Identification and Characterization of Vancomycin-resistant Enterococcus species Frequently Isolated from Laboratory Mice

To determine the prevalence of drug resistant bacteria colonizing laboratory mice, weisolated and characterized vancomycin-resistant Enterococcus species(VRE) from commercially available mice. A total of 24 VRE isolates were obtained from 19of 21 mouse strains supplied by 4 commercial breeding companies. Of these, 19 isolates ofE. gallinarum and 5 isolates of E. casseliflavuspossessing the vanC1 and vanC2/3 genes intrinsically,exhibited intermediate resistance to vancomycin respectively. In addition, these isolatesalso exhibited diverse resistant patterns to erythromycin, tetracycline, andciprofloxacin, whereas the use of antibiotics had not been undertaken in mouse strainstested in this study. Although 6 virulence-associated genes (ace,asa, cylA, efaA,esp, and gelE) and secretion of gelatinase and hemolysinwere not detected in all isolates, 23 of 24 isolates including the isolates of E.casselifalvus secreted ATP into culture supernatants. Since secretion of ATP bybacteria resident in the intestinal tract modulates the local immune responses, theprevalence of ATP-secreting VRE in mice therefore needs to be considered in animalexperiments that alter the gut microflora by use of antibiotics.