MLT GlobeDOH exam preparation (Abu Dhabi) – page 26
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Bacteroides fragilis is intrinsically resistant to:
Aminoglycoside uptake needs oxygen-dependent transport, so all anaerobes are resistant. Metronidazole and carbapenems remain reliably active.
On CLED agar, which urinary isolate gives green colonies with a matt surface?
P. aeruginosa gives green-blue colonies on CLED. E. coli colonies are yellow (lactose-fermenting); Proteus is blue and does not swarm.
Pus from a deep pilonidal abscess typically yields:
Pilonidal and perianal abscesses are usually polymicrobial with anaerobes and streptococci. Anaerobic culture is essential.
Which organism does NOT typically cause vaginal discharge?
Cryptococcus causes meningitis and lung disease. The others are associated with vaginosis, vaginitis or cervicitis with discharge.
A colleague says plasmid-borne antimicrobial resistance is a problem only in Gram-negative bacteria. Which statement about plasmid-mediated resistance is actually FALSE?
Gram-positive bacteria also carry resistance plasmids (e.g. blaZ penicillinase plasmids in Staphylococcus aureus, vanA-bearing plasmids in enterococci). The other statements are true of plasmid-mediated resistance.
Which statement about the host response to viral infection is INCORRECT?
Cell-mediated immunity (cytotoxic T cells, NK cells) is essential to clear virus-infected cells; antibodies mainly neutralize free virus. The other statements are true.
After primary gingivostomatitis, where does herpes simplex virus type 1 usually remain latent?
HSV-1 travels up sensory nerves and becomes latent in the trigeminal ganglion, reactivating as cold sores. EBV, not HSV, is latent in B cells.
Which statement about cytomegalovirus infection is NOT true?
CMV is carried in leukocytes (monocytes, neutrophils), not erythrocytes; this is why leukoreduced blood lowers transfusion risk. It causes retinitis, reactivates and crosses the placenta.
Which statement about human rotaviruses is NOT true?
Human rotaviruses grow poorly in routine cell culture, so antigen detection or PCR is used. They are naked dsRNA viruses and a major cause of infant diarrhoea.
Which HIV entry inhibitor works by blocking the host CCR5 co-receptor?
Maraviroc is a CCR5 antagonist, effective only against R5-tropic HIV, so tropism testing is needed first. Enfuvirtide targets gp41.
Kaposi sarcoma in a person with advanced HIV disease is caused by which virus?
HHV-8 (Kaposi sarcoma-associated herpesvirus) causes Kaposi sarcoma, primary effusion lymphoma and multicentric Castleman disease, mostly in immunosuppressed patients.
Epstein-Barr virus persists for life after infectious mononucleosis. In which cells is it latent?
EBV enters B cells via CD21 and remains latent in memory B cells; this underlies its role in B-cell lymphomas. HSV and VZV are latent in sensory ganglia.
Immune globulin is used for post-exposure prophylaxis of several viral infections. For which condition is it NOT used?
No immune globulin is used for EBV mononucleosis. Normal immune globulin protects against hepatitis A, and specific HBIG and rabies IG are part of post-exposure prophylaxis.
Which description fits astrovirus?
Astroviruses are small, star-shaped, naked +ssRNA viruses that cause mild childhood gastroenteritis.
Children at a summer camp develop fever, sore throat and conjunctivitis after using the same swimming pool. Which virus is the classic cause?
Pharyngoconjunctival fever, often linked to swimming pools, is caused by adenoviruses (commonly type 3), spread in poorly chlorinated water.
Two weeks after eating undercooked hamburger, a patient has lethargy, fatigue and tender lymph nodes; heterophil test is negative. Which organism is most likely?
Tissue cysts in undercooked meat transmit toxoplasmosis, causing a mononucleosis-like illness after 1-3 weeks. The bacteria listed cause acute gastroenteritis within hours to days.
In southern China, screening for nasopharyngeal carcinoma uses serum IgA against which virus antigen (VCA/EBNA1)?
Undifferentiated nasopharyngeal carcinoma is EBV-associated; IgA anti-VCA/EBNA1 and plasma EBV DNA are used for screening and monitoring.
Which test on post-mortem brain tissue is the reference standard for diagnosing rabies?
WHO and OIE regard DFA on brain tissue (brainstem, cerebellum) as the gold standard; Negri bodies on histology are absent in many cases.
Which human virus is large enough to be seen, just barely, with a light microscope after special staining?
Poxviruses (about 300 x 250 nm) are the largest viruses that infect humans. Their inclusions, such as Paschen bodies, were seen by light microscopy. Poliovirus is about 30 nm.
A screening anti-HCV ELISA gives a signal of 3.5 with a cut-off of 1.35. How should this be reported, and what follows?
A value above the cut-off is reactive for anti-HCV. Antibody does not distinguish past from current infection, so HCV RNA (NAT) is needed to confirm viraemia.