Antimicrobial Effect of Partially Purified Bacteriocins on Pseudomonas aeruginosa

Bacteriocins are commonly used in foods to inhibit the growth of spoilage and pathogenic bacteria, thus extending the shelf life of food products. Interest in bacteriocins is increasing because of the increasing tendency of consumers to use healthy, natural and additive-free products in foods. In this study, it was aimed to investigate the control of P. aeruginosa in milk by using partially purified bacteriocins produced from lactic acid bacteria (LAB) strains. Among the 13 reference LAB strains, four strains that showed the highest antimicrobial activity by the agar spot test were selected for bacteriocin production. The bacteriocins were partially purified with 40% ammonium sulfate. The antibacterial activity of bacteriocins on P. aeruginosa strains was determined in arbitrary unit by the well diffusion meth-od. Then, UHT milk samples inoculated with P. aeruginosa and bacteriocin cocktail were stored at +4°C for a week and bacterial counts were performed on the 1st, 3rd, 5th, and 7th days. The LAB strains that displayed the widest clear zones on P. aeruginosa were determined as L. plantarum, L. paraplantarum, L. fermentum and L. pentosus and the antimicro-bial activities of the partially purified bacteriocins of these strains were 640, 640, 160 and 80 AU/ml, respectively. Among tested P. aeruginosa strains, the highest antibacterial effect was observed against P. aeruginosa ATCC 15442 (>18mm). In the milk model, the bacteriocin cocktail caused a decrease of approximately 2 log cfu/ml in the number of bacteria for up to three days and the number remained constant until the end of the seventh day. However, the de-crease in the number of bacteria was not statistically significant (P>0.05). As a result, bacteriocins obtained from Lacto-bacillus strains showed antibacterial effect on P. aeruginosa on agar medium but could not achieve a significant de-crease on the milk. However, bacteriocins, which have generally been proven to efficient on Gram-positive bacteria, have been determined to be effective on P. aeruginosa, a Gram-negative bacterium. Moreover, this study emphasizes that in addition to in-vitro experiments, products to be used for biocontrol purposes in foods are also needed to comple-ment with food models.