Serotype Is Associated With High Rate of Colistin Resistance Among Clinical Isolates of .

To investigate the prevalence, probable mechanisms and serotype correlation of colistin resistance in clinical isolates of from patients in China, isolates were collected from fecal and blood samples of patients. In this study, 42.8% (136/318) clinical isolated were resistant to colistin. MIC distribution for colistin at serotype level among the two most prevalent serotypes originating from humans in China indicated that Enteritidis (83.9% resistance, 125/149) were significantly less susceptible than Typhimurium (15.3% resistance, 9/59, < 0.01). genes and mutations in PmrAB confer little for rate of colistin resistant isolated from human patients. Phylogenetic tree based on core-genome single nucleotide polymorphisms (SNPs) was separately by the serotypes and implied a diffused distribution of MICs in the same serotype isolates. Relatvie expression levels of colistin resistant related genes were significantly higher in non- colistin resistant Typhimurium than in colistin sensitive Typhimurium, but no discernable differences between colistin resistant and sensitive Enteritidis, indicating a different mechanism between colistin resistant Typhimurium and Enteritidis. In conclusion, colistin susceptibility and colistin resistant mechanism of clinical isolated were closely associated with specific serotypes, at least in the two most prevalent serotype Enteritidis and Typhimurium. We suggest clinical microbiology laboratory interpreting colistin MIC results in the serotype level.