The Standard Plated Count is a test performed to determine the total bacterial count of a milk sample. This test is conducted on almost all milk samples (IMS, Raw and County Samples) except those that are made with bacterial cultures, such as buttermilks, dips, sour creams and yogurts. The test is performed by removing a very small portion of milk, 0.1 mL and 0.01 mL for pasteurized products and 0.01 mL and 0.001 mL for Raw Milk, then mixing them with a growth medium. To put these volumes in perspective, 1 ounce equals 29.57 mL. The bacteria are allowed to grow in an incubator for 48 hours and then counted. Pasteurized milk is allowed to contain 20,000 colonies of bacteria, referred to as colony forming units (cfu) per mL of sample (cfu/mL). Raw milk, prior to pasteurization, from each farm can contain up to 100,000 cfu/mL and once it is mixed together with other farms, it can have up to 300,000 cfu/mL.
All pasteurized milk and milk products (from both the IMS and County Programs), including the buttermilks, dips, sour creams and yogurts are tested for Coliform Bacteria. For this test, 1.0 mL of sample is mixed with a growth media that is specific for coliform bacteria. The coliform bacteria are then allowed to grow in an incubator for 24 hours and then counted. Coliform, if present in a milk sample, is generally considered to be a contamination problem that occurs after pasteurization. Milk is allowed to have 10 coliform colonies per mL.
All milk with the IMS Program is subject to the Alkaline Phosphatase Test. Alkaline Phosphatase (ALP) is an enzyme that naturally occurs in raw milk. This enzyme is deactivated during the pasteurization process. ALP can be found in pasteurized milk if it has been contaminated with raw milk. This is referred to as Residual Phosphatase. ALP can be reactivated in pasteurized milk that is not properly handled after pasteurization and allowed to warm up for an extended period of time. This is referred to as Reactivated Phosphatase. Certain types of microorganisms can produce a type of ALP, this is referred to as Microbial Phosphatase. The Environmental Microbiology Section has an instrument that is capable of quantifying the amount of ALP in milk samples. The procedure consists of adding a milk sample to a reagent and then using an instrument to measure the production of a special compound. This is then converted to the amount of ALP activity and reported in milli units per liter (mU/L). Activity above 350 mU/L is considered positive of ALP. The laboratory has special procedures that can then be used to determine the type of ALP present (Residual, Reactivated or Microbial). Residual ALP above 350 mU/L will result in an immediate product recall. As little as 0.006% raw milk can be detected with this instrument.
Somatic Cell Counts are conducted only on raw milk. Somatic cells are also referred to as leucocytes or white blood cells and their presence in high numbers can indicate an infection in the cow's udder, such as mastitis. The somatic cell count can be determined electronically by using an electronic somatic cell counter or by preparing and staining microscope slides and then counting the somatic cells under 1,000X magnification. Somatic Cell Counts above 750,000/mL are considered high.
Antibiotic Drug Residues are one of the hottest subjects in the dairy industry to date. The push to eliminate drug residues in the nation's milk took a radical turn in December 1989 with a Wall Street Journal Article announcing milk contaminated with antibiotic drug residues. Exposing the population to low levels of antibiotics increases the risk of creating bacteria that are resistant to these antibiotics. Prior to this date, random milk samples were checked in the laboratory for drug residues. After this date, the NCIMS and FDA set up protocol that required all raw milk be checked for drug residues before it is received by the dairy plant. Also included was protocol that provided oversight by the states to ensure that dairy plant personnel were adequately trained to perform antibiotic drug residue testing.
Several staff members of the Environmental Microbiology Section has been trained by the FDA-LPET as a Laboratory Evaluation Officer (LEO). The LEO has the responsibility of training the Dairy Industry Supervisors/Back-up Supervisors by conducting hands-on training sessions once every three years, providing oversight by performing bi-annual on-site inspections of Dairy's drug testing facilities/analysts and annually, preparing milk samples spiked with drug concentrates for every analyst in the state to test.
Even with all this training and oversight, the dairies are only approved to screen the milk. Any milk that is found to contain drug residues must be confirmed in a certified facility by certified analysts. The analysts of the Environmental Microbiology Section are the only certified analysts in West Virginia that can confirm drug residues in milk. This puts someone on call 7 days a week for instances that occur at off hours. Tanker loads of milk that are found to contain drug residues are no longer available for human consumption and must be disposed of.
Both raw and pasteurized milk (with the exception of a few pasteurized products) received at the laboratory are subjected to antibiotic drug residue testing. Milk samples are monitored for Penicillin, Ampicillin, Amoxicillin, Cloxacillin, Ceftiofur, and Cephapirin. Tests that are used must be able to detect at least 4 of the 6 drugs. The Environmental Microbiology Section has at its disposal, 4 different methods that can detect anywhere from 4 to all 6 of the drugs and even identify the drug.
Pasteurized Milk Containers
Even the empty containers that are used for milk products are tested. The entire inner surface of these containers is rinsed with a special reagent. This reagent is then checked for residual bacteria and residual coliform bacteria.