Growth of Carnobacterium spp. isolated from chilled vacuum-packaged meat under relevant acidic conditions

Carnobacterium spp. are frequently isolated from vacuum-packaged (VP) meat. Specific strains of Carnobacterium and their growth characteristics may be associated with the storage life of such products. This study investigated the growth of 44 Carnobacterium isolates obtained from VP meat cuts produced at three Canadian abattoirs (A, B and C) under the following conditions: pH 5.4, 6.2 and 7.4; lactic acid at 60 and 90 mM; acetic acid at 33.6 mM. Whole genome sequencing was performed for all 44 isolates and a core genome phylogenetic tree was created to identify strain variability among isolates from different abattoirs. The isolates were clustered into 11 groups. All isolates from abattoirs B and C were identified as C. divergens, while the isolates from abattoir A included both C. maltaromaticum and C. divergens at equal proportions. C. divergens isolates from abattoir A belonged to two phylogenetic groups and none of them was found in the phylogenetic groups containing isolates from abattoirs B or C. Whole genome sequencing revealed that identical strains were isolated from different samples obtained at the same abattoir. The mean growth rate and maximum population density of the C. maltaromaticum isolates were lower than those of the C. divergens isolates. C. divergens isolates from abattoir A had higher growth rates and maximum population density than those from abattoirs B and C. In conclusion, growth characteristic and whole genome analysis both demonstrated strain variability of Carnobacterium among abattoirs, which could be a result of the difference in the antimicrobial interventions used for carcasses at different abattoirs, and may be associated with different storage lives of VP meats produced from different abattoirs.