A 30 year old patient who had a laparotomy recently developed an intraperitoneal abscess (peritonitis). The causative organism is a Gram positive coccus that is resistant to vancomycin and to bacitracin, grows well in 6.5% NaCl broth, and shows a positive optochin reaction. Which organism is the likely cause?

Question

Image below highlights jugular foramen. Which of the following structures do not pass through the marked structure “A”?

Answer 1

This is a bug identification question built from three lab clues: bacitracin resistance, growth in 6.5% NaCl broth, and vancomycin resistance, in a patient with an abscess after abdominal surgery.

Enterococcus faecalis: Matches all three clues. It tolerates high salt (6.5% NaCl), resists bacitracin, and some strains resist vancomycin (VRE), a well known cause of hospital acquired intra abdominal infection.
Streptococcus pneumoniae: Does not grow in 6.5% NaCl broth and usually causes respiratory or CNS infection, not a post surgical abdominal abscess, so it does not fit.
Staphylococcus aureus: A cluster forming, catalase positive coccus. It does not share the salt tolerant, bacitracin resistant pattern used here to identify the organism.
Peptostreptococcus: An anaerobic coccus, so it would not be picked up on the standard aerobic salt tolerance and bacitracin testing described.

Salt tolerance plus bacitracin resistance is the textbook combination for identifying enterococci, and vancomycin resistance points to VRE, a recognised cause of abscess after bowel surgery. So the organism is Enterococcus faecalis.

Let's summarize:

6.5% NaCl broth growth and bacitracin resistance together point to Enterococcus.
Vancomycin resistant Enterococcus (VRE) is a known cause of post operative intra abdominal infection.
Streptococcus pneumoniae, Staphylococcus aureus and Peptostreptococcus do not match this specific test pattern.

The likely causative organism is Enterococcus faecalis.

Answer 2

This is a bug identification question built from three lab clues: bacitracin resistance, growth in 6.5% NaCl broth, and vancomycin resistance, in a patient with an abscess after abdominal surgery.

Enterococcus faecalis: Matches all three clues. It tolerates high salt (6.5% NaCl), resists bacitracin, and some strains resist vancomycin (VRE), a well known cause of hospital acquired intra abdominal infection.
Streptococcus pneumoniae: Does not grow in 6.5% NaCl broth and usually causes respiratory or CNS infection, not a post surgical abdominal abscess, so it does not fit.
Staphylococcus aureus: A cluster forming, catalase positive coccus. It does not share the salt tolerant, bacitracin resistant pattern used here to identify the organism.
Peptostreptococcus: An anaerobic coccus, so it would not be picked up on the standard aerobic salt tolerance and bacitracin testing described.

Salt tolerance plus bacitracin resistance is the textbook combination for identifying enterococci, and vancomycin resistance points to VRE, a recognised cause of abscess after bowel surgery. So the organism is Enterococcus faecalis.

Let's summarize:

6.5% NaCl broth growth and bacitracin resistance together point to Enterococcus.
Vancomycin resistant Enterococcus (VRE) is a known cause of post operative intra abdominal infection.
Streptococcus pneumoniae, Staphylococcus aureus and Peptostreptococcus do not match this specific test pattern.

The likely causative organism is Enterococcus faecalis.

Show Hint

The Correct Option is A

Solution and Explanation

Questions Asked in NEET (PG) exam