MLT GlobeMOH exam preparation (UAE) – page 21
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A mycobacterial isolate forms yellow-orange colonies whether incubated in darkness or light. In the Runyon scheme, it is a:
Scotochromogens (Runyon group II, e.g. M. gordonae) are pigmented even in the dark. Photochromogens (group I, e.g. M. kansasii) produce pigment only after light exposure.
Pleural fluid from a patient with tuberculous pleurisy is typically an exudate in which the predominant cell type is:
Tuberculous pleural effusions are lymphocyte-predominant exudates, often with few mesothelial cells. Neutrophils dominate in bacterial parapneumonic effusions.
When performing the Kovács oxidase test on filter paper, a positive result should be read within:
A true positive turns deep purple within about 10 seconds. Later colour change can be due to reagent auto-oxidation and should be ignored.
The standard Mantoux tuberculin skin test injects intradermally:
The standard dose is 5 tuberculin units (PPD-S) or equivalent 2 TU PPD RT23, in 0.1 mL; induration is read at 48–72 hours.
Which of these gram-negative rods is motile?
P. aeruginosa has a polar flagellum and is motile. H. influenzae, B. pertussis and Y. pestis are non-motile.
In the pour-plate method for viable counts, the diluted inoculum is:
In pour plates the sample is mixed with cooled molten agar, so colonies grow both within and on the medium. Spreading on set agar is the spread-plate method.
Moraxella lacunata, a cause of angular blepharoconjunctivitis, appears on Gram stain as:
M. lacunata is a short, broad gram-negative rod typically in pairs (Morax–Axenfeld diplobacillus). Comma shapes suggest Vibrio.
Vincent's angina (acute necrotising ulcerative gingivitis/pharyngitis) is a synergistic infection involving:
A Gram stain of the ulcer shows fusiform bacilli with spirochaetes (e.g. Treponema vincentii). A pseudomembrane with toxin suggests diphtheria instead.
L-forms are wall-deficient bacterial variants. Which statement about them is FALSE?
L-forms can be cultured on osmotically protective (hypertonic) media. Loss of the wall makes them pleomorphic and variable in size.
A Neisseria isolate from a urethral discharge produces acid from glucose only, not from maltose, lactose or sucrose. Identify it.
N. gonorrhoeae utilises glucose only. N. meningitidis uses glucose and maltose; N. lactamica also uses lactose.
In industrial penicillin production, Penicillium chrysogenum was classically grown in a medium based on:
Corn steep liquor supplies nitrogen and phenylacetic acid precursors that raised penicillin yields dramatically.
Brucella species grow in culture as:
Brucella are strictly aerobic gram-negative coccobacilli; B. abortus needs added CO2 for primary isolation.
A rapid nitrocefin (chromogenic cephalosporin) test is routinely used on which isolate to predict ampicillin resistance?
Beta-lactamase detection by nitrocefin predicts ampicillin resistance in H. influenzae. Pneumococcal penicillin resistance is due to altered PBPs, not beta-lactamase.
Which feature is NOT typical of human brucellosis?
Brucellosis causes undulant fever, sweats, arthralgia, sacroiliitis and myalgia. Diarrhoea is not a prominent feature.
Branching, beaded gram-positive rods from a lung abscess stain red with a modified (weak acid) Kinyoun stain. Most likely:
Nocardia is partially acid-fast when decolourised with 1% sulphuric acid. Actinomyces is also branching but not acid-fast.
Which statement about bacterial capsules is INCORRECT?
Capsular polysaccharides are the basis of pneumococcal, meningococcal, Hib and typhoid Vi vaccines. Capsules block phagocytosis and aid adherence.
Which statement about Streptococcus pneumoniae is correct?
The polysaccharide capsule is its main virulence factor. Pneumococci autolyse and may appear gram-variable in old cultures, and are non-motile.
Which statement about Salmonella Typhi is NOT true?
Like all Enterobacterales, Salmonella is oxidase-negative. S. Typhi typically makes a small H2S 'wisp' on TSI.
Cholera toxin produces watery diarrhoea by:
The A subunit ADP-ribosylates Gs protein, keeping adenylate cyclase on. Rising cAMP drives chloride and water secretion without tissue damage.
Litmus milk inoculated with an anaerobe shows clot formation torn apart by gas ('stormy fermentation'). The organism is:
C. perfringens ferments lactose, forming acid clot that is disrupted by vigorous gas production.