Globally, clinical mastitis (CM) is a significant disease in the dairy industry and has a tremendous economic impact because of the significantly reduced amount of milk production. Antibiotics are medicines used to treat infections, particularly those of bacterial origin. Misusing these common drugs leads to emerging resistance bacteria and public health concerns in human and animal medicine worldwide. Therefore, the use of natural alternatives with low effects is recommended. This article aims to evaluate the antibacterial activity of peptide nisin on mastitis bacteria and its synergistic effect with CLF36 peptide in vitro. Recombinant peptide nisin and CLF36 were obtained from previous research. The minimum inhibitory concentration (MIC) test was performed using the microdilution method on bacteria extracted from animal mastitis, such as Clostridium perfringens, Proteus mirabilis, Enterococcus faecalis, Salmonella typhimurium, Pseudomonas aeruginosa, and Listeria monocytogenes. This study showed that nisin and CLF36 alone had an inhibitory effect on all the studied bacteria in the 64-32 and 256-32 μg/ml concentration range, respectively. Also, the combination of nisin and CLF36 showed a general synergistic interaction for all used strains (FIC I < 0.5). This study demonstrated that combining these two peptides could reduce the risk of developing drug resistance by creating synergistic effects with a minimum concentration of each of the two peptides.

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