Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 15, 2008
Publication Date: N/A
Interpretive Summary: After the Jack in the Box E. coli O157:H7 outbreak in 1993, Americans have become more aware that dangerous pathogens may be lurking in their food supplies. Recalls of meat due to detection of E coli O157 now costs the meat industry billions of dollars. ARS Scientists in Lubbock, Texas, examined a defined collection of these two lineages of E. coli O157:H7 for genetic factors that cause infection in humans and transmission from food to human hosts. Molecular and biochemical assays were utilized to investigate the difference in Shiga-like Toxin II (stx2) expression between the two lineages. It was conclusively shown that a variety of this bacteria suspected of having less potential to be transmitted and cause disease in humans, expresses significantly less toxin. A tremendous amount of research will still be needed in order to fully evaluate the existence of a less dangerous variety of O157:H7 and studies will be needed to ensure that these less pathogenic lineages cannot convert to more virulent forms. The future of this research, if one of these lineages can be conclusively proven not to be a public health risk, is of great significance to beef producers and could prevent billions of dollars in meat recalls.
Technical Abstract: The existence of two separate lineages of E. coli O157:H7 has previously been reported, and research points to one specific lineage, lineage I, possessing more pathogenicity towards human hosts. We postulate that the more pathogenic lineage expresses higher levels of shiga-like toxin 2 (Stx2) than the non-pathogenic lineage. Several methods were selected to investigate the difference in Stx2 protein and mRNA expression between the two lineages. An initial Stx2-specific ELISA was conducted and lineage I overall demonstrated significantly more toxin proteins expressed (p < 0.05). Further analyses of Stx2 were conducted on representatives from each lineage using a variety of approaches including low resolution PCR mapping, quantitative RT-PCR, and Stx2-encoding bacteriophage (933W)-targeted microarray analyses. Both microarray analyses and quantitative RT-PCR analysis showed significantly higher stx2 expression in lineage I (p=0.02). A polymerase chain reaction revealed a possible explanation for decreased amounts of stx2 transcripts in the potentially non-pathogenic LII lineage, suggesting that genomic rearrangements have interrupted the toxin-encoding region of the phage. Although E. coli O157:H7 has many virulence factors and mechanisms to employ and evade host defenses, Stx2 production has shown to be of high statistical relevance to the pathogenicity of lineage I, thus supporting the existence of two diverse lineages, one of which may have lower pathogenicity to human hosts.