DisplayTitle

42 Microorganisms Methods​

42-10.01 Microorganisms—Sampling Procedure

Sampling protocols described in this method are for collection, transport, and storage of food samples for microbial analysis. Results from such analyses are as good as the sampling technique. Sampling must be performed correctly to represent the whole food production lot.

42-11.01 Aerobic Plate Count

This method measures the total number of aerobic mesophilic bacteria contained in a food product or ingredient. High counts in finished products can be related to contaminated raw ingredients, underprocessing, or mishandling during processing. This method is applicable to all types of food products and ingredients.

42-15.02 Coliform—E. coli

The coliform/E. coli count can be a part of a measure of the overall quality of a food product or ingredient. Generally, high coliform counts indicate low product quality. In finished products, high coliform counts can be related to contaminated raw ingredients, underprocessing, or mishandling during or after processing. Elevated counts could indicate a potential health hazard in which pathogens and or toxins may be present. If coliform counts are high, conditions may be favorable for pathogenic bacteria. The identification of Escherichia coli in products or ingredients can indicate possible fecal contamination. This method is applicable to all types of food products and ingredients.

42-17.02 Clostridium perfringens Enumeration

This method details the procedure for identification and enumeration of Clostridium perfringens. C. perfringens is a spore-forming, anaerobic bacillus that is commonly found in meat, meat products, spices, and most raw foods. It can cause food poisoning when foods are cooked and held without cooling or heating the food adequately, allowing germination of spores and rapid growth to high numbers. An enterotoxin produced by C. perfringens can cause abdominal cramping and diarrhea within 8-15 hr after ingestion of contaminated food.

42-20.01 Rope Spore Count

To detect rope-producing spores in cereals and cereal products.

42-25.03 Salmonella Bacteria

This method is for the detection of Salmonella spp. in finished cereal products and other grain products with expected low rates of microbial contamination. Salmonella is a foodborne pathogen that causes enteric and systemic illness if ingested. The method described here is adapted from the Food and Drug Administration's AOAC-approved conventional Salmonella method. Current Salmonella methods (both conventional and rapid) serve to isolate and select Salmonella spp. (including injured bacteria), if present in a food sample, for detection.

42-30.04 Enumeration of Staphylococcus aureus

Staphylococcus aureus is a microorganism that can produce a heat-stable enterotoxin. Consumption of foods containing staphylcoccal enterotoxin has resulted in illness. The enumeration of S. aureus is important, but results need to be interpreted carefully. In most cases, large numbers of the pathogen must be present to produce enough enterotoxin to elicit a clinical response. Foods containing large numbers of S. aureus are not necessarily unsafe. It is therefore important to determine whether the isolated strain is enterotoxigenic or possesses markers that are linked to toxigenic strains (i.e., coagulase). Additionally, it is essential that the history of the suspect food be determined. Temperature abuse of foods, particularly those containing a protein source, and how the product was processed and handled must be reviewed. Understanding how the food was processed is important, since heating may destroy S. aureus cells but does not inactivate the heat-stable enterotoxin. In such a case, the levels of S. aureus would be low or not present, but the food would pose a health hazard if consumed. This has been shown with foods such as dried pasta and canned mushrooms. Coagulase-positive staph are also commonly used when developing microbiological specifications for foods and food ingredients. They can be a concern if that food or food ingredient contains protein or is destined for use in protein-containing foods. The method is applicable to all raw and processed foods and ingredients.

42-35.01 Enterococci

To make an estimate of total number of enterococci present in food products or ingredients. Historically, Group D streptococci have been referred to as enterococci due to the Group D antigen. Some enterococci have been implicated in foodborne disease outbreaks, although most are regarded as nonpathogenic. Enterococci levels in foods can vary with the product, storage conditions, and storage duration. These organisms grow on vegetation and are highly resistant to drying, detergents, disinfectants, and high and low temperatures. The presence of these microorganisms in foods is not necessarily an indication of fecal contamination.

42-40.01 Thermophilic Spore Counts (Total Aerobic, Flat-Sour, H2S, Non-H2S Anaerobic)

To detect and enumerate total aerobic spores, flat sour organisms, anaerobic spores producing H2S (sulfide spoilage), and anaerobic gas-producing spores in cereal products.

42-45.01 Thermophilic and Psychrotrophic Bacteria

To make an estimate of total number of thermophilic and psychrotrophic bacteria present in food products or ingredients. a) Thermophilic bacteria possess the characteristic to grow above 43° and optimally at 50-60°. These bacteria may spoil low-acid foods held in this temperature range. Thermophilic bacteria are nonpathogenic spore-formers present in cultivated soils and thus contaminate agricultural commodities in small numbers. Sugars and starches may contain high levels of thermophilic bacteria. These organisms may also occur on processing equipment held warm for extended periods. They can cause spoilage of hermetically sealed products that are inadequately cooled and subsequently stored at high temperature. b) Psychrotrophic bacteria can grow at refrigeration temperatures and are defined as those that produce visible growth at 7 ± 1° within 7-10 days. These microorganisms are commonly associated with refrigerated foods and can cause spoilage if food is held under refrigeration for extended periods of time. Other pathogenic microorganisms, Listeria monocytogenes, may grow below 7°.

42-50.02 Mold and Yeasts Counts

To detect and enumerate viable fungi associated with cereals, cereal products. The method is applicable to all types of food products and ingredients.

42-56.01 Ergot—Ether-Bicarbonate Method

Ergot is a fungal disease of the inflorescence of cereals and grasses caused especially by Claviceps purpurea. A diseased plant develops a dark sclerotium or ergot body in place of a healthy kernel; the body contains a range of toxic alkaloids that contaminate the grain. This method is applicable to wheat and rye. The Official U.S. Standards for Grain define ergoty wheat and rye as grains that contain, respectively, more than 0.05% and 0.30% ergot.

42-70.01 Smut—Microscopic Method

The Official U. S. Standards for Grain define light smutty wheat or rye as grain that has an unmistakable odor of smut, or that contains smut balls, portions of smut balls, or spores of smut in excess of a quantity equal to 5 smut balls, but not in excess of a quantity equal to 30 smut balls of average size, in 250 g of wheat or rye. In smutty wheat or rye, however, the corresponding quantity of smut is in excess of 30 smut balls.

When balls are unbroken, application of the above rule is not difficult. However, when balls become broken and spores are spread all over the kernels, this method will determine the equivalent of smut balls present in 250 g. One average size smut ball weighs 0.01 g and contains, on average, 3,750,000 spores.

42-71.01 Smut—Sedimentation Method

This simple, accurate, and inexpensive method determines the total amount of smut in wheat. The results are linearly correlated with those from the basic microscopic count (Method 42-70). The method may be used in routine inspection under the official U.S. grain standards. It is similarly applicable to rye.