis. If the bacteria are optochin resistant, what is the strain?
Optochin: Viridans is Resistant, but Pneumoniae is Sensitive (OVRPS [overpass])
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?
EHEC does not ferment sorbitol
Which gram ⊕ filamentous and weakly acid fast bacteria spread to the CNS?
Nocardia
Following severe bacteremia caused by tuberculosis, what might be seen on examination of histopathology slides from various organs?
Small, widespread granulomas in multiple organs; diagnosis: miliary tuberculosis
Where can treponemes be found during primary and secondary syphilis, and what do you use to visualize them?
Primary syphilis: in chancres; secondary syphilis: in condylomata lata; use fluorescent or dark-field microscopy to see treponemes
How do you confirm a Mycobacterium leprae infection?
M leprae is diagnosed by tissue PCR or skin biopsy; it cannot be grown in vitro
What are the possible modes of transmission of Yersinia enterocolitica?
Pet feces (eg, from puppies), contaminated milk, or pork
What are the modes of transmission of Neisseria gonorrhoeae?
N gonorrhoeae is transmitted during sex or birth
A patient with suspected syphilis has a positive VDRL test result. Why do you confirm the result with an FTA-ABS test?
An FTA-ABS test is more specific for syphilis; a VDRL test is more sensitive and more likely to yield a false-positive result
What are the drugs used to treat a gonococcal infection?
Ceftriaxone (plus azithromycin or doxycycline for concurrent chlamydial coinfection)
As a medical student, you are told a culture grows gram ⊖ diplococci. What are the 2 strains that may be growing?
Neisseria species and Moraxella species
A sexually active woman has pelvic inflammatory disease (PID) due to Chlamydia trachomatis. How do you treat her?
Azithromycin (single dose) or doxycycline, plus ceftriaxone to empirically treat for gonorrhea
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?
TMP-SMX; he may have a severe Nocardia infection, which can mimic TB but with negative PPD findings; can cause cutaneous infections after trauma
A scientist working on MRSA knocks out the bacteria’s penicillinases but finds that the bug is still resistant to several penicillins. Why?
MRSA alters its penicillin-binding proteins to resist killing by penicillinase-stable penicillins (eg, methicillin, oxacillin, nafcillin)
A 35-year-old man complains of pain and swelling along the inguinal lymph nodes, which have begun to ulcerate, forming buboes. Treatment?
Treat with doxycycline (Chlamydia trachomatis types L1, L2, and L3 cause Lymphogranuloma venereum)
Which part of the body does Helicobacter pylori typically colonize?
Antrum of the stomach
What is the vector for the pathogen causing Rocky Mountain spotted fever?
Dermacentor (dog tick); bites transmit Rickettsia rickettsii
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?
Green, partial hemolysis (α-hemolysis); Streptococcus pneumoniae is the most common cause of pneumonia in older patients
What prophylaxis should be offered to a health care worker who may have been exposed to N meningitidis?
Rifampin, ciprofloxacin, or ceftriaxone
In the lab, you grow gram ⊖ aerobic diplococci. They do not use maltose. Polymerase chain reaction (PCR) for Neisseria DNA is negative. Organism isolated?
Moraxella
What are the symptoms of Mycoplasma pneumoniae pneumonia?
Atypical “walking pneumonia”; insidious onset with nonproductive cough, headache, and patchy or diffuse interstitial infiltrates on chest x-ray
A patient is told that she has traveler’s diarrhea. What toxins are responsible for this diarrhea?
Labile and stable enteroToxins of enterotoxic Escherichia coli (ETEC) cause Traveler’s diarrhea
What is the mechanism of action of Staphylococcus aureus protein A (virulence factor)?
It binds the Fc region of IgG (Fc-IgG), inhibiting complement activation and phagocytosis
A bird trader who experiences fever and dyspnea is found to have an atypical pneumonia. What pathogen is the most likely cause?
Chlamydophila psittaci, which has an avian reservoir (parrots) and causes atypical pneumonia
A pregnant woman and her husband both have a rickettsial infection. How do you treat them?
Chloramphenicol for the pregnant woman; doxycycline for her husband
What 3 types of Escherichia coli do not invade the intestinal mucosa?
