MLT GlobeDHA exam preparation (Dubai) – page 17
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
At what temperature are most routine clinical bacterial cultures incubated?
Most human pathogens grow best near body temperature, so routine cultures are incubated at 35–37 °C.
Trimethoprim-sulfamethoxazole (co-trimoxazole) kills or inhibits bacteria by blocking:
Sulfamethoxazole and trimethoprim block two sequential steps in bacterial folate synthesis, which is needed for nucleotide production.
Spores of which organism are used as biological indicators to check that a steam autoclave is working?
G. stearothermophilus spores are highly heat resistant, so their killing shows that sterilising conditions were reached.
Thick, bloody 'currant jelly' sputum in an alcoholic patient with pneumonia classically suggests:
K. pneumoniae causes a destructive lobar pneumonia with thick, bloody, mucoid sputum, especially in alcoholics.
On XLD agar, typical Salmonella colonies appear:
Salmonella decarboxylates lysine (red colonies) and produces H2S (black centres); E. coli gives yellow colonies.
A rapidly spreading non-blanching petechial or purpuric rash in a febrile child suggests septicaemia due to:
Meningococcal septicaemia causes a petechial-purpuric rash from vascular damage and DIC.
Which antibiotic is active against most obligate anaerobes and is widely used to treat anaerobic infections?
Metronidazole is activated only inside anaerobic cells, so Bacteroides, Clostridium and most other obligate anaerobes are susceptible; gentamicin, aztreonam and colistin have no useful anaerobic activity.
Chronic urinary infection with Schistosoma haematobium is associated with which cancer?
Long-standing egg deposition in the bladder wall causes chronic inflammation that predisposes to squamous cell bladder cancer.
Which fluke, the largest intestinal fluke of humans, is acquired by eating raw water plants such as water chestnuts?
Fasciolopsis buski lives in the small intestine; metacercariae encyst on aquatic plants that are peeled with the teeth.
Why is a saline wet mount examined along with an iodine mount of fresh stool?
Iodine kills trophozoites and stops movement; saline keeps them alive so their motility can be seen.
Stool for ova and parasite examination should be collected before the patient receives:
Barium, antacids and some drugs obscure or distort parasites for 1–2 weeks, so specimens should be taken first.
Cryptococcus neoformans is commonly found in the environment in:
C. neoformans grows well in soil enriched with pigeon droppings; infection follows inhalation.
Vaginal candidiasis typically produces a discharge that is:
Candida gives a cottage-cheese-like discharge with itching; frothy discharge suggests Trichomonas and fishy grey discharge suggests bacterial vaginosis.
Enveloped viruses are more easily inactivated than non-enveloped viruses by:
The envelope is a lipid membrane, so ether, alcohol and detergents destroy it and make the virus non-infectious.
Cytopathic effect in a cell culture monolayer grown in a tube or flask is usually examined with:
An inverted microscope views cells through the bottom of the vessel, so living monolayers can be checked daily for CPE.
Chronic hepatitis B infection is defined by persistence of HBsAg in serum for more than:
HBsAg that remains positive beyond 6 months indicates chronic infection.
HIV mainly infects and destroys which cells?
HIV binds CD4 with a chemokine co-receptor; loss of CD4 T cells causes immunodeficiency.
Roseola infantum (sixth disease), with high fever followed by a rash as the fever falls, is caused by:
HHV-6 (and sometimes HHV-7) causes roseola in infants; parvovirus B19 causes fifth disease.
Influenza A viruses are divided into subtypes such as H1N1 and H3N2 according to their:
Subtypes are named from the antigenic types of haemagglutinin (H) and neuraminidase (N) on the envelope.
Small, pearly, umbilicated skin papules (molluscum contagiosum) are caused by a:
Molluscum contagiosum virus is a poxvirus; the lesions show large eosinophilic inclusion (molluscum) bodies.