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Food Safety 237

examined. Then growth and colony characteristics of bacterial Table 11-3. Procedures for the collection, transfer and
VetBooks.ir isolates will be determined using a variety of media. The pres- preservation of physical evidence.*
ence or absence of certain bacterial biochemical characteristics
and atmospheric growth conditions will also be explored.
• Collect, package and identify all samples according to the
Finally, a variety of other tests and techniques will be used to procedures listed in Table 11-4.
• Maintain a record of every person who had custody of any
facilitate the identification process (e.g., API 20E strips and sample(s) or other evidence from the time that it was collect-
Staph-Trac). d ed until presented in court (“chain of custody”) by keeping a
written log or diary of all relevant facts and sample transfers.
• Write notes documenting the time, place, description and
Analytical Chemistry circumstances of all samples entered in the log. Describe in
Metal assays are usually performed using some type of atom- detail how the samples were identified (numbered),
ic spectroscopy, e.g., atomic absorption spectroscopy and processed, packaged, stored and shipped.
• If possible, photograph any apparent pathologic lesions,
inductively coupled plasma emission spectroscopy (Galey, mold growth, foreign matter in the food, etc. Number the
1992). Organic compounds such as pesticides and solvents are photographs consecutively and describe each photograph in
usually detected by chromatography, e.g., gas chromatogra- the written notes.
• Write notes about all telephone conversations related to the
phy, high-pressure liquid chromatography, thin-layer chro- case in the log, including the date, time and content of the
matography. After a compound has been identified prelimi- conversation.
narily by chromatography, results are often confirmed using • Date all new entries in the log and have the person writing in
the log initial the entry.
mass spectrometry. • Retain and store all relevant product labels in a safe place.
Mycotoxins can be detected by chromatography methods, • Use a shipping method that expedites delivery of the sam-
radioimmunoassay (RIA) and enzyme-linked immunosorbent ples to the laboratory. Keep copies of all shipping records.
Hand carry the samples to the laboratory if possible. Obtain
assay (ELISA) (Quinn et al, 1994). Staphylococcal enterotoxins written proof of delivery (e.g., receipt).
can be identified using ELISA, RIA, serologic, precipitin and *Adapted from Grau JJ. Criminal and Civil Investigation
gel diffusion techniques (Freer and Arbuthnott, 1986). ELISA Handbook, 2nd ed., New York, NY: McGraw-Hill, Inc, 1993.
can also be used to detect the exotoxins and endotoxins of other
bacterial species. C. botulinum exotoxins can be identified by
serum neutralization using commercially available antisera fol- However, measurement of microbial populations may yield
lowed by assay in laboratory animals (Quinn et al, 1994). valuable information when used to compare one sample of a pet
food with another sample of the same product. For example, it
Significant Pathogen Levels in Food would be valuable to know whether bacterial numbers had
Commercial foods are not sterile and may contain species of increased dramatically while the food was in the pet’s bowl.
organisms associated with foodborne illnesses in people. This information helps establish the level of hygiene and time-
However, the infective dose of each foodborne pathogen can liness of the pet’s feeding schedule. In summary, the presence of
vary greatly depending on the food substrate, the immunologic an organism in a food does not alone establish the diagnosis but
status of the host and the resistance of the normal intestinal must be considered as one piece of the diagnostic “puzzle.”
flora (Council for Agricultural Science and Technology, 1994).
The same factors apply to foodborne illness in animals with Control and Prevention
the exception that the animal species can also influence the Methods for control and prevention of foodborne illness in pets
infective or toxic dose. Therefore, the relationship between apply to commercial (after purchase) and home-prepared
microbial populations and the quality of foods can only be esti- foods. Following the practices described in Table 11-5 can best
mated and must be viewed with caution, especially when one prevent foodborne illnesses in pet foods.
considers that most sampling and microbial counting proce- Food storage is an important preventive measure. Proper
dures possess inherent inaccuracies. Also, many organisms have storage depends on control of: 1) temperature, 2) moisture and
fastidious growth and unique colonization requirements (i.e., 3) availability of oxygen. First, high temperatures markedly
medium, temperature and atmosphere). Although laboratory decrease the shelf life of both canned and dry foods, especially
personnel will try various permutations, it is not always possi- when temperatures exceed 20°C (68°F) (Emsminger et al,
ble to find the correct combination given the limitations of 1995; Containers, 1968). Therefore, all commercial pet foods
sample size. In addition, the specimen may contain a microor- should be stored in the 4.4 to 15.6°C (40 to 60°F) temperature
ganism that produces antimicrobial peptides that inhibit the range. Fresh, home-prepared foods should be refrigerated at
growth of other species. Finally, the various counting proce- –1.6 to 15.5°C (29 to 60°F) before feeding. (Most household
dures will also kill some of the bacteria present in the sample. refrigerators hold foods at 4.4 to 7.2°C [40 to 45°F].) The
The scientific literature contains few data establishing the length of time that a food can be kept refrigerated depends on
relative risk of foodborne illness and the microbial content of its type and age. Fresh meats, fish and poultry can be kept for
pet foods. Measuring the microbial content of pet foods is dif- two to 10 days whereas fruits and vegetables will remain whole-
ficult but interpreting the results with respect to wholesome- some for weeks when refrigerated.
ness or food safety is even more difficult because risk quantifi- Moist products are sealed and therefore not affected by mois-
cation also depends on other factors, such as storage conditions. ture or air; control of these factors applies only to storage of