NO.90 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:

NO.91 What is the most appropriate method for sterilizing a heat-labile liquid solution containing essential proteins for use in tissue culture?

NO.92 An immunocompromised patient develops a disseminated fungal infection. Tissue biopsy reveals small (2-4
µm) yeast cells within macrophages. The patient has a history of living in the Ohio and Mississippi River valleys. The MOST likely causative agent is:

NO.93 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?

NO.94 A patient with a history of travel to an area endemic for schistosomiasis presents with hematuria. Microscopic examination of a urine sediment reveals a large oval egg with a prominent terminal spine. The MOST likely causative agent is:

NO.95 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?

NO.96 A Klebsiella pneumoniae isolate from a bloodstream infection shows the following susceptibility profile:
Meropenem (MIC = 8 µg/mL, R), Imipenem (MIC = 16 µg/mL, R), Ertapenem (MIC = 4 µg/mL, R), Ceftazidime/avibactam (MIC = 1 µg/mL, S), Aztreonam (MIC = 32 µg/mL, R). Which resistance mechanism is most strongly suggested by this pattern?

NO.97 A clinical microbiology laboratory is performing Gram staining on a sputum sample. After adding the crystal violet stain, a delay in the washing step with decolorizer (alcohol-acetone) would MOST likely result in:

NO.98 A clinical microbiology laboratory is investigating a potential outbreak of a highly contagious respiratory virus. To rapidly screen a large number of nasopharyngeal swabs, the MOST appropriate initial diagnostic test would be:

NO.99 A patient with a history of inflammatory bowel disease is diagnosed with primary sclerosing cholangitis and undergoes liver transplantation. Post-transplant, they develop a bloodstream infection with a Gram-negative bacterium that is identified as Fusobacterium nucleatum. This organism’s role in the pathogenesis of colorectal cancer is primarily attributed to its ability to:

NO.100 A patient with a history of travel to a developing country presents with chronic diarrhea, abdominal pain, and weight loss. Stool examination reveals the presence of cysts containing four nuclei and chromatoidal bars with rounded ends. The MOST likely causative organism is:

NO.101 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:

NO.102 A patient develops a localized skin infection after being bitten by a tick. The infection is characterized by a slowly expanding erythematous rash with central clearing (erythema migrans). The MOST likely causative agent is:

NO.103 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 likelycausative agent is:

NO.104 An acid-fast bacillus isolate recovered from a respiratory specimen after 3 weeks of incubation on Löwenstein- Jensen medium is initially non-pigmented when grown in the dark. After exposure to light for several hours, the colonies develop a distinct yellow-orange pigment. This organism is classified as a:

NO.105 A clinical microbiology laboratory is using Sanger sequencing to identify mutations associated with antibiotic resistance in Mycobacterium tuberculosis. This method directly determines the:

NO.106 For epidemiological tracking and outbreak investigations of Clostridioides difficile infection (CDI), which molecular typing method based on PCR amplification targeting repetitive elements within the pathogenicity locus (PaLoc) has historically been widely used and designated by specific nomenclature (e.g., NAP1/BI
/027)?

NO.107 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:

NO.108 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:

NO.109 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: