This study aims to analyze the main drug resistance mechanism of Salmonella enteritidis induced by polymyxin in vitro.In this study,the resistance of Salmonella enteritidis CMCC(B)50335(ZK)to polymyxin was induced in vitro,and the growth characteristics,exercise ability,ul-trastructure and sensitivity to 16 antimicrobial agents before and after induction were determined by turbidimetry,semi-solid agar method,transmission electron microscope and disk diffusion method,and the whole genome and single nucleotide polymorphism(SNP)were detected by Illu-mina NovaSeq PE150 method.RT-qPCR was used to detect the differences in the expression levels of six drug-resistant related genes.The recombinant strain △phoPE1-128-1,which induced drug-resistant strain E1-128-1,was constructed by homologous recombination of Red Escherichia coli,and its sensitivity to polymyxin was detected.The results showed that three strains of induced drug-resistant bacteria E1-128-1,E1-128-3 and E2-128-3 were screened out,and the MIC increased by 128,64 and 64 times respectively after drug resistance stability test.Induced drug resistance had no significant effect on the growth ability of the tested bacteria and the sensitivity of 16 antibacte-rial drugs.The exercise ability of E1-128-1was significantly increased,and the cell wall and plasma membrane obviously thicken.There was no significant difference in the genome components of E1-128-1 before and after induction,but eight missense mutations of six drug-resistance related genes,including phoP/phoQ,cpxP,lptD,csrA and acrB,were detected,including four missense mutation sites of phoP,namely Leu185Trp,His189Ser,Thr190Tyr and Ile191His.The corresponding genes were sequenced by PCR,and the results were consistent with those of SNP.RT-qPCR results showed that the expression levels of mutant genes of the three induced strains increased signifi-cantly.Compared with E1-128-1,the MIC of △phoP E1-128-1 decreased to 1 mg/L.It is sug-gested that the mutation and increased expression of phoP gene are important factors for inducing polymyxin resistance of Salmonella CMCC(B)50335 in vitro.
关键词
沙门菌/黏菌素/诱导耐药/phoP/Red大肠杆菌同源重组
Key words
Salmonella/polymyxin/inducing drug resistance/phoP/homologous recombination of Red Escherichia coli
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