Nancy A. Cornick

Intimin facilitates colonization by Escherichia coli O157:H7 in adult ruminants.

ABSTRACT We compared the magnitude and duration of fecal shedding of wild-type Escherichia coli O157:H7 to that of an isogenic intimin mutant in young adult cattle and sheep. In both ruminant species, wild-type E. coli O157:H7 was shed in greater numbers and for a longer duration than was the intimin mutant.

Long Polar Fimbriae Contribute to Colonization by Escherichia coli O157:H7 In Vivo

ABSTRACT The contribution of long polar fimbriae to intestinal colonization by Escherichia coli O157:H7 was evaluated in sheep, conventional pigs, and gnotobiotic piglets. E. coli O157:H7 strains with lpfA1 and lpfA2 mutated were recovered in significantly lower numbers and caused fewer attachment and effacement lesions than the parent strain.

Persistent colonization of sheep by Escherichia coli O157: H7 and other E. coli pathotypes.

ABSTRACT Shiga toxin-producing Escherichia coli (STEC) is an important cause of food-borne illness in humans. Ruminants appear to be more frequently colonized by STEC than are other animals, but the reason(s) for this is unknown. We compared the frequency, magnitude, duration, and transmissibility of colonization of sheep by E. coli O157:H7 to that by other pathotypes of E. coli. Young adult sheep were simultaneously inoculated with a cocktail consisting of two strains of E. coli O157:H7, two strains of enterotoxigenic E. coli (ETEC), and one strain of enteropathogenic E. coli. Both STEC strains and ETEC 2041 were given at either 107 or 1010CFU/strain/animal. The other strains were given only at 1010 CFU/strain. We found no consistent differences among pathotypes in the frequency, magnitude, and transmissibility of colonization. However, the STEC strains tended to persist to 2 weeks and 2 months postinoculation more frequently than did the other pathotypes. The tendency for persistence of the STEC strains was apparent following an inoculation dose of either 107 or 1010 CFU. One of the ETEC strains also persisted when inoculated at 1010 CFU. However, in contrast to the STEC strains, it did not persist when inoculated at 107 CFU. These results support the hypothesis that STEC is better adapted to persist in the alimentary tracts of sheep than are other pathotypes ofE. coli.

Genome-Wide Transposon Mutagenesis Reveals a Role for pO157 Genes in Biofilm Development in Escherichia coli O157:H7 EDL933

ABSTRACT Enterohemorrhagic Escherichia coli O157:H7, a world-wide human food-borne pathogen, causes mild to severe diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome. The ability of this pathogen to persist in the environment contributes to its dissemination to a wide range of foods and food processing surfaces. Biofilms are thought to be involved in persistence, but the process of biofilm formation is complex and poorly understood in E. coli O157:H7. To better understand the genetics of this process, a mini-Tn5 transposon insertion library was constructed in strain EDL933 and screened for biofilm-negative mutants using a microtiter plate assay. Ninety-five of 11,000 independent insertions (0.86%) were biofilm negative, and transposon insertions were located in 51 distinct genes/intergenic regions that must be involved either directly or indirectly in biofilm formation. All of the 51 biofilm-negative mutants showed reduced biofilm formation on both hydrophilic and hydrophobic surfaces. Thirty-six genes were unique to this study, including genes on the virulence plasmid pO157. The type V secreted autotransporter serine protease EspP and the enterohemolysin translocator EhxD were found to be directly involved in biofilm formation. In addition, EhxD and EspP were also important for adherence to T84 intestinal epithelial cells, suggesting a role for these genes in tissue interactions in vivo.

In Vivo Transduction of an Stx-Encoding Phage in Ruminants

ABSTRACT We assessed the ability of a kanamycin-marked Stx phage to move into a commensal, ovine Escherichia coli strain in the ruminant gastrointestinal tract. Transduction was detected in 19/24 sheep tested, resulting in the recovery of 47 transductants. Subtherapeutic doses of the quinolone antibiotic enrofloxacin did not increase the rate of transduction.

Escherichia coli O157:H7 Infections: Discordance between Filterable Fecal Shiga Toxin and Disease Outcome

Shiga toxin (Stx)-producing Escherichia coli O157:H7 are the most common cause of hemolytic uremic syndrome (HUS). We detected free fecal Stx in 48%, 40%, and 17% of infected children with uncomplicated diarrhea, children who subsequently developed HUS, and children with HUS, respectively. Vero cell assay detected Stx more frequently than did a commercial Stx enzyme immunoassay. In childrens stool samples obtained on or before day 4 of illness, each 10-fold decrease in titer was, paradoxically, associated with 3.8-fold increased odds of developing HUS (P=.03; 95% confidence interval, 0.77-19.7). The fecal Stx type did not correlate with the Stx expressed by bacteria grown in vitro and was not related to bacterial titer in the studied samples. These data suggest that therapeutic and diagnostic strategies directed toward binding or identifying intraintestinal fecal Stx may have limited success.

