Vancomycin-resistant enterococci from Portuguese wastewater treatment plants

The objective of this study was to evaluate the incidence of vancomycin resistant enterococci in sludge and sewage of urban and poultry-slaughterhouse wastewater treatment plants. A total of 17 vancomycin resistant enterococci (eight vanA-containing Enterococcus faecium and nine vanC1/vanC2-containing Enterococcus gallinarum/casseliflavus) were found among 499 isolates of sewage and sludge samples of 14 urban and nine poultry-slaughterhouse wastewater treatment plants. These seventeen VRE isolates showed resistance to kanamycin (n = 8), tetracycline (n = 7), erythromycin (n = 7), ciprofloxacin (n = 7), ampicillin (n = 7), streptomycin (n = 6), and gentamicin (n = 2). The tetM gene, related with tetracycline resistance, was found in six of eight vanA-containing isolates, in all seven vanC-1 isolates and in one of two vanC-2 isolates. The ermB gene in seven erythromycin-resistant isolates; and the aac6'-aph2 gene in the two high-level-gentamicin-resistant isolates. Moreover, two vanA-containing E. faecium isolates harbored the hyl virulence gene, and three isolates the entA bacteriocin gene. The purK-1 allele was detected in our urban vanA-containing E. faecium isolate, and we found as well the purK-6 allele in one poultry-slaughterhouse vanA-containing E. faecium isolate. This study suggests that the wastewater treatment plants might be an important source of dissemination of antibiotic-resistant enterococci in Portugal.