Oral Presentation Australian Society for Microbiology Annual Scientific Meeting 2013

Inter-strain inhibitory activity within the bacterial community of Australian vacuum-packaged beef (#127)

Peipei Zhang , Michelle Williams , Tom Ross , John Bowman , Mark Tamplin

Australian vacuum-packaged beef is recognised for its exceptionally long shelf-life. The factors responsible for this benefit are poorly understood. Evidence indicates that interactions among the bacterial community may, in part, lead to extended shelf-life. This study screened the inhibitory spectra of 45 isolates against 20 target isolates by an agar assay method. Both inhibitory and target bacteria were isolated from vacuum-packaged beef from six Australia export abattoirs, and included 10 and 11 genera, respectively. These genera included Carnobacterium, Brochothrix, Hafina, Yersinia, Bacillus, Pseudomonas, Rahnella, Leuconostoc, Serratia and Staphylococcus. Inhibition strength was measured as the radius of the inhibition zone following incubation on Tryptic Soya Agar at 25°C. Approximately 20% of effector-target strain combinations (180 among 895 pairs in total) showed inhibitory activity. Nine and 37 of the effector-target strain combinations displayed inhibition zones >3mm and 1-3mm, respectively. All nine Pseudomonas strains displayed antagonist properties against at least three target isolates, with two strains of Pseudomonas putida, D0b and D0j, producing the two strongest levels of inhibition; these strains inhibited 90% (18) and 85% (17) of target isolates. Three Bacillus spp. isolates inhibited at least 50% of target isolates, with one Bacillus vallismortis strain, A30g, inhibiting 14 of 19 (74%) of the target isolates. However, Carnobacterium and Lecunostoc did not display wide inhibitory spectra, where the strongest inhibitory strain, C. divergens B0f, inhibited only three targets. Intra-species inhibition was also observed, where the growth of C. divergens D30f was inhibited by seven C. divergens isolates. In conclusion, changes in the bacterial spoilage community on vacuum-packaged beef are likely influenced by inhibitory interactions, especially by Pseudomonas and Bacillus isolates in the early stages of storage. Further studies will identify the types of inhibitors and how the environment influences bacterial interactions.