Inhibitory effect and cell damage on bacterial flora of fish caused by chitosan, nisin and sodium lactate

Abstract

The effect of the combined use of chitosan, nisin and sodium lactate on the growth of Listeria innocua, Shewanella putrefaciens and psychrophilic bacteria isolated from fish was investigated in broth by means of minimum inhibitory concentrations (MIC). Furthermore, the sites of cell-injury caused by mentioned antimicrobials and their combinations on L. innocua and S. putrefaciens were studied. MIC of antimicrobial mixtures were evaluated by Berembaum design and check board method. Antimicrobials' sites of injury were investigated by the evaluation of cell constituents' release, cell surface hydrophobicity and differential scanning calorimetry. Results depended on antimicrobial used; several combinations inhibited the growth of L. innocua and S. putrefaciens and all combinations inhibited psychrophilic bacteria. Besides, some mixtures showed synergistic effects. All the mixtures affected ribosomes and DNA of the studied bacteria. Regarding cellular envelope, antimicrobials acted according to the structural characteristics of target microorganisms. Cell damage was higher when antimicrobials were combined, which could explain the observed synergistic effects. This study demonstrates and justifies the synergistic action of chitosan, nisin and sodium lactate on the inhibition of microorganisms related to fish spoilage and remarks the promissory use of the synergic combination of antimicrobials for fish preservation.