Hemolysins are best defined as:
Enzymes that inhibit bacterial growth
Toxins that lyse red blood cells
Structural proteins in bacterial capsules
Antibiotic resistance factors
The Correct Answer is B
A. Enzymes that inhibit bacterial growth: Hemolysins do not inhibit bacterial growth; instead, they act on host cells. They are not antimicrobial agents but rather virulence factors that facilitate bacterial survival and spread within the host.
B. Toxins that lyse red blood cells: Hemolysins are exotoxins produced by certain bacteria, such as Streptococcus and Staphylococcus species. They disrupt the membrane of red blood cells, causing hemolysis and releasing hemoglobin. This action provides bacteria with access to nutrients, particularly iron, which is essential for their metabolism and pathogenicity.
C. Structural proteins in bacterial capsules: Capsules are composed of polysaccharides or proteins that protect bacteria from phagocytosis. Hemolysins are not structural components of capsules; they are secreted proteins that damage host cells rather than forming protective layers around the bacterium.
D. Antibiotic resistance factors: Hemolysins do not confer resistance to antibiotics. Antibiotic resistance factors include enzymes such as beta-lactamases or efflux pumps that prevent drugs from killing the bacteria. Hemolysins function solely as cytotoxins targeting host cells.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Staphylococcus aureus: Mannitol Salt Agar (MSA) is both selective and differential. It contains high salt concentration, which inhibits most bacteria except staphylococci, and mannitol with a pH indicator to detect fermentation. Staphylococcus aureus ferments mannitol, producing acid that lowers the pH and turns the medium yellow.
B. Enterococcus faecalis: Enterococcus faecalis can tolerate salt but does not typically ferment mannitol on MSA, so the medium generally remains red or pink. It is more commonly identified using other selective media like bile-esculin agar.
C. Salmonella enterica: Salmonella species do not grow well on high-salt MSA and do not ferment mannitol, so they would not produce yellow colonies on this medium. They are typically detected using selective media like XLD or Hektoen enteric agar.
D. Pseudomonas aeruginosa: Pseudomonas aeruginosa is inhibited by the high salt concentration in MSA and does not ferment mannitol. While it may grow slowly under some conditions, it will not produce yellow colonies, making it unlikely to be the pathogen here.
Correct Answer is B
Explanation
A. The organism cannot tolerate salt: Mannitol Salt Agar (MSA) contains 7.5% NaCl, which inhibits the growth of most bacteria except halotolerant organisms. Growth on this medium indicates that the organism can tolerate high salt concentrations, so inability to tolerate salt is not supported by the observation.
B. The organism ferments mannitol: MSA contains mannitol and a pH indicator (phenol red). When bacteria ferment mannitol, acidic byproducts lower the pH, turning the agar yellow around the colonies. The presence of a yellow zone surrounding growth indicates that the organism is a mannitol fermenter, commonly seen with Staphylococcus aureus.
C. The organism is Gram-negative: MSA is selective for Gram-positive bacteria due to its high salt concentration. Gram-negative bacteria are typically inhibited and do not grow well on this medium. Therefore, growth on MSA suggests the organism is Gram-positive, not Gram-negative.
D. The organism produces hemolysin: Hemolysis is detected on blood agar, where lysis of red blood cells produces clear or greenish zones around colonies. The yellow zone on MSA is due to mannitol fermentation and not hemolysin production, so this observation does not indicate hemolysis.
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