Lawrence D. Goodridge
McGill University, Canada
Title: Using whole genome analysis to develop novel approaches to controlling Salmonella
Biography
Biography: Lawrence D. Goodridge
Abstract
Salmonella is an important cause of global foodborne illness. The World Health Organization estimates that, each year,rnapproximately 600 million people become sick, and 420,000 die from foodborne illnesses. Of these, Salmonella accountsrnfor 93 million illnesses and 150,000 deaths. While foods such as poultry have long been recognized as causes of Salmonella food poisoning, fresh fruits and vegetables have recently emerged as important sources of Salmonella. Thus, there is a needrnto develop better methods to reduce the presence of Salmonella in foods. Ideally these methods should also be applicable torncontrol of other foodborne pathogens. Whole genomic sequence analysis of Salmonella isolated from diverse sources revealedrna large number of prophages residing within the chromosome. Many of these prophages can be induced, resulting in lysis ofrntheir bacterial host. We were therefore interested in evaluationg induction of prophages and subsequent bacterial death couldrnbe employed as a novel strategy to control Salmonella in foods. Growth of Salmonella from diverse serovars exposed to a phagerninducer (0 or 2 ug/ml mitomycin C) was monitored by OD600. Release of induced prophages from the host was confirmed byrnsubjecting the lysates to PCR to detect phage-specific integrases. Additionally, the ability of mitomycin C to induce prophagesrnin Salmonella Duesseldorf growing on fresh produce was evaluated by inoculating the stem scar of red greenhouse tomatoesrnor spinach leaves with 5x107 and 5x108 cells, respectively. After drying, mitomycin C (6 ug/mL) was sprayed onto eachrnsample, while control samples were sprayed with water. Following overnight incubation, the bacterial cells were recovered andrnplate counts were performed. Beginning at 3 hours after addition of mitomycin C, growth of Salmonella strains resulted in arnmarked decrease in OD600. PCR confirmed bacterial release of prophages in these lysates. For example, a three-log reductionrnin S. Duesseldorf (and E. coli O157:H7) was observed on tomatoes sprayed with mitomycin C compared to those sprayedrnwith water, while a one-log reduction in E. coli O157:H7 was obtained on spinach.These findings serve as a proof of conceptrndemonstrating that prophage induction can efficiently control bacterial foodborne pathogens on fresh produce.