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CASTELANI, L. Use of bacteriocin and cationic lipid nano-fragment s against resistant Staphylococcus spp. isolated from bovine mastitis. 2016. 71 p. Ph.D. Thesis (Microbiology) Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brasil, 2016. Staphylococcus pp. are reported as a major etiological agent of bovine mastitis, where the diversity of virulence factors and high antimicrobi al resistance profiles contribute to the poor prognosis of the infection. With regard to treatmen ts, many of the commercially available antimicrobials for bovine mastitis generate waste t hat alters the food quality and safety of milk and dairy products. In this scenario, the sear ch for new alternatives for control and treatment become essential. Bacteriocins and nanopa rticles have emerged as promising alternatives for future development of antimicrobia l agents. The aim of this study was to evaluate the “in vitro” antibacterial activity of t he bacteriocin nisin (NS), cationic lipid nanofragments of dioctadecyldimethylammonium bromide (D DA) and NS/DDA complex against drug-resistant Staphylococcus pp. strains isolated from mastitis in primiparous heifers and lactating dairy cows in herds from both experimenta l and commercial properties. For all isolates, the antibacterial susceptibility profile was determined by disk-diffusion method and the “in vitro” activity of nisin and DDA was evalua ted by determining the minimum bactericidal concentration (MBC). Synergistic effec t of NS/DDA complex was determined by time-kill and checkerboard methods. Cell viability was further evaluated by fluorescence microscopy. The size (nm), polydispersity and zeta potential (ζ) of NS/DDA complex, as well as, their interaction with a representative strain of S. aureus were determined by dynamic light scattering (DLS). For nisin and DDA the MBC 50 was 50 and 4 μg/mL, respectively, whereas MBC50 of NS/DDA was 3/2 μg/mL (partially synergistic eff ct, ΣFBC from > 0.5 to ≤ 1.0). Time-kill studies with NS/DDA revealed ≥ 3 log10 CFU/mL at an hour interaction. In fact, fluorescence microscopy confirmed loss viability af ter six hours interaction. NS/DDA assemblies resulted in cationic complexes (+ 8.84 m V) at nanoscale (148.5 nm), which contributes for the interaction with the negatively charged bacterial surface (-27.32 mV), favoring the bactericidal action of the NS/DDA comp lex. The NS/DDA complex has shown to be a promising alternative for the control of dr ug-resistant Staphylococcus spp. strains isolated from bovine mastitis.

Uso de bacteriocina e nanofragmentos de lípides catiônicos contra <i>Staphylococcus</i> spp. resistentes isolados de mastite bovina.