Clinical Bacteriology Flashcards
What are 2 serologic tests that are specific for treponemal infections?
Fluorescent treponemal antibody–absorbed (FTA-ABS) test and Treponema pallidum particle agglutination (TPPA) assay
What stain is used to visualize Chlamydiae, and what characteristic finding would be seen?
Giemsa or fluorescent antibody stain; cytoplasmic inclusions (reticulate bodies)
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)
What tests are used to screen for and confirm a case of secondary syphilis?
Screen: VDRL/RPR; confirm: FTA-ABS (or dark-field microscopy)
In a patient with peptic ulcers caused by Helicobacter pylori, how are the bacteria able to thrive in the stomach’s acidic mucosa?
Helicobacter pylori is urease ⊕ and can produce ammonia, thus creating an alkaline environment
What are the laboratory characteristics of Pseudomonas aeruginosa?
Aerobic, motile, catalase ⊕, oxidase ⊕, gram ⊖ rod with a grape-like odor
How is Yersinia enterocolitica typically transferred to humans?
Pet feces (eg, from puppies), contaminated milk, or pork
What similarities are there in laboratory characteristics and pathogenicity of Salmonella and Shigella?
Both are gram ⊖ rods, oxidase ⊖, non-lactose fermenters, and can invade the GI tract by way of M cells of Peyer patches
Among lactose nonfermenters, which gram ⊖ bacilli are oxidase negative?
Shigella, Salmonella, Proteus, and Yersinia
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
What are the modes of transmission of Neisseria meningitidis?
Respiratory and oral secretions
What virulence factor is produced by Haemophilus influenzae?
Immunoglobulin A (IgA) protease
How sensitive to novobiocin is Staphylococcus saprophyticus?
It is novobiocin resistant
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 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)
Which spirochete can be visualized on light microscopy using aniline dyes (Wright or Giemsa stain)?
Borrelia (Borrelia is Big); due to size, this is the only spirochete visible on light microscopy
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 Legionella pneumophila
What is the duration of onset and resolution of food poisoning symptoms from food contaminated with Clostridium perfringens spores?
Symptoms occur within 10-12 hours and resolve in 24 hours
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
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
What lab methods are used to diagnose a chlamydial infection?
Nucleic acid amplification tests, such as PCR and visualization on Giemsa or fluorescent antibody-stained smear
Name 2 polymyxin antibiotics that can be used to treat Pseudomonas aeruginosa infection.
Polymyxin B, colistin
You find oxidase ⊖, gram ⊖, lactose-nonfermenting bacilli. Which agar can be used to differentiate bacteria based on H2S production?
Triple sugar iron (TSI) agar
How do Salmonella and Shigella compare with regard to the production of H2S gas?
Salmonella spp. (including Salmonella typhi) produce H2S; Shigella do not
What is the vector and the pathogen causing Rocky Mountain spotted fever?
Dermacentor (dog tick); bites transmit Rickettsia rickettsii
What 2 techniques are used to visualize Treponema?
Dark-field microscopy or direct fluorescent antibody (DFA) microscopy
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 patient is diagnosed with bacterial vaginosis secondary to Gardnerella vaginalis. What do you expect to see on wet prep?
Clue cells with stippled outer margins (vaginal epithelial cells covered with bacteria)
How does Listeria monocytogenes infection commonly present in a healthy individual?
As mild, self-limited gastroenteritis
What kind of infection occurs after initial exposure to Mycobacterium tuberculosis?
Primary tuberculosis
Describe the vaccine used against Haemophilus influenzae.
The vaccine consists of a type b capsular polysaccharide (polyribosylribitol phosphate) conjugated to diphtheria toxoid or another protein
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)
Name an aerobic, gram ⊕, acid-fast branching filament.
Nocardia
What is the most common serotype of enterohemorrhagic Escherichia coli (EHEC) in the US?
O157:H7
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
Which drugs of the penicillin class are appropriate for treatment of Pseudomonas infection?
Extended-spectrum penicillins (eg, piperacillin, ticarcillin)
A risk of enterohemorrhagic Escherichia coli (EHEC) contamination is typically associated with what foods?
Undercooked meats and raw leafy vegetables
What pathogen causes leprosy, and from where do humans acquire it?
