Pseudomonas biofilms can aid the survival of Listeria monocytogenes cells even after disinfection, according to a recent study. Although Pseudomonas are often overlooked as a food safety hazard due to being associated with food spoilage rather than with human foodborne illnesses, the study’s findings suggest that the bacteria may pose a direct threat to food safety in the processing environment.
Pseudomonas are the most commonly found bacteria in food processing environments due to characteristics such as a high growth rate at low temperatures, a high tolerance of antimicrobial agents, and biofilm formation. The bacteria have been of special interest as colonizers in food processing environments, as a food spoilage organism, and as protectors of foodborne pathogens.
Previous research has demonstrated the possibility of surviving bacteria exposed to sub-lethal concentrations of disinfectants being able to co-select for both disinfectant- and antibiotic-resistant properties. Several studies also indicate that interspecies interactions in a biofilm could serve as an accelerator for horizontal gene transfer, as well as facilitate adaptation to environmental conditions and the subsequent decreased susceptibility to antimicrobials. It has been suggested that multi-species, Pseudomonas-dominated biofilms could host and shelter pathogens like L. monocyotogenes.
In the study, researchers from the Norwegian University of Science and Technology isolated Pseudomonas samples from cleaned and disinfected surfaces in a salmon processing facility. A total of 186 isolates were screened for biofilm formation at 12 °C, and were graded as strong, medium, or weak biofilm producers. A high variation in biofilm formation was observed, with 12 percent rated as strong, 29 percent as medium, and 27 percent as weak biofilm producers, as well as 29 percent not producing a detectable biofilm.
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