Evaluation of anaerobic culture and effect of culture medium supplementation with factor V on colonial morphology and efficacy of isolation of Streptococcus pneumoniae from sputum

Abstract

The use of anaerobic incubation for the culture of Streptococcus pneumoniae from sputum was compared with incubation in carbon dioxide in air. A coaggutination test for pneumococcal antigen was used as an index of the number of specimens containing pneumococci. A total of 334 specimens were examined. There was evidence of pneumonoccal colonisation by culture or coagglutination, or both, in 48 (14.37%), of which 41 (12.27%) yielded S pneumoniae on culture. Anaerobic incubation was better than incubation in carbon dioxide in air for the primary culture of S pneumoniae from sputum. Primary isolation of S pneumoniae was achieved in 11 of the 41 strains (26.82%) by anaerobic incubation alone, by incubation only in carbon dioxide in air in one strain (2.43%), and by both anaerobic incubation and incubation in carbon dioxide in air in 29 strains (70.73%). Anaerobic incubation gave large moist or mucoid colonies that were easy to recognise, but it suppressed the typical draughtsman colony of S pneumoniae. The factor V supplement routinely used in our medium also inhibited the formation of draughtsman colonies. It is suggested that draughtsman colonies occur because of a relative lack of the coenzyme nicotinamide adenine dinucleotide (factor V), which is required as a reducing agent in aspartate and glutamate metabolism. This nutritional deficiency may lead to bacterial cell wall defect and hence to the autolysis which gives the typical draughtsman colony.