Molecular Characterization of Escherichia coli O157 Contamination Routes in a Cattle Slaughterhouse

Abstract

In a cattle slaughterhouse, sampling was performed over a 1-week period to examine the prevalence and possible contamination routes of Escherichia coli O157. Each sampling day, swab samples were collected from the slaughterhouse environment before onset of slaughter, from the slaughterline, and from 20 successively slaughtered animals. Isolation of E. coli O157 consisted of a 6-hour enrichment followed by immunomagnetic separation and selective plating. From the 394 samples taken, 84 (21%) were positive for E. coli O157. Pulsed-field gel electrophoresis (PFGE) of collected isolates produced 26 different profiles, from which 5 PFGE profiles carried two or more Stx genes. The combination of PFGE profiles and Stx types resulted in 32 different E. coli O157 types. E. coli O157 was found in the slaughterhouse environment before the onset of slaughter. The first two sampling days, feces and carcasses were found negative. On the third sampling day, five fecal samples and four carcasses from animals negative in the feces were positive. Hide of the anal region and the shoulder were found positive every sampling day. The shoulder hide was more than twice as contaminated as the anal region hide. Typing of different isolates from a sample showed that frequently different E. coli O157 types were presented. On sampling days 1 and 2, types present in the environment and on the hides of the slaughtered animals differed. On the third sampling day, two dominant types were found in the environment (even before the onset of slaughter), as well as on the hides, feces, and carcasses. Although examined animals originated from different farms, one (two on day 3) dominant E. coli O157 type was present on their hides each sampling day. These data indicated that (i) the progress of contamination can differ from day to day within a slaughterhouse and (ii) contact between animals after the departure from the farm can have a large effect on the spread of E. coli O157 hide contamination.

Transportation and Lairage Environment Effects on Prevalence, Numbers, and Diversity of Escherichia coli O157:H7 on Hides and Carcasses of Beef Cattle at Processing

“…Similarly, Small et al (26) recovered E. coli O157:H7, Salmonella, and Campylobacter in cattle lairages; E. coli O157:H7 was present in 27.2% of the lairage samples. E. coli O157:H7 can persist in lairage environments for several days and through cleaning periods (27). Few previous studies have addressed the issue of transport trucks as a source of E. coli O157: H7.…”

“…McGee et al (19) found that within 24 h of introducing animals known to be shedding E. coli O157:H7 the hides of cohort animals became contaminated, and at 48 h 66% of the penmates had E. coli O157:H7 on their hides. In another study performed using molecular tracking methods, direct hide-to-hide contamination was a viable route for the transmission of E. coli O157:H7 during transport and lairage (27).…”

Modeling and Predicting the Simultaneous Growth of Escherichia coli O157:H7 and Ground Beef Background Microflora for Various Enrichment Protocols

“…Nevertheless, some authors have reported an optimal growth temperature for E. coli O157:H7 of around 40°C (31,44), and in recent studies workers have also used this temperature for incubation of enrichment cultures (1,2,32). However, there have been few studies in which the workers tried to compare the efficacies of different enrichment protocols, and the few results obtained have been different in different studies (21,39,42,58).…”

“…These methods require an enrichment step to improve their limits of detection (8,25,39,58). Cui et al (20) reported that the PCR detection limit decreases from 3 log 10 CFU g Ϫ1 with no prior enrichment to 0 log 10 CFU g Ϫ1 with a 6-h enrichment step at 37°C.…”

“…The main enrichment protocol factors are the enrichment broth (basal medium), the addition of antibiotics, the temperature, and the length of the enrichment period. In previous studies, Trypticase soy broth (TSB) and E. coli broth (EC) have frequently been used as basal media, often with one antibiotic added (novobiocin in most studies) (1,20,22,24,41,58). For incubation, the enrichment broth is most often incubated at 37°C for 16 to 24 h (1,22).…”