Transmission and Infectious Dose of Escherichia coli O157:H7 in Swine

ABSTRACT Escherichia coli O157:H7 is only occasionally isolated from healthy swine, but some experimentally infected animals will shed the organism in their feces for at least 2 months. Potential explanations for the paucity of naturally occurring infections in swine, as compared to cattle, include a lack of animal-to-animal transmission so that the organism cannot be maintained within a herd, a high infectious dose, or herd management practices that prevent the maintenance of the organism in the gastrointestinal tract. We hypothesized that donor pigs infected with E. coli O157:H7 would transmit the organism to naïve pigs. We also determined the infectious dose and whether housing pigs individually on grated floors would decrease the magnitude or duration of fecal shedding. Infected donor pigs shedding <104 CFU of E. coli O157:H7 per g transmitted the organism to 6 of 12 naïve pigs exposed to them. The infectious dose of E. coli O157:H7 for 3-month-old pigs was approximately 6 × 103 CFU. There was no difference in the magnitude and duration of fecal shedding by pigs housed individually on grates compared to those housed two per pen on cement floors. These results suggest that swine do not have an innate resistance to colonization by E. coli O157:H7 and that they could serve as a reservoir host under suitable conditions.

Prevalences of Some Virulence Genes among Escherichia Coli Isolates from Swine Presented to a Diagnostic Laboratory in Iowa

1. Anver MR, Park JS, Rush HG: 1976, Dermatophilus in the marble lizard (Calotes mystaceus). Lab Anim Sci 26:817–823. 2. Biberstein EL: 1990, The skin as a microbial habitat: bacterial skin infections. In: Review of veterinary microbiology, ed. Biberstein EL, Zee YC, pp. 268–270. Blackwell, Cambridge, MA. 3. Chineme CN, Addo PB: 1980, Pathologic changes in lizards (Agama agama) experimentally infected with Dermatophilus congolensis. J Wild Dis 16:407–412. 4. Gordon MA: 1964, The genus Dermatophilus. J Bacteriol 88: 509–522. 5. Jacobson ER: 1989, Dermatophilosis in reptiles. Int Colloq Pathol Reptiles Amphib 3:47. [Abstr.] 6. Jacobson ER: 1991, Diseases of the integumentary system of reptiles. In: Dermatology for the small animal practitioner, exotics, feline, canine, ed. Nesbitt GH, Ackerman LJ, pp. 225– 239. Veterinary Learning Systems, Trenton, NJ. 7. Jones RT: 1976, Subcutaneous infection with Dermatophilus congolensis in a cat. J Comp Pathol 86:415–421. 8. LaScola B, Raoult D: 1998. Molecular identification of Gemella species from three patients with endocarditis. J Clin Microbiol 36:866–871. 9. Lloyd DH: 1984, Immunology of Dermatophilus: recent developments and prospects for control. Prev Vet Med 2:93–102. 10. Masters AM, Ellis TM, Carson JM, et al.: 1995, Dermatophilus chelonae sp. nov., isolated from chelonids in Australia. Int J Syst Bacteriol 45:50–56. 11. Montali RJ, Smith EE, Davenport M, et al.: 1975, Dermatophilosis in Australian bearded lizards. J Am Vet Med Assoc 167: 553–555. 12. Roberts DS: 1961, The life cycle of Dermatophilus dermatonomus, the causal agent of ovine mycotic dermatitis. Aust J Exp Biol Med Sci 39:463–476. 13. Simmons GC, Sullivan ND, Green PE: 1972, Dermatophilus in a lizard (Amphibolurus barbatus). Aust Vet J 48:465–466.

Persistence of Escherichia coli O157:H7 in experimentally infected swine

These experiments determined the ability of Escherichia coli O157:H7 to colonize and persist in pigs simultaneously inoculated with other pathogenic E. coli strains. Three-months-old pigs were inoculated with a mixture of five E. coli strains. The mixture included two Shiga toxigenic E. coli (STEC) O157:H7 strains, two enterotoxigenic E. coli (ETEC) strains and one enteropathogenic E. coli (EPEC) strain. A high dose mixture with all five strains at 10(10)CFU/animal (CFU: colony forming units) and a low dose mixture with the STEC strains at 10(7)CFU and the EPEC and ETEC strains remaining at 10(10)CFU were used. The STEC strains persisted in the alimentary tracts of some pigs at 2 months post-inoculation, following inoculation with both the high and low dose mixtures. When all strains were given at 10(10)CFU (high dose) the STEC strains persisted in greater numbers and in more pigs than did the other E. coli strains. The results demonstrated that persistent colonization (> or =2 months) by E. coli O157:H7 can occur in pigs. These findings were similar to those reported from sheep inoculated with the same mixture of E. coli strains. The results are consistent with reports suggesting that pigs have the potential to be reservoir hosts for STEC O157:H7.

Indirect transmission of Escherichia coli O157:H7 occurs readily among swine but not among sheep.

ABSTRACT Transmission of Escherichia coli O157:H7 among reservoir animals is generally thought to occur either by direct contact between a naïve animal and an infected animal or by consumption of food or water containing the organism. Although ruminants are considered the major reservoir, there are two reports of human infections caused by E. coli O157:H7 linked to the consumption of pork products or to the contamination of fresh produce by swine manure. The objective of this study was to determine whether E. coli O157:H7 could be transmitted to naïve animals, both sheep and swine, that did not have any direct contact with an infected donor animal. We recovered E. coli O157:H7 from 10/10 pigs with nose-to-nose contact with the infected donor or animals adjacent to the donor and from 5/6 naïve pigs that were penned in the same room as the donor pig but 10 to 20 ft away. In contrast, when the experiment was repeated with sheep, E. coli O157:H7 was recovered from 4/6 animals that had nose-to-nose contact with the infected donor or adjacent animals and from 0/6 naïve animals penned 10 to 20 ft away from the donor. These results suggest that E. coli O157:H7 is readily transmitted among swine and that transmission can occur by the creation of contaminated aerosols.