Antimicrobial susceptibility of Rhodococcus equi strains isolated from foals in Chile.

Rhodococcus equi is responsible for foal pneumonia worldwide, with a significant economic impact on the production and breeding of horses. In Chile, the first case was reported in 2000, and since then, its incidence has been increasing. Distinctive characteristics of R. equi as an intracellular pathogen in macrophages, emergence of virulence plasmids encoding surface lipoprotein antigens, and appearance of antibiotic resistance against macrolides and rifampicin have significantly complicated the treatment of R. equi pneumonia in foals. Therefore, in vitro susceptibility studies of first-line and newer antibiotics against R. equi are the first step to establishing effective treatments and optimizing new therapeutic options. The aim of the present study is to determine the susceptibility profile of fourteen strains of R. equi isolated from foals in Chile to several antibiotics of the macrolide group including azithromycin, amikacin, tildipirosin and gamithromycin as well as others such as rifampicin, doxycycline and ceftiofur. Identification of R. equi in collected isolates from foals in Chile has been performed by CAMP test and PCR based on detecting of the gene encoding the 16 S rRNA. The presence of genes encoding virulence plasmids was also determined using PCR. Results obtained have demonstrated presence of virulent R. equi strains in Chile. In vitro susceptibility pattern to different antibiotics has shown better results for doxycycline and rifampicin similar to previous studies performed. Current macrolides have been evaluated in order to consider alternative treatment options in a context of emerging resistance to classic macrolides and rifampicin, obtaining better results with gamithromycin (MIC range of 0.125 to 128 mg/ml) than with tildipirosin (MIC range of 16 to 128 mg/ml). An adequate diagnosis of bacterial susceptibility based on antibiograms is necessary to treat the Rhodococcus equi infection in foals.

Susceptibility of caprine mastitis pathogens to tildipirosin, gamithromycin, oxytetracycline, and danofloxacin: effect of serum on the in vitro potency of current macrolides.

Mastitis is a significant disease in dairy ruminants, causing economic losses to the livestock industry and severe risks to public health. Antibiotic therapy is one of the most crucial practices to treat mastitis, although the susceptibility of caprine mastitis pathogens to current antibiotics has not been tested under standard or modified incubation conditions. This work evaluated the in vitro activity of tildipirosin, gamithromycin, oxytetracycline, and danofloxacin against caprine mastitis pathogens incubated following standard conditions of Clinical and Laboratory Standards Institute (CLSI) and deviation method by 25% supplementation with goat serum. Mycoplasma agalactiae, Escherichia coli, Staphylococcus aureus, Streptococcus spp., and coagulase-negative Staphylococci (CNS) were isolated from dairy goats with mastitis in Spain. Minimum inhibitory concentrations (MICs) were determined using the broth microdilution technique. The lowest MIC90 under standard conditions was obtained with danofloxacin for mastitis-causing pathogens. An exception was M. agalactiae, where danofloxacin and oxytetracycline obtained low values. However, after adding serum, gamithromycin showed the lowest MIC50 for S. aureus, Streptococcus spp., and CNS. The lowest MIC50 was obtained with all the antibiotics tested (< 0.125 µg/ml) against M. agalactiae. Supplementing with serum resulted in a significant variation in tildipirosin and gamithromycin MIC values for CNS, S. aureus, M. agalagtiae, and E. coli. In brief, the MIC for antibiotics used against mastitis should be determined under conditions closely resembling intramammary infections to obtain representative susceptibility patterns against mastitis pathogens. Caprine mastitis pathogens were broadly susceptible to danofloxacin under standard conditions. The potency of macrolides against caprine mastitis pathogens increases when serum is present in culture media.

Pharmacokinetics of tildipirosin in horses after intravenous and intramuscular administration and its potential muscle damage.

Tildipirosin is a novel semisynthetic macrolide antibiotic exclusively used in veterinary practice to treat respiratory infections. There are no pharmacokinetic or safety information available regarding the use of tildipirosin after intramuscular administration in horses. Thus, the objective of this work was to determine the disposition kinetics of tildipirosin after intravenous (IV) and intramuscular (IM) administration in horses and its potential muscle damage and cardiotoxicity. Six mature, Spanish-breed horses were used in a crossover study with a washout period of 30 days. Tildipirosin (18%) was administered at single doses by IV (2 mg/kg) and IM (4 mg/kg) routes. Tildipirosin plasma concentrations were determined by HPLC assay with ultraviolet detection. Muscle damage and inflammation were assessed by creatine kinase (CK) and haptoglobin (Hp), respectively. Creatine kinase myocardial band (CK-MB) and troponin (Tn) were used to evaluate cardiotoxicity. Tildipirosin in horses reached peak concentrations (Cmax = 1.13 µg/mL) at 0.60 h (tmax) after IM administration with an absolute bioavailability of 109.2%. Steady-state volume of distribution and clearance were 3.31 ± 0.57 L/kg and 0.22 ± 0.02 L/h/kg, respectively. Tildipirosin did not cause cardiotoxicity since CK-MB and Tn basal levels were not significantly different from those obtained after several days post-administration. Mild local reactions were observed after IM administration. This local inflammation was associated with mild myolysis (CK 239-837 UI/L), which was detectable for 48 h. In brief, tildipirosin could help to treat respiratory infections in horses because it showed extensive distribution, high bioavailability and did not provoke general adverse reactions.