Enterohemorrhagic (EHEC), enterotoxigenic (ETEC), and enteropathogenic (EPEC); only the enteroinvasive (EIEC) type invades intestinal mucosa
A patient with cystic fibrosis presents with cough productive of blue-green sputum. Which drugs of the penicillin class are appropriate for treatment?
Extended-spectrum penicillins (eg, piperacillin, ticarcillin) can be used to treat his likely Pseudomonas aeruginosa infection
A patient who has had the bacille Calmette-Guérin (BCG) vaccine is being evaluated for tuberculosis. What is the most appropriate test to order?
Interferon-γ release assay (IGRA), a more specific test that yields fewer false ⊕ results than PPD yields from BCG vaccination
What areas of the body are likely to be infected by Mycobacterium leprae?
The skin and superficial nerves, causing “glove and stocking” loss of sensation; M leprae likes cool temperatures
In what population infected with tuberculosis is progressive lung disease most likely to occur?
Individuals who are malnourished and/or HIV ⊕
A man with a chronic peptic ulcer has a positive result on urease breath testing. What is the first-line treatment?
Triple therapy: Amoxicillin (metronidazole if allergic to penicillin), Clarithromycin, Proton pump inhibitor (Antibiotics Cure Pylori)
You are given a group of gram ⊖ bacilli. They are differentiated by their ability to ferment what substance?
Lactose
What are the laboratory characteristics of Pseudomonas aeruginosa?
It is an aerobic, motile, catalase ⊕, oxidase ⊕, gram ⊖ rod; is a nonlactose fermenter with a grape-like odor
What spirochete causes destruction of the vasa vasorum of the aorta?
Treponema pallidum, which causes syphilis; diagnosis: aortitis
What 2 diseases are associated with Bartonella infections in patients who are immunocompromised?
Bacillary angiomatosis and cat scratch disease
Name 2 polymyxin antibiotics that can be used to treat P aeruginosa infection.
Polymyxin B, colistin
A bacteria is identified to be hippurate test ⊕, PYR ⊖, bacitracin resistant, and β-hemolytic. Name the bacteria.
Streptococcus agalactiae
A 9-year-old boy has ascending weakness. If this is related to an infection, what did he most likely eat to cause it?
Poultry, meat, or unpasteurized milk, which can harbor Campylobacter jejuni, and which can cause Guillain-Barré syndrome
What spirochete is responsible for causing syphilis?
Treponema pallidum
Differentiate Legionnaires’ disease from Pontiac fever.
Legionnaires’ disease is marked by severe pneumonia (unilateral, lobar) with fever, CNS and GI symptoms; Pontiac fever is a mild, flu-like syndrome
A colleague tells you that your next patient has confirmed tetanus toxin in his system. What symptoms do you expect this patient to exhibit?
Spastic paralysis, risus sardonicus (open grin and raised eyebrows), trismus (lockjaw), and opisthotonos (spinal extensor spasms)
A positive Venereal Disease Research Laboratory (VDRL) test indicates that antibodies have formed against what molecule?
Beef cardiolipin
In what 4 ways can Shigella be transmitted between humans?
The Four Fs = Fingers, Flies, Food, and Feces
In what states is Rocky Mountain spotted fever commonly found?
South Atlantic states, especially North Carolina (despite its name)
What are the 2 virulence factors of Streptococcus pneumoniae?
IgA protease and its capsule
What pathogen causes leprosy, and from where do humans acquire it?
Mycobacterium leprae; mainly from infected humans (rarely, armadillos)
How do you counsel a pregnant woman to prevent transmission of Listeria monocytogenes?
Avoid ingestion of unpasteurized dairy products and cold deli meats; L monocytogenes grows well at 4°-10°C, refrigeration temperatures
What type of lesion is seen on an x-ray of the lung fields of a patient with secondary tuberculosis?
A fibrocaseous cavitary lesion in the upper lobe
In the lab, you identify a streptococcal species sensitive to bacitracin. Which strain is this?
Bacitracin: group B streptococci are Resistant; group A streptococci are Sensitive (B-BRAS)
An unvaccinated boy contracts meningitis. Bacteria grow on chocolate agar containing factors V and X. Treatment plan?
