ABMM ABMM Questions and Answers

A patient develops a severe diarrheal illness after consuming raw oysters. Stool cultures grow a Gram-negative, comma-shaped bacterium that is oxidase-positive and grows on thiosulfate-citrate-bile salts-sucrose (TCBS) agar, producing green colonies. The MOST likely virulence factor contributing to the watery diarrhea is:

A microbiology laboratory receives a blood culture from a patient with suspected bacterial endocarditis. After 24 hours of incubation, Gram-positive cocci in clusters are observed on the Gram stain. Catalase test is positive, and coagulase test is negative. Further testing reveals susceptibility to novobiocin. The MOST likely organism is:

A patient develops a severe diarrheal illness after consuming raw seafood. Stool culture yields a Gram-negative, comma-shaped bacterium that is oxidase-positive and grows on thiosulfate-citrate-bile salts-sucrose (TCBS) agar, producing blue-green colonies. The MOST significant virulence factor contributing to the severe, cholera-like diarrhea caused by this organism is:

An elderly patient in a long-term care facility develops a localized outbreak of painful vesicles along a dermatome. Tzanck smear of a vesicle reveals multinucleated giant cells. The MOST likely causative agent is:

A clinical microbiology laboratory is using Sanger sequencing to identify mutations associated with antibiotic resistance in Mycobacterium tuberculosis. This method directly determines the:

A public health investigation is underway following several cases of encephalitis in a specific geographic region during the summer months. Mosquitoes are abundant in the area. Serological testing of patient CSF samples reveals IgM antibodies against a flavivirus. The MOST likely causative agent is:

A microbiology laboratory is processing a sputum sample from a patient with chronic cough and night sweats. After Ziehl-Neelsen staining, acid-fast bacilli are observed. Culture on Lowenstein-Jensen medium is positive after several weeks. Drug susceptibility testing reveals resistance to isoniazid and rifampin. This patient is MOST likely infected with:

During the processing of stool specimens for ova and parasite examination, the formalin-ethyl acetate concentration procedure primarily serves to:

A traveler returning from Southeast Asia presents with fever, headache, and a maculopapular rash that started on the trunk and spread to the extremities, including the palms and soles. Serological testing is positive for Orientia tsutsugamushi. The vector responsible for transmitting this organism is a:

The primary mechanism of action of aminoglycoside antibiotics, such as gentamicin, involves:

Clavulanic acid is often combined with amoxicillin (e.g., Augmentin™) to overcome certain types of bacterial resistance. What is the primary mechanism by which clavulanic acid enhances amoxicillin's activity?

A clinical microbiology laboratory encounters a Gram-negative bacillus isolated from a bloodstream infection. The isolate exhibits resistance to multiple antibiotics, including carbapenems. Further phenotypic testing reveals the production of a metallo-beta-lactamase (MBL). Which of the following antibiotic combinations might still retain activity against this isolate?

A clinical microbiology laboratory is evaluating a new rapid diagnostic test for influenza viruses. The test has a high sensitivity but a lower specificity compared to RT-PCR. In a setting with a low prevalence of influenza, the use of this rapid test is MOST likely to result in a high number of:

A patient develops a severe skin and soft tissue infection following a boating accident in the Gulf Coast. Wound cultures grow a Gram-negative, halophilic bacterium that is oxidase-positive. The MOST likely organism is:

A research laboratory is investigating the mechanisms of viral latency in herpes simplex virus type 1 (HSV-1). During latency in sensory neurons, the viral genome exists as a circular episome. Which of the following viral gene products is thought to play a crucial role in maintaining this latent state and preventing viral gene expression?

A clinical microbiology laboratory is using isothermal nucleic acid amplification techniques for rapid detection of Mycobacterium tuberculosis in sputum. Compared to conventional PCR, isothermal methods offer the advantage of:

A foodborne outbreak is suspected after several individuals who attended a potluck dinner develop nausea, vomiting, and abdominal cramps within 1-6 hours of eating. No fever or diarrhea is reported. The MOST likely bacterial toxin involved is:

A clinical microbiology laboratory is performing quality control on Gram stain reagents. A control slide containing Escherichia coli and Staphylococcus aureus shows both organisms staining purple after the complete staining procedure. The MOST likely cause of this error is:

A research team is investigating the mechanisms of antifungal resistance in Candida albicans. They identify a strain that exhibits resistance to azole antifungal agents. Further analysis reveals overexpression of a specific ATP-binding cassette (ABC) transporter protein in the resistant strain. This mechanism of resistance involves:

A clinical microbiology laboratory is monitoring the emergence of antimicrobial resistance. The detection of a bacterial isolate with reduced susceptibility to multiple classes of antibiotics, often due to horizontal gene transfer of resistance determinants, is characteristic of:

