title: Inhibition of verocytotoxigenic Escherichia coli by antimicrobial peptides caseicin A and B and the factors affecting their antimicrobial activities.
abstract: The antimic robial activities of caseicin A and B antimicrobial peptides (AMPs) were assessed against a selection of verocytotoxigenic Escherichia coli (VTEC) strains (n=11), other bacterial pathogenic and spoilage bacteria (n=7), using a model broth system. The ability of the AMPs to retain their antimicrobial activities against a strain of E. coli O157:H7 380-94 under various test conditions (pH, temperature, water activity, sodium chloride concentrations, inoculum size and the presence of competitive microflora) was assessed and the minimum inhibitory concentrations (MIC) and number of surviving E. coli O157:H7 calculated. The mean number of VTEC surviving after exposure to 2 mg/ml caseicin A and B was reduced by 4.96 and 4.19 log(10) cfu/ml compared to the respective controls. The susceptibility of E. coli O157:H7 to the caseicin AMPs decreased as temperature, pH, water activity and inoculum size were reduced. The presence of sodium chloride (0.5-2.5%) did not affect the activity of caseicin A (p>0.05), however it did inhibit the activity of caseicin B. The presence of a competitive microflora cocktail did not significantly (p>0.05) affect the activities of the AMPs for the majority of the concentrations tested. Using a quantitative PCR assay, the levels of verotoxins (vt1 and vt2) expressed by E. coli O157:H7 following exposure to a sub-inhibitory concentration (0.5 mg/ml) of caseicin A showed that the verotoxin levels did not differ from the levels produced by the control cultures. The antimicrobial activity of caseicin A against E. coli O157:H7 was also tested in a model rumen system, however concentrations of ≥2 mg/ml did not significantly (p>0.05) reduce E. coli O157:H7 numbers in the model system over a 24 h period. The application of caseicin AMPs in food and/or animal production may be valuable in combination with other antimicrobials although further research is required.
authors.affiliation: Teagasc Food Research Centre, Ashtown, Dublin 15, Ireland.
authors.forename: Mary J
authors.initials: MJ
authors.lastname: McDonnell
authors.forename: Lucia
authors.initials: L
authors.lastname: Rivas
authors.forename: Catherine M
authors.initials: CM
authors.lastname: Burgess
authors.forename: Séamus
authors.initials: S
authors.lastname: Fanning
authors.forename: Geraldine
authors.initials: G
authors.lastname: Duffy
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology*; D002364:Caseins / Q000494:pharmacology*; D004926:Escherichia coli; D004927:Escherichia coli Infections; D019453:Escherichia coli O157 / Q000187:drug effects* / Q000378:metabolism; D005506:Food Contamination / Q000517:prevention & control*; D006863:Hydrogen-Ion Concentration; D008460:Meat; D008826:Microbial Sensitivity Tests; D008962:Models, Theoretical; D010446:Peptide Fragments / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology*; D022622:Shiga Toxin 1 / Q000378:metabolism; D022641:Shiga Toxin 2 / Q000378:metabolism; D012965:Sodium Chloride; D013696:Temperature
chemical_list: D000890:Anti-Infective Agents; D002364:Caseins; D010446:Peptide Fragments; D010455:Peptides; D022622:Shiga Toxin 1; D022641:Shiga Toxin 2; C572873:caseicin A; C572875:caseicin B; D012965:Sodium Chloride