Isolation and characterization of bacteriocins produced by lactic acid bacteria

This study presents the characterization of eight bacteriocins produced by lactic acid bacteria (LAB) previously isolated from a traditional cheese, Pico cheese. All isolates were active against Listeria monocytogenes and only three against Clostridium perfringens. Bioactivity was studied after treatment with different enzymes, organic solvents, surfactants, temperature, pH and NaCl. The antimicrobial activity of LAB isolates was inactivated by the addition of proteases, thus confirming the proteinaceous nature of active substances. Bacteriocins were found to be heat resistant and remained active at a wide range of pH values. However, bioactivity was sensitive to some organic solvents tested. Surfactants had no influence in the antimicrobial activity with the exception of sodium dodecyl sulfate (SDS). Bacteriocin activity was stable in the presence of 2% NaCl. Bacteriocins revealed a bacteriocidal and bacteriostatic mode of action towards the indicator strain L. monocytogenes. Adsorption of bacteriocins to producer cells was not observed. Bacteriocins were further purified by ammonium sulfate precipitation, SDS-PAGE, anionic chromatography and RP-HPLC. Molecular weight was calculated as 3-3,5kDa by SDS-PAGE. Bacteriocins spectrums of activity and interesting properties as heat-resistant, pH tolerance and stability in presence of surfactants make them advantageous for application as biopreservatives in food industry.