Amar A Telke1, Abiola Olumuyiwa Olaitan1, Serge Morand2, Jean-Marc Rolain1. 1. Unité de recherche sur les maladies infectieuses et tropicales émergentes (URMITE), UM63, CNRS 7278, IRD 198, INSERM 1095, Méditerranée Infection, Faculté de Médecine et de Pharmacie, Aix-Marseille-Université, Marseille, France. 2. Institut des Sciences de l'Évolution, CNRS-IRD-UM2, CC065, Université Montpellier 2, 34095 Montpellier cedex 05, France.
Abstract
Background: Colistin is the last drug option for the treatment of MDR Gram-negative bacterial infections. Several types of resistance to colistin have been identified, including hetero-resistance, which has been observed in several Gram-negative pathogens. During a routine surveillance project on antimicrobial resistance, we found abnormal colistin-resistant Enterobacter asburiae and Enterobacter cloacae isolates. E. cloacae is an intestinal commensal bacterium and a well-known opportunistic nosocomial pathogen. Objectives: To characterize the molecular mechanism of colistin hetero-resistance in Enterobacter spp. Methods: Several approaches (WGS, transposome mutagenesis and RT-PCR analysis) were used to discover the molecular mechanism of colistin hetero-resistance. Results: Genomic analysis of mutant clones generated by transposome mutagenesis suggests that hetero-resistance is linked with overexpression of the acrAB-tolC efflux pump. Transcriptional analysis further found that naturally elevated soxRS triggers the induction of the acrAB-tolC efflux pump proteins followed by the development of colistin hetero-resistance in E. asburiae and E. cloacae. Transcriptional analysis results were further verified as demonstrating the development of hetero-resistance in colistin-susceptible strains by plasmid-based overexpression of soxRS. Conclusions: Our observations highlight the importance of such findings, which previously were only superficially described because of the challenges associated with their detection, in the context of common modes of colistin resistance in Gram-negative bacteria. This study constitutes a unique demonstration of efflux-based high-level colistin hetero-resistance, controlled by a soxRS regulator in Gram-negative bacteria.
Background: Colistin is the last drug option for the treatment of MDR Gram-negative bacterial infections. Several types of resistance to colistin have been identified, including hetero-resistance, which has been observed in several Gram-negative pathogens. During a routine surveillance project on antimicrobial resistance, we found abnormal colistin-resistant Enterobacter asburiae and Enterobacter cloacae isolates. E. cloacae is an intestinal commensal bacterium and a well-known opportunistic nosocomial pathogen. Objectives: To characterize the molecular mechanism of colistin hetero-resistance in Enterobacter spp. Methods: Several approaches (WGS, transposome mutagenesis and RT-PCR analysis) were used to discover the molecular mechanism of colistin hetero-resistance. Results: Genomic analysis of mutant clones generated by transposome mutagenesis suggests that hetero-resistance is linked with overexpression of the acrAB-tolC efflux pump. Transcriptional analysis further found that naturally elevated soxRS triggers the induction of the acrAB-tolC efflux pump proteins followed by the development of colistin hetero-resistance in E. asburiae and E. cloacae. Transcriptional analysis results were further verified as demonstrating the development of hetero-resistance in colistin-susceptible strains by plasmid-based overexpression of soxRS. Conclusions: Our observations highlight the importance of such findings, which previously were only superficially described because of the challenges associated with their detection, in the context of common modes of colistin resistance in Gram-negative bacteria. This study constitutes a unique demonstration of efflux-based high-level colistin hetero-resistance, controlled by a soxRS regulator in Gram-negative bacteria.