Transient intestinal carriage after ingestion of antibiotic-resistant Enterococcus faecium from chicken and pork

Antibiotic-resistant enterococci are often present in retail meats, but it is unclear whether the ingestion of these contaminants leads to sustained intestinal carriage.

We conducted a randomized, double-blind study in 18 healthy volunteers. Six ingested a mixture of 10(7) colony-forming units (CFU) of two glycopeptide-resistant strains of Enterococcus faecium obtained from chicken purchased at a grocery store, six ingested 10(7) CFU of a streptogramin-resistant strain of E. faecium obtained from a pig at slaughter, and six ingested 10(7) CFU of a glycopeptide-susceptible and streptogramin-susceptible strain of E. faecium from chicken purchased at a grocery store. Suspensions of enterococci were prepared in 250 ml of whole milk and were well within the amounts deemed acceptable by Danish food regulations. Stool samples were collected before exposure, daily for 1 week after ingestion, and at 14 and 35 days. Resistant enterococci in stools were identified by selective culture techniques; further molecular characterization of the organisms was also conducted.

At the outset, none of the subjects were colonized with glycopeptide-resistant or streptogramin-resistant E. faecium. After ingestion of the study strains, these same strains were isolated from the stools of all subjects, in various concentrations. The test strain was isolated in stool from 8 of 12 subjects on day 6, and from 1 of 12 on day 14. All stool samples were negative at 35 days.

The ingestion of resistant E. faecium of animal origin leads to detectable concentrations of the resistant strain in stools for up to 14 days after ingestion. The organisms survive gastric passage and multiply.