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Comparison of media and methods for counting Clostridium perfringens in poultry meat and further-processed products
Abstract:
A Most Probable Number (MPN) method involving Differential Reinforced Clostridial Medium followed by streaking on Willis & Hobbs medium was compared with direct plating of samples on Tryptose-Sulphite-Cycloserine agar without egg yolk, and two forms of Oleandomycin-Polymyxin-Sulphadiazine-Perfringens agar, one being prepared from a commercial, dehydrated product. With skin samples taken from chicken carcasses at different stages of processing, the three direct plating media gave similar counts of Cl. perfringens whereas results obtained with the MPN method were consistently lower. Although counts of Cl. perfringens from various further processed products were usually less than 10/g, the three plating media showed similar specificity for this organism. All media supported good growth of reference strains of Clostridium perfringens but it was found that physiologically similar species, including Cl. absonum, Cl. paraperfringens and Cl. perenne also grew uninhibited in these media and produced colonies identical with those of Cl. perfringens, thus indicating the need for confirmatory tests for Cl. perfringens when examining natural samples.
Insights
Direct plating methods offer higher Clostridium perfringens counts than the Most Probable Number (MPN) method for chicken samples. However, confirmatory tests are essential due to similar growth of related species on all tested media.
Area of Science:
- Food Microbiology
- Microbial Detection Methods
- Poultry Science
Background:
- Accurate enumeration of Clostridium perfringens is crucial for food safety, particularly in poultry processing.
- Traditional methods like Most Probable Number (MPN) and direct plating are used for Cl. perfringens detection.
Purpose of the Study:
- To compare the efficacy of an MPN method with three direct plating media for quantifying Clostridium perfringens in chicken samples.
- To assess the specificity of the tested media for Cl. perfringens.
Main Methods:
- Comparison of a Most Probable Number (MPN) method with three direct plating media: Tryptose-Sulphite-Cycloserine (TSC) agar and two variations of Oleandomycin-Polymyxin-Sulphadiazine-Perfringens (OPSP) agar.
- Samples included chicken skin from various processing stages and further processed chicken products.
- Evaluation of colony morphology and growth of reference strains and physiologically similar species.
Main Results:
- Direct plating methods yielded consistently higher counts of Cl. perfringens than the MPN method for chicken skin samples.
- All three direct plating media demonstrated similar specificity for Cl. perfringens in further processed products (counts <10/g).
- Physiologically similar species (e.g., Cl. absonum, Cl. paraperfringens, Cl. perenne) grew on all media, producing colonies indistinguishable from Cl. perfringens.
Conclusions:
- Direct plating methods are more effective for enumerating Cl. perfringens in chicken processing samples compared to the MPN method used.
- Confirmatory identification tests are necessary when using these media for Cl. perfringens detection in natural samples due to cross-reactivity with similar species.