A comparison of the performance of bacitracin-incorporated chocolate bloodagar with chocolate blood agar plus a bacitracin disk in the isolation of Haemophilus influenzae from sputum

The lack of selectivity of chocolated blood agar (CBA), routinely used for the isolation of Haemophilus influenzae, may lead to masking of the growth of H, influenzae due to overgrowth of competing flora. Bacitracin can be us ed as a selective agent, either incorporated into the medium or applied to the medium in a filter paper. However, neither method has been evaluated or compared in a large study. Sputum samples (1990) were examined in four lab oratories and the isolation rates of R; influenzae on chocolated blood agar with bacitracin added to the medium (BCA) and chocolated blood agar (CBA) with a bacitracin disk were compared. A plain blood agar plate was also ino culated to facilitate the isolation of Streptococcus pneumoniae so that ifs effects on the isolation of H. influenzae could be assessed. No significan t difference was found between the isolation rates of H, influenzae on BCA and CBA with a bacitracin disk, although competing flora was greatly reduce d and quantity of growth of H, influenzae increased on BCA, The presence of S, pneumoniae did not affect the isolation of H. influenzae in this study.