Multi-drug resistance (MDR) and transfer of mobile genetic elements (MGEs) among enteric pathogens is increasing rapidly. Commensal E. coli and Shigellae were known to acquire and disseminate MGEs responsible for fluoroquinolones and cephalosporins resistance. Thus the study was hypothesized to investigate the role of transferable plasmids in commensal MDR E. coli and MDR Shigella flexneri, vs Salmonella spp.
Of 638 clinical faecal isolates (one year), 20.2% were E. coli, 25.7% were Salmonella spp. and 25.5% were Shigella spp. MDR commensal E. coli and MDR Shigella spp. were screened for the presence of plasmids, quinolone resistance (qnrA, B and S) and cephalosporinases (CTX-M-1,2,8,9 and 25). Conjugation was performed using commensal MDR E. coli (FC673) and MDR S. flexneri (FC1846) as donor strains and susceptible Salmonella (FC1932) as a recipient. Phenotypic expression of antimicrobial resistance was confirmed by MICs pre- and post-conjugation. The donor FC673, and transconjugants TEC1932 (E. coli to Salmonella) and TSH1932 (Shigella to Salmonella) were sequenced using Ion torrent to confirm identity of the plasmids transferred.
FC1932 successfully received the plasmid from E. coli and S. flexneri through natural conjugation. Plasmid pECSAL1 (colKP3 replicon type) from TEC1932 was found to harbour qnrS1 and blaOXA-181 with IS26-like elements responsible for reduced susceptibility to ciprofloxacin and cefuroxime (2nd gen.) (0.38 and 8 µg/ml). Similarly, plasmid pSHSAL2 (colRNAI type) with qnrS1 and blaCTX-M-15 from TSH1932 was responsible for ciprofloxacin reduced susceptibility (0.25 µg/ml) and cefixime resistance (>32 µg/ml) (3rd gen.). However blaCTX-M-15 was not transferred from E. coli as it was integrated in chromosome due to which cephalosporin resistant determinants are less frequently transferred.
The current drug of choice for Salmonella is fluoroquinolones, and resistance to cephalosporins is still not common. Nevertheless, the observed ability of the plasmid transfer from commensal E. coli and Shigella to susceptible Salmonella is a potential source for dissemination of fluoroquinolones and cephalosporins resistance and is a significant public health concern.
N. K. Devanga Ragupathi,
R. Gajendiran, None
S. Anandan, None
K. Walia, None
B. Veeraraghavan, Indian Council of Medical Research: Grant Investigator , Grant recipient and Research grant