Related Experiment Videos
Multiple plating from enrichment media as an aid to salmonella isolation
Abstract:
Faeces samples enriched for salmonellas in selenite F broth incubated at 43 degrees C were subcultured to brilliant green MacConkey agar after 6 h. Four platings were made. As a control technique, each sample was enriched in selenite F incubated at 37 degrees C for 24 h and subcultured once to brilliant green MacConkey agar. Of the specimens plated at 6 h, out of a total of 25 positive samples, 6 required more than a single subculture to reveal the presence of salmonellas. Twenty-four positive isolations were made from the selenite broths incubated at 37 degrees C for 24 h and subcultured once only. All faecal samples positive by enrichment were also positive by direct plating. Nine samples seeded by 6 h produced only 1-2 salmonella colonies per plate. Convalescent specimens are, therefore, unlikely to be efficiently diagnosed by early subculture even if it is combined with multiple plating.River Taff samples, after pre-enrichment in buffered peptone water, were enriched in Rappaport's medium at 37 degrees C for 6 h. Subcultures were made to four plates of brilliant green MacConkey agar. A control subculture was made at 24 h to a single plate of brilliant green MacConkey. Although multiple subculture at 6 h improved salmonella isolation, the method was not as efficient as a single plating from the same enrichment culture at 24 h. There was no evidence that subculture at 6 h combined with multiple plating had a value either for faecal examination or for the isolation of salmonellas from sewage-polluted natural water.Samples of other natural waters submitted routinely by Environmental Health Officers were pre-enriched in buffered peptone water before subculture to Rappaport's medium. The enrichment cultures were incubated at 37 degrees C for 24 h and duplicate platings were made to brilliant green MacConkey agar. By double plating at 24 h, a gain of 16% in salmonella recovery was made. This compares favourably with the gain obtained by subculture from Rappaport after 24 and 48 h incubation. It also saves 24 h in examination time.
Insights
Early subculturing of salmonella from faeces is inefficient, even with multiple plates. Delayed plating from enrichment cultures improves salmonella isolation from faecal and water samples.
Area of Science:
- Microbiology
- Food Safety
- Environmental Science
Background:
- Salmonella detection is crucial for public health.
- Optimizing laboratory methods for Salmonella isolation is essential for timely diagnosis and surveillance.
Purpose of the Study:
- To evaluate the efficiency of early (6-hour) versus delayed (24-hour) subculturing for Salmonella isolation.
- To compare single versus multiple plating techniques in Salmonella detection.
Main Methods:
- Faecal and natural water samples were enriched using selenite F broth and Rappaport's medium.
- Subcultures were performed at different time points (6h and 24h) onto brilliant green MacConkey agar.
- Multiple plating strategies were assessed against single plating controls.
Main Results:
- Early subculturing (6h) from faecal samples required multiple platings and was less efficient than 24h incubation.
- For natural water samples, 6h subculturing with multiple plates was less efficient than single plating at 24h.
- Double plating at 24h for natural water samples increased Salmonella recovery by 16% and saved examination time.
Conclusions:
- Early subculturing is not recommended for efficient Salmonella diagnosis in faecal samples.
- Delayed plating (24h) with optimized methods, like double plating for water samples, enhances Salmonella recovery and diagnostic efficiency.