Resumo

Lactic acid bacteria (LAB) represent a heterogeneous group of micro-organisms that are naturally present in many foods. It has been shown that these micro-organisms can produce antimicrobial compounds, such as bacteriocins. Bacteriocins are defined as ribosomally synthesized proteins usually antagonistic to genetically closely related organisms, but some bacteriocins are also active against Gram-negative bacteria, such as Escherichia coli, and Campylobacter sp. The aim of this research was the production of bacteriocin by LAB strains SJR7521, SJR37, SJR55, SJR6542, SJR5582 and SJR6562 which were isolated from water-buffalo mozzarella cheese. They were identified as Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus casei, Leuconostoc mesenteroides subsp. mesenteroides, Leuconostoc citreum, Leuconostoc mesenteroides subsp. mesenteroides and Leuconostoc mesenteroides subsp. mesenteroides, respectively, based on the 16S rRNA gene sequencing. The screening for antimicrobial activity of LAB using the agar-spot-test against the strains of Gram-negative bacteria from clinical cases: Kblebisiella pneumoniae (3 strains), Escherichia coli (3 strains), Citrobacter freundii, Citrobacter braakii, Citrobacter sp., Aeromonas sobria, Salmonella Runsen, Salmonella sp. (2 strains), Aeromonas sp. and Campylobacter sp. (2 strains) was carried out The antimicrobial effect ascribed to lactic acid was eliminated by adjusting the pH of the supernatants to 6.0 with sterile 1 N NaOH. Effects of proteolytic enzymes and H2O2 were overcome by heat treatment (10 min at 80 °C) of cell free supernatants. Activity was expressed as arbitrary units (AU)/mL, defined as the reciprocal of the highest serial two-fold dilution showing a clear zone of growth inhibition of the indicator strain. All the LAB strains were active against of Aeromonas sobria, Citrobacter braakii and Campylobacter sp. The LAB strains SJR7521, SJR37 were active against 9/16 and 8/16 strains, respectively, and the LAB strains SJR6542, SJR5582, SJR6562 were active against 5/16 strains of Gram-negative bacteria. These findings are very important because there are few researches about LAB producer of antimicrobial compounds against Gram-negative bacteria. Additional studies are needed to evaluate the potential application of these antimicrobial compounds in clinical area.