Epidemiological relatedness and clonal types of natural populations of Escherichia coli strains producing Shiga toxins in separate populations of cattle and sheep

Abstract

Two separate animal populations consisting of a herd of cattle (19 animals) and a flock of sheep (25 animals) were investigated for strains of Escherichia coli producing Shiga toxins (STEC) over a time period of 6 months. Thirty-three STEC were isolated from 63.2% of cattle and grouped into 11 serotypes and eight electrophoretic types (ETs) by multilocus enzyme analysis. In sheep, 88% of the animals excreted STEC (n ‫؍‬ 67 isolates) belonging to 17 different serotypes and 12 different ETs. STEC from cattle and sheep differed with respect to serotype, and only 4 of the 16 ETs occurred in both animal populations. In cattle, ET14 (O116:H21) strains predominated, whereas other STEC serotypes occurred only sporadically. The predominating STEC types in sheep were ET4 (O125 strains), ET11 (O128:H2 and others), and ET14 (O146:H21). In contrast to their diversity, STEC originating from the same animal population were similar with respect to Shiga toxin (stx) genes. Almost all STEC isolated from cattle were positive for stx 2 and stx 2c ; only one was positive for stx 1. In sheep, almost all STEC isolated were positive for stx 1 and stx 2 , whereas stx 2c was not found. XbaI-digested DNAs of genetically closely related O146:H21 strains have different restriction profiles which were associated with size alterations in XbaI fragments hybridizing with stx 1-and stx 2-specific DNA probes. Our results indicate that stx-encoding bacteriophages might be the origin of the genetic heterogeneity in STEC from animals.

Type III effector genes and other virulence factors of Shiga toxin‐encoding Escherichia coli isolated from wastewater

“…The occurrence of each variant in a given origin or serotype was consistent with those reported in previous studies. For example, stx2e is a variant predominantly found in pigs (Marques et al, 1987), stx2c show a high prevalence in cattle (Beutin et al, 1997), stx2d is associated with strains isolated from human (Wang et al, 2002), and variant stx2g was found in cattle, which is in accordance with previous reports that have indicated this variant as a new evolutionary event that is spreading (Prager et al, 2010).…”

“…Molecular analysis of major virulence factor genes is commonly used for the detection and evolutionary studies of pathogenic Escherichia coli. These studies are conducted to evaluate the putative risk of these strains for human infection (Beutin et al, 1997;Wang et al, 2002;Coombes et al, 2008;Ogura et al, 2009;Prager et al, 2010;Creuzburg et al, 2011). The information available mostly refers to isolates associated with human or animal infection or strains isolated from food samples involved in sporadic cases or outbreaks.…”

Concentration and prevalence of Escherichia coli O157 and Salmonella serotypes in sheep during slaughter at two Australian abattoirs

“…27 Different animal species may have specific STEC populations, which vary in the presence of various virulence markers. [36][37][38] In the study by Fegan et al, 17 the isolation rate of Salmonella spp. from cattle faeces (16%) was similar to that found in sheep faeces (20%) in the current study, whereas the isolation rate from cattle hides (68%) was much higher than that from sheep fleece (13%), which suggests that there may be differences in the contamination routes, survival and/or detection of bacteria between the hair of cattle and fleece of sheep.…”

Growth and survival of non-O157:H7 Shiga-toxin-producing Escherichia coli in cow manure

“…The STEC inoculum level was fitted to 10 6 -10 7 CFU g )1 in order to be in conditions simulating a high STEC quantity in faeces, which can reach 10 8 CFU g )1 (Fukushima and Seki 2004). Moreover, a large diversity of STEC strains isolated from faecal samples of a same dairy farm was previously reported (Beutin et al 1997;Nielsen et al 2004).Consequently and in an attempt to be closed to dairy farm conditions, a mix of eight STEC strains was used to inoculate all manure heaps. In compliance with European rules set for the utilization of STEC and genetically modified organisms, we placed the manure heaps in a lazaret of P2 safety level to ensure environmental protection.…”