Effects of a Carnobacterium maltaromaticum strain at natural contamination levels on the microbiota of vacuum-packaged beef steaks during chilled storage

We investigated the impact of a Carnobacterium maltaromaticum strain at a natural contamination level on the dynamics of microbiota and survival of Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium on chilled vacuum-packaged (VP) beef. C. maltaromaticum A5 up to 2 log CFU/cm2 was spiked onto beef steaks with or without E. coli O157:H7 and S. Typhimurium. The steaks were vacuum-packaged and stored at 2 °C for 12 weeks. The dynamics of the microbiota were determined using plating and 16S rRNA gene amplicon sequencing methods. The predominant bacterial species in the final microbiota were determined using whole metagenome and genome sequencing. C. maltaromaticum on inoculated meat peaked at week 2 (>80%) even though the initial relative abundance was as low as <1%. The relative abundance of indigenous Latilactobacillus was 0.1–0.5%, but gradually increased to 75.7–100% at week 12, displacing Carnobacterium. The predominant species in the final microbiota was identified as Latilactobacillus sakei subsp. carnosus, which harbored gene clusters encoding Sakacin G and a putative class IIc bacteriocin. Neither of the two pathogens was affected by C. maltaromaticum A5. Taken together, this study indicates that the initial microbial composition plays an important role in the fate of an introduced LAB strain.