Western blot detection of the species-specific pneumococcal product,
pneumolysin (SPN), was shown to be almost as sensitive as PCR for the non-cultural detection of pneumococci in 27 Streptococcus pneumoniae culture-positive sputa from patients stated to have chest
infections. Both techniques were considerably more sensitive than counter-current immuno-electrophoresis for pneumococcal capsular
polysaccharide antigens (CPS-CIE) on the same specimens. Sensitivities for PCR, SPN-immunoblotting and CPS-CIE were 100%, 85% and 67%, respectively. In 11 S. pneumoniae culture-negative sputa taken from patients receiving
antibiotics, but with proven recent
pneumococcal infection, 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 receiving
antibiotics, all three tests were negative in eight, PCR was positive in three (in one of which CPS-CIE was also positive), but SPN-blot was negative in all 11. In 16 S. pneumoniae culture-negative samples from patients receiving
antibiotics and with no known recent
pneumococcal infections, one or more non-cultural test was positive in 11. Although further evaluation is 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 approach to the non-cultural diagnosis of pneumococcal chest
infection.