Mycobacterium leprae; mainly from infected humans (rarely, armadillos)
What findings (eg, morphology, lab results, growth temperature) help identify Campylobacter jejuni as a cause of infection?
Comma or S-shaped with polar flagella, oxidase ⊕, grows at 42°C (Campylobacter likes the hot campfire)
Overgrowth of what type of bacteria occurs in the vagina of a patient with bacterial vaginosis?
Anaerobic bacteria (including the pleomorphic, gram-variable Gardnerella vaginalis)
What are 2 common modes of transmission for Campylobacter jejuni?
Fecal-oral, through person-to-person contact; ingestion of contaminated poultry, meat, or milk; note that contact with infected animals (dogs, cats, pigs) is also a risk factor
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)
Name the 4 illnesses most commonly caused by infection with Streptococcus pneumoniae.
Meningitis, otitis media (in children), sinusitis, pneumonia
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
What is the strategy of management in a Bacillus cereus infection?
Supportive care; antibiotics are ineffective against toxins
How do you confirm a Mycobacterium leprae infection?
M leprae is diagnosed by tissue polymerase chain reaction (PCR) or skin biopsy; it cannot be grown in vitro
Neisseria meningitidis and N gonorrhoeae both ferment what type of sugar and produce which type of immunoglobulin (Ig) protease?
Both ferment glucose and produce IgA protease
What unique property of chlamydial cell walls makes β-lactam antibiotics ineffective?
Chlamydial cell walls lack classic peptidoglycan (have less muramic acid residues)
How are gonococcal and meningococcal infections diagnosed?
Gonococcus: nucleic acid amplification test; meningococcus: culture-based tests or polymerase chain reaction (PCR)
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)
How would you differentiate Pseudomonas from other nonlactose fermenters?
It is oxidase positive; other nonlactose fermenters are oxidase ⊖
In a patient with virulent Mycobacterium tuberculosis infection, what inhibits phagolysosome fusion?
Sulfatides (surface glycolipids)
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
What stabilizes the membrane of Mycoplasma pneumoniae?
Sterols in the bacterial membranes; M pneumoniae lack cell walls
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)
What is the last clinical stage of an infection caused by Bordetella pertussis?
Convalescent stage; gradual recovery from persistent cough
Which gene from the staphylococcal chromosomal cassette is involved in penicillin resistance?
mecA gene
What diseases are caused by Chlamydia trachomatis?
Neonatal and follicular adult conjunctivitis, urethritis, pelvic inflammatory disease, and reactive arthritis
Under the microscope, you observe gram ⊕, spore-forming, obligate anaerobic bacilli. Diagnosis?
Clostridium spp
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
How do levels of Shiga toxin compare between Shigella boydii, Shigella sonnei, Shigella dysenteriae, and Shigella flexneri?
Most to least: S dysenteriae > S flexneri > S boydii > S sonnei; invasion of M cells causes pathogenicity so even organisms that produce little toxin can cause disease
Describe the morphology of Leptospira interrogans.
Spirochete with hook-shaped ends
Name some conditions that are treated using local botulinum toxin A (Botox)
Focal dystonia, muscle spasms, hyperhidrosis, and cosmetic reduction of facial wrinkles
How would you treat a patient with profuse rice-water diarrhea caused by gram ⊖ flagellated bacteria?
Oral rehydration therapy (diagnosis: Vibrio cholerae)
In a woman who 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 with rectal and vaginal swabs
Name the aerobic gram ⊕ bacilli.
Corynebacterium, Listeria, and Bacillus
What medications would be used to treat the lepromatous form of leprosy (Hansen disease)?
Dapsone, rifampin, and clofazimine
How does Staphylococcus epidermidis ferment mannitol?
It does not; S epidermidis cannot ferment mannitol (unlike Staphylococcus aureus)
What 2 tests can be used to diagnose infection with Helicobacter pylori?
Urea breath test and fecal antigen test
Where do viridans group streptococci commonly colonize in the human body?
The oropharynx
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)
Describe the clinical presentation associated with Gardnerella vaginalis infections.
Gray discharge with a fishy odor; nonpainful (vs vaginitis)
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)
Name 3 types of infections caused by nontypeable strains of Haemophilus influenzae.
