Comparative Pharmacokinetics of Gentamicin C1, C1a and C2 in Healthy and Infected Piglets.

Gentamicin, an aminoglycoside antibiotic, is a mixture of therapeutically active C1, C1a, C2 and other minor components. Despite its decades-long use in pigs and other species, its intramuscular (IM) pharmacokinetics/pharmacodynamics (PKs/PDs) are unknown in piglets. Furthermore, the PKs of many drugs differ between healthy and sick animals. Therefore, we investigated the PKs of gentamicin after a single IM dose (10 mg/kg) in healthy piglets and piglets that were intranasally co-infected with Actinobacillus pleuropneumoniae and Pasteurella multocida (PM). The plasma concentrations were measured using validated liquid chromatography/mass spectrometry. The gentamicin exposure was 36% lower based on the area under the plasma concentration-time curve and 16% lower based on the maximum plasma concentration (Cmax) in the infected piglets compared to the healthy piglets, while it was eliminated faster (shorter half-life and larger clearance) in the infected piglets compared to the healthy piglets. The clearance and volume of distribution were the highest for the C1 component. C1, C1a and C2 accounted for 22-25%, 33-37% and 40-42% of the total gentamicin exposure, respectively. The PK/PD target for the efficacy of aminoglycosides (Cmax/minimum inhibitory concentration (MIC) > 10) could be exceeded for PM, with a greater magnitude in the healthy piglets. We suggest integrating this PK information with antibiotic susceptibility data for other bacteria to make informed antibiotic and dosage regimen selections against piglet infections.

Probiotic properties and adsorption of Enterococcus faecalis PSCT3-7 to vermiculite.

The probiotic properties of Enterococcus (E.) faecalis PSCT3-7, a new strain isolated from the intestines of pigs fed dietary fiber containing 50% sawdust, were investigated. E. faecalis PSCT3-7 tolerated a pH range of 3 to 8 and 0.3% bile salts, and it inhibited the growth of Salmonella Typhimurium in a concentration-dependent manner. In addition, E. faecalis showed resistance to several antibacterial agents. Vermiculite, a nutrient and microbial carrier, increased the bile tolerance of the strain. Scanning electron microscope images revealed good adsorption of E. faecalis PSCT3-7 onto vermiculite. E. faecalis PSCT3-7 represents a potential probiotic candidate to administer with vermiculite to swine.

Using In Vitro Dynamic Models To Evaluate Fluoroquinolone Activity against Emergence of Resistant Salmonella enterica Serovar Typhimurium.

The objectives of this study were to determine pharmacokinetic/pharmacodynamic (PK/PD) indices of fluoroquinolones that minimize the emergence of resistant Salmonella enterica serovar Typhimurium (S Typhimurium) using in vitro dynamic models and to establish mechanisms of resistance. Three fluoroquinolones, difloxacin (DIF), enrofloxacin (ENR), and marbofloxacin (MAR), at five dose levels and 3 days of treatment were simulated. Bacterial killing-regrowth kinetics and emergence of resistant bacteria after antibacterial drug exposure were quantified. PK/PD indices associated with different levels of antibacterial activity were computed. Mechanisms of fluoroquinolone resistance were determined by analyzing target mutations in the quinolone resistance-determining regions (QRDRs) and by analyzing overexpression of efflux pumps. Maximum losses in susceptibility of fluoroquinolone-exposed S Typhimurium occurred at a simulated AUC/MIC ratio (area under the concentration-time curve over 24 h in the steady state divided by the MIC) of 47 to 71. Target mutations in gyrA (S83F) and overexpression of acrAB-tolC contributed to decreased susceptibility in fluoroquinolone-exposed S Typhimurium. The current data suggest AUC/MIC (AUC/mutant prevention concentration [MPC])-dependent selection of resistant mutants of S Typhimurium, with AUC/MPC ratios of 69 (DIF), 62 (ENR), and 39 (MAR) being protective against selection of resistant mutants. These values could not be achieved in veterinary clinical areas under the current recommended therapeutic doses of the fluoroquinolones, suggesting the need to reassess the current dosing regimen to include both clinical efficacy and minimization of emergence of resistant bacteria.

BaeR protein acts as an activator of nuclear factor-kappa B and Janus kinase 2 to induce inflammation in murine cell lines.

BaeR, a response regulator protein, takes part in multidrug efflux, bacterial virulence activity, and other biological functions. Recently, BaeR was shown to induce inflammatory responses by activating the mitogen-activated protein kinases (MAPKs). In this study, we investigated additional pathways used by BaeR to induce an inflammatory response. BaeR protein was purified from Salmonella enterica Paratyphi A and subcloned into a pPosKJ expression vector. RAW 264.7 cells were treated with BaeR, and RNA was extracted by TRIzol reagent for RT-PCR. Cytokine gene expression was analyzed by using the comparative cycle threshold method, while western blotting and ELISA were used to assess protein expression. We confirmed that BaeR activates nuclear factor-kappa B (NF-κB), thereby inducing an inflammatory response and increases the production of interleukins (IL-)1ß and IL-6. During this process, the Janus kinase 2 (JAK2)-STAT1 signaling pathway was activated, resulting in an increase in the release of interferons I and II. Additionally, COX-2 was activated and its expression increased with time. In conclusion, BaeR induced an inflammatory response through activation of NF-κB in addition to the MAPKs. Furthermore, activation of the JAK2-STAT1 pathway and COX-2 facilitated the cytokine binding activity, suggesting an additional role for BaeR in the modulation of the immune system of the host and the virulence activity of the pathogen.

