Colistin Resistance Mechanisms in Human Salmonella enterica Strains Isolated by the National Surveillance Enter-Net Italia (2016–2018)

Abstract

Background: A collection of human-epidemiologically unrelated S. enterica strains collected over a 3-year period (2016 to 2018) in Italy by the national surveillance Enter-Net Italia was analysed. Methods: Antimicrobial susceptibility tests, including the determination of minimal inhibitory concentrations (MICs) for colistin, were performed. Colistin resistant strains were analysed by PCR to detect mobile colistin resistance (mcr) genes. In mcr-negative S. enterica serovar Enteritidis strains, chromosomal mutations potentially involved in colistin resistance were identified by a genomic approach. Results: The prevalence of colistin-resistant S. enterica strains was 7.7%, the majority (87.5%) were S. Enteritidis. mcr genes were identified only in one strain, a S. Typhimurium monophasic variant, positive for both mcr-1.1 and mcr-5.1 genes in an IncHI2 ST4 plasmid. Several chromosomal mutations were identified in the colistin-resistant mcr-negative S. Enteritidis strains in proteins involved in lipopolysaccharide and outer membrane synthesis and modification (RfbN, LolB, ZraR) and in a component of a multidrug efflux pump (MdsC). These mutated proteins were defined as possible candidates for colistin resistance in mcr-negative S. Enteritidis of our collection. Conclusions: The colistin national surveillance in Salmonella spp. in humans, implemented with genomic-based surveillance, permitted to monitor colistin resistance, determining the prevalence of mcr determinants and the study of new candidate mechanisms for colistin resistance.

Genomic characterization of Salmonella isolated from retail chicken and humans with diarrhea in Qingdao, China

“…Moreover, several Salmonella isolates showed resistance to colistin, which is considered as one of the last-resort therapeutic options for the defense of multidrug-resistant Enterobacteriaceae ( Elbediwi et al, 2019 ). This finding of colistin resistance agreed with results reported by other recent studies in Salmonella isolates from poultry and humans ( Fortini et al, 2022 ; Tang et al, 2022 ). Of note, two carbapenems (imipenem and meropenem) resistant Salmonella isolates were also found in this study.…”

The Occurrence and Genomic Characteristics of mcr-1-Harboring Salmonella from Retail Meats and Eggs in Qingdao, China

“…As colistin has been a last-resort antimicrobial for defending against MDR Gram-negative bacteria, we are surprised to see the high detection rate of mcr-1 in Salmonella from food products. Given mcr-1 has been found in Salmonella from animals in many countries [ 6 , 53 ] and also occurred in Salmonella of human origin [ 17 , 19 ], food products, especially fresh eggs, may play a key role in disseminating such pathogens between animals and humans. In this study, all the mcr-1 -positive Salmonella isolates were ST34 S .…”

“…Although the detection rate of mcr-1 in clinical Salmonella isolates in many countries remains very low [ 18 , 19 ], mcr-1 -positive Salmonella isolates have already occurred in food animal products, especially retail meats [ 20 , 21 ], and S . Typhimurium has been the prevalent serotype for both clinical and foodborne mcr-1 -positive Salmonella isolates [ 22 , 23 ].…”

Polymyxin Resistance in Salmonella: Exploring Mutations and Genetic Determinants of Non-Human Isolates

“…Despite structural similarities between abequose and tyvellosis, subtle differences in the hydroxyl group's position may reduce susceptibility to colistin across different serotypes. Tyvellosis may prevent colistin from reaching its target, the LPS component of the bacterial outer membrane, the initial cellular target of polymyxin [32,33].…”

“…Resistance to polymyxin antibiotics relies on an intricate mechanism involving multiple genes that affect the cell surface, compromising its integrity or leading to modifications [32,33]. The identification of plasmid-mediated mechanisms of resistance to polymyxins prompts us to consider the perspective and assess the extent of the dissemination of this resistance in both human and veterinary medicine, along with understanding its impact.…”