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A 42 y/o male presents to the ED following a seizure episode. PE reveals oral thrush and cervical LAD. An MRI of his brain shows multiple ring enhancing lesions. Which of the following is the most likely cause of his symptoms?

A. Neurocysticercosis
B. Mycobacterium tuberculosis
C. Toxoplasmosis
D. Aspergillus fumigatus
E. Glioblastoma multiforme

C. Toxoplasmosis


A 54 y/o male is brought to the ER with a 1-week hx of headaches and progressive confusion. He was hospitalized 6 mos ago for viral esophagitis and 2 mos ago with pneumocystic pneumonia. Lumbar puncture is performed and shows a moderate increase in CSE protein concentration and CSE pleocytosis. The latex agglutination test is positive for soluble polysaccharide Ag. Light microscopy of this patient’s CSF is most likely to reveal:

A. Nonseptate hyphae
B. Germ tubes
C. Budding yeast
D. Spherules
E. Sporangium

C. Budding yeast

[this is cryptococcus neoformans, causes meningoencephalitis in HIV pts; india ink staining of c.neoformans shows round or oval budding yeast]


Several students returning from a cave exploration trip to the eastern US develop fever, cough, and malaise. Pulmonary infiltrates and hilar adenopathy are apparent on CXR. Lung tissue specimens would most likely show:

A. Multinucleated spherules
B. Ovoid cells within macrophages
C. Budding yeast with a thick capsule
D. Pseudohyphae and blastoconidia
E. Septate hyphae with dichotomous branching

B. Ovoid cells within macrophages

[this is Histoplasma capsulatum, which is located intracellularly within macrophages]


A 35 y/o male presents to your office with c/o a hard mass under his jaw. He reports that the mass developed 3 mos ago, shortly after a tooth extraction. The mass has since grown in size and has recently begun to drain yellowish pus through the overlying skin. Which of the following is the most likely cause of this patient’s condition?

A. Borrelia burgdorferi
B. Pasteurella multocida
C. Sporothrix schenckii
D. Actinomyces israelii
E. Bacillus anthracis
F. Rickettsia rickettsiae

D. Actinomyces israelii


A 35 y/o male hospitalized with extensive trauma following a tractor accident complains of severe pain in his injured right leg. The leg swells rapidly, and radiographs reveal gas in the tissues. The microorganism likely responsible for this patient’s condition is also commonly associated with:

A. Persistent cough
B. Transient watery diarrhea
C. Polyarthritis
D. Urinary frequency and burning
E. Relentless headaches and nausea

B. Transient watery diarrhea

[this is C.perfringens which causes gas gangrene and food poisoning -diarrhea]


A small outbreak of self-limited infection is reported in a summer camp. Several children develop low grade fever, throat pain, red eyes, and cervical LAD. Which is most likely cause of the outbreak?

A. Calicivirus
B. Paramyxovirus
C. Parvovirus
D. Adenovirus
E. Arenavirus
F. Poxvirus

D. Adenovirus


A 65 y/o male taking amoxicillin for sinusitis is hospitalized with diarrhea and abdominal cramps. CBC shows leukocytosis. The toxin responsible for his current condition primarily damages which of the following components of intestinal mucosal cells?

A. Mitochondrial energy depletion
B. Cytoskeleton integrity
C. Apical ion transport
D. Ribosomal protein synthesis
E. Cell membrane integrity

B. Cytoskeleton integrity

[C. difficile causes actin depolymerization, loss of cell cytoskeleton integrity, cell death, and mucosal necrosis]


A 34 y/o white male with advanced HIV infection complains of headaches and fever. India ink stain of his CSF reveals spherical yeast forms with thick capsules. Which of the following is the most likely primary focus of this pt’s infection?

A. Nasopharynx
B. Lungs
C. Intestine
D. Skin
E. Urinary tract

B. Lungs

[this is cryptococcus neoformans; lungs are primary site of entry - spreads from there to CNS]


A 23 y/o pregnant woman is found to have chronic viral hepatitis B on liver biopsy. The presence of which of the following serologic markers is most likely to increase the risk of vertical transmission of the virus?

A. HBcAg
B. HBsAg
C. HBeAg
D. Anti-HBcAg IgG
E. Anti-HBeAg IgM
F. Anti-HBsAg IgG

C. HBeAg


A 35 y/o female presents to the ED with a diffuse pruritic papulopustular rash. Her friend was brought to the ED with similar symptoms 2 days ago. Pustular fluid demonstrates oxidase-positive gram-negative rods that produce pigment on culture medium. Which of the following is the most likely source of this patient’s infection?

A. Human contact
B. Insects
C. Food
D. Water
E. Soil
F. Pets

D. Water

[this is hot tub folliculitis, caused by Pseudomonas aeruginosa — pigment described is the pyocyanin, properdin during culture]


A group of investigators has developed monoclonal Abs to the meningococcal pilus. They believe that these Abs may decrease the risk of infection by meningococci. If effective, these antibodies would directly interfere with which of the following processes?

A. Intestinal attachment
B. Endothelial adhesion
C. Pharyngeal colonization
D. Incomplete phagocytosis
E. Hematogenous dissemination

C. Pharyngeal colonization


During the first trimester of pregnancy a 22 y/o immigrant from the middle east develops a low grade fever and maculopapular rash. Over 48 hours the rash spreads from her face and chest to her trunk and extremities. PE also detects post-auricular LAD. The mother and fetus are at risk for which of the following complications? [answer choices list mother;fetus]

A. Polyarthralgia; deafness
B. Deafness; bowlegs
C. Polyarthralgia; macrocephaly
D. Meningitis; malformed teeth
E. Pneumonia; cataracts

A. Polyarthralgia; deafness


There is a specific bacterial product, that when injected locally into muscles of patients with relentless focal dystonias such as torticollis, produces a dramatic but temporary relief of symptoms. This substance is produced by bacteria that demonstrate:

A. Antiphagocytic capsule
B. Hypervariable pili
C. IgG-binding outer membrane protein
D. Intracellular polyphosphate granules
E. Subterminal spore formation

E. Subterminal spore formation

[clostridia are gram+ spore forming anaerobic rods]


A 2 y/o male is brought to clinic with fever, irritability, and decreased oral intake. PE reveals swollen gums with ulcerative lesions and enlarged, tender cervical LNs. Oral lesion scrapings demonstrate cells with intranuclear inclusions. Which of the following is most likely responsible for this patient’s disease?

