Abstract
A test was carried out in vitro to identify nitrosodimethylamine (NDMA)-forming aerobic bacteria isolated from the gastric contents of the monkey, Macaca irus. In it, the following cultural conditions established by a preliminary test were used: (1) The medium used was the filtrate of brain heart infusion with gastric juice containing 1, 000ppm sodium nitrite and 500ppm dimethylamine. (2) The inoculum size used was about 5×108 cells per ml of the medium. (3) Incubation was done at pH 6 for 3 hours. NDMA in the medium was determined with a gas chromatograph-thermal energy analyzer (detection limit: 0.2ng).
When 35 strains of bacteria were examined repeatedly three times for ability to form NDMA, the following eight species were recognized to have the ability: Streptococcus equi, Neisseria sicca, Corynebacterium pseudotuberculosis, Staphylococcus aureus, Staphylococcus epidermidis, and Citrobacter freundii isolated from the gastric contents of the monkey, and Streptococcus faecalis and Escherichia coli from the feces of the monkey.
With respect to changes in the pH of the medium during incubation, it is of interest to note that the level of pH was a little high, or 6, in the culture of Neisseria sicca and Streptococcus equi, and low, or near 5.5, in that of any other strain.
