Molecular Epidemiology of Staphylococcus epidermidis Clinical Isolates from U.S. Hospitals

Abstract

ABSTRACTThe epidemiology ofStaphylococcus epidermidisin U.S. hospitals remains limited. This study aimed to address the genetic backgrounds of linezolid-susceptible and -resistantS. epidermidisstrains (isolated in 2010), includingcfr-carrying strains. In addition, the antimicrobial susceptibility profiles and linezolid resistance mechanisms among clonal lineages were assessed. A total of 71S. epidermidisisolates were selected, and linezolid-resistant strains were screened forcfrand mutations in 23S rRNA, L3, and L4. All isolates were subjected to multilocus sequence typing (MLST), and the results were analyzed by eBURST. Overall, 27 sequence types (STs) were detected, and ST5 (21.1%) and ST2 (16.9%) predominated. The majority (62/71; 87.3%) of STs belonged to clonal complex 2 (CC2), which was mostly comprised of subclusters CC2-II (41/62; 66.1%) and CC2-I (21/62; 33.9%). Other STs were grouped within CC23 or CC32 or were singletons. CC2-I strains were more likely to display a methicillin (95.2% versus 33.3 to 70.7%), a linezolid (47.6% versus 0.0 to 7.3%), or a multidrug (81.0% versus 33.3 to 36.6%) resistance phenotype. Among linezolid-resistant isolates,cfrwas noted only within CC2 strains, and it was detected equally in the CC2-I (3/10; 30.0%) and CC2-II (1/3; 33.3%) subclusters. 23S rRNA mutations (G2576 [seven strains] and C2534 [one strain]) were observed only among CC2-I (8/10; 80.0%) isolates. Strains showing a G2576 alteration also had M156 (7/7; 100.0%) and/or H146 (6/7; 85.7%) L3 modifications. This study provides an overview of theS. epidermidisclonal distribution and reports higher resistance rates among CC2-I strains. The results show thatcfrmay be acquired and expressed by both CC2 main subclusters, while 23S rRNA mutations appeared more often within CC2-I strains. Interestingly, these 23S rRNA mutants also had L3 alterations, which may act synergistically or in a compensatory manner to minimize the fitness cost while providing survival advantages under selective pressure.