MLT GlobeDOH exam preparation (Abu Dhabi) – page 5
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which cell is the main source of circulating antibody?
Plasma cells are terminally differentiated B cells that secrete large amounts of immunoglobulin. Helper T cells assist B cells but do not make antibody.
For routine venipuncture, the vein of first choice in the antecubital fossa is the:
The median cubital vein is large, well anchored and away from major nerves and the brachial artery. The basilic vein lies near the artery and median nerve.
The primary lymphoid organs where lymphocytes develop are the:
B cells develop in bone marrow and T cells mature in the thymus. Spleen, nodes and tonsils are secondary organs where mature lymphocytes meet antigen.
Serum differs from plasma because serum:
Serum is the fluid left after blood clots, so fibrinogen and factors V and VIII are consumed. Plasma comes from anticoagulated blood and retains them.
A laboratory wants to isolate a suspected virus from a clinical sample. Which system is unsuitable?
Viruses are obligate intracellular parasites and cannot multiply on cell-free media such as nutrient agar; they need living cells, eggs or animals.
The heat-stable DNA polymerase that made automated PCR thermal cycling practical was isolated from:
Taq polymerase comes from the hot-spring bacterium Thermus aquaticus and survives repeated 94-95 °C denaturation steps, so it need not be replaced after each cycle.
A lactose-fermenting Gram-negative rod produces a red ring after Kovac's reagent is added to tryptone broth. The organism is most likely:
Kovac's reagent detects indole from tryptophan breakdown. E. coli is indole-positive; K. pneumoniae and most Salmonella are indole-negative.
A patient with 7 days of sustained fever is suspected to have enteric fever. Which test is the reference (gold-standard) routine laboratory diagnosis?
Culture isolates S. Typhi and allows susceptibility testing; blood culture is the routine standard (bone marrow is even more sensitive). Widal and rapid serology have poor specificity in endemic areas.
A yeast incubated in serum at 37 °C for 2-3 hours produces short hyphal outgrowths without constriction at the base. This identifies:
A positive germ tube test is the rapid presumptive identification of C. albicans (and C. dubliniensis). C. glabrata and Cryptococcus do not form germ tubes.
An infected burn on the arm yields large, flat, non-lactose-fermenting colonies on MacConkey agar that are oxidase-positive. The likely organism is:
P. aeruginosa is a major burn-wound pathogen; it is a non-lactose-fermenting, oxidase-positive Gram-negative rod with spreading colonies. E. coli ferments lactose; staphylococci are Gram-positive.
An alpha-haemolytic Gram-positive diplococcus shows a zone of inhibition around an ethylhydrocupreine disc. This identifies Streptococcus pneumoniae, which is sensitive to:
Optochin (ethylhydrocupreine) susceptibility separates S. pneumoniae from other viridans streptococci. Bacitracin screens S. pyogenes; novobiocin separates S. saprophyticus.
Haemophilus influenzae needs both X factor (haemin) and V factor (NAD). Which medium supports its growth?
Heating blood lyses red cells, releasing X and V factors and inactivating V-factor-degrading enzymes. Sheep blood agar only supports growth as satellite colonies near S. aureus.
A technologist is opening blood tubes at the bench, where splashing may occur. Which PPE combination is appropriate?
Standard precautions require a closed lab coat and gloves for specimen handling, plus eye/face protection (or a splash shield) wherever splashes or aerosols are possible.
A plasma tube test is used on Gram-positive cocci from a blood culture. It separates which organisms?
Free coagulase clots rabbit plasma; S. aureus is positive, while S. epidermidis and other CoNS are negative.
Albert's stain of Corynebacterium diphtheriae shows bluish-black granules that stain differently from the dye colour. These volutin granules are also called:
Volutin (polyphosphate) granules stain metachromatically, a feature used to identify C. diphtheriae. They are storage inclusions, not spores or flagella.
A patient passes profuse 'rice-water' stools with rapid dehydration. The most likely cause is:
Cholera toxin raises cAMP in enterocytes, driving massive secretion of watery, mucus-flecked stool. Shigella and EIEC cause dysentery.
During a Gram stain, immediately after the alcohol-acetone step and before the counterstain, Gram-negative cells appear:
The decolouriser removes crystal violet-iodine from the thin Gram-negative wall, leaving the cells colourless until safranin is applied.
A tease mount of a mould in lactophenol cotton blue is examined. This preparation is used to identify:
Lactophenol kills and preserves the fungus while cotton blue stains chitin in hyphae and spores, showing structures for identification.
A wet preparation on a cavity slide (hanging drop) is examined under the microscope. What bacterial property does it assess?
The hanging drop lets live bacteria move freely so true directional motility can be distinguished from Brownian movement.
Christensen's urea agar turns pink within hours when inoculated with Proteus. In this role the medium is best described as a(n):
Urease releases ammonia, raising pH so phenol red turns pink; the medium distinguishes organisms by a colour change rather than suppressing growth.