Treat with ceftriaxone for Haemophilus influenzae meningitis; close contacts should receive rifampin prophylaxis
Name the enzyme produced by E coli that breaks down lactose into glucose and galactose.
β-galactosidase
Blood agar grows a β-hemolytic organism. How would you differentiate both Streptococcus pyogenes and Streptococcus agalactiae from Staphylococcus aureus?
Both are catalase ⊖, unlike S aureus, which is catalase ⊕
In the lab, you have a coagulase ⊖ Staphylococcus bacterium. You notice that it is novobiocin sensitive. Identify it.
NOvobiocin: Saprophyticus is Resistant; Epidermidis is Sensitive (NO StRESs on the office “staph” retreat)
How would the presentation be different if a patient had Staphylococcus aureus toxic shock syndrome (TSS) versus Streptococcus pyogenes TSS?
S aureus TSS: fever, vomiting, shock, desquamation, rash, and end-organ failure; S pyogenes TSS: painful skin infection
You culture a sputum sample, suspecting either Staphylococcus or Streptococcus. How can you differentiate the bacteria?
Staphylococcus is catalase ⊕ and grows in clusters; Streptococcus is catalase ⊖ and grows in pairs or chains (both are gram ⊕ cocci)
Name 6 inflammatory diseases that can result from infection with Staphylococcus aureus.
Skin infection, endocarditis, pneumonia (often following influenza virus infection), organ abscess, septic arthritis, and osteomyelitis
A hospitalized patient develops severe diarrhea with a foul odor. Which toxin produced by the causative bacteria binds the gut’s brush border?
Toxin A, which is an enterotoxin produced by Clostridium difficile that alters fluid secretions
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?
He likely has Guillain-Barré syndrome triggered by Campylobacter jejuni infection (bloody diarrhea)
How do levels of Shiga toxin compare between S boydii, S sonnei, S dysenteriae and S flexneri?
From most to least: S dysenteriae, S flexneri, S boydii, and S sonnei
A man has watery, nonbloody diarrhea after eating reheated rice 9 hours earlier. Explain how the causative organisms likely survived heating.
This is likely a Bacillus cereus infection; spores survive cooking; rewarming the rice promotes spore germination and enterotoxin formation
A medical student finds gram ⊕ spherical bacteria appearing in clusters. What is the most likely strain?
Staphylococcus
Chlamydia trachomatis can cause conjunctivitis in which age group?
Neonates as well as adults
In the lab, you discover an oxidase ⊕, comma-shaped, gram ⊖ organism that grows in alkaline media. Identify this bacterium.
Vibrio cholerae
What 5 disease states might Neisseria gonorrhoeae present as?
Gonorrhea, pelvic inflammatory disease (PID), septic arthritis, Fitz-Hugh–Curtis syndrome, and neonatal conjunctivitis (2-5 days after birth)
What are the laboratory characteristics of Vibrio cholerae?
Gram ⊖, comma-shaped, flagellated, oxidase ⊕ bacteria that grow in alkaline media and is sensitive to stomach acid (acid labile)
In a patient with Mycoplasma pneumoniae pneumonia, how does the chest x-ray finding compare to the severity of clinical illness?
X-ray usually looks worse than the patient
What antibiotics are used to treat infection with Salmonella typhi and other Salmonella species?
Salmonella typhi: ceftriaxone or fluoroquinolone
Salmonella spp. (except S typhi): antibiotics not indicated
Name the aerobic gram ⊕ bacilli.
Corynebacterium, Listeria, and Bacillus
Name the 4 illnesses most commonly caused by infection with Streptococcus pneumoniae.
Meningitis, otitis media (in children), pneumonia, sinusitis
A sexually active woman has pelvic inflammatory disease (PID). If it is caused by Chlamydia trachomatis, what do you see on microscopy?
Cytoplasmic inclusions (reticulate bodies) on Giemsa or fluorescent antibody staining
What property of S epidermidis allows it to easily infect prosthetic devices (eg, hip implants, heart valves) and intravenous catheters?
