High-level aminoglycoside resistance among enterococci and group A streptococci

Abstract

The occurrence of high-level aminoglycoside resistance (HLAmR) was determined for 73 enterococci and 54 group A streptococci by the high-load disc method, tube macrodilution and the polymerase chain reaction (PCR). The PCR method revealed the presence of genes coding for aminoglycoside-3′-O-phosphoryltransfcrase-III (APH(3′)-III), aminoglycoside-6′-N-acetyltransferase/2′-O-phosphoryltransferase (AAC(6′)/APH(2′)) or both, in 20·6%, 9·6% and 4·1% of the enterococci, respectively. The prevalence of HLAmR to at least one aminoglycoside among local enterococci was 37% (27/73). Only one of 54 Streptococcus pyogenes isolates produced APH(3′)-III and exhibited high-level resistance to kanamycin and streptomycin. In general, the three methods yielded comparable results, with only three discrepancies among the 127 isolates examined. High-load disc screening and tube macrodilution proved to be practical, reliable and reproducible, and thus suitable for routine screening. Of 20 Enterococcus faecalis strains tested, all were penicillin-tolerant. Only one of seven penicillin-tolerant S. pyogenes strains was HLAmR. No association between the two forms of resistance was found.