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Bacterial Enumeration of Milk Samples

PHL Location

Amite Laboratory

CPT Code



Plate Count Method

Brief Description of Test

Used for the enumeration of bacteria colonies of a given sample in raw milk and pasteurized fluid milk products.

Possible Results

Number of colonies per ml or gm.

Reference Range

  • Raw milk samples: <2500/ ml ESPC to 100,000/ml for individual producers and <2500/ml ESPC to 300,000/ml for raw commingled milk.
  • Pasteurized fluid milk products: <250/ ml or gm ESPC to 20,000/ml or gm.

Specimen Type

Raw milk or pasteurized fluid milk products (not for cultured products, i.e. buttermilk).

Specimen Container(s):

Raw milk samples: collected and submitted in sterile Whirl-Pak bag or sterile plastic vials normally used by industry. Pasteurized fluid milk products are collected in the container in which they are sold in the retail outlet.

Minimum volume accepted:

  • Raw fluid milk: at least 40 ml. 
  • Pasteurized fluid milk products: at least a half-pint (when collecting half-pints there are normally two samples collected to insure volume needs are met).

Collection Instructions

Collect a representative sample according to established protocol. In using the sterile Whirl-Pak bag or sterile vial leave at least ¨ö-1 inch air space at the top of the container.  If using the Whirl-Pak bag close it so that the tabs are not twisted together.

Storage and Transport Instructions

Samples must be stored on ice, the ice cannot cover the sample, and the sample must not be under water anytime during transport or upon receipt. The sample must be received so that the initial testing can be completed prior to 48 hours from original collection time. Samples must be received into the lab with a pilot temperature sample that is of equal size to the samples for raw milks and half the largest container size for pasteurized fluid milk products. The temperature of the pilot sample upon receipt must be between 0.0-4.4¢ªC (an exception to this is: the temperature of the pilot sample can be up to 7.0¢ªC as long as the original collection temperature was not >7.0¢ªC, the time between collection and receipt by the lab is ¡Â 3 hours, and the temperature at receipt is not higher than the actual temperature at collection).

Causes for Rejection

  1. Temperature of pilot sample does not meet requirements.
  2. Time of receipt > 48 hours from collection.
  3. Sample container is unprotected or under ice or under water when received.
  4. Sample frozen.
  5. Temperature control is missing.
  6. Sample leakage.
  7. Unsatisfactory container.
  8. Insufficient sample quantity.

Limitations of the Procedure

This procedure does not provide the source of a high bacteria count nor does it provide for speciation of the bacteria.

Interfering Substances

The presence of any substance that interferes with bacteria count, i.e. disinfectants, chlorine, antibiotics, can cause interference.


  • Standard Methods for the Examination of Dairy Products.
  • FDA 2400 Series for the Examination of Dairy Products: Standard Plate Count.
  • US FDA/CFSAN Grade ¡°A¡± Pasteurized Milk Ordinance.     
  • Laboratory Milk and Dairy Products SOP Manual.

Additional Information

A completed Lab 50 form must accompany the sample(s) with the date and time of collection, temperature at collection, name of the submitter, milk region from which sample is being submitted, and if a finished product the sample code dates must be listed along with the sample type and codes. Each ice chest must have its own pilot accompanying the samples. If the sample is being submitted for specific testing that testing must be listed in the remarks section.