Have we improved food safety in live cattle?

Abstract Text:

A number of technologies for reducing food-borne pathogens have been evaluated in live cattle such as direct-fed microbials, vaccines, bacteriophages and bacteriocidal feed ingredients.  Many of these have been targeted to E. coli O157:H7, but efficacy in some cases has been variable, while regulatory approval of others has been less than forth-coming.  As strategies to control Salmonella in live cattle have been even less successful, different approaches may be needed. For E. coli, Shiga-toxins are primary causative factors for human disease and carried on prophages integrated into the bacterial genome. As transfer of these Shiga-toxin phages can convert previously non-pathogenic E. coli to pathogens and as these phages can be carried by other bacterial species such as Citrobacter freundii, should we direct more future live animal food safety efforts to better controlling these endogenous phages?   Fight phages with phages?  Having a phage already integrated in the bacterial genome has been shown to block lysogeny by stx-carrying phages of the same species.  Alternatively, as E. coli are commensal organisms in the bovine gastrointestinal tract and E. coli compete within the microflora for access to nutrients and valuable real estate, would it be possible to utilize the strategies of highly-competitive E. coli to supress growth of other E. coli with Shiga toxins?  Could the safety of a direct-fed microbial containing a non-pathogenic, but highly competitive strain of E. coli ever be assured?  The CRISPR system evolved to protect prokaryote DNA from integration of viruses and plasmids. Could CRISPR-cas be used to block possible integration sites for Shiga-toxin phages in a highly-competitive non-pathogenic strain of E. coli?  Should CRISPR-cas be used in this way?  As contamination of hides is the primary route leading to contamination of meat, more emphasis on control of pathogens on hides is warranted. A bacteriophage-based hide wash for control of E. coli O157:H7 has been approved by the USDA, but research data has been limited. However, a recent study by our laboratory demonstrated that non-O157 E. coli outweigh the pathogenic potential of O157 in feces of slaughter cattle as serogroups such as O103, O45  were relatively ubiquitous year-round and 55 to 65% of isolates of these serogroups carried Shiga toxins.  New pre-harvest approaches that will more successfully control the gamut of current and potential bacterial pathogens in live cattle are warranted.

Keywords: Shiga toxins, E. coli, cattle