Molecular epiderniologic study on prevalence of penicillin-resistant enterococci in Japan

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Enterococcus has been become an important pathogen of nosocomial infections recently. In this research project, we studied prevalence of drug resistance of recent clinical isolates of enterococci by using molecular epiderniologic methods, focusing on resistance to penicillin, aminoglycoside, and tetracycline. Study subject was 748 clinical strains of enterococci isolated from 1997 to 1998, and from 2001 to 2004 in Sapporo Medical University Hospital. Penicillin resistance was highly prevalent in Efaecium and E.rafnosus in contrast to low frequencies in other enterococcal species. A high-level gentamicin resistance gene aac(6')-aph(2'') was detected in 40.5% of Efaecalis and 3.5% of Efaecium. The ant(9)Ia, a spectinomycin resistance gene which had been reported only in Staphylococcus aureus was detected in one strain each of Efaecalis, Efaecium, and Eavium. A tetracycline resistance gene tetM was highly prevalent in Efaecalis (75.2%) and Efaecium (71.7%). The tetT which had been reported only in S.pyogenes was detected in 5 strains of Efaecalis and its sequence was identical to that of S.pyogenes except for 4 nucleotides (4 amino acids). The tetS and tetO were also found in some strains. Nucleotide sequence of tetS was identical to that of Listeria monocytogenes, while some genetic variations were found in tetO. These results indicated that some novel resistance genes have been prevalent in enterococci, suggesting a need for continuous surveillance of drug resistance in enterococci.