Horizontal Transfer of Plasmids Bearing blaCTX-M Between Gut Commensals and Pathogenic Escherichia coli in Indian Patients

Indiscriminate use of antibiotics has exerted selective pressure on the gut microbiota, increasing the prevalence of antibiotic-resistant bacteria among the commensal population. However, in a state of intestinal dysbiosis, the patient’s flora contributes to the spreading of genes bearing determinants for antibiotic-resistance via horizontal transfer of drug-resistant plasmid. Although the in vivo spread of antibiotic resistance through this mechanism is well-known, limited studies demonstrate evidence of it occurring between commensal and pathogenic Enterobacteriaceae in patients. This study investigated the possibility of horizontal transfer of plasmids bearing blaCTX-M, from a gut E. coli to pathogenic Enterobacteriaceae and vice versa. Clinical specimens from twelve patients were screened for beta-lactamase producing Enterobacteriaceae, followed by isolating corresponding gut Enterobacteriaceae from stool samples. Standard bacteriological procedures and antibiotic sensitivity testing were performed to identify and confirm ESBL, AmpC beta-lactamase, and carbapenemase producers. PCR to confirm beta-lactamase genes, ERIC PCR to assess clonal similarity, PCR-based replicon typing for plasmid profiling, conjugation by broth mating assay for evaluating the horizontal transfer of plasmids, were performed to study the possibility of horizontal transfer of blaCTX-M gene between gut and pathogenic E. coli. In two patients, we demonstrated the potential for horizontal transfer of blaCTX-M carrying IncFIA and IncFIB plasmids between uropathogenic E. coli and gut E. coli, in vivo. This study confirms in vivo horizontal transfer of plasmids bearing blaCTX-M types IncFIA and IncFIB between gut commensal and uropathogenic E. coli, highlighting the need for stringent antibiotic stewardship to curb multidrug-resistant pathogen spread.