The globalization of food production- along with advances in agronomics, processing, preservation, and distribution- translates to ready consumer access to fresh produce year-round. This level of demand strains producers who must maintain both quality and safety standards, requiring them to combat pathogen survival mechanisms like preferential localization and biofilm formation, as reported by Allende et al.1 While most consumers associate foodborne illness with animal products, outbreaks linked to foods of non-animal origin have been increasing. Indeed, for outbreaks with known etiology reported to the Centers for Disease Control between 1998 and 2007, fresh produce accounted for greater incidence of foodborne illness than animal products. Foodborne Illness in the US, 1998 to 20072
|food product||outbreaks of foodborne illness|
Further, the 2011 outbreak of Shiga Toxin-producing Escherichia coli O104:H4 in German alfalfa sprouts demonstrated that foodborne pathogens in fresh produce can be deadly. This brought to light the necessity of determining and implementing best practices, including risk assessment tools, to protect consumer health. The European Food Safety Association Biological Hazards Panel developed a semi-quantitative model to rank high risk food/pathogen combinations: Top 5 Food/Pathogen Combinations3
|Salmonella spp. and Norovirus||raw leafy greens|
|Salmonella, Yersinia, Shigella, and Norovirus||bulb, stem, and root vegetables|
|Salmonella spp. and Norovirus||tomatoes|
|Salmonella spp. and Norovirus||berries|
The obvious response to this consumer health threat is the development of guidelines to control pathogen contamination at every point along the food supply chain. Unfortunately, while it is possible to minimize microbial hazards during some stages of production (irrigation, worker hygiene), there are no control measures capable of reasonably reducing pathogens in primary production environments like open fields (manure/compost, animal intrusion, etc.). Further, post-harvest decontamination strategies can decrease but not eliminate contamination. These include washing with chemical sanitizers (chlorine dioxide, peroxyacetic acid, hydrogen peroxide, and ozone) and physical disruption of pathogens (high pressure pulsed electric fields, oscillating magnetic fields, ultrasound treatments, ionizing radiation, and pulsed UV-C light). Unfortunately, these strategies carry low efficacy, potential for negative side effects, and limited consumer acceptance. Indeed, the industry generally acknowledges that no intervention can reliably eradicate pathogen contamination of fresh produce. The goal of most decontamination techniques is simply to reduce the microbial load and avoid cross-contamination. The predominant reason for this failure to fully decontaminate fresh produce is that pathogens are highly effective colonizers. Not only do they preferentially localize to surface irregularities, which are less accessible for cleaning protocols, but they also form biofilms- a “slime” or matrix of extracellular DNA, proteins, and polysaccharides that protects microorganisms from environmental stressors, including antibiotics and disinfectants. Since standard cleaning protocols rarely disrupt biofilms, the pathogens that persist there pass through the production process, thriving on plant-based food products. Previous research has demonstrated that the quorum sensing (QS) system regulates biofilm formation, including adhesion, motility, maturation, and dispersion.4 This finding may be key to increasing food safety using QS signal blockers to regulate pathogen virulence and facilitate microorganism removal from fresh produce. Previous studies identified likely candidate blockers derived from natural microbiota. Bifidobacterium spp., found in the human digestive tract, weakens E. coli O157:H7 and reduces biofilm formation by 36%.5 Urolithins, metabolites of human microflora, may also inhibit pathogens when applied to fresh produce. Allende et al. offer these novel control strategies as a focal point for future research. Deeper understanding of the natural microbiota of fresh produce, including how these microorganisms compete with invading pathogens and how the QS regulated gene systems impact bacterial adhesion and biofilm formation, could reinvent existing decontamination protocols for fresh produce and increase consumer safety. To learn more about Strategies to Combat Microbial Hazards in Fresh Produce, read the the full Culture article. References: 1 Allende, A. and Ölmez, H. (2015) ‘Strategies to Combat Microbial Hazards Associated with Fresh Produce,’ Culture, 35: 2 2 Center for Science in the Public Interest (2009) ‘Outbreak alert: Analyzing foodborne outbreaks 1998 to 2007.’ Available at: http://www.cspinet.org/new/pdf/outbreakalertreport09.pdf. 3 EFSA Panel on Biological Hazards (2013) ‘Scientific Opinion on the risk posed by pathogens in food of non-animal origin, Part 1: outbreak data analysis and risk ranking of food/pathogen combinations.’ EFSA Journal, 11, 3025-3163. doi:110.2903/j.efsa.2013.3025. 4 Koutsoudis, M.D. et al. (2006) ‘Quorum-sensing regulation governs bacterial adhesion, biofilm development, and host colonization in Pantoea stewartii subspecies stewartii.’ Proceedings of the National Academy of Sciences of the United States of America, 103, 5983-5988. 5 Kim, Y. et al. (2012) ‘Bifidobacterium spp. Influences the production of autoinducer-2 and biofilm formation by Escherichia coli O157:H7.’ Anaerobe, 18, 539-545.