MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 48
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Aminoglycosides such as gentamicin inhibit protein synthesis by binding to which bacterial ribosomal subunit?
Aminoglycosides bind the 30S subunit and cause misreading of mRNA; 40S and 60S are eukaryotic subunits.
A beta-haemolytic, catalase-negative coccus from a throat swab is PYR positive. Which organism is most likely?
Among beta-haemolytic streptococci, group A S. pyogenes is PYR positive; S. agalactiae is PYR negative and S. aureus is catalase positive.
The capsule of Bacillus anthracis is unusual because it is made of:
Unlike most bacterial capsules, which are polysaccharide, the anthrax capsule is a polypeptide of D-glutamic acid.
Diphtheria toxin damages cells by:
Diphtheria toxin ADP-ribosylates elongation factor 2, halting host protein synthesis; blocking acetylcholine release is the action of botulinum toxin.
A single blood culture bottle grows a non-diphtheria Corynebacterium species in a patient with no line or implant. This most likely represents:
Diphtheroids are common skin flora; growth in only one bottle without a risk factor usually indicates contamination.
A positive methyl red test (red colour) shows that the organism:
Methyl red turns red below about pH 4.4, showing strong mixed-acid fermentation, as in E. coli; acetoin is detected by the VP test.
Which of these Gram-negative non-fermenters is oxidase positive?
P. aeruginosa is oxidase positive; Acinetobacter and Stenotrophomonas are characteristically oxidase negative.
In carbohydrate utilisation tests, Neisseria meningitidis produces acid from:
N. meningitidis uses glucose and maltose; N. gonorrhoeae uses glucose only, and N. lactamica also uses lactose.
About how many acid-fast bacilli per mL of sputum are needed for a Ziehl-Neelsen smear to be reliably positive?
Smear microscopy needs roughly 5,000–10,000 bacilli/mL, which is why culture and NAAT are more sensitive.
Reactivation pulmonary tuberculosis typically affects the upper lobes (apices) of the lungs because M. tuberculosis:
The lung apices have the highest oxygen tension, which suits the strictly aerobic tubercle bacillus.
In a stained smear, the nucleus of an Entamoeba histolytica trophozoite typically shows:
Fine even peripheral chromatin with a small central karyosome is typical of E. histolytica; coarse chromatin with an eccentric karyosome suggests E. coli.
Cough, wheeze and eosinophilia with transient lung shadows (Loeffler's syndrome) occur in Ascaris infection when:
Ascaris larvae pass from the blood into the alveoli before being swallowed, causing pneumonitis with eosinophilia.
Taenia eggs are seen in a stool sample. Why is the result reported as 'Taenia species' rather than naming the species?
The eggs of the two species cannot be told apart, so species identification needs a gravid proglottid (uterine branches) or the scolex.
Histoplasma capsulatum is classically acquired by inhaling spores from soil contaminated with:
Histoplasmosis ('cave disease') follows inhalation of microconidia from soil rich in bat or bird guano.
Which dermatophyte is the most common cause of tinea pedis and fungal nail infections worldwide?
T. rubrum is the leading cause of chronic foot and nail infection; M. canis mainly causes scalp and body ringworm from pets.
On dermatophyte test medium (DTM), a dermatophyte is suggested by:
Dermatophytes use protein and make the medium alkaline, turning the phenol red indicator red.
Oseltamivir is used to treat influenza. It works by inhibiting the viral:
Neuraminidase inhibitors stop the release of new virions from infected cells.
For the Westergren ESR method, blood is mixed with sodium citrate in a ratio of:
The Westergren ESR uses 4:1 blood to citrate (black-top tube), unlike the 9:1 ratio used for coagulation tests.
A serum lithium level is requested for a patient on lithium therapy. Which tube must be avoided?
Lithium heparin adds lithium to the sample and gives a falsely high result.
9 g of glucose (molecular weight 180 g/mol) is dissolved in water to a final volume of 500 mL. What is the molarity?
9 ÷ 180 = 0.05 mol, and 0.05 mol ÷ 0.5 L = 0.1 mol/L.