A clinical microbiology laboratory is investigating a potential outbreak of Legionella pneumophila associated with a hospital's water system. The MOST appropriate environmental samples to collect for culture and comparison to clinical isolates would be:

A patient with a history of chronic obstructive pulmonary disease (COPD) experiences an acute exacerbation. Sputum culture grows numerous Gram-negative coccobacilli that are oxidase-positive and grow on chocolate agar but not on sheep blood agar. The MOST likely organism is:

A patient presents with a chronic cough, weight loss, and night sweats. Chest X-ray shows cavitary lesions in the upper lobes. Sputum is acid-fast positive. Drug susceptibility testing reveals resistance to isoniazid but susceptibility to rifampin, ethambutol, and pyrazinamide. The MOST appropriate treatment regimen should include:

A microbiology laboratory isolates a Gram-negative rod from a wound infection. The organism is oxidase-negative, ferments lactose on MacConkey agar, and produces indole. The MOST likely identification is:

A 30-year-old female who recently returned from a hiking trip in the northeastern United States presents to her physician with a two-week history of a slowly expanding, erythematous rash with central clearing on her thigh. She also reports intermittent fatigue, arthralgias, and mild headache. Serological testing reveals a positive IgM and IgG response to Borrelia burgdorferi. Which of the following mechanisms is MOST significant in the pathogenesis of the clinical manifestations observed in this patient?

A patient returning from a hiking trip in a Lyme disease-endemic area presents with a unilateral facial nerve palsy, headache, and neck stiffness. Serological testing for Borrelia burgdorferi by ELISA is positive, but a Western blot shows only IgM bands. The MOST appropriate interpretation of these results is:

Which serological marker pattern is most consistent with chronic Hepatitis B virus infection with high infectivity?

A laboratory worker sustains a needlestick injury while handling a blood sample known to be positive for Hepatitis B surface antigen (HBsAg) and Hepatitis B e antigen (HBeAg). The worker has completed the HBV vaccination series and has a documented anti-HBs titer > 10 mIU/mL one month ago. What is the recommended post-exposure prophylaxis?

A patient develops a febrile illness with jaundice and dark urine after receiving a blood transfusion. Laboratory testing reveals an elevated level of unconjugated bilirubin and a positive direct Coombs test. Serological testing is positive for antibodies against a protozoan parasite that infects erythrocytes. The MOST likely causative agent is:

A patient with HIV infection and a CD4+ T-cell count below 50 cells/µL develops a progressive neurological illness characterized by confusion, motor deficits, and seizures. Brain MRI reveals multiple white matter lesions without mass effect. PCR of the CSF is positive for JC virus. The pathogenesis of this condition, progressive multifocal leukoencephalopathy (PML), involves:

A clinical microbiology laboratory is implementing whole-genome sequencing (WGS) for enhanced surveillance of Listeria monocytogenes isolates associated with foodborne outbreaks. WGS provides several advantages over traditional subtyping methods like pulsed-field gel electrophoresis (PFGE). Which of the following is the MOST significant advantage of WGS in this context?

A research laboratory is developing a novel diagnostic assay for early detection of sepsis. They are investigating the use of host biomarkers that are rapidly upregulated in response to bacterial infection. Which of the following biomarkers has shown promise for differentiating between systemic inflammatory response syndrome (SIRS) and sepsis?

A patient with a history of neutropenia following chemotherapy develops a severe pneumonia. Bronchoalveolar lavage fluid reveals the presence of hyaline, septate hyphae with frequent dichotomous branching at acute angles. Culture yields a filamentous fungus that produces conidiophores with a vesicle bearing phialides that release chains of conidia. The MOST likely genus is:

A research team is investigating the mechanism of bacterial resistance to a novel fluoroquinolone antibiotic. They isolate a resistant strain of Escherichia coli from a patient with a urinary tract infection. Genetic analysis of this strain reveals a point mutation in the gyrA gene. This mutation MOST likely results in:

During the investigation of a foodborne illness outbreak linked to raw sprouts, several bacterial isolates are obtained from patient stool samples and the implicated food source. Which of the following molecular methods would be MOST useful for establishing a definitive link between the clinical isolates and the food isolate?

