APPENDIX 4

Bacterial Pathogen Growth and Inactivation

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This appendix contains information on the growth and inactivation of bacterial pathogens.

Table #A-1 contains information on: the minimum water activity (a_w), acidity (pH), and temperature; the maximum, pH, water phase salt, and temperature; and oxygen requirements that will sustain growth for the bacterial pathogens that are of greatest concern in seafood processing. Data shown are the minimum or maximum values, the extreme limits reported among the references cited. These values may not apply to your processing conditions.

Table #A-2 contains information on maximum, cumulative time/internal temperature combinations for exposure of fish and fishery products that, under ordinary circumstances, will be safe for the bacterial pathogens that are of greatest concern in seafood processing. These maximum, cumulative exposure times are derived from published scientific information. Because the nature of bacterial growth is logarithmic, linear interpolation using the time/temperature guidance is not appropriate.

In summary, the table indicates that:

• If the product is held at internal temperatures above 70°F (21°C) during processing, exposure time should ordinarily be limited to two hours (three hours if Staphylococcus aureus is the only pathogen of concern);
• If the product is held at internal temperatures above 50°F (10°C), but not above 70°F (21°C), exposure time should ordinarily be limited to six hours (twelve hours if Staphylococcus aureus is the only pathogen of concern);
• If the product is held at internal temperatures both above and below 70°F (21.1°C), exposure times above 50°F (10°C) should ordinarily be limited to 4 hours, as long as no more than 2 of those hours are above 70°F (21.1°C).

It is not possible to furnish recommendations for each pathogen, process, type of seafood, and temperature or combination of temperatures. Programmable models to predict growth rates for certain pathogens associated with various foods under differing conditions have been developed by the U.S. Department of Agriculture ("Pathogen Modeling Program" [PMP]) and the United Kingdom ("Food MicroModel" [FMM]). These programs can provide growth curves for selected pathogens. You indicate the conditions, such as pH, temperature, and salt concentration that you are interested in and the models provide pathogen growth predictions (e.g., growth curve, time of doubling, time of lag phase, generation time). FDA does not endorse or require the use of such modelling programs, but recognizes that the predictive growth information they provide may be of assistance to some processors. However, you are cautioned that significant deviations between actual microbiological data in specific products and the predictions do occur, including those for the lag phase of growth. Therefore, you should validate the time-temperature limits derived from such predictive models.

Table #A-3 contains information on the destruction of Listeria monocytogenes. Lethal rate, as used in this table, is the relative lethality of one minute at the designated internal product temperature as compared to the lethality of one minute at the reference internal product temperature of 158°F (70°C) (i.e. z = 13.5°F [7.5°C]). For example, one minute at 145°F (63°C) is 0.117 times as lethal as one minute at 158°F (70°C). The times provided are the length of time at the designated internal product temperature necessary to deliver a 6D process for L. monocytogenes. The length of time at a particular internal product temperature needed to accomplish a six logarithm reduction in the number of L. monocytogenes (6D) is, in part, dependent upon the food in which it is being heated. The values in the table are generally conservative and apply to all foods. You may be able to establish a shorter process time for your food by conducting scientific thermal death time studies. Additionally, lower degrees of destruction may be acceptable in your food if supported by a scientific study of the normal innoculum in the food.

Table #A-4 contains information on the destruction of Clostridium botulinum type B (the most heat resistant form of nonproteolytic Clostridium botulinum). Lethal rate, as used in this table, is the relative lethality of one minute at the designated internal product temperature as compared to the lethality of one minute at the reference product internal temperature of 194°F (90°C) (i.e. for temperatures less than 194°F [90°C] z = 12.6°F [7.0°C] ; for temperatures above 194°F [90°C] z = 18°F [10°C];). The times provided are the length of time at the designated internal product temperature necessary to deliver a 6D process for C. botulinum. The values in the table are generally conservative. However, they may not be sufficient for the destruction of nonproteolytic C. botulinum in dungeness crabmeat, because of the potential protective effect of lysozyme. You may be able to establish a shorter process time for your food by conducting scientific thermal death time studies. Additionally, lower degrees of destruction may be acceptable in your food if supported by a scientific study of the normal innoculum in the food.

See also:

FDA Seafood List

Foodborne Pathogenic Microorganisms and Natural Toxins Handbook (Bad Bug Book)

Seafood Information and Resources

Seafood HACCP   |   Fish & Fisheries Products Hazards & Controls Guidance: 3rd Edition (2001)

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