Mastitis is the most common and costly production disorder of dairy cattle. In the United States, approximately 40% of clinical mastitis cases from which a pathogen is isolated are attributed to gram -negative organisms (Erskine et al., 1991). The most common Received February 28, 2006. Accepted March 31, 2006. 1 Corresponding author: rz26@cornell.edu 3425 gramnegative causes of clinical mastitis are coliform bacteria, specifically Escherichia coli and Klebsiella spp. (Smith et al., 1985; Erskine et al., 1991; Todhunter et al., 1991). Considering the damage caused by infections, and the poor response of Klebsiella mastitis to treatment, prevention is of paramount importance in control of Klebsiella mastitis. The primary source of Klebsiella spp. in the cows’ environment is organic bedding. Outbreaks of Klebsiella are commonly associated with sawdust bedding (National Mastitis Council, 1999). The antimicrobial effect of lactobacilli is primarily linked to the production of organic acids, such as lactic acid, acetic acid, propionic acid, and sometimes hydrogen peroxide, bacteriocins, and antimicrobial peptides (AMPs) with a variable range of action (CortesZavaleta et al. 2014; Gemechu 2015). A combination therapy, including probiotic and antibiotic may offer better antimicrobial activity and lessen the dose of antibiotic required. As LAB enjoy the ‘generally recognized as safe’ (GRAS) status, their metabolites have captivated substantial interest as natural drugs in recent years (Reis et al., 2012). In this study based on the information provided by the researchers the supernatant of the lactic acid bacterial strains were used in different concentrations to assessing the growth of Klebsiella pneumoniae., causing cow mastitis which has been isolated from the cow farm house. The supernatant of lactic acid bacteria which consist of several organic acids and some metabolites in it. That was treated with one of the important human and cattle pathogen Klebsiella pneumoniae., with the three different concentrations. And this current study was successfully comes with the expected inhibitory effect to the K. pneumoniae.,

Keywords : Anti-Bacterial Activity, Cow Mastitis, Organic Acid, Supernatant.