Food industry operators dealing with seafood must understand the importance of microbial biofilms and their impact on food safety. Mizan et al. (2015) recently published a comprehensive review on biofilms and seafood production, discussing the epidemiology of the main foodborne pathogens affecting these products. In addition to reviewing this important microbial feature, they also looked at how it affects hygiene measures necessary for supplying safe seafood products for human consumption1.
Seafood is a source of high quality nutrition, gaining in popularity worldwide. Japanese consumers eat the most, with 53.7kg eaten annually per person. China comes second with 32.8kg per person, with the United States has risen to third place with residents eating 21.7kg annually on average. Unsurprisingly, reports of seafood as a source of foodborne illness are increasing. The rising statistic is also due in part to the way that consumers eat seafood; it is frequently consumed with minimal processing post purchase. For example, products like oysters are eaten either raw or lightly cooked, and there is also a rise in ready-to-eat seafood meals.
Foodborne pathogen contamination can occur at any stage of the seafood production chain. Sources include the environment that seafood is harvested from (wild catch or farmed), contamination by workers, and equipment used for preparation (kitchen and industrial). Producers must be remain vigilant and manage the risks inherent at all steps through Good Management Practices (GMP) and attention to HACCP protocols.
Mizan et al. list the microbial species commonly associated with foodborne contamination of seafood as Aeromonas hydrophila; Vibrio species V. parahemolyticus, V. cholera, and V. vulnificus; Salmonella species, and Listeria monocytogenes. In addition to being potent human pathogens that thrive in food matrices and are also waterborne (sea and fresh water), these microbes share another feature – biofilm formation – that makes them tricky to manage in a seafood production environment.
Defined as “densely colonized sessile communities”, biofilms play an important role in bacterial life. They can develop on many surfaces including vegetation, rocks, teeth, still water and food processing equipment materials such as stainless steel, in addition to food itself. Once in contact with a suitable surface, the bacterial communities secrete extracellular polysaccharide scaffold binders that adhere firmly to a variety of materials and develop as a three-dimensional microcolony structure. Microbial structures such as flagellae and pili are also important in developing biofilms. Molecular studies show the genes involved and thus offer potentially useful methods for controlling bacterial biofilm development.
The benefits that microbial communities get from living within a biofilm are stability, longevity and protection. Biofilm communities are usually resistant to environmental stresses such as desiccation, low pH or starvation. As biofilm inhabitants, bacteria can resist cleaning agents, disinfection and antimicrobials. Furthermore, biofilms also help promote bacterial spread since they can detach as intact units under the right conditions, allowing protected spread and onward colonization once they reach a suitable growth surface.
Biofilm inhabitants use quorum sensing, bacterial cell-to-cell communication, to coordinate community activity through the release of extracellular signaling molecules sensed by the microbial population as a whole. Signaling activities vary with population density, driving further biofilm development or the release of virulence factors involved in the pathogenesis of common foodborne disease.
The authors note that food producers have various control measures to minimize biofilm formation. These include reducing bacterial survival through low storage temperature with the option of ice immersion for specific seafoods, compliance with GMP for food safety hygiene among staff and for processing plant decontamination, and high pressure and supercritical carbon dioxide treatments that reduce microbe populations. Other methods proposed include the use of preservatives and additives; essential oils such as cinnamon are effective in controlling pathogen contamination within the seafood itself in addition to winning consumer acceptance. The authors also discuss use of biological controls such as bacteriophages and probiotics to target foodborne pathogens, thus reducing contamination and disrupting biofilm formation. Other measures available include heat treatment, pasteurization and irradiation, all of which are currently used by seafood producers.
The authors also note that studies indicate chitosan in food packaging may prove effective. This compound has antimicrobial activity against several seafood-borne pathogens and could be combined with polymeric packaging materials as a biofilm inhibitor.
In summary, Mizan et al. agree that while there is no single strategy appropriate for biofilm eradication, control is possible by implementing the various methods available across the seafood production environment.
1. Mizan, F.R., et al. (2015) “Microbial biofilms in seafood: A food-hygiene challenge“, Food Microbiology 49 (2015) 41e55 http://dx.doi.org/10.1016/j.fm.2015.01.009