TNI Logo The NELAC Institute

Combined Interpretations of the 2003, 2009, and 2016 Standards that apply to Volume 1 of the 2016 TNI Standard


MODULE 5: MICROBIOLOGY TECHNICAL REQUIREMENTS
Section: 1.7.3.1

Question:  How are other AB's interpreting this standard: "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 non-selective growth media."  Are you requiring a sterility check with non-selective growth media for any dilution water (i.e. Deionized, distilled, etc.) or just those dilution waters whose preparation is described in microbiological procedures, like phosphate buffer water or peptone water?

TNI Response:  If sterility is required for use (whether in-house or purchased), then sterility must be checked prior to use. If the water is being used to prepare media or buffered water, then a sterility check is not needed until after the reagent has been prepared. A sterility check must be performed on any dilution water.  Clarified in the 2016 Standard by adding in 1.7.3.1.a) "All materials and supplies that would be needed to process…." 

 

Question:  Can the standard be interpreted to mean a sterility blank is not required every 10 samples, as implied in the last sentence of the section, if the funnels are single use?  It is assumed that the point of running the blanks every 10 samples is to show proper rinsing technique for multi-use funnels. Because the final sentence in this section begins with "In addition," and is displaced from the sentence that says, "For pre-sterilized single use funnels a sterility check shall be performed on one funnel per lot," it seems to add a requirement to filtration series using all types of funnels, but I do not believe that was the intent.

TNI Response:  It was the intent that single use funnels, provided they are only used once, would not require any additional sterility check beyond once per lot as written in the Standard.  However, if the method being followed has more stringent requirements, those requirements must be followed.  The basic issue with this SIR is that until the 2016 standard made clear that sterility checks and method blanks are different things required for different reasons the language was confusing.  Section 1.7.3.1 is about sterility checks, but this question is about method blanks. 

 

Question:  The lab conducts SM9020a testing on potable water only. We purchase single use sterile water from IDEXX who also manufactures the Colilert media. It is their recommendation to use sterile water in blanks and dilutions. This is the only use our lab has for sterile water as everything else is prepackaged ready to use. The sterile water comes in sealed 100ml aliquots with reagent water criteria certification from IDEXX. The water is purchased in lots and the lot is verified upon receipt for pH, conductance and sterility. It is stored in a refrigerator at 4C. The lab is small and only conducts 20 tests per month. Is the in-house QA and manufacture certification of the sterile water sufficient for the use of the water as a lot per TNI standards - or should it be conform to pre-dispensed buffer water standards?

TNI Response:  The requirement is to check the purchased water once per lot and, in addition, once per month when using a bottle that lasts longer than one month. If the water is to be used for preparation of media, reagents or as a diluent, which will put it in contact with microorganisms, then the requirements of verification as stated in 1.7.3.5(c) are needed along with the verification of sterility.  As this is something that is somewhat static and the source is not changing over time as an In-house DI system may be an initial check that mirrors the DI water requirements is reasonable with some relief regarding frequency as noted in 1.7.3.1.d) v.  Refer to 1.7.3.1 e).