Phenotypic and genotypic characteristics of a carbapenem-resistant Serratia marcescens cohort and outbreak: describing an opportunistic pathogen

Serratia marcescens is an emerging opportunistic pathogen with high genetic diversity. This article describes the microbiological characteristics of isolates and the risk factors for infections caused by carbapenem-resistant S. marcescens. A retrospective study of patients colonized (n=43) and infected (n= 20) with carbapenem-resistant S. marcescens over a 3-year period was conducted. Polymerase chain reaction for carbapenemase genes and molecular typing of all available strains was performed. Forty-two isolates were analysed, including three environmental samples identified during an outbreak. Thirty-five carbapenem-resistant S. marcescens carried bla KPC-2, one isolate was bla(NDM)-positive and four isolates carried bla(OXA)-101. The genomes were grouped into three clusters with 100% bootstrap; three patterns of mutations on ompC and ompF were found. The strains carried virulence genes related to invasion and haemolysis, and the environmental strains presented fewer mutations on the virulence genes than the clinical strains. Multi-variate analysis showed that previous use of polymyxin (P= 0.008) was an independent risk factor for carbapenem-resistant S. marcescens infection. This study highlighted that bla KPC-2 in association with ompC or ompF mutation was the most common mechanism of resistance in the study hospital, and that previous use of polymyxin was an independent risk factor for carbapenem-resistant S. marcescens. There was a predominant clone, including the environmental isolates, suggesting that crosstransmission was involved in the dissemination of this pathogen. (C) 2021 Elsevier Ltd and International Society of Antimicrobial Chemotherapy. All rights reserved.

Automated summary

This study retrospectively examined patients infected with carbapenem-resistant S. marcescens and found that the combination of bla KPC-2 with ompC or ompF mutation was the main mechanism of resistance. Additionally, previous use of polymyxin was identified as an independent risk factor for infection with this pathogen.