Isolation and antimicrobial activity of lactic acid bacteria isolated from pineapple and watermelon

Abstract

Probiotics are living microorganism which when consumed in adequate amount provide health benefit to the host, examples are lactic acid bacteria which are gram positive organisms that can withstand different environmental stress during production and storage of products containing them. This study aims to evaluate probiotic potential of lactic acid bacteria (LAB) strains isolated from pineapple and water melon. The materials used in the evaluation were properly sterilized including the different media like De-man Rogosa & Sharpe agar (MRS), MRS broth for the isolation of LAB by streaking method, nutrient agar, and Mueller Hinton agar for the antibiotic susceptibility test using Disc diffusion method. Out of 168 bacteria counted on plate count agar, a total of six strains were screened based on their cultural and biochemical characteristics. The fruit isolates were screened for antibacterial activity and for their antibiotics susceptibility; the six isolates showed antibacterial behaviour towards both gram-positive and gram-negative human pathogens (Proteus mirabilis, Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Staphylococcus aureus, and Corynebacteria spp.), while some showed no zone of inhibition. The antibiotic susceptibility test was also promising with P1 showing 31 mm against Amoxicav. Molecular identification analysis (16sRNA sequencing) revealed that the isolates were different species belonging to the same group, Lactobacillus fermentum, Lactobacillus plantarum and Weissella cibaria. Conclusively, these results demonstrate that bacteria isolated from fruit samples have interesting properties and could potentially be used as probiotics and in the preparation of functional fruit products.