Molecular Evaluation of Expression Changes in Genes Associated With Colistin Resistance and Virulence Development in Salmonella enterica From Two Iran Hospitals.

Salmonella entericais one of the most frequent causes of gastroenteritis in humans. The emergence of antimicrobial-resistant strains of the bacterium, especially those which are resistant toward colistin (CST), the latest antibiotic introduced to cure this bacterial disease, has become a severe health problem. Beside pmrA and pmrB genes, CST resistance is determined by mobilized colistin resistance (mcr) genes. Accordingly, in the present study, the expression pattern of these genes and fliC (encoding the flagellin protein) and agfA (encoding the bacterial fimbriae) was evaluated. To this end, a total of 50 S. enterica isolates were collected from two hospitals in Shiraz, Iran, during 2019-2020. The pattern of antimicrobial resistance of the isolates was determined by the disk diffusion method. Then, after the antibiotic sensitivity test, following RNA extraction, the expression of selected genes was evaluated running real-time PCR. Results revealed that the occurrence of CST resistance in Salmonella isolates was 16%. The transcription levels of pmrA and fliC genes were increased in CST-resistant isolates. The results demonstrated the widespread distribution of multidrug-resistant and CST-resistant strains of S. enterica in the hospital setting. To overcome this issue, further actions, such as fast detection and eradication and appropriate preventive measures, should be undertaken to face this challenge.