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Comparison of media for isolation of salmonellae and shigellae from fecal specimens
Abstract:
Five transport media, eight plating media, and three enrichment broth media for the isolation of salmonellae and shigellae were evaluated. Eight laboratories in widely separated regions of the United States participated in this evaluation by submitting 490 fecal specimens in the transport media provided. The results suggest that the newer transport media may not offer any advantage over the use of buffered glycerol-saline in the isolation of these enteric pathogens. Shigellae were best isolated by direct inoculation, whereas salmonellae were isolated in greater numbers after tetrathionate (without Brilliant Green) enrichment with subsequent culturing on the plating medium. The use of a variety of plating media is recommended for the recovery of a larger number of these enteric pathogens.
Insights
Evaluating transport, plating, and enrichment media for isolating enteric pathogens like salmonellae and shigellae revealed that buffered glycerol-saline remains effective. Direct inoculation best isolates shigellae, while tetrathionate enrichment aids salmonellae recovery.
Area of Science:
- Clinical Microbiology
- Bacteriology
- Diagnostic Microbiology
Background:
- Accurate isolation of enteric pathogens Salmonella and Shigella is crucial for public health.
- Various transport, plating, and enrichment media are available, but their comparative efficacy requires evaluation.
Purpose of the Study:
- To evaluate the performance of different transport, plating, and enrichment media for the isolation of Salmonella and Shigella species.
- To compare newer media formulations against established methods for enteric pathogen detection.
Main Methods:
- Multi-laboratory evaluation involving eight geographically diverse US laboratories.
- Testing of five transport media, eight plating media, and three enrichment broths using 490 fecal specimens.
- Direct inoculation and enrichment methods were employed for pathogen isolation.
Main Results:
- Newer transport media did not demonstrate significant advantages over buffered glycerol-saline for isolating these enteric pathogens.
- Shigellae isolation was most successful via direct inoculation.
- Salmonellae were recovered in higher numbers using tetrathionate enrichment (without Brilliant Green) followed by plating.
Conclusions:
- Buffered glycerol-saline is a reliable transport medium for Salmonella and Shigella.
- A combination of direct inoculation for Shigella and tetrathionate enrichment for Salmonella, alongside diverse plating media, is recommended for optimal recovery.
- Further research into optimized media combinations may improve enteric pathogen detection rates.