MLT GlobeDOH exam preparation (Abu Dhabi) – page 8
700 practice MCQs for the DOH medical laboratory exam. Level: Basic to intermediate.
To recover Staphylococcus aureus from faeces with mixed flora, the best medium is:
7.5% NaCl suppresses most other bacteria, and S. aureus ferments mannitol giving yellow colonies. EMB and MacConkey select gram-negatives.
A lung biopsy in pulmonary tuberculosis would characteristically show which necrosis?
Caseous necrosis gives a cheese-like centre within granulomas. Liquefactive necrosis is seen in bacterial abscesses and brain infarcts.
Mycobacterium tuberculosis on Löwenstein–Jensen medium usually takes how long to show visible colonies?
M. tuberculosis divides every 15–20 hours, so colonies take 3–6 weeks on LJ; LJ is held up to 8 weeks. Liquid MGIT systems are faster.
Which immunoglobulin, secreted in dimeric form into saliva, tears and intestinal fluid, chiefly protects mucosal surfaces against viruses?
Secretory IgA, a dimer joined by J chain and carrying secretory component, neutralises viruses at mucosal surfaces such as the respiratory and intestinal tracts.
Which statement about varicella and herpes zoster is NOT true?
Varicella is a generalised vesicular rash of primary infection; zoster is a painful dermatomal eruption from reactivated VZV, usually in older or immunosuppressed people.
Which virus is NOT recognised as a sexually transmitted pathogen?
Rubella spreads by respiratory droplets and transplacentally. HBV, HIV and HSV-2 are all transmitted sexually.
How do cytotoxic CD8 T lymphocytes mainly contribute to recovery from viral infection?
CTLs recognise viral peptides on MHC class I and kill infected cells with perforin, granzymes and Fas ligand. Antibodies, not CTLs, neutralise free virus.
Picornaviruses cause many diseases. Which of these is NOT caused by a picornavirus?
Infectious mononucleosis is caused by EBV, a herpesvirus. HAV (a hepatovirus) and enteroviruses (herpangina, myocarditis) are picornaviruses.
Plant viruses usually need wounds or insect vectors to enter host cells. Which plant cell structure is the main barrier?
The rigid cellulose wall blocks direct entry, so plant viruses enter through mechanical damage or insect feeding and then spread via plasmodesmata.
Which virus is NOT a member of the family Picornaviridae?
Rabies virus is an enveloped, bullet-shaped rhabdovirus. Coxsackie, echo, polio and rhinoviruses are small naked picornaviruses.
Which retroviral enzyme, encoded by the pol gene, inserts the viral DNA copy into the host chromosome?
Integrase cuts host DNA and joins the viral cDNA to form the provirus; drugs such as dolutegravir inhibit it. Reverse transcriptase makes the DNA copy first.
Urban yellow fever passes from person to person through which vector?
In the urban cycle, Aedes aegypti transmits yellow fever between humans. Anopheles transmits malaria.
Which of these viruses causes an almost uniformly fatal encephalitis that can be prevented by timely vaccination even after exposure?
Symptomatic rabies is nearly always fatal, but the long incubation allows post-exposure vaccine plus rabies immune globulin to prevent disease.
Common warts are unsightly, and some related types cause cervical cancer. Which virus group is responsible?
HPV types cause skin warts (e.g. 1, 2, 4), genital warts (6, 11) and cervical cancer (16, 18 and other high-risk types).
A student has malaise, fatigue, sore throat, many atypical lymphocytes and a positive heterophil antibody test. What is the likely cause?
A positive heterophil (Monospot/Paul-Bunnell) test with atypical lymphocytosis indicates EBV mononucleosis. Toxoplasma and CMV give heterophil-negative illness.
Which statement about hepatitis A is INCORRECT?
HAV never causes chronic infection or a carrier state. It is milder in children than adults, confers lifelong immunity, and vaccine is recommended for risk groups.
Enteric adenovirus types 40 and 41 cause diarrhoea in young children. Which specimen is used to detect them?
Adenovirus 40/41 replicate in the gut and are shed in feces; they are detected by stool antigen assays or PCR, not culture.
Which hepatitis virus is defective and can replicate only in a person also infected with HBV, because it borrows HBsAg for its envelope?
Hepatitis delta virus is a satellite RNA agent coated with HBsAg, so it needs HBV co-infection or superinfection. HBV vaccination therefore also prevents HDV.
Coliphage T2, like T4, contains which type of genome?
T-even phages have large linear dsDNA genomes. ssDNA phages include phiX174, and ssRNA phages include MS2.
A phage that can either lyse its host or integrate and persist with it as a prophage for generations is a:
Temperate phages such as lambda can enter lysogeny. Virulent (lytic) phages always kill their host.