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.