Production of an adherent biofilm
In the lab, you have a coagulase ⊖ Staphylococcus bacterium. You notice that it is novobiocin resistant. Identify it.
NOvobiocin: Saprophyticus is Resistant; Epidermidis is Sensitive (NO StRESs on the office “staph” retreat)
What 2 patient populations are susceptible to Streptococcus pneumoniae sepsis?
Patients with sickle cell disease and asplenia
What is the classic triad of symptoms of Rocky Mountain spotted fever?
Fever, headache, and rash (vasculitis)
What features help in isolating Streptococcus pneumoniae from a culture medium?
It is a gram ⊕, α-hemolytic, lancet-shaped diplococci, which is sensitive to optochin
What are the Gram stain characteristics of Legionella?
Legionella is a gram-⊖ bacillus but does not react well to Gram stain; use silver stain
A patient tells you that he started vomiting about an hour after eating reheated rice. What is the most likely causative toxin?
Cereulide, the preformed toxin in Bacillus cereus (patient has reheated rice syndrome)
A sexually active patient develops Gardnerella vaginalis infection but her partner does not. What is the reason?
It is not sexually transmitted but, it is associated with sexual activity
What are the 2 forms of Hansen disease?
Lepromatous and tuberculoid (Hansen disease is also known as leprosy)
What staining property do all mycobacteria have in common?
All are gram ⊕, acid-fast rods
What is the vector for the pathogen causing endemic typhus?
Fleas; transmit Rickettsia typhi
One patient has an Actinomyces infection; another has a Nocardia infection. How do you treat each patient?
Sulfonamides can treat Nocardia; Actinomyces is treated with Penicillin (Treatment is a SNAP)
N meningitidis and N gonorrhoeae both ferment what type of sugar and produce which type of immunoglobulin protease?
Both ferment glucose and produce IgA protease
Where do viridans group streptococci commonly colonize in the human body?
The oropharynx
A patient has severe diarrhea; exam reveals pseudomembranous colitis, and culture shows gram ⊕ spore-forming bacilli. Treatment?
Metronidazole or oral vancomycin (this is infection with Clostridium difficile [Difficile causes diarrhea])
A man who swims in a cove has fever, fatigue, body aches, photophobia, and conjunctival suffusion. What is the water contaminated with?
Animal urine containing Leptospira interrogans; diagnosis: leptospirosis
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?
Bordetella, a gram ⊖ coccobacillus
Explain the mechanism through which viridans group streptococci cause subacute bacterial endocarditis.
Streptococcus sanguinis makes dextrans, which bind to fibrin-platelet aggregates on damaged heart valves (sanguinis = blood, in the heart)
Where does Staphylococcus saprophyticus normally inhabit the human body?
The female genital tract and perineum
A patient with pseudomembranous pharyngitis and arrhythmias has diphtheria. What is the toxin, and how does it inhibit protein synthesis?
Exotoxin (encoded on a β-prophage); it inhibits protein synthesis by adenosine diphosphate- (ADP) ribosylation of elongation factor 2 (EF-2)
An infant who is fed breast milk mixed with honey and jaggery, presents with ↓ tone in all limbs. How would you treat the condition?
Treat with human botulinum immunoglobulin
What abnormalities may present in a case of congenital syphilis?
Saber shins, saddle nose, cranial nerve VIII deafness, Hutchinson (notched) teeth, mulberry molars, rhagades, snuffles, short maxilla
A 27-year-old man has spastic paralysis. Renshaw cell neurotransmitter release is inhibited. Name the toxin and explain how it works.
Tetanospasmin exotoxin (from Clostridium tetani); cleaves SNARE proteins, thus blocking release of glycine and γ-aminobutyric acid (GABA), which are inhibitory neurotransmitters
How is Vibrio cholerae transmitted?
By consumption of contaminated water or uncooked food (eg, raw shellfish)
What 3 illnesses can Klebsiella cause?
Aspiration pneumonia, abscesses in lungs and liver, and nosocomial UTIs
A girl presents with a strawberry tongue, circumoral pallor, sore throat, fever, and sandpaper-like body rash. Causative agent?
