Abstract
Microorganisms in dairy industries can form monospecies, dual-species, or multispecies biofilms, showing cooperative or competitive behaviors, which might contribute to the reduction of efficiency of cleaning and sanitization processes and eventually turn into a potential source of contamination. This study proposes to evaluate the behavior of Listeria monocytogenes in monospecies biofilms, cocultured with Bacillus cereus. The isolates were of dairy origin, and the selection occurred after studies of competition among species. The biofilm formations on AISI 304 stainless steel at 25°C in a stationary culture were analyzed to observe the cooperative or competitive interactions among species, as well as the effect of pre-adhered cells. Biofilm formation assays were performed in four experiments: Experiment 1: in the presence of strains of antagonistic substance producer B. cereus (+); Experiment 2: extract of the antagonistic substance of B. cereus; Experiment 3: pre-adhered cells of B. cereus; and Experiment 4: pre-adhered cells of L. monocytogenes. Subsequently, cooperative behavior was observed by scanning electron microscopy. The L. monocytogenes monospecies biofilm counts of greater than 5 log colony-forming units (CFU)/cm2 were also observed in dual-species biofilms in the presence of B. cereus (non-producers of antagonist substance), showing cooperative behavior between species. However, in the presence of antagonistic substance produced by B. cereus, the counts were lower, 1.39 and 1.70 log CFU/cm2 (p > 0.05), indicating that the antagonistic substance contributes to competitive interactions. These data are relevant for the development of new studies to control L. monocytogenes in the dairy industry.
Highlights
Listeria monocytogenes and Bacillus cereus are pathogens that cause foodborne diseases and are commonly reported in the literature due the presence on environmental surfaces of dairy industries and in dairy products (Kabuki et al, 2004; Karthikeyan et al, 2015; Spanu, 2016; Saldivar et al, 2018)
We evaluated the production of antimicrobial substance for 23 isolates of B. cereus against 5 strains of L. monocytogenes according to the methodology used by Nascimento et al (2009); modified methodology is reported in Supplementary Table S1
Peptides and bacteriocins produced by this species may inhibit L. monocytogenes, Bacillus subtilis, Escherichia coli, and Salmonella enteritidis, Salmonella typhi, and Staphylococcus aureus (Bizani et al, 2005; Yusra and Novelina, 2014)
Summary
Listeria monocytogenes and Bacillus cereus are pathogens that cause foodborne diseases and are commonly reported in the literature due the presence on environmental surfaces of dairy industries and in dairy products (Kabuki et al, 2004; Karthikeyan et al, 2015; Spanu, 2016; Saldivar et al, 2018). B. cereus sensu stricto can be characterized by diarrheal type and emetic type (Fiedoruk et al, 2017; Fayad et al, 2019). These pathogens can produce monospecies, dual-species, or multispecies biofilms on abiotic surfaces such as stainless steel (Kim et al, 2018; Silva et al, 2018; Alonso and Kabuki, 2019). The biofilm formations may cause biocorrosion and result in the loss of millions of dollars to the industries (Palmer et al, 2015)
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