Location: Meat Safety & Quality ResearchTitle: Rapid estimation of Salmonella enterica contamination level in ground beef – application of the time-to-positivity method using a combination of molecular detection and direct plating
Submitted to: Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2020
Publication Date: N/A
Interpretive Summary: Salmonella is a leading cause of foodborne illness worldwide with over 1,700 types noted for causing human illness. In spite of the use of numerous process controls in food production industries, there has been little progress in decreasing the occurrence of Salmonella food poisoning over the past decade. One reason for this is that current testing capabilities only show the presence or absence of Salmonella, but do not measure how much contamination is in the tested product. Here we evaluated the use of a novel strategy for estimating Salmonella contamination levels in raw ground beef using the sample enrichment time required to first detect Salmonella based on samples at three timepoints. The results indicate this approach can be used to successfully estimate Salmonella contamination levels in ground beef samples. The ability to detect high levels of Salmonella contamination would enable meat companies to improve their process control as well as remove more highly contaminated products from the food chain which will improve the safety of meat.
Technical Abstract: Little progress has been made in decreasing the incidence rate of salmonellosis in the US over the past decade. Mitigating the contribution of contaminated raw meat to the salmonellosis incidence rate requires rapid methods for quantitating Salmonella, so that highly contaminated products can be removed before entering the food chain. Here we evaluated the use of Time-to-Positivity (TTP) as a rapid, semi-quantitative approach for estimating Salmonella contamination levels in ground beef. Growth rates of 14 Salmonella strains (inoculated at log 1 to -2 CFU/g) were characterized in lean ground beef mTSB enrichments and time-to-detection was determined using culture and molecular detection methods. Enrichments were sampled at five timepoints and results were used to construct a prediction model of estimated contamination level by TTP (superscript indicates time in hours) defined as TTP4: =5 CFU/g; TTP6: =5, =1 CFU/g; TTP8: =1, =0.01 CFU/g; with samples negative at 8h estimated =0.01 CFU/g. Model performance measures showed high sensitivity (100%) and specificity (83% and 93% for two detection methods) for samples with a TTP4, with false negative rates of 0%.