Use of Blood Powder (Ground and Irradiated) for the Manufacture of Chocolate Agar

Abstract

Chocolate agar (CA) is an enriched medium for the isolation and identification of fastidious bacteria. Defibrinated blood is used to manufacture CA, but this expensive product is not always affordable for companies in developing countries. Blood powder (BP) is potentially a cheaper alternative, although its pre-treatment by autoclaving can impair the quality of the media. Therefore, optimization of BP as a substitute of defibrinated blood for CA manufacture deserves further research. CA was manufactured with irradiated BP (dehydrated bovine blood powder) and its physical and microbiological characteristics were compared with those of conventional CA and CA prepared with autoclaved BP. Each medium was seeded with 20-200 CFU of target bacteria using the spiral-pouring method. Finally, another medium was prepared using BP pre-treated by grinding and gamma-irradiation and its performance assessed. Compared to conventional CA, the medium containing ground and irradiated BP provided a similar CFU count for both fastidious (Neisseria, Haemophilus, Campylobacter and Streptococcus) and non-fastidious (Moraxella, Staphylococcus, Enterococcus, Klebsiella and Pseudomonas) species, unlike the medium with BP only subjected to irradiation, which provided a lower growth of fastidious species. Morphology and characteristics of all bacterial colonies were very similar in conven-tional CA and the new medium, the number of Pseudomonas CFU being higher in the latter. The medium prepared with ground-plus-irradiated vs irradiated BP more closely resembled conven-tional CA, having a browner background. A new CA medium prepared with ground and gamma irradiation-sterilized BP presents comparable productivity properties to conventional CA. Therefore, it could be a more practical and economical methodology to facilitate large-scale CA manufacture.