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Antimicrobial Activity of Lactobacilli and Bifidobacteria Isolates against Pathogenic Bacteria in Dairy Product

Arish University, Dept. of Food and Dairy Sciences and Technology, Egypt

Abstract

Food-borne illnesses are still a major concern for consumers, the food industry and food safety authorities. Meanwhile, consumers have been questioning the safety of synthetic preservatives of food.
Four lactic acid bacteria were isolated from a traditional Egyptian fermented dairy product. The isolates were identified using genus-specific PCR technique as Lactobacillus plantarum HM1, Lactobacillus rhamnosus HM1, Bifidobacterium bifidum Bb11 and B12.These isolates showed different antibacterial agents against pathogens in their culture cell filtrates. The protective effects of isolated lactic acid bacteria against pathogenicity induced by Staphylococcus aureus, Salmonella, Listeria monocytogenes and E.coli O157:H7. The antimicrobial agents were bacteriocin and organic acids. HPLC analysis indicated that the isolates produced lactic and acetic acids. Propionic acid was produced only by bifidobacteria isolates. The inhibition activity of these substances has been reported to be strain-dependent. Inhibition zones diameters were affected by the addition of Proteinase K and / or neutralisation of cell filtrates. All isolates were observed to behave a good antagonistic activity against the tested indicator strains with differences in size of inhibition zone (mm), meanwhile Listeria monocytogenes and E.coli O157:H7 were not inhibited by the extract of Lactobacillus rhamnosus HM1and Bifidobacterium bifidum Bb11 respectively.
Supernatant and cell pellets of isolates were used as biopreservation system in yoghurt and Karish soft cheese. The sensory and microbiological analyses were followed during the storage at 4°C for 21 days. Data showed that no apparent or detectable of pathogenic bacteria growth to the end of the storage period up to 21days. Sensory evolution showed that, use of the combination between supernatant and cell pellets at concentration of 1:1, enhanced the antimicrobial activity and improved the organoleptic properties and the viability of starter culture of the resulted dairy products. These results indicate that isolated lactic bacteria can be used as control agent for food contamination by pathogenic bacteria as bio-preservation system.
We can conclude that, the application of antimicrobial compounds-producing protective cultures may provide an additional parameter of processing in order to improve the safety and ensure food keeping quality.

Keywords: Antimicrobial activity, biopreervation, isolation, pathogens

Contact Address: Hassan Abdel Moneem Ibrahim El Demerdash, Arish University, Dept. of Food and Dairy Sciences and Technology, Arish, Egypt, e-mail: eldemerdashhassangmail.com