Transferable blaCTX-M Carrying Multidrug Resistant Escherichia coli from Pig Population of North Eastern Region of India

Abstract

Background: We investigated the occurrence of blaCTX-M carrying extended spectrum beta lactamase (ESBL) producing Escherichia coli in pigs from 8 North-eastern states of India with special emphasis on the transferability of ESBL gene from resistant E. coli strains to the susceptible Salmonella strains by in vitro and in vivo.Methods: Fecal samples (n=790) were collected from pigs reared under organized and unorganized farming set up of entire North-eastern region of India. All the samples were processed for isolation and identification of E. coli. All the isolates were subjected to antimicrobial sensitivity assay by disc diffusion method followed by determination of ESBLs producing ability by double disc synergy test (DDST). All the ESBLs producing isolates were screened for blaCTX-M gene by PCR using specific primers. The representative blaCTX-M gene positive isolates were used as donor to determine the ability to transfer of resistance gene in Salmonella by in vitro and in vivo assays with and without antibiotic selection pressure. Result: A total of 2,291 E. coli was isolated, of which 1113 and 1178 were from organized and unorganized farms, respectively. Majority of the isolates were multi-drug resistant with highest resistance against amoxicillin (84.81%) followed by cefalexin (77.17%), sulphafurazole (56.79%), piperacillin (46.40%), tetracycline (38.29%) and cefexime (35.66%). Isolates from unorganized farms showed higher resistance than the isolates recovered from organized farms. A total of 654 (28.55%) isolates were confirmed as ESBL producers by double disc synergy test (DDST) method, of which 65 (2.84%) isolates were positive for blaCTX-M gene. Genotypically, isolates with specific amino acids substitution revealed variation in their antibiotic susceptibility by phenotypic method. blaCTX-M gene could be successfully transferred horizontally from E. coli (donor) to Salmonella (recipient) by in vitro (3.6±2.07x10-8 to 4.4±2.88x10-8 transconjugate per donor) and in vivo method. By in vivo method in pig model, the frequency of transfer was higher under the antibiotic selection pressure (6.6±3.05x10-5 to 7.2±1.92x10-5 trans-conjugants per donor) than without antibiotic pressure (5.6±2.3x10-4 to 6.8±3.35x10-4 trans-conjugants per donor).