RESUMEN
Fecal samples were collected from pens of cattle in a total of 100 feedlots in 13 states. Fecal samples were cultured for Escherichia coli O157. E. coli O157 isolates were probed for the genetic coding for verotoxin production. At the time of sample collection, data were collected on the type of cattle present in the pen, as well as the length of time these cattle were in the feedlot, ingredients for the current ration, and cattle health history since arriving in the feedlot. Factors associated with increased likelihood of a pen being positive (one or more samples probe-positive for E. coli O157) included feeding of barley (odds ratio [OR] = 2.75) and cattle being on feed less than 20 days (OR = 3.39). Factors associated with a reduced likelihood of a pen being positive included feeding soy meal (OR = 0.50), a cattle entry weight of at least 700 lb (ca. 317.5 kg) (OR = 0.54), and at least 85% of the cattle in the pen being beef-type heifers (OR = .33).
RESUMEN
Fecal samples from cattle in 100 feedlots in 13 states were bacteriologically cultured for Escherichia coli O157 that did not ferment sorbitol, lacked beta-glucuronidase, and possessed genes coding for Shiga-like toxin. In each feedlot 30 fresh fecal-pat samples were collected from each of four pens: with the cattle shortest on feed, with cattle longest on feed, and with cattle in two randomly selected pens. E. coli O157 was isolated from 210 (1.8%) of 11,881 fecal samples. One or more samples were positive for E. coli O157 in 63 of the 100 feedlots tested. E. coli O157 was found at roughly equal prevalence in all the geographical regions sampled. The prevalence of E. coli O157 in the pens with cattle shortest on feed was approximately threefold higher than for randomly selected and longest on feed pens. Of the E. coli O157 isolates found in this study, 89.52% expressed the H7 flagellar antigen. E. coli O157 was found to be widely distributed among feedlot cattle, but at a low prevalence, in the United States.
RESUMEN
In a 1995 national survey of 937 unpasteurized liquid egg samples collected in breaker plants, 179 of 937 samples (19%) were Salmonella enterica serotype Enteritidis ( S. Enteritidis ) positive. The proportion of unpasteurized liquid egg samples positive for S. Enteritidis was highest in the Northern Region where 106 of 267 samples collected (40%) were S. Enteritidis -positive. These Northern Region results were over three times the S. Enteritidis prevalence detected from the other three regions, whose results ranged between 10% and 12% S. Enteritidis -positive samples. In a 1995 national survey of spent hens at slaughter, 136 of 305 flocks (45%) had at least one S. Enteritidis -positive pooled sample detected. Flock prevalence was highest in the Northern and Central Regions (64% and 40%, respectively); Southeastern and Western Regional flock prevalence levels were much lower (17% and 23%, respectively). A comparison of the 1991 and 1995 unpasteurized liquid egg and spent hen results suggest there has been no decline in S. Enteritidis occurrence in the commercial egg industry between 1991 and 1995. Salmonella Enteritidis phage type 4 was detected in the 1995 surveys of both spent hens and unpasteurized liquid egg but was not found in either survey in 1991. With the exception of one liquid egg sample from the Southeastern Region, S. Enteritidis phage type 4 was found only in the Western Region of the U.S. S. Enteritidis phage type 4 has emerged in the egg industry in the Western U.S. concurrently with an increase in the number of sporadic human phage type 4 isolates in California and Utah.