Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/24/2002
Publication Date: 7/24/2002
Citation: Interpretive Summary: Food safety of fresh produce is a high priority. Survival of pathogens such as Salmonella typhimurium on fresh-cut produce is a serious cause of concern. Apple cider and apple juice, as well as fresh-cut melons and tomatoes have been implicated in recent outbreaks of infections caused by S. typhimurium. The ability of human pathogens to survive in an acidic environment plays a crucial role in food and water borne diseases. Understanding the biochemical and genetic basis of acid tolerance of S. typhimurium will help us design better methods of control. In this study we demonstrate that acid resistance of S. typhimurium increases if the cells are attached to solid surfaces. The cells appeared to withstand produce acidity better at low temperatures. Both old and young cells of S. typhimurium gained acid tolerance upon attachment to solid surfaces. Understanding various environmental factors that influence survival of human pathogens will benefit the fresh produce industry. These results show that effective control measures during produce processing must take into account the increased resistance of surface-attached pathogens. Both the fresh produce industry and consumers will benefit from the results of this research.
Technical Abstract: Survival of pathogens such as Salmonella typhimurium for extended periods of time on fresh-cut produce is a serious problem. In this study, we demonstrate that acid resistance of S. typhimurium increases by several log-fold at low temperatures or if the cells are inoculated on fresh-cut apples. The low temperature-mediated protection was observed only for stationary growth phase cells, and actively growing logarithmic growth phase cells were susceptible to acid-challenge. The cells from stationary, as well as logarithmic growth phase, acquired increased acid tolerance upon surface-contact with inert surface such as nylon membrane. The alternative sigma-transcription factor (RpoS) was not required to acquire adherence-mediated acid tolerance. Effective control measures during produce processing must take into account the different susceptibilities of planktonic versus surface-associated pathogens.