Isolation And Characterization Of Shiga Toxin-producing Escherichia Coli Isolated From Animals In China

Shiga toxin-producing Escherichia coli (STEC) are recognized globally as major food-borne pathogens, which can cause watery diarrhea, hemorrhagic colitis (HC) and fatal hemolytic uremic syndrome (HUS) complications. Ruminants, especially cattle, are the major reservoirs of STEC. More than470serotypes of STEC have been reported to cause human diseases, with Ol17:H7being most important.The method for detection and isolation of O157:H7STEC has been well eatablised, while there is no effective isolation method targeting all non-O157serotypes. In this study we established a method for detection and isolation of STEC of different serotypes based on the relevant studies reported and investigated the prevalence of non-O157STEC in different hosts including yaks, pigs, beef cattle, marmots, diarrhea patients in China. We found11.68%,6.18%,4.00%,2.47%,0.34%of the above samples were positive for non-O157STEC by culture respectively, indicating that animals and human carried non-O157STEC exist in China.We intensively determined the occurrence and characteristics of the STEC in yaks that live in special geographical environment in Qinghai-Tibetan plateau, China. A total of728yak fecal samples was collected from June to August,2012.138samples (18.96%) were detected stxand/or stx2positive and85(11.68%) samples were confirmed to have at least1STEC isolate, from which128STEC isolates were recovered. All STEC isolates were serotyped, characterized for virulent genes and genotyped by pulsed-field gel electrophoresis (PFGE). Fifteen different O serogroups and36different O:H serotypes were identified in the128STEC isolates with O8:H16, O2:H45, O117:H21, O78:H8, O8:H9, Ont:H8being predominant.53isolates were stx1positive, which all belonged to stx1a subtype,95stX2positive isolates were genotyped into5stx2subtypes (stx2a, stx2b, stx2c, stx2d and stx2g). Apart from lpfAO157/OI-141,lpfAO157/OU-154, lpfAI113, katP and toxB which were all absent, other virulence factors screened (eaeA, iha, efal, saa,paa, cnfl, cnf2, astA, sub A, exhA and espP) were variably present in the128STEC isolates. PFGE were successful for all except5isolates and separated them into67different PFGE patterns, demonstrating quite high genetic diversity of the STEC in the yaks. This study was the first report on occurrence and characteristics of STEC isolated from yaks (Bos grunniens) in China suggesting that yaks are also important reservoirs of STEC, which could be sources of STEC transmission and pose a threat to public health.To understand the pathogenicity and evolutionary relationship of the STEC isolates isolated from different resources in China, multi-locus sequencing typing (MLST) anaysis of111STEC isolates from different resources was conducted, which showed high genetic diversity of these STEC isolates and relatively closer genetic relationship of the isoaltes from the same resource. Notably, there exisit STEC isolates from different hosts that belong to the same ST or showed close ralationships with HUSEC collection and STEC of026, O103,0111,0121, O145and0157serogroups, suggesting the STEC isolates from different animals may have the potential to cause human diseases, thus empasising the need to detecte and monitor STEC in animals and food in China and the significance to find the effective molecular markers to distinguish STEC, which will contribute to prevent the outbreaks of potential emerging pathogens and impoved the ability to deal with the outbreaks timely.