UCLA

Many PCR-based methods for microbial source tracking (MST) have been developed and validated within research laboratories, but require inter-laboratory validation before implementation. As part of the State of California Source Identification Protocol Project (SIPP), a blinded set of challenge filters were analyzed by three to five laboratories with a suite of PCR-based methods utilizing standardized methods. Repeatability (within lab agreement) and reproducibility (between lab agreement) of results were assessed by multiple metrics and compared to previously observed values for other environmental methods. Repeatability and reproducibility were found to be generally comparable to previously observed values for other methods (Median CV .001-.033 and .020-.106, respectively). Variance component analysis showed contribution of laboratory to total variability to be larger but of similar magnitude to inherent intra-laboratory variability among laboratories using standardized methods. Results among laboratories using non-standardized protocols for the same methods were also observed to have >2 log differences at times. These findings verify the repeatability and reproducibility of these MST methods and highlight the need for standardization of protocols and consumables prior to implementation of larger scale microbial source tracking studies involving multiple laboratories.