Development of a blood‐free Campylobacter medium: screening tests on basal media and supplements, and the ability of selected supplements to facilitate aerotolerance

Abstract

The capacity of 6 basal media to support the growth of thermophilic campylobacters was tested. The most successful was Nutrient Broth No. 2 (Oxoid) solidified with New Zealand agar but it gave, at best, only a 9% recovery rate. Various blood products, Fe compounds, detoxifying agents, reducing agents, growth stimulants and an antimetabolite were added to the selected basal medium and counts of inoculated organisms were compared with counts on basal medium containing 5% lysed horse blood. Of 22 supplements tried, only blood, Fildes'' peptic digest of blood, hematin, Fe salts, charcoal, sodium metabisulfite and sodium pyruvate greatly improved the basal medium. The ability of these supplements used singly and in combinations to facilitate aerotolerance of campylobacters was investigated. Two aspects of aerotolerance were tested: the ability of the supplements to sustain the viability of campylobacters seeded onto culture plates left on the bench for up to 6 h before microaerobic incubation: and the ability of the supplements to facilitate the growth of campylobacters at increasing O2 tension (6, 10 and 17% O2). A combination of 0.4% charcoal, 0.025% ferrous sulfate and 0.025% sodium pyruvate was as effective as blood in both tests.