MLT GlobeSCFHS exam preparation (Saudi Arabia) – page 17
749 practice MCQs for the SCFHS medical laboratory exam. Level: Intermediate.
Helicobacter pylori is a major cause of which condition?
H. pylori causes chronic gastritis and most duodenal and gastric ulcers.
Epidemic typhus caused by Rickettsia prowazekii is transmitted by the:
R. prowazekii is spread by the body louse, typically in crowded, unhygienic conditions.
Pseudomembranous colitis following antibiotic therapy is caused by:
Antibiotics disturb the gut flora, allowing toxigenic C. difficile to overgrow and produce toxins A and B.
A foul, putrid smell from pus or a wound specimen most strongly suggests infection with:
Anaerobes produce volatile fatty acids and amines that give a characteristic foul odour.
Which part of the human body has the highest numbers of anaerobic bacteria as normal flora?
Anaerobes vastly outnumber aerobes in the colon; the bladder, lower airways and CSF are normally sterile.
The BCG vaccine contains:
BCG (bacille Calmette-Guérin) is a live attenuated strain of M. bovis.
In the Ziehl-Neelsen stain, which counterstain is usually applied after decolourisation?
Methylene blue stains the background and non-acid-fast cells blue, contrasting with red acid-fast bacilli.
In the Ziehl-Neelsen method, carbol fuchsin is heated on the slide in order to:
Heat softens the lipid-rich wall so carbol fuchsin can enter; once inside, it resists acid-alcohol.
Trypanosoma cruzi, the cause of Chagas disease, is transmitted by:
Infective trypomastigotes are passed in the bug's faeces and enter through the bite wound or mucous membranes.
African sleeping sickness (Trypanosoma brucei) is transmitted by the bite of the:
Tsetse flies transmit T. brucei gambiense and rhodesiense; sandflies transmit Leishmania.
Which inherited red cell condition gives partial protection against severe falciparum malaria?
Red cells of HbAS carriers sickle and are removed when parasitised, reducing the risk of severe falciparum malaria.
Guinea worm (Dracunculus medinensis) infection is acquired by:
Larvae inside water fleas (Cyclops) are swallowed in unfiltered drinking water; filtering water prevents infection.
Loa loa, the African 'eye worm', is transmitted by the bite of:
Day-biting Chrysops flies transmit Loa loa, which is why its microfilariae show daytime periodicity.
Children usually acquire the dog tapeworm Dipylidium caninum by:
The larval stage develops in fleas, so children who swallow fleas while playing with pets become infected.
Amphotericin B and the azole antifungals act on which component that is found in fungal cell membranes but not in human ones?
Ergosterol is the main fungal membrane sterol; amphotericin binds it and azoles block its synthesis.
Dermatophytes infect which tissues?
Dermatophytes use keratin, so they infect only the outer skin, hair and nails.
A mould whose colony is dark brown to black on both the surface and the reverse, due to melanin in its walls, is described as:
Dematiaceous fungi have melanin in their hyphae and conidia; hyaline moulds are colourless or light-coloured.
In an adult with HIV infection, a CD4 count below which level is used to define AIDS?
A CD4 count below 200 cells/µL (or an AIDS-defining illness) meets the definition of AIDS.
The classic triad of congenital rubella syndrome is:
Rubella in early pregnancy classically causes cataract, sensorineural deafness and congenital heart disease such as PDA.
Dye uptake by tissue in routine staining is best explained by:
Staining involves ionic and other chemical bonds together with physical factors such as adsorption, diffusion and tissue permeability. Neither mechanism alone explains most staining.