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Environmental Microbiology

The Environmental Microbiology Unit performs bacteriological analyses on water samples from both public and private water systems. Samples are examined for the presence of the coliform group of bacteria, which are indicators of fecal contamination. Water is not examined for pathogenic bacteria, as the prospect of isolating them from water is very remote.

Public water system samples are submitted to this Laboratory by the Water Supply Section. DHHS form #3757 must be sent with the sample.

Samples from existing private wells will be analyzed for coliform bacteria only if the sample is submitted through a local health department. The well should be inspected at the time the sample is collected by a health department representative. DHHS form #1294 must be submitted with each sample. For new private well analysis, collection kits may be purchased from the NC State laboratory mailroom. No sample for sanitary analysis should be submitted from an open well, an unprotected spring, or from any source where there is visible evidence of contamination. Such supplies are unsafe for drinking purposes, regardless of laboratory findings.

Samples of non-drinking water, such as those from lakes, streams, rivers, and ponds, that are submitted by health departments may also be examined for total and fecal coliform bacteria to determine the degree of contamination. DHHS form #1704 must be submitted with each sample.

Milk Microbiology

The Environmental Microbiology Unit provides analyses of dairy products on reference samples received from the Milk Sanitation Branch. Proper shipping measures must be observed to maintain integrity of samples and to meet the regulatory requirements of the National Conference of Interstate Milk Shippers (NCIMS). Dairy products may be analyzed by the following procedures:

  1. Pretrifilm Aerobic Plate Count
  2. Petrifilm Coliform County and Petrifilm High-Sensitivity Coliform Count
  3. Inhibitory Substances Test
  4. Direct Microscopic Somatic Cell Count
  5. Alkaline Phosphatase Test
  6. Milk Containers

Reporting and Interpretation

Test results for drinking water analyses are sent within two working days after the sample is received by the Laboratory. If coliform bacteria are present, the water is considered unsafe for drinking purposes. Results are reported as the presence or absence of both Total Coliform and E-coli bacteria. An analysis refers only to the sample as received and should not be regarded as a complete report on the water supply. Non-drinking water sample results are forwarded as soon as complete, typically 4-5 days after receipt of the sample and initiation of testing. Laboratory reports for private water systems are held for five years and then destroyed. Reports for public water systems are held for one year in the Laboratory then transferred to Environmental Health Central Files.

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Last Modified: April 27, 2009 8:57 AM