A 68-year-old woman in a nursing home develops a UTI of Enterococcus faecalis which is sensitive to vancomycin. Which of the following antibiotics would be appropriate for this type of infection? A. aztreonam B. erythromycin C. clindamycin D. metronidazole
The correct answer and explanation is:
The correct answer is B. erythromycin.
Explanation:
Enterococcus faecalis is a Gram-positive bacterium commonly causing urinary tract infections (UTIs), especially in elderly or hospitalized patients such as those in nursing homes. Treatment of enterococcal infections depends on the antibiotic susceptibility of the strain, and Enterococcus faecalis often shows variable resistance patterns.
- Vancomycin-sensitive means the strain does not have vancomycin resistance, so vancomycin is effective against it. However, vancomycin is typically reserved for more serious infections or resistant strains due to its broad spectrum and toxicity concerns.
- Among the options:
- A. Aztreonam: This antibiotic is a monobactam that targets Gram-negative bacteria only. Enterococcus faecalis is Gram-positive, so aztreonam would be ineffective.
- B. Erythromycin: This is a macrolide antibiotic effective against many Gram-positive bacteria, including some strains of Enterococcus faecalis. It is considered appropriate here because erythromycin can cover Enterococcus species that are sensitive.
- C. Clindamycin: This lincosamide antibiotic also targets Gram-positive anaerobes and some Gram-positive aerobes, but Enterococcus species are often resistant to clindamycin, making it a poor choice for UTI caused by Enterococcus faecalis.
- D. Metronidazole: This antibiotic is effective only against anaerobic bacteria and some protozoa, but Enterococcus faecalis is a facultative anaerobe (can survive in oxygen) and typically not susceptible to metronidazole.
Additional context:
- Enterococcus faecalis is known for intrinsic resistance to many antibiotics, so treatment must be carefully selected based on sensitivity tests.
- For UTIs caused by Enterococcus faecalis, common effective antibiotics include ampicillin, vancomycin (if sensitive), and sometimes erythromycin or other macrolides if sensitivity is confirmed.
- Since the strain in this case is sensitive to vancomycin, but erythromycin is a suitable alternative among the given options, erythromycin is the correct choice.