High-Level Resistance to Erythromycin and Tetracycline and Dissemination of Resistance Determinants among Clinical Enterococci in Iran

Abstract

<b><i>Objectives:</i></b> The purpose of this study was to investigate the distribution pattern of genes responsible for erythromycin and tetracycline resistance and their association with resistance phenotypes in enterococcus isolates. <b><i>Materials and Methods:</i></b> Eighty-six <i>Enterococcus faecalis</i> and 26 <i>E. faecium</i> isolates were collected from 2 hospitals in Kerman, Iran. Minimum inhibitory concentration of erythromycin and tetra­cycline was determined and then genes encoding resistance to erythromycin – <i>erm</i> (A-C), <i>mef,</i> and <i>msr</i> – and tetracycline – <i>tet</i> (M), <i>tet</i> (O), <i>tet</i> (S), <i>tet</i> (K), and <i>tet</i> (L) – were investigated. <b><i>Results:</i></b> In all resistant isolates (<i>n</i> = 72, 64%), high-level resistance to both tested antibiotics was found. The most prevalent <i>erm</i> gene was <i>erm</i> (B) (77.7%), followed by <i>erm</i> (A) (15.2%) and <i>erm</i> (C) (8.3%). Genes mediating erythromycin efflux were detected in 70.8% (<i>mef</i>) and 9.7% (<i>msr</i>) of resistant isolates. Regarding tetracycline, <i>tet</i> (M) was detected at the highest rate (50%), followed by <i>tet</i> (O) (31%) and <i>tet</i> (S) (11%). Export of tetracycline was found in 31% (<i>tet</i> (K)) and 12% (<i>tet</i> (L)) of isolates. <b><i>Conclusion:</i></b> A high prevalence of high-level resistance to both erythromycin and tetracycline was documented. Alterations at the ribosomal level was more frequently detected in erythromycin and tetracycline resistance than efflux systems. Concurrent resistance mechanisms were more involved in resistance to erythromycin than tetracycline.