PCR Detection of Bacillus and Staphylococcus in Various Foods
A broad-range PCR assay for the detection of bacteria belonging to Bacillus and Staphylococcus genera was developed. Primers targeting the bacterial 16S rRNA gene were newly designed and used
in a PCR assay. To determine the specificity of the assay, 81 different bacterial strains (of 50 genera), 2 fungi, 3 animals, and 4 plants were tested. Results were positive for every tested Bacillus,
Staphylococcus, or Aerococcus strain. In addition, the result for Listeria grayi was positive with lower PCR product. For all other bacterial strains and eukaryotes tested, results
were negative. Bacterial DNA was prepared with the use of achromopeptidase and Chelex 100 resin from culture after growth in brain heart infusion medium. To test the sensitivity of this PCR assay for Bacillus
or Staphylococcus genus, either Bacillus cereus or Staphylococcus aureus was inoculated into various foods with undetectable levels of endogenous microbial contamination as an indicator.
Inoculation of bacteria at 10 to 30 CFU/g of food was followed by a 5-h enrichment culture step after which the PCR assay allowed the detection of bacterial cells. When the inoculation (B. cereus
or S. aureus) of 10 to 90 CFU/g into noodle foods containing endogenous microflora (103 to 105 CFU/g) was followed by a 6-h enrichment culture step, the PCR assay detected the
bacteria. Including the enrichment culture step, the entire PCR detection process can be completed within 8.5 h.
Document Type: Short Communication
Food Safety Research Institute, Nissin Food Products Co. Ltd., 2247, Noji-cho, Kusatsu, Shiga 525-0055, Japan