Antimicrobial resistance, virulence & plasmid profiles among clinical isolates of Shigella serogroups

Bacillary dysentery caused by Shigella spp. remains an important cause of the crisis in low-income countries. It has been observed that Shigella species have become increasingly resistant to most widely used antimicrobials. In this study, the antimicrobial resistance, virulence and plasmid profile of clinical isolates of Shigella species were determined.

Sixty clinical Shigella isolates were subjected to whole-genome sequencing using Ion Torrent platform and the genome sequences were analyzed for the presence of acquired resistance genes, virulence genes and plasmids using web-based software tools.

Genome analysis revealed more resistance genes in Shigella flexneri than in other serogroups. Among β-lactamases, bla_OXA-1was predominantly seen followed by the bla_TEM-1B and bla_EC genes. For quinolone resistance, the qnr S gene was widely seen. Novel mutations in gyr B, par C and par E genes were observed. Cephalosporins resistance gene, bla_CTX-M-15 was identified and plasmid-mediated AmpC β-lactamases genes were found among the isolates. Further, a co-trimoxazole resistance gene was identified in most of the isolates studied. Virulence genes such as ipaD, ipaH, virF, senB, iha, capU, lpfA, sigA, pic, sepA, celb and gad were identified. Plasmid analysis revealed that the IncFII was the most commonly seen plasmid type in the isolates.

The presence of quinolone and cephalosporin resistance genes in Shigella serogroups has serious implications for the further spread of this resistance to other enteric pathogens or commensal organisms. This suggests the need for continuous surveillance to understand the epidemiology of the resistance.