Otitis media, conjunctivitis, and bronchitis (all mucosal infections)
A farm girl develops bloody diarrhea, abdominal cramps, nausea, vomiting, and fever. What is the likely diagnosis?
Salmonella spp infection (excluding S typhi)
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 (most cases occur in unvaccinated individuals)
How is anaplasmosis transmitted?
The Ixodes tick transmits Anaplasma spp from deer and mice
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 and more commonly precedes glomerulonephritis than pharyngitis
A 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
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
Besides Neisseria gonorrhoeae, which gram ⊖ aerobic diplococci do not use maltose?
Moraxella
Tabes dorsalis with general paresis may present in which stage of syphilis?
Tertiary syphilis; this is neurosyphilis
How would you prevent disease transmission of Neisseria gonorrhoeae?
Condoms decrease sexual transmission; erythromycin ointment prevents neonatal blindness
Of α-hemolytic cocci, which are bile soluble and insoluble?
Streptococcus pneumoniae is bile soluble; viridans streptococci are bile insoluble
What 2 clinical syndromes are caused by Legionella?
Legionnaires’ disease and Pontiac fever
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
Name 4 diseases caused by Haemophilus influenzae infection.
Epiglottitis, Meningitis, Otitis media, and Pneumonia (caused by HaEMOPhilus)
An unvaccinated patient has pseudomembranous pharyngitis with lymphadenopathy. What is the treatment?
Antibiotic therapy +/- diphtheria antitoxin (the patient has diphtheria infection)
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 (the infant likely has botulism)
What 3 illnesses can Klebsiella cause?
Aspiration pneumonia in alcoholics and diabetics, abscesses in lungs and liver, nosocomial UTIs
A bird trader who experiences fever and dyspnea is found to have an atypical pneumonia. What pathogen is the most likely cause?
A bird trader who experiences fever and dyspnea is found to have an atypical pneumonia. What pathogen is the most likely cause? flip_to_backCLICK FOR ANSWERbookmark_borderthumb_upthumb_down Chlamydophila psittaci, which has an avian reservoir (parrots) and causes atypical pneumonia
Which form of leprosy presents with hypoesthetic, hairless skin nodules?
Tuberculoid leprosy
Describe the Gram staining, hemolysis, and unique antibiotic resistance pattern(s) of viridans group streptococci.
Gram ⊕, α-hemolytic cocci, resistant to optochin and bile insoluble (unlike Streptococcus pneumoniae)
How does a streptococcal strain that shows complete hemolysis and has PYR ⊖ status react to bacitracin?
It is bacitracin resistant; this is group B (Streptococcus agalactiae) beta-hemolytic streptococci
What staining property do all mycobacteria have in common?
All are gram ⊕, acid-fast rods
In which 3 populations can Listeria monocytogenes infection lead to meningitis, and what is the empiric treatment of meningitis for them?
Neonates, immunocompromised patients, and older adults; ampicillin
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
What laboratory tests can be done that indicate a recent Streptococcus pyogenes infection?
ASO titer and anti-DNase B antibodies
What are 2 ways to directly test for syphilis?
Darkfield microscopy and polymerase chain reaction (PCR)
In what medium is Legionella pneumophila grown in vitro?
Charcoal yeast extract medium with iron and cysteine
What immunologic diseases result from Streptococcus pyogenes pharyngitis?
Rheumatic fever, glomerulonephritis (“Ph”yogenes pharyngitis can result in rheumatic “phever” and glomerulonephritis)
Helicobacter pylori is triple ⊕ for what 3 enzymes?
Catalase, oxidase, and urease
What 2 vaccination options are available to prevent Salmonella typhi infection?
Oral vaccine with live attenuated S typhi and IM vaccine with Vi capsular polysaccharide
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
Shiga-like toxin can cause hemolytic-uremic syndrome, which is a triad of…
Anemia, thrombocytopenia, acute kidney injury
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 (atypical presentation) with ARDS
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 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 is the life-threatening complication that can occur in a patient with Clostridium difficile diarrhea?
Toxic megacolon
What drug could prevent disseminated Mycobacterium 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
Describe the symptoms seen in pulmonary anthrax most commonly due to inhalation of spores from contaminated animals or animal products.
