Escherichia coli is a heterogeneous species that can be part of the normal flora of humans but also include strains of medical importance. Among pathogenic members, Shiga-toxin producing E. coli (STEC) are some of the more prominent pathogenic E. coli within the public sphere. STEC disease outbreaks are typically associated with contaminated beef, contaminated drinking water, and contaminated fresh produce. These water- and food-borne pathogens usually colonize cattle asymptomatically; cows will shed STEC in their feces and the subsequent fecal contamination of the environment and processing plants is a major concern for food and public safety. This is especially important because STEC can survive for prolonged periods of time outside its host in environments such as water, produce, and farm soil. Biofilms are hypothesized to be important for survival in the environment especially on produce, in rivers, and in processing plants. Several factors involved in biofilm formation such as curli, cellulose, poly-N-acetyl glucosamine, and colanic acid are involved in plant colonization and adherence to different surfaces often found in meat processing plants. In food processing plants, contamination of beef carcasses occurs at different stages of processing and this is often caused by the formation of STEC biofilms on the surface of several pieces of equipment associated with slaughtering and processing. Biofilms protect bacteria against several challenges, including biocides used in industrial processes. STEC biofilms are less sensitive than planktonic cells to several chemical sanitizers such as quaternary ammonium compounds, peroxyacetic acid, and chlorine compounds. Increased resistance to sanitizers by STEC growing in a biofilm is likely to be a source of contamination in the processing plant. This review focuses on the role of biofilm formation by STEC as a means of persistence outside their animal host and factors associated with biofilm formation.
Escherichia coli 045 isolates associated with swine postweaning diarrhea in Quebec were characterized with respect to virulence determinants genetically and investigated for their attaching and effacing (A/E) activities by experimental inoculation of gnotobiotic piglets and by the HEp-2 cell adherence assay. All of 32 isolates tested were negative for enterotoxigenic and verotoxigenic E. coli virulence determinants, heat-labile enterotoxin (LT), heat-stable enterotoxins (STap, STb), verotoxins (VT1, VT2), and F4 (K88), F5 (K99), F6 (987P), and F41, except one STh-positive and two F4-positive isolates. A total of 25 isolates hybridized with an EaeA probe, and 11 hybridized with an enteropathogenic E. coli adherence factor (EAF) probe. None of 32 isolates hybridized with a bundle-forming pilus (BFP) probe. The EAF, EaeA, and BFP factors have been associatedwith human enteropathogenic E. coli strains. A total of 10 of 12 eaeA-positive porcine 045 isolates induced A/E lesions characterized by intimate adherence of bacteria to the intestinal epithelial cell membrane with effacement of the microvilli, similar to those of human attaching-effacing E. coli. However, A/E lesions were not observed in the piglets inoculated with any one of three eaeA-negative 045 isolates. All E. coli 045 isolates were non-adherent to HEp-2 cells. Thus, we have demonstrated the production of typical A/E lesions by nonenterotoxigenic E. coli 045 isolates from swine postweaning diarrhea. The results indicate the significance of the eaeA gene in A/E activities of these isolates and suggest that EAF and BFP are not involved in 045 E. coli infection of weaning piglets.
Using a porcine ileal in vitro organ culture model, we have demonstrated that egg yolk-derived antibodies specific for the attaching and effacing Escherichia coli (AEEC) virulence factors intimin and translocated intimin receptor (Tir), but not those specific for the AEEC-secreted proteins EspA, EspB and EspD, significantly reduced the bacterial adherence of the porcine enteropathogenic E. coli strain ECL1001, formerly 86-1390. Moreover, antibodies specific for intimin and Tir also significantly reduced bacterial adherence of heterologous AEEC strains, including human, bovine and canine enteropathogenic E. coli strains, as well as of O157:H7 Shiga toxin-producing E. coli strains in this model. In addition, we demonstrated that the oral administration of these anti-intimin antibodies significantly reduced the extent of attaching and effacing lesions found in the small intestine of weaned pigs challenged with the porcine enteropathogenic E. coli strain ECL1001. Overall, our results underline the potential use of specific egg yolk-derived antibodies as a novel approach for the prevention of AEEC infections.
In our ongoing efforts to develop a vaccine against Streptococcus suis infection, we tested the potential of S. suis enolase (SsEno), a recently described S. suis adhesin with fibronectin-binding activity, as a vaccine candidate in a mouse model of S. suis-induced septicemia and meningitis. Here, we show that SsEno is highly recognized by sera from convalescent pigs and is highly immunogenic in mice. Subcutaneous immunization of mice with SsEno elicited strong immunoglobulin G (IgG) antibody responses. All four IgG subclasses were induced, with IgG1, IgG2a and IgG2b representing the highest titers followed by IgG3. However, SsEno-vaccinated and nonvaccinated control groups showed similar mortality rates after challenge infection with the highly virulent S. suis strain 166'. Similar results were obtained upon passive immunization of mice with hyperimmunized rabbit IgG anti-SsEno. We also showed that anti-SsEno antibodies did not increase the ability of mouse phagocytes to kill S. suis in vitro. In conclusion, these data demonstrate that although recombinant SsEno formulated with Quil A triggers a strong antibody response, it does not confer effective protection against infection with S. suis serotype 2 in mice.
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