Inhibitory effect on biofilms
Among the bacteria evaluated, the CFS generated by L. plantarum7.1 at a dose of 40 mg/mL was the only one that resulted in a significant reduction of biofilm production by E. coli F4. The inhibition of biofilms presented here corroborates several studies; CFS generated by LAB from goat milk demonstrated inhibitory potential on biofilms from L. monocytogenes and Cronobacter sakazakii[22]. CFS of LAB isolated from human feces and curd had an inhibitory action on the biofilm of Pseudomonas aeruginosa [23], and L. plantarum CFS had an inhibitory effect on P. aeruginosa , S. aureus and multiresistant E. coli biofilms [24].
Furthermore, the results of the plate assays with L. plantarum6.2 and L. fermentum 5.2 CFS do not rule out the possibility of these bacteria acting, for example, in reducing the thickness of theE. coli biofilm, since these lactobacilli were also able to coaggregate with the pathogenic bacteria [25]. However, future studies with confocal microscopy will be necessary to confirm or deny this property.
The mechanism of biofilm inhibition by CFS has not been fully described. According to the composition of the CFS, the action may be justified by the production of bacterial surfactants that interact with the polymeric matrix of the biofilms, degrading it and exposing the microorganisms[7].
It can be observed that the direct use of LAB presented bioprotective potential in vitro by coaggregating E. coli F4, while the use of L. plantarum 7.1 metabolites in the form of CFS was effective in controlling biofilms at a dose of 40 mg/mL. In vitrotests are needed to assess the effect of lower doses of the aforementioned CFS on biofilms and to confirm the bioprotective potential of the strains.
New tests with different techniques must also be conducted to confirm the absence of antimicrobial activity of the three CFS used in agar against the pathogen, in addition to in vivo tests with the direct use of LAB and CFS to assess their effects on animal organisms.