MLT GlobeDOH exam preparation (Abu Dhabi) – page 6
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
Which component of the Gram-negative outer membrane acts as endotoxin?
Lipid A of LPS triggers fever and septic shock. Teichoic acids are Gram-positive; cellulose and pectin are plant cell wall components.
In a sugar fermentation broth, a small inverted Durham tube is used to detect:
Gas from fermentation collects as a bubble in the inverted tube. pH change is shown separately by the broth's indicator.
Which type of hypersensitivity is NOT mediated by antibody?
Types I-III involve IgE, IgG/IgM or immune complexes. Type IV is caused by sensitised T cells and macrophages.
Which antibiotic is a macrolide rather than an aminoglycoside?
Erythromycin is a macrolide binding the 50S subunit. Amikacin, neomycin and gentamicin are aminoglycosides acting on the 30S subunit.
Milk pasteurised at 72 °C for 15 seconds is considered:
Pasteurisation kills vegetative pathogens such as Mycobacterium bovis, Brucella and Salmonella but not endospores, so it is not sterilisation.
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 serological test detects agglutinating antibodies to Salmonella Typhi O and H antigens?
The Widal test measures anti-O and anti-H agglutinins; it supports but cannot replace culture. VDRL and RPR screen for syphilis; ASO indicates recent streptococcal infection.
Neutrophils migrate toward C5a and IL-8 released at an infection site. This directed movement is called:
Chemotaxis is directional movement along a gradient of chemoattractants. Opsonisation coats microbes for uptake; phagocytosis is engulfment.
Which stain is the primary differential stain for initial bacterial classification in routine bacteriology?
The Gram stain divides most bacteria into Gram-positive and Gram-negative groups by cell wall structure. ZN is for acid-fast organisms; Giemsa and Leishman are blood stains.
Which temperature and holding time is standard for sterilising glassware in a hot air oven?
Dry heat needs higher temperature and longer time than steam: 160 °C for 2 h (or 170 °C for 1 h). 121 °C for 15 min is the autoclave cycle.
Campylobacter needs a 'microaerobic' incubation atmosphere. What does this term describe?
Microaerophiles need oxygen but only at low tension (roughly 5–10% O2). A candle jar or CO2 incubator still contains about 15–18% O2, which is too much; anaerobes need no oxygen at all.
While preparing reagents for a Ziehl–Neelsen stain, which one of these would a technologist NOT need?
ZN uses carbol fuchsin (primary stain), acid-alcohol (decolouriser) and methylene blue or malachite green (counterstain). Crystal violet is the primary stain of the Gram method.
On sheep blood agar, pinpoint colonies grow only close to a streak of Staphylococcus aureus. Which organism typically shows this pattern?
Satellitism: S. aureus releases V factor (NAD) and its haemolysis frees X factor (haemin) from red cells, supporting growth of H. influenzae nearby.
A slit-skin smear from a patient with numb, hypopigmented skin patches shows acid-fast bacilli; the organism cannot be grown on artificial media. Most likely agent?
M. leprae causes leprosy with anaesthetic skin lesions and has never been cultured in vitro. M. ulcerans and M. marinum cause skin ulcers but grow in culture.
A light microscope objective forms an image because a glass lens bends light rays passing through it. This bending is called:
Refraction is the change in direction of light passing between media of different refractive index. Resolution is the ability to separate two close points.
An S. aureus isolate carries mecA, encoding PBP2a, and is resistant to oxacillin and most beta-lactams. It is reported as:
Methicillin-resistant S. aureus has altered penicillin-binding protein 2a with low beta-lactam affinity. VISA refers to reduced vancomycin susceptibility, not mecA.
A patient passes large volumes of pale, watery stool flecked with mucus ('rice-water'). Which infection is suspected?
Cholera toxin causes massive secretory diarrhoea with rice-water stools. Dysentery gives small-volume stools with blood and pus.
A stool sample from a suspected cholera case should be plated on which selective medium?
Thiosulphate-citrate-bile salts-sucrose agar is alkaline and selective for vibrios. Blood and nutrient agar are non-selective; CLED is for urine.
A 5-day-old neonate has suspected E. coli meningitis. Which specimen gives the definitive diagnosis?
Meningitis is confirmed by Gram stain and culture of the infant's CSF. Maternal swabs only show colonisation.
The smallest free-living bacteria, about 0.2–0.3 µm and similar in size to large viruses, belong to the genus:
Mycoplasmas are about 0.2–0.3 µm and can pass through bacterial filters. Poxviruses, the largest viruses, are of similar size.