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Bovine mastitis is a worldwide disease of dairy cattle associated with significant economic losses for the dairy industry. One of the most common pathogens responsible for mastitis is Staphylococcus (S.) aureus. Due to the development and spreading of antibiotic resistance, the search for novel antimicrobial substances against S. aureus is of great importance. The aim of this study was to evaluate two dihydroxybenzaldehydes for the prevention of bovine mastitis. Therefore we determined the minimal inhibitory concentration (MICs) of gentisaldehyde (2,5-dihydroxybenzaldehyde) and 2,3-dihydroxybenzaldehyde of a diverse set of 172 bovine mastitis S. aureus isolates using an automated robot-based microdilution method. To characterize the bovine isolates we determined the genotype by spa-typing, the antimicrobial resistance to eight antibiotic classes using the disk diffusion method and the MICs of three commonly used antiseptics (benzalkonium chloride, chlorhexidine, and iodine). Further we investigated the cytotoxicity of gentisaldehyde and 2,3-dihydroxybenzaldehyde in bovine mammary epithelial MAC-T cells using the XTT assay. The S. aureus strains showed a high genetic diversity with 52 different spa-types, including five novel types. Antibiotic susceptibility testing revealed that 24% of isolates were resistant to one antimicrobial agent and 3% of isolates were multi-resistant. The occurrence of antibiotic resistance strongly correlated with the spa-type. Both dihydroxybenzaldehydes showed antimicrobial activities with a MIC50 of 500 mg/L. The MIC of gentisaldehyde significantly correlated with that of 2,3-dihydroxybenzaldehyde, whereas no correlation was observed with the MIC of the three antiseptics. Cytotoxicity testing using bovine mammary epithelial MAC-T cells revealed that gentisaldehyde and 2,3-dihydroxybenzaldehyde show low toxicity at MIC50 and MIC90 concentrations. In conclusion, gentisaldehyde and 2,3-dihydroxybenzaldehyde exhibited antimicrobial activities against a diverse range of bovine mastitis S. aureus strains at low-cytotoxic concentrations. Therefore, both compounds are potential candidates as antiseptics to prevent bovine mastitis and to reduce the use of antibiotics in dairy cows.

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This research aimed to elucidate effects of an essential oil (EO) supplementation including thymol, limonene and carvone as main active compounds on parameters of feed efficiency (FE) in early lactating Simmental cows. Two balanced groups of cows (n = 16) were used. The EO group received a total mixed ration (TMR) and a concentrate plus 0.56 g EO blend per kg of dry matter (DM), the control group (CON) was fed the same feed without EO dietary supplementation. Results showed higher DM intake (DMI) of TMR and daily milk yield for CON (22.48 and 39.17 kg) than for EO cows (21.03 and 37.10 kg, P < 0.001), while intake of the concentrate and FE (milk yield/DMI) did not differ. FE was increased as an effect of EO supplementation (1.84 vs 1.80, P = 0.001), if body weight and pre-experimental FE were respected as co-variates. The FE progress during the 4-week test period displayed a strong negative correlation of trend line slopes and intercepts (r = −0.887, EO group). An inherent FE of 1.69 separated the predicted FE progress by treatment. EO cows with a higher inherent FE proceeded in steeper FE slopes than CON. No evidence of a general increase of FE after EO intake in dairy cows could be determined, unless additional individual parameters are considered.

The recommended antimicrobial agents for treatment or chemoprophylaxis of pertussis are erythromycin, azithromycin and clarithromycin.Trimethoprim-sulfamethoxasole (cotrimoxazole) can also be used. We tested the susceptibility to first-line and alternative antibiotics of 135 Bordetella pertussis (B. pertussis) strains recovered from patients with whooping cough through national pertussis surveillance in the Czech Republic (CR) in 1967 -2015. Isolates of B. pertussis were divided according to the year of isolation into 3 periods: from the years 1967 to 1999 (42 strains), 2004 -2010 (43 strains) and 2011 -2015 (50 strains).Methods & Materials: The minimal inhibitory concentrations (MICs) of erythromycin, clarithromycin, azithromycin, ciprofloxacin, and co-trimoxazole were tested by the reference agar dilution method on Bordet-Gengou agar with 15% defibrinated sheep blood.Results: Individual MICs of antibiotics were nearly identical in all three time periods. Each of the 135 study strains of B. pertussis was inhibited by two concentrations of erythromycin and azithromycin (0.06 and 0.12 mg/l) with the exception of one strain. All strains were inhibited by three concentrations of clarithromycin (0.03, 0.06, and 0.12 mg/l). All study strains were inhibited by a single concentration of ciprofloxacin (0.06 mg/l) and three concentrations of co-trimoxazole (0.12, 0.25 mg/l and 0.5 mg/l). Conclusion:The MICs of antibiotics were in the narow range of two to three low concetrations in all three time periods. The group of 135 Czech strains of B. pertussis appears to be homogeneous in terms of the MICs of the antibiotics tested, with two to three low concentrations being effective against all strains. To be inhibited, no strain required a higher concentration of erythromycin, clarithromycin, azithromycin, ciprofloxacin, or co-trimoxazole. No changes were observed in the MICs range of individual antibiotics during the period of 55 years.