Streptococcus Questions and Answers

Q: A urine sample was taken from a 30 year old who had symptoms related with urinary tract infection, she complained of painful and frequent urination with blood in the urine. Which of the following pathogen is Not most commonly found in the urine sample?

Correct answer: Streptococcus mutansS. mutans is an oral organism and is not a urinary pathogen. The others are all found in urine cultures: E. coli overwhelmingly the commonest, S. aureus in catheterised or bacteraemic patients, and S. agalactiae particularly in pregnancy, where its presence in urine indicates heavy genital colonisation.

Q: Which of the following toxins cause damage to the tissue cells by its phospholipase action?

Correct answer: beta toxinStaphylococcal beta toxin is a sphingomyelinase C, an enzyme that hydrolyses the sphingomyelin of the cell membrane and so destroys the cell from its lipid outwards. Alpha toxin damages membranes by a different route, assembling into a pore; protein A binds the Fc region of immunoglobulin and blocks opsonisation; and coagulase clots plasma rather than attacking cells.

Q: Which of the following microorganism causes lesions in the form of abscesses?

Correct answer: Staphylococcus aureusThe walled-off abscess is the characteristic staphylococcal lesion: coagulase clots the surrounding plasma into a fibrin barrier that keeps phagocytes and antibiotics out while the organism multiplies inside. Streptococcal infection spreads diffusely instead, through tissue planes, because streptokinase and hyaluronidase break down exactly the barriers that staphylococci build.

Q: Antibiotics can easily reach the staphylococci.

Correct answer: FalseThe staphylococcal abscess is designed to keep them out. Coagulase converts fibrinogen to fibrin around the lesion, producing an avascular wall that antibiotics cannot cross in useful concentration, and the organisms inside are metabolically slow and correspondingly tolerant. This is why an abscess must be drained surgically and why antibiotic therapy alone so often fails.

Q: Streptococus pyogenes comprises which Lancefield group?

Correct answer: AS. pyogenes carries the group A cell wall carbohydrate, which is what the Lancefield grouping detects and what gives it its everyday name of group A streptococcus. Group B is S. agalactiae, the neonatal pathogen, and group D covers the enterococci and S. bovis.

Q: Which of the following microbe does not belong to Group D enterococci group?

Correct answer: S. bovisS. bovis carries the group D antigen but is not an enterococcus: it fails to grow in 6.5 per cent salt and remains bile-aesculin positive, so it is distinguished from the true enterococci by the salt test. The distinction has clinical value, since S. bovis bacteraemia and endocarditis are associated with colonic carcinoma and prompt a search for one.

Q: Scarlet fever is similar to the pharyngitis in all respects.

Correct answer: FalseScarlet fever is streptococcal pharyngitis plus the effects of the pyrogenic exotoxin: a diffuse erythematous rash sparing the area around the mouth, a strawberry tongue, and subsequent desquamation. It occurs only when the infecting strain carries the toxin gene and the patient lacks neutralising antibody, which is what the Dick test detects.

Q: Which of the following immunity is protective against infection by S.pyogenes?

Correct answer: humoral immunityProtection against S. pyogenes is antibody-mediated and directed against the M protein, and it is type specific: antibody to one M type protects against that type alone, which is why repeated infections with different types are possible throughout life. The type specificity is also the chief obstacle to a vaccine, since there are more than a hundred M types.

Q: Puerperal fever is a streptococcal infection of the _____________

Correct answer: uterusPuerperal fever is streptococcal infection of the endometrium following childbirth, spreading from there to the bloodstream. It was the great killer of maternity wards until Semmelweis showed that hand disinfection prevented it, and it remains the historical demonstration that the organism is carried on the hands of attendants rather than arising within the patient.

31.

A urine sample was taken from a 30 year old who had symptoms related with urinary tract infection, she complained of painful and frequent urination with blood in the urine. Which of the following pathogen is Not most commonly found in the urine sample?

A.Staphylococcus aureus
B.E.coli
C.Streptococcus mutans
D.Streptococcus agalactiae

Answer: C

Correct answer: Streptococcus mutans

S. mutans is an oral organism and is not a urinary pathogen. The others are all found in urine cultures: E. coli overwhelmingly the commonest, S. aureus in catheterised or bacteraemic patients, and S. agalactiae particularly in pregnancy, where its presence in urine indicates heavy genital colonisation.

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32.

All of the following statement regarding coagulase negative Staphylococcus spp (CONS) are true, Except?

