A compilation of material describing what bacteria the Aerobic Plate Count analysis detects and what the results mean.

The Aerobic Plate Count (APC) is used as an indicator of bacterial populations on a sample. It is also called the aerobic colony count, standard plate count, Mesophilic count, or Total Plate Count.

The test is based on an assumption that each cell will form a visible colony when mixed with agar containing the appropriate nutrients. It is not a measure of the entire bacterial population; it is a generic test for organisms that grow aerobically at mesophilic temperatures (25 to 40°C; 77 to 104°F).

APC does not differentiate types of bacteria.

APC can be used to gauge sanitary quality, organoleptic acceptability, adherence to good manufacturing practices, and, to a lesser extent, as an indicator of safety. APC may also provide information regarding shelf life or impending organoleptic change in a food.

APCs are poor indicators of safety in most instances, since they do not directly correlate to the presence of pathogens or toxins. A low APC result does not mean the product or ingredient is pathogen-free. However, some products or ingredients showing excessively or unusually high APCs may reasonably be assumed to be potential health hazards, pending pathogen screening results. Interpretation of the APC results must take into consideration knowledge of the product and whether a high APC is expected.

Depending on the situation, APC can be valuable in evaluating food quality. Large numbers of bacteria may be an indication of poor sanitation or problems with process control or ingredients. Certain products, such as those produced through fermentation, naturally have a high APC. Again, low APC numbers do not equate to an absence of pathogens. Often, it is necessary to assay foods for specific pathogens or spoilage organisms before ruling on food safety or food quality.

Quality and safety guidelines or specifications are often applied to raw materials and finished goods. Using APC for ingredients may or may not be appropriate as a quality indicator. A food manufacturer’s decision to apply APC guidelines on ingredients must be based on the ingredient’s effect on the finished product. For instance, in dried foods, APC can be used as a means of assessing the adequacy of moisture control during the drying process. For meats, APC can be used to check the condition of incoming carcasses to potentially identify suppliers with excessively high counts. APC can also be used to evaluate sanitary conditions of equipment and utensils. This can be done during processing to monitor buildup and after sanitation to gauge its effectiveness.

The table below offers some general guidelines for expected aerobic plate counts on ingredients and finished products. Bear in mind, APC specifications are not always appropriate. For example, raw agricultural commodities can have widely fluctuating plate counts. In these situations, APC can provide meaningful data to the processor who has a better understanding of factors that may influence the count, but they provide little value in relation to acceptance criteria.