Question

Question 29 the Calcofluor Stain, the fluorochrome binds with which of the following structures? O A) Cell Wall Mycolic Acid OB) Metachromatic granules OC) Chitin OD) Polysaccharide Capsular material E) Cell Wall Peptidoglycan

Answer 1

29. The calcofluor white stain is a fluorescent stain that binds to chitin and cellulose. Chitin and cellulose are present in fungi. These fungi express bright green to blue fluorescence when stained with this dye.

Mycolic acid is present in cell wall of Mycobacterium species and is stained by Ziel Nielsen acid fast staining. Metachromatic granules are stained red by methylene blue. Polysaccharide capsules are stained using combination of acidic (Nigrosine, congo red) and basic dyes (crystal violet, safranin). Cell wall peptidoglycan is stained by Gram staining procedure.

Right choice: C) Chitin.

31. Staphylococcus aureus is a normal flora organism of skin that can cause opportunistic infections. It produces different virulence factors. Toxins produced include alpha, beta and gamma toxin. Coagulase coats the surface of S aureus with fibrin. S. aureus also encodes hyaluronidase enzyme that can cleave hyaluronic acid. However, its exact role is not clear. Protein A secreted by this organism will bind to Fc portion of antibodies and prevent opsonization. However, S. aureus doesn’t produce protein M. Protein M is produced by Streptococcus species.

Right choice: d) protein M.

34. Fibrinogen binding protein A or clumping factor is produced by S. aureus that binds to fibrinogen and helps in adhesion. Clumping factor is associated with the cell surface of S. aureus. It promotes attachment of the bacterium to blood clots. Most strains expressed clumping factor, although some strains also lack it.

S. aureus is a gram positive bacterium and will therefore have teichoic acids in their cell wall. All strains are also encapsulated. It is not clear if coagulase is a virulence factor for this organism. Lt is expressed by most strains of S. aureus. The S. aureus that lack Staphylocoagulase are known as coagulase negative staphylococci. However, this is not a cell associated, but an enzyme. Protein is expressed by all strains.

Right choice: D) clumping factor.

37. Both S. aureus and S. pyogenes produce DNase enzyme that can cleave DNA to release free nucleotides and phosphate.

S. pyogenes is PYR (Pyrrolidonyl Aminopeptidase) positive while S. aureus is PYR negative. S. aureus and S. pyogenes do not produce beta lactamases. Only S. aureus can grow in 6.5% NaCl as it is halophilic. S. aureus is beta hemolytic while S. pyogenes is alpha hemolytic.

Right choice: C) DNase positive.

46. Staphylococcus aureus can cause gastrointestinal food poisoning in humans. It is beta hemolytic, PYR positive gram positive coccobacilli. However, another species Corynebacterium is gram positive rod shaped bacilli S. aureus is catalase positive while S. pyogenes is catalase negative. S. aureus is a halophile growing at 6.5% NaCl concentration.

Right choice: C) Its gram stain morphology can be confused with Corynebacterium species.