How Microbiology Labs Can Validate Procedures and Routinely Verify Compliance

If a client insists on retesting, a subsequent negative pathogen test result does not negate a previous positive. Because samples may not be uniformly homogenous and the analyte in question may not be uniformly distributed in a lot, an out-of-spec result is not always associated with laboratory error. Clear articulation is needed to justify retesting.

Because environmental monitoring is an effective assessment tool to determine if the laboratory environment is fit for purpose, testing for pathogens and amplicon in the pathogen handling portion of the lab will provide data points showing how the risk of cross-contamination is being managed. Eurofins advocates using a zone approach to laboratory EMP.

For example, lower-risk areas in the lab include media preparation and materials supply storage. The sample reception area can be greater risk if samples are high count or have a history of pathogen detections, such as sponges, swabs, or raw meats and poultry. In such cases, designated sample receiving and sample preparation areas should be used and considered higher risk.

Because the goal of a food micro lab is to cultivate large numbers of microbes (indicators, spoilers, or pathogens), downstream areas where such high-count materials are handled should be considered high risk. For example, plate counting, enrichment transfers, pathogen detections, positive control handling, and waste disposal are considered greatest risk. Indicator (aerobic plate count, coliform count, E. coli count, Enterobacteriaceae count, yeast and mold count) environmental sampling may show surfaces in the laboratory that have been poorly cleaned and sanitized. Direct swabbing of employee hands, gloves, and lab coats can inform personal hygienic practices and conformance.

The value of laboratory EMP testing is most realized when clients blame the laboratory for out-of-spec results, including elevated indicator counts or positive pathogen detections. One major way to rebut such claims is to rely on routine laboratory quality control data points. Such data can help argue that laboratory cross-contamination is not the mostly likely cause of the out-of-spec result.

Dr. Marshall is chief scientific officer at Eurofins Microbiology Laboratories, Inc. Reach him at 970-217-6854.