Occurrence and Characterization of Verocytotoxigenic Escherichia coli (VTEC) Strains from Dairy Farms in Trinidad

Abstract

A cross-sectional study was conducted to determine the prevalence and characteristics of verocytotoxigenic Escherichia coli (VTEC) on 25 dairy farms each located in Waller field and Carlsen field farming areas in Trinidad. On each selected farm, faecal samples were collected from milking cows, calves and humans; rectal swabs were obtained from pet farm dogs; bulk milk was sampled as well as effluent from the milking parlour. Escherichia coli was isolated from all sources on selective media using standard methods. Isolates of E. coli were subjected to slide agglutination test using E. coli O157 antiserum, vero cell cytotoxicity assay to detect verocytotoxin (VT) and heat labile toxin (LT) production, the polymerase chain reaction (PCR) to detect VT genes, and the dry spot test to screen for E. coli O157 and non-O157 strains. In addition, faecal samples from animal and human sources were tested for VT genes using PCR. Of a total of 933 E. coli isolates tested by the slide test, eight (0.9%) were positive for the O157 strain. The vero cell cytotoxicity assay detected VT-producing strains of E. coli in 16.6%, 14.6%, 3.2% and 7.1% of isolates from cows, calves, farm dogs and humans respectively (P < 0.05; chi(2)). For LT production, the highest frequency was detected amongst isolates of E. coli from calves (10.8%) and the lowest (0.0%) amongst isolates from humans and bulk milk (P < 0.05; chi(2)). Of the 61 VT-producing isolates by vero cell cytotoxicity assay tested by PCR, the VT, LT and eae genes were detected in 62.3%, 4.9% and 1.6% respectively (P < 0.05; chi(2)). Amongst the 45 E. coli isolates that were VT positive (vero cell) or VT-gene positive by PCR, 2.2%, 2.2%, 4.4% and 6.7% belonged to non-O157 strains O91, O111, O103 and O157, respectively, as determined by the Dry spot test. Detection of VTEC strains in milk and dairy animals poses a health risk to consumers of milk originating from these farms. In addition, the demonstration of VTEC strains in humans, VT gene in faecal samples and E. coli isolates as well as non-O157 VTEC strains of E. coli are being documented for the first time in the country.

Detection of Verocytotoxigenic &lt;i&gt;Escherichia coli&lt;/i&gt; O157 Serotype in Dairy Products in Abuja, Nigeria

“…VTEC were detected in 2% raw cow's milk [20], of the 30 E. coli isolates screened for VTEC, 7 (23.33%) VTEC organisms were isolated [5]. In another study from dairy farms in Trinidad, 8 (0.9%) VTEC O157 out of the 933 E. coli isolates tested were isolated [21]. In this study Nunu yielded a prevalence of 2 (1.57%) for O157 VTEC out of the 127 E. coli isolates tested and none for the 132 samples from yoghurt.…”

A review on major bacterial causes of calf diarrhea and its diagnostic method

“…Many studies also showed that both healthy and diarrheic calves harbor STEC in their intestine (Roopnarine et al, 2007) and shed the bacteria for several months and in great quantities (Widirasih et al, 2004). In addition to economic losses, diarrhea in livestock is important because of the public health implications.…”

Animal Reservoirs of Shiga Toxin-ProducingEscherichia coli

“…These dogs move freely among animals and humans, thus potentiating the spread of enterohemorrhagic E. coli (167). Dogs have also been reported to shed non-O157 STEC serotypes in their feces (163). Human infections due to canine exposure were also reported; one outbreak in Sweden resulted in 50 cases in humans after they attended a dog show (168).…”

“…Pets, especially dogs and cats, are capable of shedding a diverse range of STEC serotypes in their feces (163)(164)(165)(166). Interestingly, although both O157 and non-O157 STEC have been recovered from dogs, there are no published reports indicating that O157 STEC has ever been recovered from cat feces.…”