A clinical microbiology laboratory is performing quality control on antimicrobial susceptibility testing. The zone diameter for Escherichia coli ATCC 25922 tested against ciprofloxacin is consistently smaller than the acceptable range published by CLSI. The MOST likely cause of this discrepancy is:

A patient with a history of intravenous drug use develops a fever and new heart murmur. Blood cultures are positive for Gram-positive cocci that are catalase-positive and coagulase-positive. The MOST likely complication of this infection is:

An immunocompromised patient develops a disseminated fungal infection. Blood cultures are negative, but a serum galactomannan assay is strongly positive. A CT scan of the chest reveals multiple nodular lesions with a halo sign. Bronchoalveolar lavage (BAL) fluid is analyzed by PCR, yielding a positive result for Aspergillus fumigatus. The halo sign observed on the CT scan is primarily attributed to:

A patient with a history of neutropenia develops a severe sinus infection. Tissue biopsy reveals broad, ribbon-like, non-septate hyphae with right-angle branching. The MOST likely causative organism belongs to the order:

A patient with a history of chronic lung disease develops a severe pneumonia. Bronchoalveolar lavage fluid reveals the presence of numerous cysts containing multiple nuclei, which stain positively with silver stains but poorly with Gram stain. The patient's CD4+ T-cell count is within the normal range. The MOST likely causative organism and the preferred treatment are:

A research team is investigating the development of a novel vaccine against influenza virus. They are focusing on conserved epitopes within the hemagglutinin (HA) and neuraminidase (NA) proteins to elicit broadly neutralizing antibodies. Which of the following approaches is MOST likely to achieve this goal?

A patient with a history of heart valve replacement develops subacute bacterial endocarditis. Blood cultures grow a Gram-positive coccus that is alpha-hemolytic on blood agar, catalase-negative, and optochin-resistant. The MOST likely organism is:

What is considered the "gold standard" for routine monitoring of the lethality of steam sterilization (autoclave) cycles in healthcare facilities?

A patient presents with perianal itching, particularly at night. Microscopic examination of cellophane tape preparation from the perianal area reveals oval-shaped eggs with one flattened side. The MOST likely causative organism is:

A clinical microbiology laboratory is using flow cytometry to analyze lymphocyte subsets in a patient with suspected immunodeficiency. Which of the following cell surface markers is typically used to identify helper T cells?

In a clinical microbiology laboratory, quality control testing of Mueller-Hinton agar used for disk diffusion susceptibility testing involves checking the zone sizes for E. coli ATCC 25922, S. aureus ATCC 25923, and P. aeruginosa ATCC 27853. What is the primary purpose of including P. aeruginosa ATCC 27853 in this QC?

A microbiology laboratory receives a bronchoalveolar lavage sample from a patient with suspected ventilator-associated pneumonia. Quantitative culture yields > 10^5 CFU/mL of a Gram-negative rod. Identification reveals Stenotrophomonas maltophilia. The MOST significant resistance mechanism commonly associated with this organism is:

What is the most appropriate method for sterilizing a heat-labile liquid solution containing essential proteins for use in tissue culture?

Microscopic examination of a trichrome-stained stool smear reveals amoebic trophozoites approximately 25 µm in diameter, containing ingested red blood cells. The nucleus, when visible, has fine, evenly distributed peripheral chromatin and a small, central karyosome. These features are diagnostic for:

A clinical microbiology laboratory is implementing a new quality control procedure for blood culture media. To ensure the media supports the growth of a wide range of clinically significant organisms, they should include:

A clinical microbiology laboratory is investigating a cluster of Clostridium difficile infections in a hospital. Which of the following methods is MOST appropriate for determining if the isolates from different patients are related?

Histopathological examination of lung tissue from an immunocompromised patient reveals large (8-15 µm), spherical yeast cells with thick, refractile walls and characteristic single, broad-based budding. These findings are most suggestive of infection with:

A patient with HIV infection and a CD4+ T-cell count of 30 cells/µL develops progressive multifocal leukoencephalopathy (PML). The causative agent of PML is:

A patient presents with a pruritic rash consisting of raised, serpiginous tracks on their skin. The patient recently returned from a Caribbean vacation and reported walking barefoot on the beach. The MOST likely causative organism is:

A research laboratory is investigating the mechanism of action of a novel antiviral compound. In vitro studies demonstrate that the compound effectively inhibits the replication of a specific enveloped RNA virus. Further analysis reveals that the compound does not interfere with viral entry, genome replication, or protein synthesis. However, electron microscopy of infected cells treated with the compound shows an accumulation of viral glycoproteins within the endoplasmic reticulum and Golgi apparatus, with a significant reduction in the release of infectious virions. The MOST likely target of this antiviral compound is:

A previously healthy 28-year-old female develops a severe, watery diarrhea after attending a picnic where she consumed potato salad that had been left unrefrigerated for several hours. Stool culture reveals numerous Gram-positive bacilli. Further biochemical testing shows the organism is beta-hemolytic on blood agar and produces a heat-stable enterotoxin. The MOST likely causative agent is:

A clinical microbiology laboratory is performing antimicrobial susceptibility testing using the broth microdilution method. The minimum bactericidal concentration (MBC) is determined by: