Microbial Indicators in Restaurant Salads: Correlation Between Salad Type, Restaurant Ownership Format, and Customer Business Volumes

Foodborne illness outbreaks associated with fresh produce have increased over the past decade. Food workers employed at full-service restaurants are found to perform risky food practices more often than food workers employed in other segments of the foodservice industry. The goal of this study was to determine if differences in restaurant ownership format, business volume, and salad type influenced the level of indicator organisms present in restaurant salads. Overall levels of heterotrophic bacteria, total coliforms, Escherichia coli, Enterococcus, male-specific coliphages, and somatic coliphages were determined by aerobic plate counts (APC), Colilert?, Enterolert?, and U.S. EPA (Method 1601 and 1602), respectively. Molecular methods including automated rep-PCR DiversiLab? system and reverse transcriptase-PCR were used for the DNA fingerprinting of E. coli and the genotyping of male-specific coliphages, respectively.

All of the above mentioned indicator organisms were present in the restaurant salads. Comparisons between restaurant types found that levels of APC, Enterococcus, and male-specific coliphages were significantly higher in locally owned restaurants and levels of total coliforms and somatic coliphages were significantly higher in corporate restaurants. The levels for all indicator organisms were significantly higher in specialty salads compared to leafy greens salads. Comparisons between business volumes suggested that indicator organism counts were higher during low customer traffic sampling periods. These results suggested that there were differences in safe food handling practices between locally owned and corporate restaurants. Staffing and labor issues as a result of low customer traffic and the need for additional handling and preparation of specialty salads seemed to increase the risk of cross-contamination issues for fresh produce. DNA fingerprinting for E. coli revealed that the same organism was found at multiple restaurants. These results indicate that there was a common source of contamination somewhere between field production and distribution. Genotyping results for male-specific coliphages found that some of the produce had been exposed to human and animal sources of contamination. Overall, the monitoring for indicator organisms in restaurant salads found that there is still a need for improved education-based programs in the area of safe food handling practice associated with fresh produce for food workers in restaurants.