We investigated for the first time the occurrence, stability and antibiotic resistance of 593 enterococci in six samples collected from three urban sewage treatment plants (STPs) located in the north, south and west part of Tehran, Iran between October 2004 and September of 2005. Isolates were typed with a biochemical fingerprinting method (the PhPlate system) and tested for their resistance to six antibiotics. The most prevalent species in all three STPs were E. faecium followed by E. hirae and E. faecalis accounting for 93% of the total isolates examined. In all, 317 (55%) isolates were susceptible to all six antibiotics tested and the remaining isolates were resistant to between 1 and 6 antibiotics. Biochemical fingerprinting with PhPlate system showed a high diversity for E. faecalis (D i = 0.95), E. hirae (D i = 0.93) and E. faecium (D i = 0.95) populations with an overall diversity of D i = 0.97 for the whole enterococcal populations found in all three STPs. Our data indicate a high degree of polyclonality among the enterococci populations of human origin. This study suggest that the municipal wastewaters might be an important source of dissemination of antibiotic-resistant enterococci in Iran.

The prevalence and diversity of antibiotic resistant enterococci populations in samples collected four times from urban sewage treatment plant in Tehran, Iran between June 2005 and July 2006 were studied. Filtered samples were grown on mEnterococci medium containing 4 μg/ml vancomycin after which the enterococci isolates were identified to the species level. All strains were then tested for their resistance against nine antibiotics. Of the 131 isolates, 98 (75%) isolates were identified as Enterococcus gallinarum, followed by 24 (18%) and 9 (7%) for E. faecium and E. casseliflavus, respectively. All E. gallinarum isolates carried vanC1 gene with 64 (65%) and 14 (14%) isolates concomitantly harboured either vanA or vanB gene, respectively. Some E. casseliflavus concomitantly harboured vanA and vanC2 or vanB and vanC2. Typing the total enterococci isolates with a high resolution biochemical fingerprinting method showed a high diversity (D i = 0.91). We have shown by biochemical fingerprinting the presence of highly diverse glycopeptide resistant E. gallinarum and E. casseliflavus that have captured vanA and vanB genetic determinants under natural conditions. To our knowledge this is the first report in this geographical region showing high frequency antibiotic resistant enterococcal populations in particular E. gallinarum carrying assorted vancomycin resistance genes.