A survey was performed to estimate the frequency of enterohemorrhagic Escherichia coli O157:H7 or O157:nonmotile (EHEC O157) in feces and on hides within groups of fed cattle from single sources (lots) presented for slaughter at meat processing plants in the Midwestern United States, as well as frequency of carcass contamination during processing from cattle within the same lots. Of 29 lots sampled, 72% had at least one EHEC O157-positive fecal sample and 38% had positive hide samples. Overall, EHEC O157 prevalence in feces and on hides was 28% (91 of 327) and 11% (38 of 355), respectively. Carcass samples were taken at three points during processing: preevisceration, postevisceration before antimicrobial intervention, and postprocessing after carcasses entered the cooler. Of 30 lots sampled, 87% had at least one EHEC O157-positive preevisceration sample, 57% of lots were positive postevisceration, and 17% had positive postprocessing samples. 43% (148 of 341), 18% (59 of 332) and 2% (6 of 330), respectively. Reduction in carcass prevalence from preevisceration to postprocessing suggests that sanitary procedures were effective within the processing plants. Fecal and hide prevalence were significantly correlated with carcass contamination (P ‫؍‬ 0.001), indicating a role for control of EHEC O157 in live cattle. Prevalence of EHEC O157 in the three postprocessing samples wasAbbreviation: EHEC, enterohemorrhagic Escherichia coli.

Single-base-pair csgD promoter mutations in human outbreak Escherichia coli O157:H7 strains ATCC 43894 and ATCC 43895 coincided with differential Congo red dye binding from curli fiber expression. Red phenotype csgD::lacZ promoter fusions had fourfold-greater expression than white promoter fusions. Cloning the red variant csgDEFG operon into white variants induced the red phenotype. Substrate utilization differed between red and white variants.Many Escherichia coli organisms and salmonellae express coiled surface appendages, known as curli fibers and thin, aggregegative fimbriae, respectively, that are typically produced under stressful environmental conditions, such as low temperature, low osmolarity, and stationary growth (3, 9, 10). Curli fibers bind fibronectin, laminin, certain serum proteins, and Congo red dye (4,8,9,18). Two divergently transcribed operons are required for curli expression: csgBA encodes the curli subunit protein (CsgA) and a nucleator protein (CsgB); csgDEFG encodes a transcriptional regulator (CsgD), an outer membrane lipoprotein (CsgG), and two putative curli assembly factors (CsgE and CsgF). Transcription from the csgBA promoter requires csgD expression; both operons require stationary-phase sigma factor ( s ) for expression (1, 4, 10). Expression of thin, aggregative fimbriae in Salmonella enterica serovar Typhimurium is regulated by a similar agf operon (13).Curli expression has not been reported for enterohemorrhagic E. coli (EHEC) O157:H7, the most common Shigatoxigenic serotype associated with human disease (11). In order to identify potential factors involved in this pathogen's survival and persistence outside of the mammalian host, we screened 49 diverse bovine and human E. coli O157:H7 isolates for curli expression on Congo red indicator (CRI) plates after 48 h at 28°C (5). The 41 bovine isolates were from infected beef calves in five states (6). The eight human-associated isolates were American Type Culture Collection (ATCC, Rockville, Md.) strains ATCC 35150, ATCC 43888, ATCC 43889, ATCC 43890, ATCC 43894, and ATCC 43895 and Washington state strains Tarr4A and Tarr1A (2, 19). All of the bovine and six of the human isolates displayed smooth, moist, white colonies typical of the curli-deficient E. coli strain HB101 on CRI plates (9). However, strains ATCC 43894 and ATCC 43895 displayed mixed red and white colonies. Red colonies were dry, rough, and curliated as verified by electron microscopy (results not shown). Red and white colonies retained their parental phenotypes when subcultured on CRI plates with or without 1% NaCl and at either 28 or 37°C, suggesting that curli expression was neither low-temperature nor low-osmolarity dependent. Red variants passaged daily (1:100) in Luria-Bertani broth (Difco Laboratories, Detroit, Mich.) at 37°C generated mixed red and white phenotypes in as few as 3 passages, with white variants persisting at 40 to 60% of total colonies over 10 passages. White variants were stable under all growth conditions tested except for one, strain ATCC 4389...

This study was designed to determine the prevalence of Escherichia coli O157:H7 infection of beef calves at weaning, prior to arrival at the feedlot or mixing with cattle from other sources. Fifteen range cow-calf herds, which weaned calves in October and November, were sampled in Kansas, Missouri, Montana, Nebraska and South Dakota. Faecal culture for E. coli O157:H7 was performed and anti-O157 serum antibody titres were determined by blocking ELISA. Thirteen of the 15 herds (87%) were found to have at least one positive isolation of E. coli O157:H7 in faecal samples. Within positive herds, prevalence ranged from 1.7-20.0%, with an average of 7.4+/-6.2% S.D. of individual animals shedding E. coli O157:H7 in faeces. All herds had high prevalence of anti-O157 antibodies, ranging 63-100% of individuals within herds seropositive. This study indicates that E. coli O157:H7 infection before weaning, prior to entry into feedlots, is widespread. Furthermore, serologic evidence suggests that most calves (83%) and all herds (100%) have been exposed to E. coli O157.