Streptococcus pyogenes (Diagnosis: scarlet fever caused by the erythrogenic toxin)
What 2 pigments are produced by Pseudomonas aeruginosa?
Pyoverdine and pyocyanin (blue-green pigment, generates reactive oxygen species)
What property of Pseudomonas may contribute to the chronic pneumonia in patients with cystic fibrosis?
The mucoid polysaccharide capsule causes chronic pneumonia in patients with cystic fibrosis as a result of biofilm formation
What are 2 common modes of transmission for Campylobacter jejuni?
Fecal-oral (for person-to-person contact) or via ingestion
How does Salmonella spread through the body compared with Shigella?
Salmonella spreads hematogenously, whereas Shigella spreads from cell to cell without hematogenous spread
What populations are most likely to experience a Mycoplasma pneumoniae outbreak?
Individuals <30 years of age, military recruits, and inmates
In the lab, you discover an oxidase ⊕, comma-shaped, gram ⊖ bacterium that grows at 42°C. Identify it.
Campylobacter jejuni
How does coagulase positivity contribute to the pathogenicity of Staphylococcus aureus?
It allows the organism to form a fibrin clot around itself, permitting abscess formation
In what medium is Legionella pneumophila grown in vitro?
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)
How long does Staphylococcus aureus toxin take to cause nonbloody diarrhea and emesis?
Preformed Staphylococcal enterotoxins causing food poisoning have a short incubation period of 2-6 hours
A farmer has cycling fevers, night sweats, and arthralgias after drinking unpasteurized milk. What is the causative organism?
Brucella (the farmer likely has brucellosis)
What culture medium could you use to grow Mycoplasma pneumoniae?
Eaton agar; this is not routinely done for diagnosis because culture takes 2-3 weeks to grow
What symptoms would you observe in a patient in the second (early disseminated) stage of Lyme disease?
Secondary lesions, atrioventricular block, facial nerve (Bell) palsy, migratory myalgias/transient arthritis, carditis
A sheep farmer inhales Bacillus anthracis spores. What sort of symptoms do you expect to arise?
Flu-like symptoms, rapidly progressing to fever, mediastinitis, pulmonary hemorrhage, and shock
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?
Yes; these are nonenterococcus bacteria (eg, Streptococcus bovis), which will grow in bile
What rickettsial organism is commonly responsible for culture ⊖ endocarditis?
Coxiella burnetii
What is the vector for the pathogen that causes Lyme disease?
Ixodes ticks that dwell on deer and mice
A culture is growing a nonlactose-fermenting, gram ⊖ rod that is commonly associated with wound infection in burn victims. Name the bacteria
Pseudomonas aeruginosa
A shepherd presents with hemoptysis. A chest x-ray shows mediastinal widening. Diagnosis?
Bacillus anthracis infection (also called woolsorter’s disease; mediastinal widening is due to mediastinitis)
A woman is 36 weeks pregnant. What bacterium should you screen for?
Streptococcus agalactiae colonizes the vagina and is screened for at 35-37 weeks of gestation
What 3 diseases start with a rash on the palms and soles?
Coxsackievirus A infection, Rocky Mountain spotted fever, and secondary syphilis (you drive CARS using your palms and soles)
In the microbiology lab, you identify a β-hemolytic organism that is both catalase and coagulase ⊕. What organism did you find?
Staphylococcus aureus
What agar, other than EMB, can be used to diagnose a possible Klebsiella infection?
MacConkey agar; you will observe pink colonies
Overgrowth of what type of bacteria occurs in the vagina of a patient with bacterial vaginosis?
Anaerobic bacteria including Gardnerella vaginalis
What 2 immediate complications are possible if a patient contracts an infection with Streptococcus bovis?
Bacteremia and subacute endocarditis
What laboratory tests can be done that indicate a recent Streptococcus pyogenes infection?
ASO titer and anti-DNase B antibodies
What similarities are there in laboratory characteristics and pathogenicity of Salmonella and Shigella?
Both are gram ⊖ rods, oxidase ⊖, nonlactose fermenters, and able to invade the GI tract via M cells of Peyer patches
You are administering vaccines at the pediatrician’s office. Typically, the Haemophilus influenzae vaccine is given to which age group?
