Molecular Characterization by Whole-Genome Sequencing of Clinical and Environmental Serratia marcescens Strains Isolated during an Outbreak in a Neonatal Intensive Care Unit (NICU)

Abstract

The whole-genome sequencing (WGS) of eighteen <i>S. marcescens</i> clinical strains isolated from 18 newborns hospitalized in the Neonatal Intensive Care Unit (NICU) at Pescara Public Hospital, Italy, was compared with that of <i>S. marcescens</i> isolated from cradles surfaces in the same ward. The identical antibiotic resistance genes (ARGs) and virulence factors were found in both clinical and environmental <i>S. marcescens</i> strains. The <i>aac(6')-Ic</i>, <i>tetA(41)</i>, <i>bla</i>_SRT-3, <i>adeFGH</i>, <i>rsmA</i>, and PBP3 (D350N) genes were identified in all strains. The SRT-3 enzyme, which exhibited 10 amino acid substitutions with respect to SST-1, the constitutive AmpC β-lactamase in <i>S. marcescens</i>, was partially purified and tested against some β-lactams. It showed a good activity against cefazolin. Both clinical and environmental <i>S. marcescens</i> strains exhibited susceptibility to all antibiotics tested, with the exception of amoxicillin/clavulanate.