Differences in levels of secreted locus of enterocyte effacement proteins between human disease-associated and bovine Escherichia coli O157

McNally, A., Roe, A. J. , Simpson, S., Thomson-Carter, F. M., Hoey, D.E. E., Currie, C., Chakraborty, T., Smith, D. G.E. and Gally, D. L. (2001) Differences in levels of secreted locus of enterocyte effacement proteins between human disease-associated and bovine Escherichia coli O157. Infection and Immunity, 69(8), pp. 5107-5114. (doi: 10.1128/IAI.69.8.5107-5114.2001)

Abstract

Ongoing extensive epidemiological studies of verotoxin-carrying <i>Escherichia coli</i> O157 (stx + eae + ) have shown this bacterial pathogen to be common in cattle herds in the United States and the United Kingdom. However, the incidence of disease in humans due to this pathogen is still very low. This study set out to investigate if there is a difference between strains isolated from human disease cases and those isolated from asymptomatic cattle which would account for the low disease incidence of such a ubiquitous organism. The work presented here has compared human disease strains from both sporadic and outbreak cases with a cross-section, as defined by pulsed-field gel electrophoresis, of <i>E. Coli</i> O157 strains from cattle. Human (n = 22) and bovine (n = 31) strains were genotyped for carriage of the genes for Shiga-like toxin types 1, 2, and 2c; <i>E. Coli</i> secreted protein genes <i>espA, espB</i>, and <i>espP</i>; the enterohemolysin gene; <i>eae</i> (intimin); <i>ast</i> (enteroaggregative <i>E. Coli</i> stable toxin [EAST]); and genes for common <i>E. Coli</i> adhesins. Strains were also phenotyped for hemolysin, EspP, Tir, and EspD expression as well as production of actin and cytoskeletal rearrangement associated with attaching and effacing (A/E) lesions on HeLa cells. The genotyping confirmed that there was little difference between the two groups, including carriage of <i>stx</i>² and<i>stx</i>^2c, which was similar in both sets. <i>ast</i> alleles were confirmed to all contain mutations that would prevent EAST expression. <i>espP</i> mutations were found only in cattle strains (5 of 30). Clear differences were observed in the expression of locus of enterocyte effacement (LEE)-encoded factors between strains and in different media. EspD, as an indicator of LEE4 (<i>espA</i>, <i>-B</i>, and <i>-D</i>) expression, and Tir levels in supernatants were measured. Virtually all strains from both sources could produce EspD in Luria-Bertani broth, although at very different levels. Standard trichloroacetic acid precipitation of secreted proteins from tissue culture medium produced detectable levels of EspD from the majority of strains of human origin (15 of 20) compared with only a few (4 of 20) bovine strains (P < 0.001), which is indicative of much higher levels of protein secretion from the human strains. Addition of bovine serum albumin carrier protein before precipitation and enhanced detection techniques confirmed that EspD could be detected after growth in tissue culture medium for all strains, but levels from strains of human origin were on average 90-fold higher than those from strains of bovine origin. In general, levels of secretion also correlated with ability to form A/E lesions on HeLa cells, with only the high-level protein secretors in tissue culture medium exhibiting a localized adherence phenotype. This research shows significant differences between human- and bovine-derived <i>E. Coli</i> O157 (<i>stx + eae </i>+) strains and their production of certain LEE-encoded virulence factors. These data support the recent finding of Kim et al. (J. Kim, J. Nietfeldt, and A. K. Benson, Proc. Natl. Acad. Sci. USA 96:13288–13293, 1999) proposing different <i>E. Coli</i> O157 lineages in cattle and humans and extend the differential to the regulation of virulence factors. Potentially only a subset of <i>E. Coli</i> O157 isolates (<i>stx + eae +</i>) in cattle may be capable of causing severe disease in humans.

• Item Type: Articles
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Smith, Professor David and Roe, Professor Andrew
• Authors: McNally, A., Roe, A. J., Simpson, S., Thomson-Carter, F. M., Hoey, D.E. E., Currie, C., Chakraborty, T., Smith, D. G.E., and Gally, D. L.
• College/School: College of Medical Veterinary and Life Sciences > School of Infection & Immunity
• Journal Name: Infection and Immunity
• Journal Abbr.: IAI
• Publisher: American Society for Microbiology
• ISSN: 0019-9567
• ISSN (Online): 1098-5522