A.S. epidermidis and S. saprophyticus are coagulase negative staphylococci
B.Infection with S. epidermidis are usually hospital acquired
C.S. saprophyticus is normal flora of humans skin surface
D.Both are common pathogens in urinary tract infections

Answer: C

Correct answer: S. saprophyticus is normal flora of humans skin surface

S. saprophyticus belongs to the genitourinary flora rather than being a general skin commensal; it is S. epidermidis that colonises skin everywhere. The distinction matters clinically, because S. saprophyticus in a urine culture from a young woman is a genuine pathogen while S. epidermidis in a blood culture is more often a contaminant.

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33.

Which of the following toxins cause damage to the tissue cells by its phospholipase action?

A.alpha toxin
B.beta toxin
C.protein A
D.coagulase

Answer: B

Correct answer: beta toxin

Staphylococcal beta toxin is a sphingomyelinase C, an enzyme that hydrolyses the sphingomyelin of the cell membrane and so destroys the cell from its lipid outwards. Alpha toxin damages membranes by a different route, assembling into a pore; protein A binds the Fc region of immunoglobulin and blocks opsonisation; and coagulase clots plasma rather than attacking cells.

Discuss in Forum

34.

Which of the following microorganism causes lesions in the form of abscesses?

A.Staphylococcus aureus
B.Streptococcus pyogenes
C.Streptococcus pneumoniae
D.Clostridium perfringens

Answer: A

Correct answer: Staphylococcus aureus

The walled-off abscess is the characteristic staphylococcal lesion: coagulase clots the surrounding plasma into a fibrin barrier that keeps phagocytes and antibiotics out while the organism multiplies inside. Streptococcal infection spreads diffusely instead, through tissue planes, because streptokinase and hyaluronidase break down exactly the barriers that staphylococci build.

Discuss in Forum

35.

Antibiotics can easily reach the staphylococci.

A.True
B.False

Answer: B

Correct answer: False

The staphylococcal abscess is designed to keep them out. Coagulase converts fibrinogen to fibrin around the lesion, producing an avascular wall that antibiotics cannot cross in useful concentration, and the organisms inside are metabolically slow and correspondingly tolerant. This is why an abscess must be drained surgically and why antibiotic therapy alone so often fails.

Discuss in Forum

36.

Streptococus pyogenes comprises which Lancefield group?

Answer: A

Correct answer: A

S. pyogenes carries the group A cell wall carbohydrate, which is what the Lancefield grouping detects and what gives it its everyday name of group A streptococcus. Group B is S. agalactiae, the neonatal pathogen, and group D covers the enterococci and S. bovis.

Discuss in Forum

37.

Which of the following microbe does not belong to Group D enterococci group?

A.S. faecalis
B.S. faecium
C.S. durans
D.S. bovis

Answer: D

Correct answer: S. bovis

S. bovis carries the group D antigen but is not an enterococcus: it fails to grow in 6.5 per cent salt and remains bile-aesculin positive, so it is distinguished from the true enterococci by the salt test. The distinction has clinical value, since S. bovis bacteraemia and endocarditis are associated with colonic carcinoma and prompt a search for one.

Discuss in Forum

38.

Scarlet fever is similar to the pharyngitis in all respects.

A.True
B.False

Answer: B

Correct answer: False

Scarlet fever is streptococcal pharyngitis plus the effects of the pyrogenic exotoxin: a diffuse erythematous rash sparing the area around the mouth, a strawberry tongue, and subsequent desquamation. It occurs only when the infecting strain carries the toxin gene and the patient lacks neutralising antibody, which is what the Dick test detects.

Discuss in Forum

39.

Which of the following immunity is protective against infection by S.pyogenes?

A.cell-mediated immunity
B.innate immunity alone
C.humoral immunity
D.no cure present

Answer: A

Correct answer: humoral immunity

Protection against S. pyogenes is antibody-mediated and directed against the M protein, and it is type specific: antibody to one M type protects against that type alone, which is why repeated infections with different types are possible throughout life. The type specificity is also the chief obstacle to a vaccine, since there are more than a hundred M types.

Discuss in Forum

40.

Puerperal fever is a streptococcal infection of the _____________

A.kidney
B.skin
C.uterus
D.heart

Answer: C

Correct answer: uterus

Puerperal fever is streptococcal infection of the endometrium following childbirth, spreading from there to the bloodstream. It was the great killer of maternity wards until Semmelweis showed that hand disinfection prevented it, and it remains the historical demonstration that the organism is carried on the hands of attendants rather than arising within the patient.

Discuss in Forum

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