Microbiota in lymph nodes of cattle harvested in a Canadian meat processing plant

Lymph nodes (LN) harboring bacteria, when being incorporated into ground beef, may impact the microbial safety and quality of such products. We tested two main foodborne pathogens Salmonella and Shiga toxin-producing Escherichia coli (STEC) and profiled the microbiota in LNs (n = 160) of cattle harvested at a Canadian abattoir, by conventional plating methods, PCR, and high throughput sequencing. LNs at two anatomical locations, subiliac and popliteal from 80 cattle were included. All cattle had bacteria detected in popliteal and/or subiliac LNs with the maximum bacterial load of 5.4 and 2.8 log10CFU/g in popliteal and subiliac LNs, respectively. Neither Salmonella nor STEC was found in LNs although STEC was detected in a significant percentage of samples from beef hides (50.6 %) by plating and/or PCR. Both 16S rRNA gene amplicon and metagenome sequencing found the predominance of Escherichia (13-34.6 % among bacterial community), Clostridium (12.6-20.6 %) and Streptococcus (9.7-10 %) in popliteal LNs. Metagenomic sequencing was able to identify the predominant taxa at species level with E. coli (13 %), Clostridium perfringens (11.1 %) and Streptococcus uberis (6 %) predominant in LNs. Low prevalence/abundance of Salmonella was found by metagenomic sequencing. In conclusion, the relatively high bacterial load and diversity in LNs may affect the shelf life of ground beef and high relative abundance of E. coli would warrant further monitoring.

Growth parameters of Escherichia coli O157:H7, Salmonella spp., Listeria monocytogenes, and aerobic mesophilic bacteria of apple cider amended with nisin-EDTA

The effect of nisin (0 or 300 IU/mL), ethylenediamine tetraacetic acid (EDTA, 20 mM), and nisin (300 IU)-EDTA (20 mM) on growth parameters, including lag period (LP) and generation time, of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella spp. in the presence or absence of aerobic mesophilic bacteria of apple cider during storage at 5 degrees C for up to 16 days or 23 degrees C for 16 h was investigated. The growth data were analyzed and fitted to the modified Gompertz model. The LP values for aerobic mesophilic bacteria of apple cider (control) and those amended with EDTA and nisin during storage at 5 degrees C were 1.61, 1.76, and 5.45 days, respectively. In apple cider stored at 23 degrees C for 16 h, the LP values for the same bacteria and treatment were 3.24, 3.56, and 5.85 h, respectively. The LP values for E. coli O157:H7 determined in the presence of aerobic mesophilic bacteria of apple cider stored at 23 degrees C for 16 h was 1.48 h, while populations for L. monocytogenes and Salmonella in the same cider declined. In sterile apple cider left at 23 degrees C for 16 h, the LP values for E. coli O157:H7, Salmonella, and L. monocytogenes averaged 2.74, 2.37, and 3.16 h, respectively. The generation time for these pathogens were 0.402, 0.260, and 0.187 log (CFU/mL)/h, respectively. Addition of nisin and EDTA combination caused a decline in lag phase duration and the populations for all pathogens tested, suggesting possible addition of this additive to freshly prepared apple cider to enhance its microbial safety and prevent costly recalls.