Investigation of clonality among high level gentamicin resistant E. faecalis and E. faecium isolated from sewage treatment plants in Tehran

The development of high-level resistance to aminoglycosides, penicillin and glycopeptides singly and in combination by enterococci, has important clinical implications. Enterococci are normal flora of intestine and are released into the environment through faeces. One of the investigation methods on enterococcal population is the screening of sewage treatment plants for presence of enterococci. The aim of this study was to determine clonal diversity among HLGR enterococcal isolates, obtained from the sewage treatment plants (STPs) in Tehran. From November 2005 to May 2006 a total of 140 enterococcal isolates were collected from 3 sewage treatment plants (STP) located at different parts of Tehran. Confirmation of species and detection of gentamicin resistance genes were performed by PCR method. Antimicrobial susceptibility and MIC determination tests were performed on the basis of CLSI standard. Php typing was used for typing of enterococcal HLGR isolates. E. faecalis (26%) and E. faecium (74%) were the most common species in STPs samples. E. faecium had the highest rate of resistance to tetracycline. The MICs for all of enterococcal HLGR isolates were ≥1024 µg/ml and most enterococci contained aac (6')-Ie-aph (2'')-Ia gene. Only one E. faecium isolate showed aph (2")-Ic gene. Php typing of sewage HLGR E. faecalis and E. faecium isolates yielded 16 and 50 patterns with a diversity index of 0.910 and 0.945, respectively. The presence of aac (6')-Ie-aph (2'')-Ia gene in most of HLGR isolates, suggested widespread dissemination of this gene in the enterococcal isolates in sewage. Clonal diversity in HLGR and MDR entrococcal population showed wastewater could be a possible reservoir for circulation of these isolates in the community.