Which organism grows on MacConkey agar and is often implicated in nosocomial infections?

Which organism grows on MacConkey agar and is often implicated in nosocomial infections?

• A. Enterococcus faecalis
• B. Acinetobacter baumannii
• C. Staphylococcus aureus
• D. Streptococcus pneumoniae

Answer: (B)

MacConkey agar is selective for Gram-negative bacteria and helps distinguish lactose fermenters from non-fermenters; Gram-positive organisms are generally inhibited and won’t grow well on it. Acinetobacter baumannii fits both clues: it is a Gram-negative bacterium commonly implicated in hospital-acquired infections, especially in ICUs, and it grows on MacConkey (typically as a colorless, non-lactose-fermenting colony). The other organisms are Gram-positive and are not characteristic MacConkey growers, so they’re less associated with this medium in the context of nosocomial infections.

MacConkey agar is selective for Gram-negative bacteria and helps distinguish lactose fermenters from non-fermenters; Gram-positive organisms are generally inhibited and won’t grow well on it. Acinetobacter baumannii fits both clues: it is a Gram-negative bacterium commonly implicated in hospital-acquired infections, especially in ICUs, and it grows on MacConkey (typically as a colorless, non-lactose-fermenting colony). The other organisms are Gram-positive and are not characteristic MacConkey growers, so they’re less associated with this medium in the context of nosocomial infections.