Purpose: The purpose of this study was 1) to study the change in microbial community by E. coli O157:H7 in ground beef (GB) during storage, 2) to identify the bacteria involve in the competition and to understand mechanism of the competition.
Methods: Imported and domestic GB (13 and 37 samples, respectively) were purchased from local stores in Korea and their microbial community was compared using PCR-DGGE analysis method. Based on this information, major meat spoilage bacteria such as lactic acid bacteria, Pseudomonas spp., Enterobacteriaceae and Brochothrix thermosphacta, and total aerobic bacteria was monitored during storage at 5 and 10°C for 0, 1, 3, 7 and 10 days. E. coli O157:H7 was inoculated at the concentration of 5.11 x 102 log CFU/g and growth with other bacteria during storage was monitored. The result was confirmed by plate counting and PCR-DGGE analysis.
Results: PCR-DGGE analysis showed the presence of Lactobacillus plantarum, Proteus mirabilis and Photobacterium spp and others by contamination of E. coli O157:H7 while Enterobacter and Citrobacter spp were identified in the native GB. During early stage of storage, the growth of B. thermosphacta was significantly reduced by E. coli O157:H7 by 1.28 log CFU/g (P < 0.05). Cell free supernatant of E. coli O157:H7 treatment, metabolite analysis and co-inoculation with B. thermosphacta showed the competitive growth and presence of potential antimicrobials in E. coli O157:H7 to inhibit the growth of B. thermosphacta.
Significance: This study is the first to show the competitive interaction between E. coli O157:H7 and B. thermosphacta and to show the change of microbial ecology in GB by E. coli O157:H7.