Effect of Matrix on Food Microbiology Proficiency Testing Samples

Introduction: For U.S. clinical laboratories, proficiency testing (PT) has evolved into an essential component of quality assurance programs. These laboratories are regulated by CLIA 1988, which mandates participation in an approved PT program. Food laboratories may soon be subject to similar requirements with passage of the Food Safety Modernization Act, which may require laboratory accreditation for foods regulated by the FDA. American Proficiency Institute, a federally approved clinical PT provider, and an ISO/IEC 17043 accredited Food Microbiology and Chemistry PT provider via A2LA, offers PT programs for the food industry.

Purpose: Our objective was to determine if a select matrix of either dehydrated meat or non-fat dry milk, will influence the false negative or false positive rates on qualitative analysis for three food pathogens. This PT study includes data from 2011 and 2012 for Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium.

Methods: A total of 7,789 proficiency testing results were submitted over three test events for each year. Participants tested the proficiency samples using the method of their choice; methods used included cultural techniques as well as immunoassay and PCR. The false negative and false positive rates were then determined.

Results: A null hypothesis test was conducted for the false negative and false positive rate for each matrix, per food pathogen. Using a 95% confidence limit, it was determined that no significant statistical difference exists in the rate of false positive results or the rate of false negative results when comparing data for the dehydrated meat matrix to data for the non-fat dry milk matrix, for all three food pathogens.

Significance: Selection of matrix in this study did not influence false negative or false positive detection rates. No statistically significant difference in rates was found between the matrices.