Like most microorganisms, Listeria monocytogenes and Pseudomonas fluorescens are able to form biofilms and
are rarely found as monoculture biofilms in natural environments. Previous works showed that associations
between bacteria from different genus commonly found in food-processing environments may affect their
growth, attachment and biofilm formation. This work studied L. monocytogenes and P. fluorescens monoculture
and multispecies biofilm formation, and investigated how different culture media and temperatures may
influence such bacterial interactions.
L. monocytogenes strains assayed were CECT 4031T, 747 and 994 (food isolates), 1559 (environmental isolate)
and 1562 (clinical isolate). P. fluorescens strains used were ATCC 27663 and PF7A (food isolate). Each strain
was tested for monoculture and mixed culture biofilm formation with each one of the other bacterium’s strains.
Assays were performed during three days in 96-weel microtitre plates, at 4ºC, 22ºC and 37ºC. Brain Heart
Infusion (BHI) and Skim Milk (SM) were the culture media and biofilm formation was assessed by Crystal
Violet staining.
Overall results showed that both media and temperature affect biofilm formation, as monoculture and as
multispecies biofilms, and confirmed that the influence of different bacterial genus on biofilm formation is
dependent on strains. Although a decrease of biomass was observed on multispecies biofilms formed at 22ºC
in SM and at 37ºC in BHI, significantly higher OD values were found at 4ºC in both media, and at 22ºC in SM,
indicating that the combination of these two bacteria on meat and dairy food processing environments may
seriously compromise food safety potentiating higher contamination levels
