美国食品药品局细菌分析手册（BAM）第 2 章：食品的显微镜检查（2000 年 11 月版）BAM Chapter 2 Microscopic Examination of Foods

If there is reason to suspect that a food has caused food poisoning or has undergone microbial spoilage, the original product or a low serial dilution of it should be used to prepare a slide for direct microscopic examination. The Gram stain reaction and cellular morphology of the bacteria on the slide may indicate the need for other types of examination. A microscopic examination must be made, even though the food may have undergone heat treatment and the microorganisms involved may no longer be viable. Large numbers of Gram-positive cocci on the slide may indicate the presence of staphylococcal enterotoxin, which is not destroyed by the heat treatments that destroy enterotoxigenic Staphylococcus aureus strains. Large numbers of sporeforming, Gram-positive rods in a frozen food specimen may indicate the presence of Clostridium perfringens, an organism that is sensitive to low temperatures. Other Gram-positive, sporeforming rods such as Clostridium botulinum or Bacillus cereus may also be present in the food. When the microscopic examination of suspect food discloses the presence of many Gram-negative rods, consider the symptoms and incubation periods reported for the illness under investigation and select the specific examination method for isolating one or more of the following genera: Salmonella, Shigella, Escherichia, Yersinia, Vibrio, or Campylobacter.

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