Submitted to: Antimicrobial Agents and Chemotherapy
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/20/2005
Publication Date: 10/20/2005
Citation: Poole, T.L., Hume, M.E., Campbell, L.D., Scott, H.M., Alali, W.Q., Harvey, R.B. 2005. Vancomycin-resistant Enterococcus faecium strains isolated from community wastewater from a semi-closed agri-food system in Texas. Antimicrobial Agents and Chemotherapy. 49:4382-4385. Interpretive Summary: Antibiotics have been in use for fifty years to combat bacterial infections. When antibiotics were first discovered many thought bacterial diseases would be eradicated; however, this has not happened. In fact, some disease causing bacteria are reemerging due to the development of resistance to antibiotics. The use of antibiotics among food-producing animals is believed to have created a reservoir of antimicrobial resistant microflora. Further speculation suggests that resistant bacteria from this reservoir may enter the human population via contaminated food products. During a longitudinal study of a uniquely integrated, multi-site, semi-closed swine operation, several vancomycin-resistant Enterococcus faecium were isolated from human wastewater samples. This type of bacterium is of great concern to public health officials but has never been found outside of human hospitals. This research is the first known documentation of vancomycin-resistant Enterococcus faecium among healthy humans. It is important to note the vancomycin-resistant Enterococcus faecium were not found among the swine population.
Technical Abstract: Vancomycin-resistant Enterococcus faecium (VRE) have emerged as important nosocomial pathogens, but have rarely been isolated outside of a hospital setting in the United States. A longitudinal epidemiological study of wastewater effluents from a multi-site, semi-closed, vertically integrated population of humans and swine in Texas resulted in the isolation of VRE from the human community. Heterogeneity of the isolates was determined by PCR, pulsed-field gel electrophoresis (PFGE), PCR fragment length polymorphism analysis and susceptibility testing. Fifty clonal and non-clonal VRE were obtained from human wastewater effluent at multiple, geographically separated locations from 2002 to 2004. To date, no VRE have been isolated from swine fecal samples. Forty-nine of the VRE carried the vanA glycopeptide resistance gene cluster and one carried the vanB gene cluster. Twenty-one PFGE types were identified and segregated into three groups (I, II, and III). Fourteen different PFGE types were isolated from sites with affiliated swine farms, and the remaining seven were isolated from non-farm sites. PFGE type A was the most prevalent and was disseminated among four different farm-affiliated locations. PCR fragment length polymorphism analysis of Tn1546 revealed the presence of two Tn1546 types, one possessing an insertion sequence (IS1251) between the vanS and vanH genes (n=39), and the second lacking IS1251, but possessing a polymorphism in the vanYZ region. Although it is not known how long any of the VRE may have existed among the human population, there is evidence of clonal dissemination among groups of healthy individuals across geographically separated sites. This is the first longitudinal study to isolate VRE from a substantially non-clinical source in the United States.