Virulence factors and phylotyping of Escherichia coli isolated from non-diarrheic and diarrheic water buffalo calves

ABSTRACT: This study aimed to determine the virulence factors, phylogenetic groups, and the relationships between pathovars and phylogenetic groups of E. coli strains isolated from feces of buffalo calves. A total of 217 E. coli strains were obtained from feces after culture and were screened by PCR for detection of virulence factors EAST-1, enterohemolysin, Saa, CNF2, F41, F5, STa, intimin, Stx1 and Stx2. One hundred and thirty-four isolates were positive for one or more virulence factors: eighty-four from diarrheic animals, and fifty from non-diarrheic calves. The pathovars of E. coli identified in diarrheic feces were ETEC (F5+) (2/84), NTEC (16/84), STEC (20/84), EPEC (3/84), EHEC (3/84), and EAEC (EAST-1+) (33/84). Pathovars identified in non-diarrheic animals were NTEC (21/50), STEC (17/50), EHEC (1/50) and EAEC (7/50). E. coli strains positive for EAST-1 (P=0.008) and phylogroup C (P = 0.05) were associated with the presence of diarrhea. Phylogenetic analysis showed that 58.95% of the isolates belonged to phylogroup B1, followed by E (9.70%), B2 (5.90%), C (5.90%), D (5.22%), A (2.24%), and F (1.50%). Phylogroup B1 predominated in pathogenic E. coli isolated from water buffalo, and phylogroup C constituted an enteropathogenic E. coli for water buffalo calves.摘要：本研究旨在明确从水牛犊牛粪便中分离的大肠埃希氏菌（E. coli）菌株的毒力因子、系统发育群，以及致病型与系统发育群之间的关联。本研究通过培养法从粪便样本中共分离得到217株大肠埃希氏菌，采用聚合酶链式反应（PCR）对其携带的EAST-1、肠溶血素、Saa、CNF2、F41、F5、STa、紧密素、Stx1及Stx2等毒力因子进行检测筛选。其中134株菌株携带至少一种毒力因子，包括84株分离自腹泻犊牛，50株分离自非腹泻犊牛。从腹泻粪便中鉴定出的大肠埃希氏菌致病型包括：产肠毒素大肠埃希氏菌（ETEC，F5+）2株（2/84）、非典型大肠埃希氏菌（NTEC）16株（16/84）、产志贺毒素大肠埃希氏菌（STEC）20株（20/84）、肠致病性大肠埃希氏菌（EPEC）3株（3/84）、肠出血性大肠埃希氏菌（EHEC）3株（3/84）以及肠集聚性大肠埃希氏菌（EAST-1+）33株（3/84）。从非腹泻动物粪便中鉴定出的致病型包括NTEC 21株（21/50）、STEC 17株（17/50）、EHEC 1株（1/50）及EAEC 7株（7/50）。携带EAST-1（P=0.008）及系统发育群C（P=0.05）的大肠埃希氏菌菌株与腹泻症状存在显著关联。系统发育分析显示，58.95%的分离株属于系统发育群B1，其次依次为E群（9.70%）、B2群（5.90%）、C群（5.90%）、D群（5.22%）、A群（2.24%）及F群（1.50%）。系统发育群B1在水牛源致病性大肠埃希氏菌中占优势，而系统发育群C为水牛犊牛的肠致病性大肠埃希氏菌类群。