MLT GlobeDHA exam preparation (Dubai) – page 8
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
Sabouraud dextrose agar with low pH, often supplemented with chloramphenicol, is used for fungi. It is classified as a:
Its acidic pH (about 5.6) and added antibiotics inhibit bacteria while allowing fungi to grow, which makes it selective.
Which process achieves sterility, i.e. killing all microbes including spores?
Moist heat under pressure kills vegetative cells and endospores. Pasteurisation and disinfection reduce pathogens but do not kill spores; asepsis only prevents contamination.
Oral thrush (moniliasis) with removable white plaques is caused by:
Moniliasis is an old term for candidiasis; Candida albicans causes oral and vaginal thrush.
Which statement about Streptococcus pneumoniae (formerly Diplococcus pneumoniae) is INCORRECT?
Pneumococci are lancet-shaped Gram-positive cocci in pairs or short chains; the polysaccharide capsule is the main virulence factor.
The solid egg-based LJ medium for mycobacteria is named after:
LJ stands for Löwenstein–Jensen. Levey–Jennings is a quality-control chart, and Loeffler serum is used for C. diphtheriae.
Which penicillin keeps its activity against penicillinase-producing Staphylococcus aureus?
Isoxazolyl penicillins such as cloxacillin have a side chain that blocks staphylococcal beta-lactamase. Ampicillin, penicillin G and carbenicillin are hydrolysed.
Gram-positive cocci in grape-like clusters that are catalase-positive belong to which genus, rather than Streptococcus?
Staphylococci are catalase-positive and form clusters. Streptococci, enterococci and lactococci are catalase-negative and grow in chains or pairs.
MacConkey agar contains crystal violet and bile salts. What is the role of the crystal violet?
Crystal violet and bile salts inhibit gram-positive organisms, making the medium selective. Neutral red is the pH indicator showing lactose fermentation.
Which organism naturally lacks a cell wall and is therefore unaffected by penicillin?
Mycoplasmas have no peptidoglycan cell wall, so beta-lactams have no target. Fungi have walls of chitin and glucan, and typical bacteria have peptidoglycan.
In an Albert-stained smear of Corynebacterium diphtheriae, the volutin (metachromatic) granules appear:
Albert stain shows green bacilli containing bluish-black metachromatic granules, a feature supporting C. diphtheriae in throat smears.
The historical Schick test, an intradermal toxin injection, was used to assess immunity to:
A small dose of diphtheria toxin was injected; no reaction meant circulating antitoxin (immunity). It is now obsolete, replaced by serology.
Beta-lactam antibiotics such as penicillins and cephalosporins act by inhibiting:
Beta-lactams bind penicillin-binding proteins and block peptidoglycan cross-linking, causing cell lysis.
Aspergillus niger is used industrially to produce:
A. niger fermentation is the main source of citric acid. Ethanol comes from yeast, lactic acid from Lactobacillus, penicillin from Penicillium.
A foreign molecule that can trigger an immune response and bind specific antibodies is called an:
Antigens are usually complex molecules such as proteins or polysaccharides recognised by B- and T-cell receptors.
A grey pharyngeal membrane that bleeds when scraped off, with a 'bull-neck' swelling, suggests:
Diphtheria pseudomembrane is adherent and bleeds on removal. Candida plaques wipe off easily; mononucleosis gives exudative tonsillitis.
Tiny pleomorphic gram-negative coccobacilli from CSF grow on chocolate agar but on nutrient agar only around an X+V factor disc. Identify them.
H. influenzae requires both haemin (X) and NAD (V). Listeria and Bacillus are gram-positive; E. coli needs no factors.
A throat smear is stained with Albert stain to look for metachromatic granules. This screens for:
Albert stain shows green rods with bluish-black volutin granules, typical of C. diphtheriae. Confirmation needs culture and toxin testing.
What term describes a complete, infectious virus particle outside a host cell?
A virion is the complete extracellular particle (genome, capsid and any envelope). Prions are proteins, viroids are naked RNA, and a provirus is integrated viral DNA.
For a woman with suspected gonorrhoea, which specimen is preferred for culture of Neisseria gonorrhoeae?
N. gonorrhoeae infects columnar epithelium of the endocervix, so an endocervical swab is best for culture; NAAT also accepts vaginal swabs. Clue cells indicate bacterial vaginosis.
Which hepatitis virus is transmitted mainly by blood and body fluids rather than by the fecal-oral route?
HDV, like its helper HBV, spreads parenterally and sexually. HAV, HEV and astrovirus are shed in stool and spread fecal-orally.