Louisiana Department of Health & Hospitals | Kathy Kliebert, Secretary

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Bacteriological Examination of Shellfish

PHL Location

Central Laboratory

CPT Code




Brief Description of Test

Oysters are received in the shell and must be shucked. 200 grams of oyster meats and 200 grams of sterile buffered diluent are weighed then blended. This process uses the Multiple Tube Fermentation (MTF) method to detect and estimate the fecal coliform population in oyster meat samples by use of multiple dilutions of a sample inoculated into replicate tubes of Lauryl Tryptose Broth (LTB) incubated. A Standard Plate Count is performed on dilutions of 1-100, 1-1000, 1-10,000, and 1-100,000 while the fecal Most Probable Number (MPN) LTB uses 1-1, 1-10, 1-100, and 1-1000 dilutions.

Possible Results

fecal coliform MPN/gram, count /milliliter

Reference Range


Specimen Type

Raw un-shucked oysters.

Specimen Container(s):

Heavy duty bags tied and tagged to insure sample integrity.

Minimum volume accepted:

According to the size of the oysters, normally 15-20 oysters that would generate a raw meat weight of at least 200 grams.

Collection Instructions

Samples are collected according to established protocols directly from oyster growing beds.

Storage and Transport Instructions

Store and transport in clean iced cooler. Submitters are encouraged to hold the samples at 0-10ºC during transport.

Causes for Rejection

Sample >24 hours old; No sample ID; Sample information form not complete.

Limitations of the Procedure

Overgrowth by non-coliform bacteria. Coliforms may be found with the absence of E. coli.

Interfering Substances



  • FDA/CFSAN National Shellfish Sanitation Program (NSSP) 2005 Microbiology Laboratory Guide.
  • Quality Assurance Manual for the Laboratory Analysis of Shellfish and Shell Growing Water LA DHH-OPH Laboratories.

Additional Information

Complete a Lab form 47. The name of the collector, date and time of collection and location of where sample was taken must be noted.