Characterization of Heterogeneous MRSA and MSSA with Reduced Susceptibility to Chlorhexidine in Kuwaiti Hospitals

Abstract

The objective of this investigation was to identify the lineages of MRSA and MSSA with reduced susceptibility to chlorhexidine in Kuwaiti hospitals. 121 clinical MRSA and 56 MSSA isolates were included in this study. Antimicrobial susceptibility testing was performed for a selection of agents including chlorhexidine and resistance genes were amplified and sequenced. PFGE, spa typing, and MLST were completed for a selection of isolates. The results showed SCC<i>mec</i> II, III, IV, and V were present in 0.8, 21.5, 69.4, and 8.3% of the MRSA isolates. <i>agr-1</i>_<i>Sa</i> was the most prevalent type in both MSSA (48%) and MRSA (54%). Forty-five percentage of MRSA contained <i>pvl</i> and 39% contained <i>lukE-lukD</i>, however, as many as 86% of MSSA contained <i>pvl</i> and 96.4% contained <i>lukE-lukD. qac</i> A-C genes were identified in 12.3% of MRSA, <i>nor</i>A was present in 82.6% and <i>bla</i>Z in 94.2%. Among MSSA only 5.4% harbored <i>qac</i>A, 83% contained <i>nor</i>A, and 91% <i>bla</i>Z. Multi-drug resistant ST239/t945 lineage containing a <i>qac</i> gene was the most identified <i>S. aureus</i>. However, other lineages, including ST772-MRSA-V/t4867/<i>pvl</i>(+)<i>qacC/smr</i> and non-<i>qac</i> harboring lineages of ST217-MRSAIV/t3244/<i>pvl</i>(-), ST34-MSSA/t161/<i>pvl</i>(+), ST5-MSSA/t688/<i>pvl</i>(+), ST5-MSSA/t4867/<i>nor</i>A(+), and ST672-MSSA/t003/<i>pvl</i>(-), also showed reduced susceptibility to chlorhexidine. The observed reduced susceptibility of non-<i>qac</i> dependent MSSA isolates to chlorhexidine suggests the involvement of other elements in promoting higher MBC (≥30 mg/L). Our results confirm that monitoring MSSA is essential as they may have the potential to survive low level biocide exposure.