Genetic characterization and comparative genomics of a multi drug resistant (MDR) Escherichia coli SCM-21 isolated from a subclinical case of bovine mastitis.

Escherichia coli is one of the major pathogens causing mastitis that adversely affects the dairy industry worldwide. This study employed whole genome sequence (WGS) approach to characterize the repertoire of antibiotic resistance genes (resistome), virulence genes (virulome), phylogenetic relationship and genome wide comparison of a multi drug resistant (MDR) E. coli(SCM-21) isolated from a case of subclinical bovine mastitis in Bangalore, India. The genome of E. coli SCM- 21 was found to be of 4.29 Mb size with 50.6% GC content, comprising a resistome of 22 genes encoding beta-lactamases (blabla), polymyxin resistance (arnA) and various efflux pumps (acr, ade, emr,rob, mac, mar, rob), attributing to the bacteria's overall antibiotic resistance genetic profile. The virulome of E. coli SCM-21 consisted of genes encoding different traits [adhesion (ecp, fim, fde), biofilm formation (csg) and toxin production (ent, esp, fep, gsp)], necessary for manifestation of the infection. Phylogenetic relationship of E. coli SCM- 21 with other global E. coli strains (n = 4867) revealed its close genetic relatedness with E. coli strains originating from different hosts of varied geographical regions [human (Germany) bos taurus (USA, Belgium and Scotland) and chicken (China)]. Further, genome wide comparative analysis with E. coli (n = 6) from human and other animal origins showed synteny across the genomes. Overall findings of this study provided a comprehensive insight of the hidden genetic determinants/power of E. coli SCM-21 that might be responsible for manifestation of mastitis and failure of antibiotic treatment. Aforesaid strain forms a reservoir of antibiotic resistance genes (ARGs) and can integrate to one health micro biosphere.