MLT GlobeMOH exam preparation (UAE) – page 7
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A urine culture on MacConkey agar grows large, pink, very mucoid colonies that string when touched with a loop. Which genus is most likely?
Klebsiella ferments lactose (pink) and has a large polysaccharide capsule giving mucoid, stringy colonies. Salmonella is non-lactose fermenting; Gram-positive cocci are inhibited on MacConkey.
Sputum from a suspected pulmonary TB patient is decontaminated for culture. Which solid medium is standard for growing Mycobacterium tuberculosis?
Lowenstein-Jensen contains egg, glycerol and malachite green to support slow mycobacterial growth and suppress contaminants. The other media are for routine bacteria.
A stool isolate forms flat, pink colonies with a hazy bile precipitate on MacConkey agar. Which organism is most likely?
E. coli ferments lactose, lowering pH so neutral red turns pink and bile salts precipitate. Salmonella forms pale non-lactose-fermenting colonies; the others do not grow on MacConkey.
Slender red rods resisting acid-alcohol decolourisation are seen on a Ziehl-Neelsen-stained sputum. Their staining is due to lipid-rich walls. The organism is most likely:
Mycolic acids make the mycobacterial wall waxy, so carbol fuchsin is retained after acid-alcohol (acid-fast). The other organisms are not acid-fast.
A Gram-stained smear from a deep wound shows Gram-positive rods with round terminal spores giving a 'drumstick' shape. Which organism is suggested?
C. tetani has spherical terminal spores wider than the cell, giving drumstick (or tennis-racket) forms. The other organisms do not form spores.
A flagellated, oxidase-positive, hospital-acquired pathogen, Pseudomonas aeruginosa, would appear on Gram stain as:
Pseudomonas is a Gram-negative, non-fermenting bacillus with a polar flagellum.
Which organism is NOT an important cause of urinary tract infection?
B. fragilis is an anaerobe of intra-abdominal abscesses and rarely causes UTI. E. coli, Klebsiella and Proteus are leading uropathogens.
Which organism is NOT a recognised cause of infectious diarrhoea?
E. faecalis is a gut commensal causing UTI and endocarditis, not diarrhoea. C. perfringens enterotoxin, diarrhoeagenic E. coli and V. cholerae all cause diarrhoea.
In the Ziehl-Neelsen stain, tubercle bacilli retain carbol fuchsin after treatment with which decolouriser?
'Acid-fast' means the waxy mycolic acid wall holds carbol fuchsin against acid decolourisation, while non-acid-fast organisms lose it and take up the methylene blue counterstain.
Albert's, Ponder's and Neisser's stains are used to show metachromatic granules in:
These stains highlight volutin granules at the poles of C. diphtheriae, supporting a presumptive diagnosis of diphtheria.
The small region of an antigen that a specific antibody binds is called the:
The epitope is on the antigen; the paratope is the complementary binding site on the antibody. Fc receptors bind antibody constant regions.
Which complement component is present at the highest concentration in normal serum?
C3 (about 1-1.5 g/L) is the most abundant complement protein and the convergence point of all three pathways.
What is the purpose of the streak plate technique?
Each successive streak thins the inoculum until single cells are deposited separately, giving isolated colonies for pure culture.
In media containing phenol red, acid production from sugar fermentation turns the indicator:
Phenol red is red at neutral pH, yellow below about pH 6.8 and deep pink above about pH 8.4, as used in TSI and urea media.
Standard blood agar for routine bacteriology, giving reliable haemolysis patterns, is prepared with blood from which animal?
Defibrinated sheep blood gives clear haemolysis reactions and inhibits Haemophilus haemolyticus; horse blood is used for some special media.
MacConkey agar is primarily used to isolate and differentiate:
Bile salts and crystal violet inhibit Gram-positives, while lactose and neutral red differentiate lactose fermenters among Gram-negative rods.
Robertson's cooked meat medium is used mainly to culture:
Meat particles contain reducing substances (glutathione) that lower the redox potential, supporting anaerobes; saccharolytic clostridia turn meat pink, proteolytic ones blacken it.
A child with meningitis has CSF showing small pleomorphic Gram-negative coccobacilli that grow on chocolate agar but not sheep blood agar, needing X and V factors. The organism is:
H. influenzae needs haemin (X) and NAD (V), both available in chocolate agar. Moraxella is a diplococcus; the others are Gram-positive.
An airborne pathogen causes latent infection in most people, detected by IGRA, with about 10% progressing to active lung disease. It is:
M. tuberculosis spreads by respiratory droplets, often remains latent, and reactivates in about 10% of infected people. M. fortuitum is an environmental rapid grower.
Which Clostridium species is NOT a cause of gas gangrene?
C. perfringens, C. novyi and C. septicum are histotoxic clostridia causing myonecrosis. C. botulinum produces a neurotoxin causing botulism.