PHYLOGENETIC ANALYSI S OF ESCHERICHIA COLI ISOLATES FROM HEALTH Y AND DIARRHOEIC CAL VES IN MASHHAD, IRAN

Summary Barzan, M., M. Rad, G. R. Hashemi Tabar & M. Azizzadeh, 2016. Phylogenetic anal y sis of Escherichia coli isolates from healthy and diarrhoeic calves in Mashhad, Iran. Bulg. J. Vet. Med. (online first). Escherichia coli is a normal inhabitant of the gastrointestinal tract of vertebrates. Certain E s che richia coli strains have been associated with neonatal diarrhoea in ruminants. These strains can be assigned to one of the four main phylogenetic groups, A, B1, B2 and D. Several studies have shown the rel ationship between phylogeny and pathogenicity of E. coli , a great deal can be obtained by dete r mining the phylogroup of unknown E. coli strains. In this study, we aimed to evaluate the influence of dia rrhoea on the genetic composition of E. coli populations isolated from calves. A total of 80 E scherichia coli isolates were obtained from healthy and dia r rhoeic calves. Phylogenetic grouping was done based on the Clermont triplex PCR method using primers ta r geted at three genetic markers, chuA, yjaA and TspE4.C2. According to our results, p hylog e netic group A stra ins was the most prevalent in both healthy (37.5%) and diarrhoeic calves (55%). Group B1 contained 27.5% of is o lates in healthy calves, followed by group B2 (17.5%), and group D (7.5%). Also, four isolates from healthy calves were not included i n the major ph y logenetic groups or subgroups. A total of 14% and 4% of isolates from diarrhoeic calves belon ed to phylogroups B2 and D respectively. A l though no isolate from dia r rhoeic calves was found to belong to group B1, there was no significant differ ence between healthy and dia r rhoeic calves for other phylogroups. There was not a dramatic shift in E. coli ph y logroup/subgroup due to occurrence of diarrhoea in calves, except for phylogroup B1 which was higher in healthy calves. This can be due to the dif ference in secretions of digestive system in dia rrhoeic calves which can prevent the conditions for instability of Escherichia coli is o lates of ph ylogroup B1. The m a jority of isolates from both healthy and diarrhoeic calves belonged to non pathogenic phylo gentic group A and B1.