How Microbiology Labs Can Validate Procedures and Routinely Verify Compliance

Is the laboratory accredited to ISO 17025 standards to perform tests? Can lab personnel describe and perform methods? Is lab capable of performing sample preparation, such as thawing, composite pooling, and experience with difficult matrices (e.g., large samples, complex samples, antimicrobial ingredients)? How is sample uniformity ensured (e.g., mixing by blending, stomaching, by hand)? Is the laboratory using appropriately validated methods (e.g., AOAC, FDA, FSIS, AFNOR, MicroVal), and are they validated for the matrices of interest? Can the lab fully justify and validate using non-standard methods?

Laboratories must have quality control procedures for monitoring the validity of tests. The resulting data must be recorded in such a way that trends are detectable and, where practicable, statistical techniques must be applied to the reviewing of the result. Good laboratory procedures include the use of quality control samples with each sample batch to demonstrate the test worked properly.

A daily process control system, or the use of a non-pathogenic microorganism sample of a known quantified amount, must be plated on a daily basis for those assays being performed. Positive controls are those that include the target microbe to see if the method is working that day or if there are interfering matrix substances. Negative controls use non-target microbes to assess for method discrimination, while sterility controls use blank samples to ensure that media and materials are sterile.

In-House Testing?

If you are a food manufacturer, is it wise to do pathogen testing in house? Doing so may be a significant biosecurity risk. Without positive controls, a lab is doing faith-based microbiology.

Separate personnel and limit culture access to prevent cross-contamination. Implement policies that govern glove and lab coat use. Understand the risk associated with the lab location in relation to food production. Care must be taken in staging positive control samples in relation to other samples to avoid cross-contamination.

Running a lab requires constant use of measurements that utilize instruments traced to national or international standards. For example, temperature hold precision adequacy is extremely important when doing coliform/E. coli testing at 44.5 or 45.5 degrees Celsius. Sample and media pH values are routinely measured, with precise adjustments sometimes necessary. Pipet and pipetor fill volumes should be periodically calibrated. Balance calibration is necessary to ensure proper sample and consumable weights. Keep records and validation of correction factors.

Integrity of analytical result data should be maintained, and laboratory information management systems secured through password protection. For physical records, labs need a hand error correction policy. To protect against unauthorized access, back up data and log off unattended computer terminals. Scrutinize results for correlation with other results and analyze all lab QC before result release.

Math errors are a common problem. Quantitative microbiology is difficult! Dilution problems are challenging! Counting rules are insanely complicated! Just as self-taught brain surgery is discouraged, don’t do the math yourself: Hire a trained microbiologist, and use a sophisticated laboratory information management system to do calculations. Regularly check performance by subscribing to a check sample proficiency program. Use prepared culture pellets to make spiked controls.

A records retention program should include how to identify, collect, record, index, file, and access records. Additional information on record storage, maintenance, and destruction must be available.

Procedure Challenges

In a world that’s far from perfect, laboratories will make mistakes, or a client will challenge results. Lab errors can happen, so a full discussion of the occurrence with the client is best.

Such complaints should have a formal recording structure that details who is responsible for dealing with complaint or error. The document should detail how to conduct a root cause investigation, identify the cause of the failure, detail corrective and preventive actions, and validate effectiveness. If the issue is serious or a common reoccurrence, conduct a reassessment of lab standard operating procedures along with routine verification.