Quantification and Determination of Stability of Tylvalosin in Pig Plasma by Ultra-High Liquid Chromatography with Ultraviolet Detection.

Tylvalosin (TV) is a macrolide antibiotic that is used for treating respiratory and enteric bacterial infections in swine and in poultry. In the coming years, the use of this drug will probably be widely studied in different species, but before its use in each veterinary species, macrolide analytical determination in various biological fluids is a pre-requisite step for the rational dose calculation of TV based on specific pharmacokinetic information. Its quantification is essential for detecting and avoiding the appearance of residues in animal products intended for human consumption. Therefore, a robust chromatographic method coupled with an ultraviolet detector was fully validated for the quantification of TV in pig plasma. A mixture (78:22) of (A) 0.3% formic acid in water and (B) acetonitrile was used as the mobile phase. TV and enrofloxacin (internal standard) were eluted at 14.1 and 5.9 min, respectively. Calibration curves ranged from 0.1 to 5 µg/mL. The accuracy and precision parameters for the quality controls were always <13.0%. Recovery ranged from 89.66 to 96.92%. The detection and quantification limits were found to be 0.05 µg/mL and 0.1 µg/mL, respectively. This method could be applied to develop pharmacokinetic studies.

Pharmacokinetics of Tildipirosin in Plasma, Milk, and Somatic Cells Following Intravenous, Intramuscular, and Subcutaneous Administration in Dairy Goats.

Tildipirosin is a macrolide currently authorized for treating respiratory diseases in cattle and swine. The disposition kinetics of tildipirosin in plasma, milk, and somatic cells were investigated in dairy goats. Tildipirosin was administered at a single dose of 2 mg/kg by intravenous (IV) and 4 mg/kg by intramuscular (IM) and subcutaneous (SC) routes. Concentrations of tildipirosin were determined by an HPLC method with UV detection. Pharmacokinetic parameters were estimated by non-compartmental analysis. Muscle damage, cardiotoxicity, and inflammation were evaluated. After IV administration, the apparent volume of distribution in the steady state was 7.2 L/kg and clearance 0.64 L/h/kg. Plasma and milk half-lives were 6.2 and 58.3 h, respectively, indicating nine times longer persistence of tildipirosin in milk than in plasma. Moreover, if somatic cells are considered, persistence and exposure measured by the area under concentration-time curve (AUC) significantly exceeded those obtained in plasma. Similarly, longer half-lives in whole milk and somatic cells compared to plasma were observed after IM and SC administration. No adverse effects were observed. In brief, tildipirosin should be reserved for cases where other suitable antibiotics have been unsuccessful, discarding milk production of treated animals for at least 45 days or treating goats at the dry-off period.

Cephalosporin susceptibility of Staphylococcus aureus strains isolated from commercial rabbit and goats farms in Spain.

Antimicrobial drug resistance is an important problem that challenges veterinary clinicians to provide effective treatments without further spreading resistance to other animals and people. The most commonly used pharmacodynamic parameter to define potency of antimicrobial drugs is minimum inhibitory concentration (MIC). The aim of this study was to evaluate the antibiotic susceptibility of thirty-six strains of Staphylococcus aureus isolated from dairy goats with mastitis and rabbits with chronic staphylococcosis. Four cephalosporins were tested: cephalexin, cephalotin, cefonicid and ceftiofur. MIC tests were performed according to the microdilution broth method. The calculated values of sensitivity in goats and rabbits were 66.67% and 72.22% for cephalexin, 72.22 % and 94.44% for cefonicid, 77.78% and 94.44% for cephalotin and 77.78% and 100% for ceftiofur, respectively. For all antibiotics, MIC90 of S. aureus from rabbits were lower than MIC90 from goats. These data suggest that more antibiotics are used in goat milk production than in rabbit farming. According to MIC values obtained in this study, ceftiofur and cephalotin may be the best option for treating S. aureus infections in lactating goats. For rabbits, ceftiofur showed lowest MIC values, therefore, it could be an alternative to treatment the infections caused by S. aureus in this species.

Resistance patterns to C and D antibiotic categories for veterinary use of Campylobacter spp., Escherichia coli and Enterococcus spp. commensal isolates from laying hen farms in Spain during 2018.

