An Escherichia coli strain, PGB01, isolated from feral pigeon Faeces, thermally fit to survive in pigeon, shows high level resistance to trimethoprim.

Arvind Kumar,Sangita Kachhap,Ashis Kumar Nanda,Bipransh Kumar Tiwary,Ranadhir Chakraborty,Yolanda Sanz

doi:10.1371/journal.pone.0119329

Arvind Kumar, Sangita Kachhap + Show 4 more

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https://doi.org/10.1371/journal.pone.0119329

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Abstract

In this study, of the hundred Escherichia coli strains isolated from feral Pigeon faeces, eighty five strains were resistant to one or more antibiotics and fifteen sensitive to all the antibiotics tested. The only strain (among all antibiotic-resistant E. coli isolates) that possessed class 1 integron was PGB01. The dihydrofolate reductase gene of the said integron was cloned, sequenced and expressed in E. coli JM109. Since PGB01 was native to pigeon’s gut, we have compared the growth of PGB01 at two different temperatures, 42°C (normal body temperature of pigeon) and 37°C (optimal growth temperature of E. coli; also the human body temperature), with E. coli K12. It was found that PGB01 grew better than the laboratory strain E. coli K12 at 37°C as well as at 42°C. In the thermal fitness assay, it was observed that the cells of PGB01 were better adapted to 42°C, resembling the average body temperature of pigeon. The strain PGB01 also sustained more microwave mediated thermal stress than E. coli K12 cells. The NMR spectra of the whole cells of PGB01 varied from E. coli K12 in several spectral peaks relating some metabolic adaptation to thermotolerance. On elevating the growth temperature from 37°C to 42°C, susceptibility to kanamycin (both strains were sensitive to it) of E. coli K12 was increased, but in case of PGB01 no change in susceptibility took place. We have also attempted to reveal the basis of trimethoprim resistance phenotype conferred by the dfrA7 gene homologue of PGB01. Molecular Dynamics (MD) simulation study of docked complexes, PGB01-DfrA7 and E. coli TMP-sensitive-Dfr with trimethoprim (TMP) showed loss of some of the hydrogen and hydrophobic interaction between TMP and mutated residues in PGB01-DfrA7-TMP complex compared to TMP-sensitive-Dfr-TMP complex. This loss of interaction entails decrease in affinity of TMP for PGB01-DfrA7 compared to TMP-sensitive-Dfr.

Highlights

IntroductionThe gastro-intestinal tract of pigeon contains diverse bacteria including Escherichia coli [1]
Feral pigeons (Columba livia) inhabit both urban and rural areas of India
In the thermal fitness assay, it was observed that the cells of PGB01 which were better adapted to 42°C could grow at 37°C while the growth of E. coli K12 (ECK12) cells, better adapted to temperature of human body (37°C), was found to be inhibited at 42°C

Summary

Introduction

The gastro-intestinal tract of pigeon contains diverse bacteria including Escherichia coli [1]. Several strains of E. coli isolated from pigeons’ gut are known to possess antibiotic resistance genes. Pigeons are considered potential reservoir for infectious E. coli strains including Shiga-toxin producing (STEC) or entero-pathogenic (EPEC) ones and several other pathogenic bacteria, Chlamydia spp., Salmonella spp., and Cryptococcus spp. As multiple antibiotic resistant (MAR) E. coli strains with pathogenicity-determinants have greater survivability in antibiotic-stressed environment of human habitation, the relevance of such studies has gained prominence in epidemiological research. Among all the mechanisms of transmission of antibiotic resistance genes in the environment, integrons, in past years, have been noted as an important genetic element. Integrons capture diverse resistance genes and contribute to the development of multiple antibiotic resistances [5]. Pigeons are known to harbor MAR bacteria having class 1 integrons [6]

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