Detection of pneumolysin in sputum

Western blot detection of the species-specific pneumococcal product, pneumo lysin (SPN), was shown to be almost as sensitive as PCR for the non-cultura l detection of pneumococci in 27 Streptococcus pneumoniae culture-positive sputa from patients stated to have chest infections. Both techniques were c onsiderably more sensitive than countercurrent immuno-electrophoresis for p neumococcal capsular polysaccharide antigens (CPS-CIE) on the same specimen s. Sensitivities for PCR, SPN-immunoblotting and CPS-CIE were 100%, 85% and 67%, respectively. In 11 S. pneumoniae culture-negative sputa taken from p atients receiving antibiotics, but with proven recent pneumococcal infectio n, PCR and SPN-blot were positive in six (in two of which CPS-CIE was also positive), PCR alone was positive in one and SPN-blot alone was positive in one. In 11 S. pneumoniae culture-negative samples from patients not receiv ing antibiotics, all three tests were negative in eight, PCR was positive i n three (in one of which CPS-CIE was also positive), but SPN-blot was negat ive in all 11. In 16 S, pneumoniae culture-negative samples from patients r eceiving antibiotics and with no known recent pneumococcal infections, one or more non-cultural test was positive in 11. Although further evaluation i s required to assess the significance of pneumolysin detection in relation to carriage and infection and to devise a more suitable test format, these preliminary studies suggest that pneumolysin detection is a promising new a pproach to the non-cultural diagnosis of pneumococcal chest infection.