efficacy of four potential antimicrobial substances againstspecies andisolated from bovine mastitis.

Abstract

Mastitis is an important disease in dairy cattle with huge influence on animal welfare and economic situation of farmers. With very limited choices in antibiotic therapy of bovine mastitis and the relevance of emerging antimicrobial resistances, discovery of new antimicrobials is one of the major challenges for veterinary pharmacological research. Thus,efficacy of four promising substances was investigated: polyvinylpyrrolidone iodine (PVP iodine), N-acetylcysteine (NAC), N-chlorotaurine (NCT), and methylglyoxal (MGO). PVP iodine is an antiseptic commonly used in all medical fields. The two amino acid derivates NAC and NCT are a potent antioxidant respective oxidant with antimicrobial properties in various indications. MGO is one of the active components in Manuka honey, causing bacterial death by repression of protein and nuclei acid synthesis. For experiments,species (spp.) andwere isolated from bovine milk samples. Subsequently, broth microdilutions with common antibiotic agents and the four potential antimicrobials for determination of minimal inhibitory concentrations (MICs) and examinations regarding minimal bactericidal concentrations (MBCs), also time-dependent, were performed according to CLSI standards. Regarding antimicrobial susceptibility, growth ofspp. isolates was not restrained by examined concentrations of benzylpenicillins, aminopenicillins, isoxazolyl penicillins, macrolides, and lincosamides. However, studied concentrations of aminopenicillins combined with beta-lactamase inhibitors, cephalosporins (partly combined with aminoglycosides) as well as fluoroquinolones inhibited their growth. In contrast, allisolates were susceptible to tested concentrations of penicillins, cephalosporins, macrolides, lincosamides, and fluoroquinolones. Broth microdilutions of the four substances revealed median MICs of PVP iodine with 5 mg/mL forspp. and 4 mg/mL forand NAC with MICs of 5 mg/mL forspp. and 1.75 mg/mL forMICs of NCT were 1.5 mg/mL forspp. and 1 mg/mL forThe lowest MICs were found for MGO with 0.4 mg/mL forspp. and 0.1375 mg/mL for. Growth of every bacterial isolate was inhibited through all four substances, even when resistant to commonly used antibiotic agents. Therefore, with positive findings in further experiments regarding biocompatibility and efficacy, they could be considered as auspicious alternatives for mastitis treatment in dairy cattle.