Effect of incubation temperature, ageing, and bisulfite content of unsupplemented Brucella agar on aerotolerance of Campylobacter jejuni

A mutant strain of Campylobacter jejuni ATCC 29428 was isolated that grows on unsupplemented Brucella agar at O2 levels as high as 21% at 37 degrees C. While measuring the degree of aerotolerance of this mutant on unsupplemented Brucella medium and comparing it with that of the wild type, we found considerable variation among our estimates. As measured by colony counts on unsupplemented Brucella agar incubated at various oxygen levels, the degree of aerotolerance was affected by incubation temperature and the age of the medium. Aerotolerance was consistently higher on plates incubated at 42 degrees C than at 37 degrees C. When the commercial dehydrated Brucella medium that was used to prepare the Brucella agar was stored in a beaker for 2.5 months, the degree of aerotolerance of C. jejuni was decreased. Addition of 0.01% sodium bisulfite reversed this inhibition. Storage of bottles of hydrated Brucella agar for 1.5 months also resulted in a decreased aerotolerance; again, in addition of 0.01% bisulfite reversed the effect. Aerotolerance was greatly decreased when Brucella agar was prepared from all its individual components except 0.01% bisulfite. The results indicate that the bisulfite component of Brucella agar deteriorates during storage of the dehydrated and hydrated media, and that this deterioration can affect measurements of aerotolerance.