Infants 2-18 months of age
How is the bacteria Legionella pneumophila transmitted?
Aerosol transmission from an environmental water source such as an air conditioner or hot water tank (no person-to-person transmission)
How do you diagnose disease in a patient with suspected Clostridium difficile infection (marked by diarrhea after antibiotic use)?
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
What are the virulence factors of Salmonella typhi?
Endotoxin and Vi capsule
A woman diagnosed wih bacterial vaginosis is prescribed metronidazole but cannot tolerate it. What second medication may be given instead?
Clindamycin is a reasonable second-line treatment (overgrowth of vaginal anaerobic bacteria characterize bacterial vaginosis)
A traveler is ill with typhoid fever and goes untreated. In which organ does the causative agent colonize?
Gallbladder (this is Salmonella typhi)
What toxigenic diseases result from infection with Streptococcus pyogenes?
Scarlet fever, necrotizing fasciitis, toxic shock-like syndrome
What unique property of chlamydial cell walls makes β-lactam antibiotics ineffective?
The cell walls lack classic peptidoglycans because there is less muramic acid
Among lactose nonfermenters, which gram ⊖ bacilli are oxidase negative?
Shigella, Salmonella, Proteus, and Yersinia
You identify 2 distinct Neisseria species in the lab. How can you distinguish between these 2 species based on their metabolism?
N meningitidis ferments maltose; N gonorrhoeae does not ferment maltose
A 2-year-old boy, unvaccinated against Haemophilus influenzae, has the flu. Which organism could be the cause?
Influenza virus causes the flu, not H influenzae
What vector is responsible for the transmission of Ehrlichiosis and Anaplasmosis?
Tick
What 2 conditions may bring about a false negative PPD test result?
Sarcoidosis or HIV (with low CD4+ counts) may show a ⊖ PPD test result despite active infection
To what condition is a female with an intrauterine device at risk if she has a confirmed Actinomyces infection?
Pelvic inflammatory disease (PID), which can be caused by Actinomyces in women with IUDs
Which bacteria is a gram ⊕, filamentous, weakly acid-fast aerobe usually found in soil and mostly affects immunocompromised hosts?
Nocardia
A man receives intramuscular penicillin for treatment of spirochetes and later has fever, chills, headache, and myalgia. What caused these symptoms?
The Jarisch-Herxheimer reaction, a flu-like syndrome due to release of toxins by bacteria (in this case, spirochetes) killed by antibiotics
Why might bacterial infection in a patient with whooping cough be mistaken for a viral infection?
Bordetella pertussis can be mistaken for a viral infection because the immune response generates a lymphocytic infiltrate
What histologic finding is characteristic of the lesions associated with Brucella infection?
Noncaseating granulomas
A baby who was recently fed honey now shows signs of floppy baby syndrome. Ingestion of what substance caused the symptoms?
Clostridium botulinum spores, classically found in honey, cause floppy baby syndrome
You find gram ⊕ bacilli in a specimen that are able to survive without oxygen. Which bacteria are they?
Cutibacterium (formerly known as Propionibacterium) and Clostridium
Which gene from the staphylococcal chromosomal cassette is involved in penicillin resistance?
mecA gene
What 2 factors help Streptococcus pyogenes impair host phagocytosis?
The hyaluronic acid capsule and M protein inhibit phagocytosis
In what region of the United States is Lyme disease common?
The northeastern United States
Evidence of what recent skin infection is noted on examination of a boy presenting with a puffy face and tea-colored urine?
Impetigo (“honey-crusted” lesions), which is caused by Streptococcus pyogenes & more commonly precedes glomerulonephritis than pharyngitis
Into what 4 shapes can gram ⊖ organisms be classified?
Diplococci, coccobacilli, bacilli, and comma-shaped rods
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?
Treat a Clostridium tetani infection with antitoxin ± vaccine booster, diazepam (for muscle spasms), antibiotics, and wound debridement
Staphylococcus aureus most commonly colonizes which parts of the body?
The nares, axilla, ears, and groin
During its life cycle, which form of chlamydia is infectious?
