Increasing trend of antibiotic resistance in Shigella in Bangladesh: a plasmid-mediated transfer of mphA macrolide resistance gene.

Shigellosis remains a common gastrointestinal disease mostly in children <5 years of age in developing countries. Azithromycin (AZM), a macrolide, is currently the first-line treatment for shigellosis in Bangladesh; ciprofloxacin (CIP) and ceftriaxone (CRO) are also used frequently. We aimed to evaluate the current epidemiology of antimicrobial resistance (AMR) and mechanism(s) of increasing macrolide resistance in in Bangladesh. A total of 2407 clinical isolates of from 2009 to 2016 were studied. Over the study period, was gradually increasing and become predominant (55%) over (36%) by 2016. We used CLSI-guided epidemiological cut-off value (ECV) for AZM in to set resistance breakpoints (zone-diameter ≤ 15 mm for and ≤ 11 mm for ). Between 2009 and 2016, AZM resistance increased from 22% to approximately 60%, CIP resistance increased by 40%, and CRO resistance increased from zero to 15%. The A gene was the key macrolide resistance factor in ; a 63MDa conjugative middle-range plasmid was harboring AZM and CRO resistance factors. Our findings show that, especially after 2014, there has been a rapid increase in resistance to the three most effective antibiotics. The rapid spread of macrolide (AZM) resistance genes among are driven by horizontal gene transfer rather than direct lineage.