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Iron milk medium method for recovering Clostridium perfringens from shellfish: collaborative study
1U.S. Food and Drug Administration, Seafood Product Research Center, Bothell, WA 98041.
Abstract:
Eleven laboratories participated in a collaborative study analyzing shellfish (oysters, Crassostrea gigas) for the detection and enumeration of Clostridium perfringens by the iron milk medium (IMM) method. The IMM method was compared to AOAC Official Method 976.30. Shellfish were artificially inoculated with C. perfringens cells (vegetative and spores) at low (1 x 10(3) colony forming units [cfu]/g), medium (1 x 10(4) cfu/g), and high (1 x 10(6) cfu/g) levels. Negative controls (zero level) were analyzed by each laboratory. C. perfringens FD-1, the strain involved in a foodborne illness, was used. Blind duplicates of each inoculum level were analyzed, giving a total of 16 samples per laboratory. The selectivity of IMM relies solely on the rapid growth of C. perfringens at 45 degrees C indicated by stormy fermentation reaction within 18 h. C. perfringens is detected and enumerated using the most probable number technique. A statistical evaluation of the data found no significant differences between the estimates from the 2 methods. The IMM method for detection of C. perfringens from shellfish has been adopted first action by AOAC INTERNATIONAL.
Insights
The iron milk medium (IMM) method accurately detects and quantifies Clostridium perfringens in shellfish. This study found IMM comparable to the official AOAC method for C. perfringens enumeration in oysters.
Area of Science:
- Food Microbiology
- Microbial Detection Methods
- Seafood Safety
Background:
- Clostridium perfringens is a significant foodborne pathogen.
- Accurate detection and enumeration in shellfish are crucial for public health.
- Existing methods require validation for new applications.
Purpose of the Study:
- To evaluate the efficacy of the iron milk medium (IMM) method for detecting and enumerating Clostridium perfringens in oysters (Crassostrea gigas).
- To compare the performance of the IMM method against the established AOAC Official Method 976.30.
- To validate a rapid method for C. perfringens analysis in shellfish.
Main Methods:
- Collaborative study involving eleven laboratories.
- Artificial inoculation of shellfish with known levels of C. perfringens (vegetative cells and spores).
- Comparison of IMM method with AOAC Official Method 976.30 using most probable number technique.
Main Results:
- No significant statistical differences were observed between the IMM method and AOAC Official Method 976.30 for C. perfringens enumeration.
- The IMM method demonstrated reliable performance across low, medium, and high inoculation levels.
- The selectivity of IMM relies on rapid C. perfringens growth at 45°C, indicated by stormy fermentation.
Conclusions:
- The iron milk medium (IMM) method is a reliable and effective technique for the detection and enumeration of Clostridium perfringens in shellfish.
- The IMM method offers a viable alternative to existing official methods, with comparable accuracy.
- AOAC INTERNATIONAL has adopted the IMM method as a first action for C. perfringens detection in shellfish.