The Elementary body (small and dense), which is “Enfectious” and Enters the cell by means of Endocytosis
How does enteropathogenic Escherichia coli (EPEC) cause diarrhea?
It adheres to the apical surface and flattens villi, decreasing absorption
What 2 features differentiate gonococcus from meningococcus?
N gonorrhoeae lacks polysaccharide capsule, produces acid via glucose; N meningitidis has a polysaccharide capsule and ferments maltose and glucose
In the lab you find an oxidase ⊕, comma-shaped, gram ⊖ bacterium that is able to produce urease. What is the likely culprit?
Helicobacter pylori
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?
He has reactive arthritis from Campylobacter jejuni infection, most likely contracted from infected pigs (can also be acquired from dogs and cats)
Compare the pathogenic mechanism of dysentery caused by enterohemorrhagic Escherichia coli (EHEC) and by enteroinvasive E coli (EIEC).
EHEC produces a Shiga-like toxin, causing necrosis and inflammation; EIEC directly invades the mucosa, causing necrosis and inflammation
How does Listeria monocytogenes infection commonly present in a healthy individual?
As mild, self-limited gastroenteritis
You isolate a gram ⊕ rod from a patient with nausea and vomiting 2 hours after eating. What foods did the patient likely ingest?
Rice or pasta contaminated with Bacillus cereus; preformed toxin can cause an emetic-type infection (nausea and vomiting within 1 to 5 hours)
What disease does Rickettsia prowazekii cause, and what is its vector?
Epidemic typhus; body lice
What symptoms and incubation period are associated with the diarrheal type of Bacillus cereus infection?
Nonbloody, watery diarrhea and gastrointestinal pain that arises 8-18 hours after ingestion of contaminated foods
What are the 2 different types of presentations with Bacillus cereus infection?
Emetic and diarrheal types
What bacteria is found in animal urine and often contaminates public recreational water supplies?
Leptospira spp
A patient has confirmed Haemophilus influenzae infection. Name 4 diseases that can be caused by this pathogen.
Epiglottitis, Meningitis, Otitis media, and Pneumonia (caused by HaEMOPhilus)
What bug is responsible for corneal ulcers in contact lens wearers?
Pseudomonas aeruginosa; causes corneal ulcers/keratitis and minor eye trauma
What findings (eg, lab results, morphology, growth temperature) help identify Campylobacter jejuni as a cause of infection?
It is comma or S shaped, has polar flagella, is oxidase ⊕, and grows at 42°C
Which cephalosporins can be used to treat a Pseudomonas aeruginosa infection?
Third- and fourth-generation cephalosporins (eg, ceftazidime, cefepime)
Which β-hemolytic bacteria is a catalase-negative, bacitracin-resistant, gram-positive cocci?
Streptococcus agalactiae (group B strep)
What two tests can be used to diagnose infection with Helicobacter pylori?
Urea breath test and fecal antigen test
What bacterium causes Lyme disease?
Borrelia burgdorferi
What symptoms are seen in the paroxysmal phase of Bordetella pertussis infection?
Paroxysms of intense cough preceding an inspiratory “whooP”
A 10-year-old boy with Escherichia coli serotype O157:H7 has thrombocytopenia, anemia, and acute renal failure. What causes these symptoms?
Shiga-like toxin, which damages endothelium; microthrombi form, → hemolysis, ↓ renal blood flow, and platelet consumption (hemolytic-uremic syndrome)
The Ixodes tick, which causes Lyme disease, relies on what animal as part of its life cycle?
The mouse, which serves as a natural reservoir
Your ill patient’s blood cultures are now growing coagulase ⊖ Staphylococcus. What are the possible pathogens?
Staphylococcus saprophyticus or Staphylococcus epidermidis (coagulase ⊖ strains are common contaminants in blood cultures)
An aerobic catalase ⊖ culture of cocci in chains exhibits complete hemolysis. How will you further categorize the species?
These are streptococci exhibiting β-hemolysis: Streptococcus pyogenes is bacitracin sensitive and Streptococcus agalactiae is resistant
A patient presents with fever, diarrhea, and rose-colored spots on his abdomen. What is the causative agent?
Salmonella typhi
