Antimicrobial compounds produced by probiotic Lactobacillus brevis isolated from dairy products
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ORIGINAL ARTICLE
Antimicrobial compounds produced by probiotic Lactobacillus brevis isolated from dairy products Abeer Ahmed Rushdy & Eman Zakaria Gomaa
Received: 13 September 2011 / Accepted: 29 February 2012 / Published online: 17 March 2012 # Springer-Verlag and the University of Milan 2012
Abstract A total of 38 lactic acid bacteria, belonging to Lactobacillus, isolated from 24 samples of traditional Egyptian dairy products, were screened for antimicrobial activity against different Gram-positive and Gram-negative bacteria. A strain of Lactobacillus brevis showed the best inhibitory activity when tested by well diffusion assay. The antibacterial activity was pronounced between early logarithmic and early stationary phases. The strain produced a heat-stable antimicrobial compound showing no reduction in activity after heat treatment from 60 to 100°C for 15 and 30 min. Since it was inactivated by proteolytic enzymes, it is considered to be proteinaceous in nature and, therefore, referred to as a bacteriocin-like substance. This compound was also active over a wide pH range (pH 2–6). The antimicrobial compound was partially purified by 40% ammonium sulfate precipitation. Lactobacillus brevis was tested for its in vitro antibiotics susceptibility, tolerance to bile salts, resistance to low pH values, acidifying activity, proteolytic activity, and haemolytic activity. The results showed the potential of L. brevis strain as a probiotic culture, and hence it can be utilized in the manufacturing of pharmaceuticals and dietary supplements.
A. A. Rushdy (*) Botany Department, University College for Women, Arts, Science and Education, Ain Shams University, Cairo, Egypt e-mail: [email protected] E. Z. Gomaa Biological and Geological Sciences Department, Faculty of Education, Ain Shams University, Cairo, Egypt
Keywords Lactic acid bacteria . Lactobacillus brevis . Antimicrobial activity . Bacteriocin-like compound . Probiotics . Dairy products
Introduction The lactic acid bacteria (LAB) family is composed of a heterogeneous group of Gram-positive, non-spore-forming, catalase- and cytochrome-negative, anaerobic or aerotolerant bacteria (Axelsson 1998). LAB consist of a number of bacterial genera within the phylum Firmicutes. Recent taxonomic studies have suggested that the LAB group includes 13 genera (Carr et al. 2002). The antimicrobial effects and safety of some genera of LAB, such as Lactobacillus and Lactococcus in food preservation, are widely accepted (Sit and Vederas 2008). In nature, LAB have several different habitats including plant surfaces, decaying plant material, and the mammalian intestine, vagina and oral cavity which provide the multiple nutrients required by these fastidious bacteria (Axelsson 1998). The food and feed industry widely utilizes LAB in the fermentation of vegetables, silage, and dairy and meat products. Lactobacilli are important organisms recognized for their fermentative ability as well as their health and nutritional benefits (Gilliand 1990). Lactobacilli have traditionally been us
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