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Recovery of heated Clostridium perfringens type A spores on selective media
Abstract:
The enumeration of Clostridium perfringens spores on sulfite-polymyxin-sulfadiazine agar (SPS), tryptone-sulfite-neomycin agar (TSN), Shahidi-Ferguson-perfringens agar (SFP), tryptone-sulfite-cycloserine agar (TSC), and TSN lacking antibiotics (BASE) was studied. The spores were heated at 105 to 120 C by the capillary-tube method. The media were about equally efficient for the enumeration of heat-activated spores. Efficiency of the media for the recovery of spores surviving heat treatments at ultrahigh temperatures varied as follows: TSC >/= SFP > BASE > SPS > TSN. Greater recovery when survivors were enumerated on TSC or SFP was attributed to germination of injured spores by the lysozyme present in the egg yolk emulsion used in these media. Low recovery of survivors on TSN and SPS was due to both the absence of lysozyme and inhibition of injured spores by the selective agents of these media. Recovery of heated spores was reduced greatly by polymyxin, neomycin, and kanamycin, and slightly by sulfadiazine and D-cycloserine. The addition of lysozyme to SPS or TSN did not improve the percentage of heat-injured spores recovered because the selective agents of these media interfered with the action of lysozyme. The suitability of the selective media for the enumeration of survivors was greatly affected by the presence of certain foods.
Insights
Tryptone-sulfite-cycloserine agar (TSC) and Shahidi-Ferguson-perfringens agar (SFP) are most effective for enumerating heat-stressed Clostridium perfringens spores. Lysozyme aids injured spore recovery, while selective agents in other media inhibit growth.
Area of Science:
- Food Microbiology
- Bacteriology
- Microbial Enumeration Techniques
Background:
- Clostridium perfringens is a significant foodborne pathogen.
- Accurate enumeration of its spores is crucial for food safety assessments.
- Heat treatment is often used to activate or inactivate C. perfringens spores.
Purpose of the Study:
- To evaluate the efficiency of five selective agars for enumerating heat-treated Clostridium perfringens spores.
- To determine the impact of selective agents and lysozyme on the recovery of heat-injured spores.
Main Methods:
- Spores were subjected to heat treatments (105-120°C) using the capillary-tube method.
- Enumeration was performed on five different agar media: SPS, TSN, SFP, TSC, and BASE (TSN without antibiotics).
- The influence of lysozyme and selective agents on spore recovery was investigated.
Main Results:
- All media showed similar efficiency for heat-activated spores.
- For heat-surviving spores, efficiency ranked: TSC ≥ SFP > BASE > SPS > TSN.
- TSC and SFP showed higher recovery due to lysozyme aiding germination of injured spores.
- TSN and SPS exhibited low recovery due to lack of lysozyme and inhibition by selective agents.
- Polymyxin, neomycin, and kanamycin significantly reduced heat-injured spore recovery.
Conclusions:
- TSC and SFP are superior for enumerating heat-stressed Clostridium perfringens spores, particularly when spore injury is a concern.
- The presence of lysozyme in egg yolk emulsion enhances recovery of heat-injured spores.
- Selective agents in media like SPS and TSN can inhibit the recovery of injured spores, necessitating careful medium selection based on expected spore condition.