Inhibitory activity of Staphylococcus aureus against Lactococcus spp. isolated from artisanal Minas cheese

Abstract Text: Production of antimicrobial substances by Staphylococcus aureus isolated from food has been reported. Since it is a highly prevalent etiologic agent for mastitis in dairy herds, inhibition of starter culture due to S. aureus inhibitory activity is possible during the processing of fermented dairy products, such as cheeses. The objective of the current work was to evaluate the antimicrobial substances produced by samples of S. aureus isolated from cow’s milk during mastitis occurrence and their effect against strains of Lactococcus spp. Individual milk samples, obtained from 54 herds, were analyzed for S. aureus presence and isolated strains were tested for inhibitory activity using the deferred-antagonism assay, with Corynebacterium fimi (NCTC 7547) as indicator. Proteic nature of the antimicrobial substances was investigated using protease type XIV from Streptomyces griseus (Sigma P-5147). Inhibitory spectrum was tested against nine Lactococcus spp. strains, previously isolated from artisanal Minas cheese. Descriptive statistics was used. Antimicrobial activity using the deferred-antagonism assay was detected in 262 (40%) of the 655 S. aureus strains tested. All 262 strains were inactivated by a proteolytic enzyme tested, indicating their proteic nature, a characteristic of bacteriocins. From 262 positive strains, 55 were selected based on the diameter of inhibition zone (>10mm) for inhibitory activity against Lactococcus spp. Noteworthy, 42 strains (76%) presented some inhibitory activity against Lactococcus spp., and one strain of S. aureus presented inhibitory activity against five Lactococcus spp. strains.   The results indicate that some S. aureus strains inhibit samples of Lactococcus spp. isolated from artisanal Minas cheese. Additional work is recommended to investigate further implications of this finding.

Keywords: Staphylococcus aureus, bacteriocins, mastitis