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The aim of this study was to determine if Campylobacter bacteriophages CP 81 und CP 84 as well as Yersinia bacteriophage PY 100 serve for post harvest application to reduce Campylobacter and Yersinia enterocolitica load in food.
Therefore, it was assessed how these bacteriophages could decrease cell number of the corresponding host bacterium at 37°C and 4°C as well as at 4°C in meat. It was shown that the Campylobacter bacteriophages could only decrease cell number of its host at 37°C in medium by 1 log, independently of applied MOI. As both Campylobacter bacteriophages could not decrease Campylobacter numbers at 4°C in medium and in meat, these bacteriophages do not serve for post harvest application. In contrast, Yersinia bacteriophage PY 100 decreased cell numbers of its host successfully by up to 5 log at 37°C in medium, by up to 3 log at 4°C in medium and by 1.5 log at 4°C in meat.
Therefore, this bacteriophage is suitable for post harvest application.
All three strains developed resistance towards the corresponding bacteriophage when incubated with this phage for 48 h at 37°C. Therefore, resistance mechanisms were analysed into further detail. A binding assay revealed that all three bacteriophages could no longer bind to the corresponding resistant clones. This indicates a change or possible loss of the bacteriophage receptor. Between phage resistant and phage sensitive Campylobacter clones no changes of the fAFLP band patterns, flaA-sequence or the CRISPR locus could be observed. Resistance mechanisms of all three strains differ in the facts that phage resistant C. jejuni NCTC 11168 clones remained resistant over the whole testing period of six week of subculturing whereas phage resistant C. coli NCTC 12668 and Y. enterocolitica 83/88/2 clones turned back to phage sensitivity. Additionally, only phage resistant C. jejuni NCTC 11168 clones showed changed motility rates as well as cross resistance towards further bacteriophages of the same group. Changes of the poly G tract of genes cj1421 and cj1422 described in literature could only be detected in some of the phage resistant C. jejuni NCTC 11168 clones. This difference can therefore not represent the main resistance mechanism.