Nosocomial acquisition of beta-lactamase--negative, ampicillin-resistant enterococcus

A recent prospective study at the Department of Veterans Affairs Medical Center, Martinez, Calif, revealed that 9% of enterococcal clinical isolates were ampicillin resistant. We prospectively studied 100 patients hospitalized in one general medicine ward and in the medical intensive care unit to study determinants of acquisition of ampicillin-resistant enterococcus.

Rectal swabs and urine cultures were obtained from patients within 72 hours of admission to the study ward and twice weekly until discharge from the ward or the intensive care unit. Cultures were obtained from the hands of personnel and from environmental surfaces in the general medical ward and the intensive care unit. Ampicillin-resistant enterococcal isolates were examined for molecular relatedness by plasmid DNA analysis.

The cultures from 23 patients yielded ampicillin-resistant enterococci. The rectal swabs yielded ampicillin-resistant enterococci before the urine cultures did except in one patient whose urine and rectal cultures were both positive on the same day. Acquisition of ampicillin-resistant enterococci was significantly associated with previous antimicrobial agents, Foley catheterization, and being bedridden. Resistant enterococci were not isolated from hospital personnel or environmental surfaces. Plasmid analysis by gel electrophoresis demonstrated nine strains, two of which predominated. Rectal and urine isolates from the same patient had identical plasmid electrophoresis patterns.

We conclude that ampicillin-resistant enterococci are common in the rectal flora, can spread to the urinary system, are associated with patient characteristics that predipose to nosocomial infection, and may become an emerging clinical problem.