Delayed-Incubation Method for Microbiological Analysis of Environmental Specimens and Samples

Five laboratories compared the quantitative recovery of heterotrophic bacteria, yeasts and molds, coliforms, Escherichia coli , Pseudomonas aeruginosa , and Staphylococcus aureus from a variety of naturally contaminated food and water samples, using traditional incubation procedures and a delayed-incubation method. Refrigeration of inoculated media for up to 3 days prior to incubation was shown to be a viable option for many quantitative analyses, but needs to be validated for each application. Some inoculated media withstood refrigeration for up to 7 days prior to incubation without any detrimental effect on the recovery of target cells, while the incubation of other media for similar types of analyses could not be delayed even for 3 days.