Flu-like symptoms, rapidly progressing to fever, mediastinitis, pulmonary hemorrhage, and shock
How would you describe the lesions generated by Actinomyces?
Oral/facial abscesses that drain through sinus tracts; drainage contains yellow “sulfur granules”
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 2 outcomes could be expected after a primary tuberculosis infection?
Recovery (>90%): fibrous healing/calcification, PPD test ⊕; progressive primary TB (<10%): seen in patients with AIDS or malnutrition
Describe Argyll Robertson pupils.
A pupil that constricts with accommodation but does not react to light (seen in tertiary syphilis)
What are some conditions that can result from toxin dissemination in diphtheria?
Myocarditis, arrythmias, neuropathies
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
What lab findings are expected when Staphylococcus saprophyticus is grown in a culture?
Gram ⊕, catalase ⊕, coagulase ⊖, urease ⊕ cocci in clusters
What lab test can differentiate enterocci from nonenterococcal group D bacteria?
Enterococci grow in 6.5% sodium chloride and bile; nonenterococcal group D bacteria cannot
What are the drugs used to treat a gonococcal infection?
Ceftriaxone (plus azithromycin or doxycycline for concurrent chlamydial coinfection)
Reactivation of Mycobacterium tuberculosis in a partially immune, hypersensitized host leads to what kind of infection?
Secondary tuberculosis
What differentiates Q fever from the diseases of the Rickettsia genus, to which it is closely related?
Q fever, caused by Coxiella Burnetii, can survive outside in endospore form; there is no rash or vector (Q fever is a Quite Complicated Bug)
What are the 2 forms of Hansen disease?
Lepromatous and tuberculoid (Hansen disease is also known as leprosy)
What bacteria is found in animal urine and often contaminates public recreational water supplies?
Leptospira spp
What determines the virulence of Streptococcus pneumoniae?
Capsule (virulence is lost in its absence)
What toxigenic diseases result from infection with Streptococcus pyogenes?
Scarlet fever, necrotizing fasciitis, toxic shock-like syndrome
Which Mycobacterium species presents with hand infection, and how is it acquired?
Mycobacterium marinum; acquired through aquatic exposure, likely through aquarium handling
A patient contracts an infection at the hospital by a gram ⊕ bacteria that are notably resistant to vancomycin therapy. Most likely causative organism?
Vancomycin-resistant enterococci (VRE), a major cause of nosocomial infections
What symptoms would you observe in a patient in the third (late disseminated) stage of Lyme disease?
Encephalopathy, chronic arthritis
Which 2 bacteria are slow lactose-fermenting gram ⊖ bacilli?
Citrobacter and Serratia
What populations are most likely to experience a Mycoplasma pneumoniae outbreak?
Individuals <30 years of age, military recruits, college students, and inmates
What histologic finding is characteristic of the lesions associated with Brucella infection?
Noncaseating granulomas
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)
What toxins are responsible for traveler’s diarrhea?
Heat-labile and heat-stable enteroToxins of Enterotoxigenic Escherichia coli (ETEC) cause Traveler’s diarrhea (watery)
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 disease
What are the common routes of transmission of Listeria monocytogenes to a newborn?
Transplacental transmission and vaginal transmission during delivery
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; Corynebacterium diphtheriae will grow black colonies (gray-white membranes indicate pseudomembranous pharyngitis)
Describe the appearance of α, β, and γ hemolysis on agar.
α: partial (green); β: complete (clear); γ: absent
A medical student finds gram ⊕ spherical bacteria appearing in clusters. What is the most likely strain?
Staphylococcus
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; “Ricketsii on the wRists, Typhus on the Trunk”
How do you classify β-hemolytic streptococci based on their PYR status?
Group A (Streptococcus pyogenes) is PYR ⊕; group B (Streptococcus agalactiae) is PYR ⊖
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
Gram ⊖ bacilli are differentiated by their ability to ferment what substance?
Lactose
What abnormal values will you see on labs in a patient with staphylococcal toxic shock syndrome?
↑ AST, ↑ ALT, ↑ bilirubin levels
What 2 risk factors are associated with staphylococcal toxic shock syndrome?
Prolonged use of vaginal tampons or nasal packing
What 2 diseases are associated with Bartonella infections in patients who are immunocompromised?
