Which antibiotic is inappropriate to report for an E. coli isolate from a wound culture?

Which antibiotic is inappropriate to report for an E. coli isolate from a wound culture?

• A. Ampicillin
• B. Cefazolin
• C. Gentamicin
• D. Nitrofurantoin

Answer: (D)

The key idea is choosing antibiotics based on where the infection is and whether the drug reaches effective levels there. Nitrofurantoin is tailored for urinary infections and achieves very high concentrations in the urine but very low levels in blood and tissues. Because of this poor tissue penetration, it does not reliably treat wound or systemic infections, so reporting susceptibility or using it for a wound E. coli isolate isn’t clinically meaningful. In wound infections, drugs that reach adequate concentrations in skin and soft tissue are preferred, so agents like ampicillin, cefazolin, and gentamicin are appropriate options to report for a wound isolate, assuming the organism is susceptible. Nitrofurantoin’s limitations for non-urinary sites explain why it is inappropriate to report for a wound culture.

The key idea is choosing antibiotics based on where the infection is and whether the drug reaches effective levels there. Nitrofurantoin is tailored for urinary infections and achieves very high concentrations in the urine but very low levels in blood and tissues. Because of this poor tissue penetration, it does not reliably treat wound or systemic infections, so reporting susceptibility or using it for a wound E. coli isolate isn’t clinically meaningful. In wound infections, drugs that reach adequate concentrations in skin and soft tissue are preferred, so agents like ampicillin, cefazolin, and gentamicin are appropriate options to report for a wound isolate, assuming the organism is susceptible. Nitrofurantoin’s limitations for non-urinary sites explain why it is inappropriate to report for a wound culture.