MLT GlobeDOH exam preparation (Abu Dhabi) – page 7
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Gram-positive cocci dividing in three planes form cubical packets of eight cells. This arrangement is called:
Division in three perpendicular planes gives packets of eight (sarcinae). Two planes give tetrads; irregular planes give clusters.
The temperature at which a bacterial species multiplies fastest is its:
Growth rate peaks at the optimum temperature (37 °C for most human pathogens). Minimum and maximum define the limits of growth.
Which process changes bacterial DNA but does NOT transfer genes between cells?
Mutation alters the cell's own DNA. Transformation (free DNA), transduction (phage) and conjugation (pilus) move DNA between bacteria.
A wet mount of a vaginal swab in saline is examined for jerky, flagellated motile organisms. This is the usual first test for:
T. vaginalis is detected by its motility in a fresh vaginal wet mount (or NAAT). Gonorrhoea needs culture or NAAT from endocervical/urethral samples.
The principal indicator of faecal contamination in drinking water is:
E. coli is abundant in faeces and rarely grows in the environment, so its presence shows recent faecal pollution.
Which streptococcus is typically beta-haemolytic on sheep blood agar?
S. pyogenes produces streptolysins giving complete haemolysis. S. salivarius and S. mitis are usually non- or alpha-haemolytic; S. pneumoniae is alpha-haemolytic.
A typical Staphylococcus cell measures approximately:
Most cocci are about 1 µm across, within the 0.2–5 µm range of common bacteria. 10 µm is closer to a red cell's size.
On MacConkey or EMB agar, Salmonella and Shigella usually form colonies that are:
These pathogens do not ferment lactose, so colonies remain pale. Pink (MAC) or green sheen (EMB) indicates lactose fermenters such as E. coli.
Correctly Gram-stained streptococci appear:
Streptococci are gram-positive and retain the crystal violet–iodine complex. Gram-negative cells appear red.
A stab culture shows diffuse cloudiness spreading from the stab line in a soft medium. The medium used for this motility test is:
Motility media contain low agar (semisolid) so motile bacteria can migrate. Solid agar would restrict growth to the stab line.
Which of these is an obligate anaerobe?
Clostridia are strict anaerobes. B. anthracis and Listeria are facultative; Nocardia is aerobic.
Enterococci carry which Lancefield group antigen?
Enterococci and the Streptococcus bovis group possess group D antigen. Enterococci are now a separate genus but keep this antigen.
Incineration in the laboratory is best suited to:
Incineration burns material to ash, so it is used for disposal. Reusable instruments and glassware are autoclaved or hot-air sterilised.
A painful genital ulcer with tender inguinal buboes yields small gram-negative rods in 'school-of-fish' chains. The agent is:
H. ducreyi causes chancroid, a painful ulcer. Syphilis (T. pallidum) gives a painless chancre and the organism is not seen on Gram stain.
Pre-packed disposable plastic syringes are sterilised commercially by:
Ionising radiation penetrates packaging and heat-sensitive plastics at room temperature. Heat methods would melt them.
Which organism is a non-lactose fermenter on MacConkey agar?
Proteus forms pale colonies. E. coli, Klebsiella and Enterobacter ferment lactose and form pink colonies.
Which of these is an enrichment broth for Salmonella from stool?
Selenite F suppresses coliforms while Salmonella multiplies, then it is subcultured. The others are plated media.
Chocolate agar, made by heating blood agar, is an example of an:
Heating lyses red cells, releasing X and V factors for fastidious organisms like Haemophilus and Neisseria.
Prepared agar plates are best stored:
Cold storage in sealed bags prevents drying and contamination, keeping plates usable for weeks. Light-sensitive media also need darkness.
Bordet–Gengou or Regan–Lowe charcoal agar is used to isolate the agent of:
These media support Bordetella pertussis, grown from nasopharyngeal swabs. Its colonies resemble mercury drops.