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Detection of pneumolysin in sputum
Janice Wheeler1, Roger Freeman1, Michael Steward2
1Newcastle Regional Public Health Laboratory, Westgate Road, Newcastle upon Tyne NE4 6BE.
Abstract:
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.
Insights
Pneumolysin detection via Western blot shows promise for diagnosing pneumococcal chest infections without cultures. This method is nearly as sensitive as PCR and more effective than CPS-CIE, offering a potential new diagnostic tool.
Area of Science:
- Microbiology
- Diagnostic Immunology
- Molecular Diagnostics
Background:
- Accurate diagnosis of pneumococcal chest infections is crucial for effective treatment.
- Traditional culture methods can be slow and may be negative in patients receiving antibiotics.
- Non-cultural diagnostic methods are needed for rapid and sensitive detection of Streptococcus pneumoniae.
Purpose of the Study:
- To evaluate the sensitivity of pneumolysin (SPN) detection by Western blot for non-cultural diagnosis of pneumococcal chest infections.
- To compare the performance of SPN-immunoblotting with Polymerase Chain Reaction (PCR) and counter-current immuno-electrophoresis (CPS-CIE).
Main Methods:
- Western blot analysis for species-specific pneumococcal pneumolysin (SPN).
- Polymerase Chain Reaction (PCR) for bacterial DNA detection.
- Counter-current immuno-electrophoresis (CPS-CIE) for pneumococcal capsular polysaccharide antigens.
- Testing performed on sputum samples from patients with and without confirmed Streptococcus pneumoniae infections.
Main Results:
- SPN-immunoblotting demonstrated 85% sensitivity compared to 100% for PCR and 67% for CPS-CIE in culture-positive samples.
- In culture-negative samples from patients with recent infection, SPN-blot and PCR showed positive results in several cases.
- SPN-blot was negative in culture-negative samples from patients without recent infection, unlike PCR in some instances.
Conclusions:
- Pneumolysin detection by Western blot is a sensitive method for the non-cultural diagnosis of pneumococcal chest infections.
- SPN-immunoblotting shows potential as a valuable diagnostic tool, nearly matching PCR sensitivity.
- Further research is needed to optimize test formats and clarify the clinical significance of pneumolysin detection.