martes, 20 de agosto de 2013

In-vitro Screening of antibacterial activity of lactic acid bacteria against common enteric pathogens

The antibacterial substances produced by lactic acid bacteria render them more advantageous in the competition with other microorganisms. Present study aims to evaluate the antibacterial activity of lactic acid bacteria (LAB) isolated from raw milk, curd, tomato and dosa batter, against common enteric pathogens. The antagonistic properties of these isolates against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus cereus were examined using agar well diffusion method. Four LAB namely Lactobacillus salivarius, Lactobacillus delbrueckii,subsp. bulgaricus, Lactobacillus fermentum and Lactobacillus acidophilus, were effective against all selected pathogenic strains. Amongst the four isolates, Lactobacillus salivarius exhibited the highest antibacterial activity, against all the indicator pathogens tested except Staphylococcus aureus. Its activity was maximum against E.coli with a Zone of Inhibition (ZOI) ranging from 18.7 to 21.3 mm and least for Staphylococcus aureus (10±1.1 mm). Lactobacillus bulgaricus also showed antibacterial property against all tested pathogens showing highest activity against Pseudomonas aeruginosa (17 ± 1.7 mm) and least against E.coli (8 ± 1.4 mm), which was in direct contrast to Lactobacillus salivarius. Lactobacillus acidophilus showed greater activity against Staphylococcus aureus (17 ± 0.8 mm) and least against E.coli (8 ± 1.7 mm). Least antibacterial property was observed in Lactobacillus fermentum, with a ZOI in the range of 2.5-7 mm. Overall, the isolated LAB showed the remarkable inhibitory effect against both Gram positive and Gram negative pathogenic strains. However, the spectrum of inhibition was different for the isolates tested. These results suggest that this potent isolates could be used as a natural biopreservatives in different food products.

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