Bacillary angiomatosis and cat scratch disease
What is the initial treatment for a Helicobacter pylori infection?
Triple therapy: Amoxicillin (metronidazole if allergic to penicillin), Clarithromycin, Proton pump inhibitor (Antibiotics Cure Pylori)
Why does Neisseria gonorrhoeae not have a vaccine?
Due to antigenic variation of pilus proteins
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)
How does hemolytic-uremic syndrome develop following an infection with enterohemorrhagic Escherichia coli (EHEC)?
EHEC releases Shiga-like toxin → microthrombi form and damage endothelium → RBC hemolysis (shistocytes), ↓ platelets, and ↓ renal blood flow
What bacterium is transmitted by fleas and causes plague in humans?
Yersinia pestis
What is latent syphilis, and when does it occur?
Latent syphilis is characterized by positive serology but no symptoms; it follows secondary syphilis
In the lab you find an oxidase ⊕, curved, gram ⊖ bacterium that is able to produce urease. What is the likely culprit?
Helicobacter pylori
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)
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
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
What vector is responsible for the transmission of ehrlichiosis and anaplasmosis?
Tick
In what population infected with tuberculosis is progressive lung disease most likely to occur?
Individuals who are malnourished, immunocompromised, and/or HIV ⊕
A patient presents with fever, abdominal pain, constipation, and rose-colored spots on his abdomen. What is the causative agent?
Salmonella typhi (diagnosis is typhoid fever)
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)
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
In the lab, you discover an oxidase ⊕, comma-shaped, gram ⊖ organism that grows in alkaline media. Identify this bacterium.
Vibrio cholerae
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
What pathogen is responsible for Rocky Mountain spotted fever?
Rickettsia rickettsii, transmitted via tick
In what states is Rocky Mountain spotted fever commonly found?
South Atlantic states, especially North Carolina (despite its name)
A gram positive bacterium growing in chains shows no hemolysis and grows in 6.5% NaCl. What is its PYR status?
PYR ⊕; this is Entercoccus species (eg, Enterococcus faecium, Enterococcus faecalis)
Lobar pneumonia with “currant jelly” sputum develops in a patient who aspirated his own vomit. Chest x-ray is concerning for an abscess. What is the most likely pathogen?
Klebsiella (ABCDE’s of Klebsiella = Aspiration pneumonia, aBscess in lungs and liver, “Currant jelly” sputum, Diabetics, EtOH abuse)
What animal reservoirs are the source of disease in those afflicted with plague?
Rats and prairie dogs; transmit Yersinia pestis
Name organisms that are gram ⊖ coccobacilli.
Haemophilus influenzae, Bordetella pertussis, Francisella tularensis, Pasteurella, Brucella, Acinetobacter baumannii
What are the 2 virulence factors of Streptococcus pneumoniae?
IgA protease and its capsule
Explain the mechanism through which viridans group streptococci cause subacute bacterial endocarditis.
Streptococcus sanguinis produces dextrans, which bind fibrin-platelet aggregates on damaged heart valves and cause subacute bacterial endocarditis (sanguinis = blood, in the heart)
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
How does Salmonella spread through the body as compared to Shigella?
Salmonella spreads hematogenously, whereas Shigella spreads from cell to cell without hematogenous spread
Typically, what part of the body does the gram ⊕ cocci Streptococcus bovis colonize?
The gut
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)
Name the enzyme produced by Escherichia coli that breaks down lactose into glucose and galactose.
β-galactosidase
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)
For which Neisseria species is a vaccine available?
N meningitidis (type B vaccine, available for individuals at risk)
What 2 factors help Streptococcus pyogenes impair host phagocytosis?
The hyaluronic acid capsule and M protein inhibit phagocytosis
What is the vector for the pathogen that causes Lyme disease?
Ixodes ticks that dwell on deer and mice
How does staphylococcal food poisoning present?
Usually presents with nonbloody diarrhea and emesis 2-6 hours after ingestion of food with preformed toxin
In a patient with virulent Mycobacterium tuberculosis infection, what specific bacterial factor activates macrophages?
Cord factor, which causes a “serpentine cord” appearance in virulent strains and activates macrophages