Section 791. Microbiology testing: sterility checks and blanks, positive and negative controls

A. Sterility checks and blanks. The laboratory shall demonstrate that the filtration equipment and filters, sample containers, media and reagents have not been contaminated through improper handling or preparation, inadequate sterilization, or environmental exposure.

1. A sterility blank shall be analyzed for each lot of pre-prepared, ready-to-use medium (including chromofluorogenic reagent) and for each batch of medium prepared in the laboratory. This shall be done prior to first use of the medium.

2. For filtration technique, the laboratory shall conduct one beginning and one ending sterility check for each filtration series. The filtration series may include single or multiple filtration units, which have been sterilized prior to beginning the series. For presterilized single use funnels a sterility check shall be performed on one funnel per lot. The filtration series is considered ended when more than 30 minutes elapses between successive filtrations. During a filtration series, filter funnels shall be rinsed with three 20-30 ml portions of sterile rinse water after each sample filtration. In addition, laboratories shall insert a sterility blank after every 10 samples or sanitize filtration units by UV light after each sample filtration.

3. For pour plate technique, sterility blanks of the medium shall be made by pouring, at a minimum, one uninoculated plate for each lot of pre-prepared, ready-to-use media and for each batch of medium prepared in the laboratory.

4. Sterility checks on sample containers shall be performed on at least one container for each lot of purchased, presterilized containers with nonselective growth media. For containers prepared and sterilized in the laboratory, a sterility check shall be performed on one container per sterilized batch with nonselective growth media.

5. A sterility blank shall be performed on each batch of dilution water prepared in the laboratory and on each batch of pre-prepared, ready-to-use dilution water with nonselective growth media.

6. At least one filter from each new lot of membrane filters shall be checked for sterility with nonselective growth media.

B. Positive controls.

1. Positive culture controls demonstrate that the medium can support the growth of the target organism or organism, and that the medium produces the specified or expected reaction to the target organism or organism.

2. Each preprepared, ready-to-use lot of medium (including chromofluorogenic reagent) and each batch of medium prepared in the laboratory shall be tested and demonstrate a known positive response. This shall be done prior to first use of the medium.

C. Negative controls. The provisions of this subsection shall not apply to wastewater treatment plants.

1. Negative culture controls demonstrate that the medium does not support the growth of nontarget organisms or does not demonstrate the typical positive reaction of the target organism or organisms.

2. Each pre-prepared, ready-to-use lot of selective medium (including chromofluorogenic reagent) and each batch of selective medium prepared in the laboratory shall be analyzed with one or more known negative culture controls (i.e., nontarget organisms) as appropriate to the method. This shall be done prior to first use of the medium.

Historical Notes

Derived from Volume 25, Issue 07, eff. January 1, 2009; amended, Virginia Register Volume 32, Issue 22, eff. September 1, 2016; Errata, 32:24 VA.R. XXX July 25, 2016.

Statutory Authority

§ 2.2-1105 of the Code of Virginia.