Approaches to characterize extended spectrum beta-lactamase/beta-lactamase producing Escherichia coli in healthy organized vis-a-vis backyard farmed pigs in India.

The study was undertaken to investigate the occurrence and to characterize the ESBL/beta-lactamase producing-Escherichia coli in healthy pigs of organized and backyard farms in West Bengal, India. Total 200 rectal swabs were collected randomly from healthy pigs maintained in four organized farms and 10 backyard farms (n=100 each) and 76 isolates were identified as E. coli from organized (48/100, 48%) and backyard pigs (28/100, 28%). Twelve E. coli isolates (6%) in the present study were detected to possess any of the ESBL/beta-lactamase genes studied. ESBL/beta-lactamase producers were isolated with significantly more frequency from backyard pigs than the organized farm pigs (p=0.026). Six of ESBL/beta-lactamase producing isolates were phenotypically confirmed as CTX-M producers and ten of them were confirmed as TEM/SHV producers. PCR and sequencing of the amplified product from representative isolates revealed the presence of blaCTX-M-9, blaSHV-12 and blaTEM-1. No unique combination of the studied beta lactamase genes for organized and backyard farm pig isolates was noted. The ESBL isolates belonged to O13, O55, O133, O153, O157, O158, O166, rough and OUT serogroups. The association of heat labile toxin (elt) (p<0.0005) with organized farm isolates and heat stable toxin (estA) (p=0.0143) with backyard piggery sector was significantly higher. The ESBL/beta-lactamase producers from organized farm (Ak/Ex) and indigenous pigs (Ak/Ex/Te; Ak/CoT/G) showed a characteristic phenotypical antibiotic resistance pattern. Two pairs of isolates from organized and backyard farm pigs showed clonal relationship indicating a possible transmission between the farms which were situated adjacently. Thus the present study revealed backyard farm pigs as major source of ESBL/beta-lactamase producing-E. coli associated with STa and characteristic antibiotic resistance pattern in India.