A. Enveloped dsDNA virus
B. Non-enveloped dsDNA virus
C. Non-enveloped ssDNA virus
D. Non-enveloped (+)sense RNA virus
E. Enveloped (+)sense RNA virus
F. Enveloped (-)sense RNA virus

A. Enveloped dsDNA virus

[HSV-1 infection]


A small UTI outbreak is reported among children in a daycare center. Several boys develop acute onset dysuria and hematuria, both of which resolve spontaneously within 3 days. PCR on urine samples is most likely to detect genomic fragments of which of the following viruses?

B. Adenovirus
C. Parvovirus B19
D. Norwalk agent
E. Rotavirus
F. Mumps virus

B. Adenovirus

[the most common known viral cause of acute hemorrhagic cystitis in children is adenovirus]


A 63 y/o male is brought to the ED with recent onset high fever, confusion, headache, watery diarrhea, and productive cough. He has been smoking 2 ppd for 30+ years and has been diagnosed with chronic bronchitis. BP is 100/170 mm Hg, pulse is 90, respirations are 34, temp is 104.9F. Sputum microscopy after gram staining reveals numerous neutrophils but no bacteria. Which of the following is the most likely cause of this patient’s disease?

A. Mycoplasma pneumoniae
B. Klebsiella pneumoniae
C. Streptococcus pneumoniae
D. Legionella pneumophilia
E. Mycobacterium kansasii
F. Coccidioides immitis

D. Legionella pneumophilia

[one of the most common causes of community-acquired pneumonia; this is classic presentation; always suspect legionella when there is pneumonia + diarrhea]


A 44 y/o male presents to the ED with severe headache, nausea, and fever. Lumbar puncture reveals bacterial meningitis. CSF gram-stain would most likely show:

A. Bean-shaped gram-negative cocci in pairs
B. Lancet-shaped gram-positive cocci in pairs
C. Gram-positive cocci in clusters
D. Non-motile gram-negative coccobacilli
E. Motile gram-positive rods

B. Lancet-shaped gram-positive cocci in pairs

[S.pneumoniae is the most common cause of meningitis in patients less than 60 years of age]


A 46 y/o male who just returned from a mission trip to Latin America presents to your office complaining of fever myalgias, dull abdominal pain, and a week long history of watery diarrhea that recently became bloody. PE reveals fever of 102 F, HSM, and rose-colored spots at the periumbilical area. Which of the following is the most likely cause of his symptoms?

A. E.coli
B. K.pneumoniae
C. S.typhi
D. S.arteritides
E. C.fetus
F. S.flexneri
G. Proetus mirabilis

C. S.typhi


Transient bacteremia is demonstrated in a healthy 22 y/o male after a dental procedure. The gram-positive bacteria isolated from the blood synthesizes dextrans from sucrose. Which of the following would be the most likely adherence site for these bacteria?

A. Endothelial surface glycoproteins
B. Subendothelial collagen
C. Subendothelial glycosaminoglycans
D. Circulating heparins
E. Fibrin-platelet aggregates

E. Fibrin-platelet aggregates

[S.viridans only binds previously damaged sites]


Stool cultures of a 4 y/o boy with self-limited diarrhea and abdominal cramps grow non-lactose-fermenting gram negative rods on MacConkey agar. Organisms do not produce gas on fermentation of glucose and are negative on TSI agar. Which of the following is the most important pathogenic mechanism for the infection caused by this bacterium?

A. Exotoxin production
B. Mucosal invasion
C. Intestinal colonization
D. Bacteremia
E. Proliferation in LNs

B. Mucosal invasion


Picornaviruses are small RNA-containing viruses. Which of the following picornaviruses are the most acid-labile?

A. Coxsackie A
B. Echovirus
C. Poliovirus
D. Rhinovirus
E. Hepatitis A virus

D. Rhinovirus


E.coli isolated from a patient with diarrhea does not ferment sorbitol on sorbitol containing MacConkey agar and does not produce glucuronidase. The toxin produced by these bacteria would most likely:

A. Activate adenylate cyclase
B. Activate guanylate cyclase
C. Inactivate ribosomal subunits
D. Inactivate EF-2
E. Disrupt the cellular cytoskeleton

C. Inactivate ribosomal subunits

[E.coli O157:H7 aka EHEC which has Shiga-like toxin — same MOA]


A 49 y/o white male with a long hx of cough and weight loss is found on CXR to have a pulmonary infiltrate. His medical hx is otherwise unremarkable. He does not use tobacco, alcohol, or drugs. Bronchoscopy with transbronchial biopsy reveals granulomatous inflammation. Which of the following agents is most likely to cause chronic penumonia in an immunocompetent host?

A. Candida albicans
B. Blastomycetous dermatitidis
C. Pneumocystis jiroveci
D. Aspergillus fumigatus
E. Mucor species

B. Blastomycetous dermatitidis

[this is a dimorphic fungus that can cause pulmonary infections in immunocompetent people; hx of travel to an endemic area like great lakes Mississippi and Ohio river basins]