Antimicrobial Resistance (AMR) is a global threat for human and animal health. Few studies have been carried out on laying hens. The aim of this work was to evaluate the antimicrobial susceptibility of commensal Campylobacter spp., E. coli, and Enterococcus spp. isolates in Spanish laying hens in 2018. Samples were collected from 39 laying hen farms. The microorganisms of interest were isolated and confirmed by PCR. The Minimum Inhibitory Concentration (MIC) to antimicrobials of C and D categories were determined. 195 E. coli, 195 Enterococcus spp. and 25 Campylobacter spp. isolates were obtained. E. coli isolates showed high resistance to D category antimicrobials (sulfamethoxazole 76.41 %, tetracycline 62.05 %, trimethoprim 50.77 %, ampicillin 30.77 %) and lower resistance to C category (azithromycin 30.26 %, gentamicin 12.31 %, chloramphenicol 4.62 %). A 10.26 % of E. coli isolates were susceptible to all antimicrobials tested, Multi Drug Resistance (MDR) to 3 antimicrobial families was found in 23.08 % of the isolates and 13.85 % were MDR to 4 families, being Erythromycin-Sulfamethoxazole-Tetracycline the most common resistance profile (10.77 %). Enterococcus spp. showed very high resistance to D category tetracycline (78.47 %) and C category erythromycin (76.42 %). The 11.79 % of Enterococcus spp. isolates were susceptible to all antimicrobials and 53.33 % were resistant to 2 families, being Erythromycin-Tetracycline the most common AMR profile (51.79 %). Regarding Campylobacter spp., resistance to tetracycline (48 %) was higher than resistance to C category antimicrobials (erythromycin 28 %, streptomycin 24 %, gentamicin 16 %). There was a 52 % sensitivity to all tested antimicrobials and 24 % showed MDR to aminoglycosides, macrolides and tetracyclines (Gentamicin-Streptomycin-Erythromycin-Tetracycline MDR profile). Novel data on AMR in laying hen commensal isolates in Spain was provided. High resistance to several antimicrobials was found, especially to key drugs for the treatment of zoonosis, which represents a public health risk. Better surveillance and careful regulation of antimicrobial use is required in laying hen production.

Pharmacokinetics of Tildipirosin in Ewes after Intravenous, Intramuscular and Subcutaneous Administration.

A single-dose disposition kinetics for tildipirosin was evaluated in clinically healthy ewes (n = 6) after intravenous (IV), intramuscular (IM), and subcutaneous (SC) administration of a commercial formulation. Tildipirosin concentrations were determined by high-performance liquid chromatography with ultraviolet detection. Plasma concentration-time data was calculated by non-compartmental pharmacokinetic methods. The apparent volume of distribution (Vz) of tildipirosin after IV administration was 5.36 ± 0.57 L/kg suggesting a wide distribution in tissues and inside the cells. The elimination half-life (t½λz) was 17.16 ± 2.25, 23.90 ± 6.99 and 43.19 ± 5.17 h after IV, IM and SC administration, respectively. Following IM administration, tildipirosin was rapidly absorbed (tmax = 0.62 ± 0.10 h) even to a greater extent than after SC administration. Time to reach peak concentration (tmax) and peak plasma concentrations (Cmax) differed significantly, but both parameters showed a more significant variability after SC than after IM administration. Bioavailabilities after extravascular administration were high (>70%). Therefore, given general adverse reactions that were not observed in any ewe and favourable pharmacokinetics, tildipirosin could be effective in treating bacterial infections in sheep.

Pharmacokinetics of cefonicid in lactating goats after intravenous, intramuscular and subcutaneous administration, and after a long-acting formulation for subcutaneous administration.

The single-dose disposition kinetics of cefonicid were determined in clinically normal lactating goats (n = 6) after intravenous (IV), intramuscular (IM) and subcutaneous (SC) administration of a conventional formulation, and after subcutaneous administration of a long-acting formulation (SC-LA). Cefonicid concentrations were determined by high performance liquid chromatography with ultraviolet detection. The concentration-time data were analysed by noncompartmental pharmacokinetic methods. Steady-state volume of distribution (Vss ) and clearance (Cl) of cefonicid after IV administration were 0.14 ± 0.03 L/kg and 0.51 ± 0.07 L/h·kg, respectively. Following IM, SC and SC-LA administration, cefonicid achieved maximum plasma concentrations of 14.46 ± 0.82, 11.98 ± 1.92 and 17.17 ± 2.45 mg/L at 0.26 ± 0.13, 0.42 ± 0.13 and 0.83 ± 0.20 hr, respectively. The absolute bioavailabilities after IM, SC and SC-LA routes were 75.34 ± 11.28%, 71.03 ± 19.14% and 102.84 ± 15.155%, respectively. After cefonicid analysis from milk samples, no concentrations were found above LOQ at any sampling time. From these data, cefonicid administered at 20 mg/kg each 12 hr after SC-LA could be effective to treat bacterial infections in lactating animals not affected by mastitis problems.