MLT GlobeMOH exam preparation (UAE) – page 20
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
For a bleeding patient with von Willebrand disease unresponsive to desmopressin, which product is preferred?
Plasma-derived concentrates rich in VWF replace the missing protein; cryoprecipitate is a fallback. Recombinant FVIII contains no VWF.
Which change occurs in red cells during prolonged refrigerated storage (storage lesion)?
Storage depletes ATP, cells lose membrane as microvesicles and become spheroechinocytes with increased osmotic fragility.
The immunodominant part of the A, B and H antigens is:
ABH specificity is set by terminal sugars (N-acetylgalactosamine for A, galactose for B, fucose for H) on glycoproteins and glycolipids.
How does the indirect antiglobulin test (IAT) differ from the direct test (DAT)?
In the IAT, patient plasma is incubated with reagent cells at 37 °C before adding AHG; the DAT tests the patient's own cells directly.
A pregnant woman eats soft cheese; her neonate later develops meningitis. The CSF isolate is most likely a:
Listeria monocytogenes is the classic food-borne cause of meningitis in neonates, the elderly and immunocompromised; it is a Gram-positive, non-sporing, tumbling-motile rod.
A Gram-negative bacterium treated with lysozyme and EDTA loses part of its wall but retains some outer membrane. The resulting osmotically fragile form is a:
Spheroplasts retain wall remnants (typically Gram-negatives); protoplasts have completely lost their wall (typically Gram-positives treated with lysozyme in hypertonic medium).
Which spore strip is used as a biological indicator to monitor hot air oven (dry heat) sterilisation?
B. atrophaeus (formerly B. subtilis var. niger) spores are highly resistant to dry heat. G. stearothermophilus is the indicator for steam autoclaves.
In vaccinated adult populations, which two bacteria cause most community-acquired bacterial meningitis?
Since Hib vaccination, H. influenzae is uncommon; pneumococcus and meningococcus dominate adult meningitis. E. coli and group B streptococci are neonatal causes.
Which organism is an obligate anaerobe with spherical terminal spores?
C. tetani is a strict anaerobe with round terminal spores. B. anthracis is aerobic with central spores; Corynebacterium and Cutibacterium do not form spores.
Which enteric pathogen can cause disease after ingestion of as few as 10-100 organisms?
Shigella is acid-tolerant and has a very low infectious dose, allowing person-to-person spread. V. cholerae and Salmonella usually need far larger inocula.
Dark-field microscopy of urine from a febrile farm worker shows thin, tightly coiled motile organisms with hooked ends. Which genus is this?
Leptospira are fine spirochetes with hooked ends, spread by animal urine. They are too thin for Gram stain and are seen by dark-field or detected by serology/PCR.
In Runyon's classification of non-tuberculous mycobacteria, 'photochromogens' such as M. kansasii are defined by:
Photochromogens are non-pigmented in the dark and turn yellow after light exposure. Scotochromogens are pigmented in the dark; non-chromogens are not pigmented.
On sorbitol-MacConkey agar, typical E. coli O157:H7 colonies appear:
Most E. coli ferment sorbitol and turn pink, whereas O157:H7 does not, giving colourless colonies that are then confirmed with O157 antisera.
Guests develop abdominal cramps and watery diarrhoea 10 hours after eating a meat stew that was cooled slowly and reheated. The likely cause is:
C. perfringens spores survive cooking, germinate as food cools and release enterotoxin in the gut. Botulism causes paralysis, not diarrhoea.
A swarming urinary isolate is indole-negative and ornithine decarboxylase-positive. Which species is it?
Both Proteus species swarm, but P. mirabilis is indole-negative and ornithine-positive, whereas P. vulgaris is indole-positive. Morganella and Citrobacter do not swarm.
A blood culture from a farmer grows small, slow-growing Gram-negative coccobacilli suspected to be Brucella. At what containment level should further culture work be done?
Brucella is among the commonest causes of laboratory-acquired infection through aerosols; suspected isolates require BSL-3 practices in a biosafety cabinet.
Chocolate agar is made by heating blood agar to about what temperature, lysing red cells to release X and V factors?
Heating to 75-80 °C lyses erythrocytes and releases haemin and NAD while inactivating NADase, supporting Haemophilus and Neisseria.
A wool-sorter develops severe pneumonia and mediastinitis after handling imported fleece. 'Wool-sorter's disease' is which form of anthrax?
Inhaling B. anthracis spores from animal fibres causes haemorrhagic mediastinitis. The 'malignant pustule' is the cutaneous form.
Ascoli's thermoprecipitation test on animal tissue extracts is used to diagnose:
Heat-stable B. anthracis antigen from tissues forms a ring precipitate with specific antiserum, useful when the carcass is decomposed.
A semisolid medium for checking bacterial motility should contain agar at roughly which concentration?
About 0.4–0.5% agar keeps the medium soft enough for flagellated bacteria to spread from the stab line. About 1.5% is standard solid agar; much higher concentrations (about 5–6%) are used to inhibit Proteus swarming.