Insights into the antagonism of Lactobacillus fermentum curd isolate against Gram-positive and Gram-negative pathogenic bacteria

Abstract

This communication characterizes the curd isolate of lactic acid bacteria having the capacity to antagonize human pathogenic bacteria. The commercially available curd, in sealed form in a plastic cup, was procured from Malda town market (West Bengal state, India) and processed microbiologically, using de Man Rogosa Sharpe medium, for the isolation of lactic acid bacteria. The pure bacteria culture obtained was identifi ed, by phenotypic characterization through conventional methods, as Lactobacillus fermentum, and designated as LMEM 22. The Lactobacillus fermen-tum LMEM 22 curd isolate had mixed antibiotic susceptibility patterns, showing resistance (ZDI: ≤15 mm) to ami-kacin, ciprofl oxacin, kanamycin, methicillin and vancomycin, sensitivity (ZDI: ≥ 21 mm) to ampicillin, amoxyclav, gentamycin, cefotaxime, imipenem, meropenem and tetracycline, and intermediate susceptibility (ZDI: 16-20 mm) to cfoxitin and trimethoprim. The L. fermentum LMEM22 antagonizes both gram-negative: Acinetobacter bauman-nii, Pseudomonas aeruginosa, Escherichia coli, Proteus vulgaris, Klebsiella pneumoniae, Salmonella enterica serovar Typhi, and gram-positive: Staphylococcus aureus, Bacillus cereus, Enterococcus faecalis, Listeria monocytogenes, bacterial pathogens, following agar overlay (ZDI: 17±1.73 mm to 20±1.00 mm, for gram-positive, and 18±2.00 mm to 33±2.65 mm for gram-negative bacteria) as well as agar-well diffusion (ZDI: 10.67±2.08 mm to 12±1.00 mm, for gram-positive, and 13.00±2.65 mm to 18.00±3.00 mm, for gram-negative bacteria) techniques. The overall bacteri-ocin activity (AU/ml) of Lactobacillus fermentum LMEM 22 for the test bacterial pathogens ranged 142.27-240.00, and the 'R' value ranged 5.5-13.5. This study underlines the usefulness of locally available lactic acid bacteria in designing the probiotic microorganisms for biotherapy.