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False no-growth blood cultures in pneumococcal pneumonia
Abstract:
The growth of Streptococcus pneumoniae in commercial media containing 14C-labeled substrates was studied experimentally; the results of blood cultures that were positive for S. pneumoniae over a 14-month period were analyzed to explain no-growth but radiometrically positive blood cultures from four patients with clinically diagnosed pneumococcal pneumonia. The growth of S. pneumonoiae in aerobic blood culture vials resulted in a chocolate color in the medium. S. pneumoniae grew rapidly in both aerobic and anaerobic media, but 14CO2 evolved from the metabolism of the labeled substrates was detected only in the aerobic culture vials. Radiometric detection lagged behind growth of the organisms and was accompanied by visual changes in the media. By 24 h, the viability of the culture was on the decline; radiometric readings remained positive even when the culture had died.
Insights
Radiometric detection of Streptococcus pneumoniae (S. pneumoniae) in blood cultures can remain positive even after the organism has died, potentially explaining false-positive results in diagnosing pneumococcal pneumonia.
Area of Science:
- Microbiology
- Clinical Diagnostics
- Infectious Diseases
Background:
- Streptococcus pneumoniae is a leading cause of bacterial pneumonia.
- Accurate and timely diagnosis of pneumococcal pneumonia is crucial for effective treatment.
- Radiometric methods are used in blood cultures to detect microbial growth.
Purpose of the Study:
- To investigate the discrepancy between radiometric signals and actual S. pneumoniae viability in blood cultures.
- To explain cases of no-growth but radiometrically positive blood cultures in patients with pneumococcal pneumonia.
Main Methods:
- Experimental study of S. pneumoniae growth in 14C-labeled media.
- Analysis of blood culture results from patients with S. pneumoniae over 14 months.
- Monitoring of radiometric detection, visual changes, and organism viability.
Main Results:
- S. pneumoniae grew in both aerobic and anaerobic media, with 14CO2 evolution observed only in aerobic cultures.
- Radiometric detection lagged behind organism growth and visual changes in the medium.
- Positive radiometric readings persisted even after S. pneumoniae viability declined or the culture died.
Conclusions:
- Radiometric detection in blood cultures may not always correlate with viable S. pneumoniae.
- The persistence of radiometric signals post-viability loss can lead to false-positive interpretations.
- This finding helps explain no-growth but radiometrically positive blood cultures in pneumococcal pneumonia cases.