Sampling
Sample the entire portion of food (whole roast, chicken, gravy, etc.) or take representative samples of 25 g each from different parts of the suspect food because contamination may be unevenly distributed.
Transporting and storage of samples
Transport and examine samples promptly without freezing, if possible, and store at about 10°C until examined. If analysis cannot be started within 8 h or if the sample must be shipped to the laboratory for analysis, treat it with sterile buffered glycerin-salt solution, store immediately at -70 to -90°F, and transport it to the laboratory with dry ice, as described below.
Use aseptic technique to prepare sample for storage or shipment. Transfer 25 g portion of sample (sliced beef, turkey, hash, etc.) to sterile 150 ml container, such as plastic Whirl-Pak bag. Add 25 ml buffered glycerin-salt solution, exclude air from bag, and mix the sample well with glycerin solution. Liquid samples such as gravy or beef juice should be mixed well with equal volume of double strength buffered glycerin-salt solution.
Store glycerin-treated samples immediately at -70 to -90°F in low temperature freezer or with dry ice so that freezing occurs as quickly as possible. Maintain samples at this temperature until analysis. Thaw samples at room temperature and transfer sample and glycerin-salt solution to sterile blender jar. Add 200 ml peptone dilution fluid to blender jar and proceed with examination.
If sample must be shipped to the laboratory, follow procedures above and pack frozen sample in contact with dry ice to maintain temperature as low as possible during shipment. Pack sample in a container such as a paint can or Nalgene bottles which are impervious to CO gas, because absorption of CO2 by the sample could lower the pH and diminish the viability of C. perfringens. Store sample at -70 to -90°F on receipt and keep at this temperature until examined, preferably within a few days.