AUTHOR=Zarei Mehdi , Rahimi Saeid , Saris Per Erik Joakim , Yousefvand Amin 

TITLE=Pseudomonas fluorescens group bacterial strains interact differently with pathogens during dual-species biofilm formation on stainless steel surfaces in milk

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.1053239

DOI=10.3389/fmicb.2022.1053239

ISSN=1664-302X

ABSTRACT=<p>In order to develop strategies for preventing biofilm formation in the dairy industry, a deeper understanding of the interaction between different species during biofilm formation is necessary. Bacterial strains of the <italic>P. fluorescens</italic> group are known as the most important biofilm-formers on the surface of dairy processing equipment that may attract and/or shelter other spoilage or pathogenic bacteria. The present study used different strains of the <italic>P. fluorescens</italic> group as background microbiota of milk, and evaluated their interaction with <italic>Staphylococcus aureus</italic>, <italic>Bacillus cereus</italic>, <italic>Escherichia coli</italic> O157:H7, and <italic>Salmonella</italic> Typhimurium during dual-species biofilm formation on stainless steel surfaces. Two separate scenarios for dual-species biofilms were considered: concurrent inoculation of <italic>Pseudomonas</italic> and pathogen (CI), and delayed inoculation of pathogen to the pre-formed <italic>Pseudomonas</italic> biofilm (DI). The gram-positive pathogens used in this study did not form dual-species biofilms with <italic>P. fluorescens</italic> strains unless they were simultaneously inoculated with <italic>Pseudomonas</italic> strains. <italic>E. coli</italic> O157:H7 was able to form dual-species biofilms with all seven <italic>P. fluorescens</italic> group strains, both in concurrent (CI) and delayed (DI) inoculation. However, the percentage of contribution varied depending on the <italic>P. fluorescens</italic> strains and the inoculation scenario. <italic>S. Typhimurium</italic> contributed to biofilm formation with all seven <italic>P. fluorescens</italic> group strains under the CI scenario, with varying degrees of contribution. However, under the DI scenario, <italic>S.</italic> Typhimurium did not contribute to the biofilm formed by three of the seven <italic>P. fluorescens</italic> group strains. Overall, these are the first results to illustrate that the strains within the <italic>P. fluorescens</italic> group have significant differences in the formation of mono-or dual-species biofilms with pathogenic bacteria. Furthermore, the possibility of forming dual-species biofilms with pathogens depends on whether the pathogens form the biofilm simultaneously with the <italic>P. fluorescens</italic> group strains or whether these strains have already formed a biofilm.</p>