A High-Throughput, Culture-Independent Approach to Identify Index and Indicator Species for E. Coli O157:H7 Contamination

Recurrent outbreaks of E. coli O157:H7 linked to lettuce and leafy greens produced in the California Central Coast region are of high concern to both the industry and public health regulators. The absence of recognized sporadic illness or outbreaks from products originating from winter-production regions in southern deserts has engendered broad speculation as to causes. <P>
One commonly held hypothesis is that although parallel risk factors for pathogen contamination exist in both regions, climatic conditions and other factors result in an exclusionary leaf surface microflora in the desert regions. <P>
In this proposal, we seek to identify bacterial species that have potential as indicators of contamination for E. coli O157:H7 on lettuce. Non-pathogenic microorganisms on the surface of fresh fruits and vegetables, including lettuce, can behave in a manner highly similar to those causing foodborne illness. Alternatively, some harmless bacteria are most abundant when conditions are not favorable for survival or growth of food borne pathogens. <P>
We will use a high-throughput DNA sequencing approach to identify bacterial species present on Romaine lettuce leaves grown in the Salinas, Imperial, and Yuma Districts. These indicator bacteria will be selected for positive or negative association with periods of E. coli O157:H7 detection or growth.<P>
The verification of both positive and negative risk indicators will result in optimized testing strategies and lower overall costs for monitoring of product for E. coli O157:H7. <P>The development of novel rapid, DNA-based tests will help focus economic resources for pathogen testing on fields and lots of significant risk.