Abstract
Back ground: Leuconostoc is one of the species of lactic acid bacteria that produced biofilms.Probiotic bacteria that produced biofilm has been used as naturopathy against different microbial pathogens.
 Objective: This study was conducted to determine the antimicrobial activity of Leuconostoc biofilm , against 24 isolates (4 of 6 different types) of food borne pathogens including Staphylococcus aureus , Salmonella spp, Escherichia coli , Klebsiella spp , Pseudomonas aeruginosa , Streptococcus mutans , Bacillus subtillus , Bacillus cereus, Bacillus sterothermophillus and Candida albicans.
 Materials and methods: using various concentration in vitro by filter paper disk diffusion method .
 Result: The present study showed the potent antimicrobial activity of the Leuconostoc mesenteroides biofilm against the all tested bacterial pathogens except Bacillus species and yeast Candida albicans. Biofilm produced by Leuconostoc mesenteroides showed highest zone of inhibition (13mm) against Escherichia coli and lowest zone of inhibition (7.0mm) against Streptococcus mutans .
 Conclusion: Consequently, Leuconostoc mesenteroides biofilm may be used as an antimicrobial agent in food products to prevent spoilage.
Highlights
Biofilms are defined as microbial communities characterized by the cells that are attached to each other, embedded in a matrix of Extracellular Polymeric Sub-stances (EPS) [1].Lactic acid bacteria could produce bio-film
Preparation of different concentrations of biofilm Different concentrations were prepared from Leuconostoc mesenteroides biofilm (1:2, 1:3,1:4) in addition of stock concentration, while the bacteria were poured in sterilized petridishes and maintained after hardening at 4 oC petridish considered to be as control sample [12]
Diameters of clear zones were (12,11,10,8 ) mm .It showed antibacterial activity of E.coli and Pseudomonas aeruginosa .The effectiveness of biofilm against Staphylococcus aurues may be due to metabolic products of bacteria Leuconostoc mesenteroides such as organic acids, diacetyl, CO2,hydrogen peroxide, and secondary metabolites [2]
Summary
Biofilms are defined as microbial communities characterized by the cells that are attached to each other, embedded in a matrix of Extracellular Polymeric Sub-stances (EPS) [1].Lactic acid bacteria could produce bio-film. Leuconostoc mesenteroides biofilm matrix contains components dextran, proteins and nucleic acids [3], and had an active action against many microbes, fungus, viruses and parasites. It was found that this biofilm had more effect on gram negative bacteria such as Escherichia coli ,Pseudomonas aeruginosa , Proteus mirabilis, Shigella flexneri ,Campylobacter jejuni, Salmonella typhimurium and gram positive bacteria such as Staphylococcus aureus, Staphylococcus epidermidis ,Enterococcus faecalis [1] .While the study of Hitendra [4] reported that Leuconostoc bacteria had antibacterial activity against Xanthomonas spp , Erwinia spp and some spoilage molds. This study aimed to observe the effect of Leuconostoc mesenteroides biofilm on the growth of some bacteria and fungi that cause food spoilage
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