Pharmacokinetics, pharmacokinetic-pharmacodynamic relationship, and withdrawal period of amoxicillin sodium in olive flounder (Paralichthys olivaceus).

1. The pharmacokinetics (PK) and withdrawal period of amoxicillin sodium in olive flounder and its activity against pathogenic bacteria of olive flounder were investigated. 2. Intramuscular administration (12.5 or 125 mg/kg, n = 160) and HPLC analysis of sera were used. 3. Rapid absorption (Tmax 2.6 and 2.2 h), prolonged action (terminal half-life, 15.52 and 10.42 h; MRT, 18.79 and 14.44 h), and dose-proportional exposure (AUC0-∞, 273.69 and 2755.37 h. µg/ml) were observed after 12.5 and 125 mg/kg doses. 4. The withdrawal period of amoxicillin sodium from muscle plus skin of olive flounder (n =40, water temperature, 23 °C) was 12 d (276 degree days). 5. Amoxicillin sodium had small MICs against Streptococcus iniae (0.008-0.06 µg/ml) and Streptococcus parauberis (0.03-1.0 µg/ml), whereas higher concentrations were required to inhibit Edwardsiella tarda isolates (0.06-16 µg/ml). 6. While large AUC0-24 h/MIC90 and Cmax/MIC90 ratios were obtained for S. iniae and S. parauberis, with drug concentrations in serum greater than MICs for the entire dosing interval (T > MIC90 of 100%), the lower dose (12.5 mg/kg) could not achieve target values of the PK-pharmacodynamic (PD) indices for E. tarda isolates, suggesting the need for higher doses to combat pathogenic bacteria with large MICs.

Pharmacokinetics and pharmacokinetic/pharmacodynamic integration of marbofloxacin after intravenous and intramuscular administration in beagle dogs.

1.The aim of the present study was to determine the PKs of marbofloxacin in beagle dogs after intravenous (i.v.) and intramuscular (i.m.) administration, the ex vivo and in vitro PK/PD indices of marbofloxacin against clinical isolates of Staphylococcus pseudintermedius, and the ex vivo AUC/MIC ratios associated with different levels of antibacterial activity. 2.After i.v. of marbofloxacin (2 mg/kg), the mean ± SEM values of AUC, t1/2ß, Vss, and CL were 8.47 ± 3.51 h µg/mL, 8.08 ± 6.25 h, 2.32 ± 1.00 L/kg and 0.23 ± 0.06 L/kg/h and corresponding values after intramuscular injection were 11.37 ± 3.07 h µg/mL, 7.51 ± 3.70, 1.80 ± 0.90 L/kg and 0.17 ± 0.04 L/kg/h. After i.m. administration, a Cmax of 1.76 ± 0.09 µg/mL was achieved at Tmax of 0.47 ± 0.08 h. The ex-vivo AUC/MIC ratios required to produce bacteriostasis, bactericidal action and elimination of S. pseudintermedius were 65.03, 97.02 and 136.84 h. 3.The in vivo AUC/MIC ratios obtained after i.v. and i.m. administration of 2 mg/kg marbofloxacin (67.76 ± 1.23 and 91.18 ± 2.61) were below the ex vivo AUC/MIC ratios required for bactericidal activity and bacterial elimination (97.02 ± 9.24 2 mg/kg and 136.21 ± 7.58), suggesting that the recommended daily dosage (2 mg/kg) may not suffice to kill and eradicate S. pseudintermedius strains encountered in clinical area.

The in vitro activity of 15 antimicrobial agents against bacterial isolates from dogs.

The in vitro activity of 15 antimicrobial agents against clinical isolates of Staphylococcus pseudintermedius, Staphylococcus aureus, Escherichia coli, Pasteurella spp. and Streptococcus canis from dogs was investigated. For Staphylococcus spp., the highest frequency of resistance was observed for penicillin, followed by ampicillin, tetracycline and chloramphenicol. The highest frequency of resistance in E. coli isolates was recorded for tetracycline and streptomycin. Pasteurella spp. and S. canis had the highest resistance rate for tetracycline and chloramphenicol. Most isolates showed full susceptibility to low-level resistance to colistin, florfenicol and fluoroquinolones. Further studies using larger number of isolates from both healthy and diseased dogs would provide a broader picture of antimicrobial resistance at a national level and promote prudent use of antimicrobial agents in companion animals.

Comparative mutant prevention concentration and mechanism of resistance to veterinary fluoroquinolones in Staphylococcus pseudintermedius.

BACKGROUND: The problem of antibacterial drug resistance is increasing worldwide, in part due to the therapeutic concentrations currently used based on the minimal inhibitory concentration (MIC) as a measure of potency are often the very concentrations required to selectively enrich the resistant mutant portion of the population. A mutant prevention concentration (MPC)-based dosing strategy is suggested to improve the therapeutic outcome based on the MIC. OBJECTIVE: Our aim was to investigate the MPC and mechanism of resistance to various fluoroquinolones using recent Staphylococcus pseudintermedius isolates from canine pyoderma. METHODS: The broth microdilution method for MIC and a series of agar plates containing different concentrations of fluoroquinolones were inoculated with ∼10(10) colony-forming units of the bacterial culture for MPC were used. PCR was used to identify mutation in the resistant isolates. RESULTS: The rank order of potency based on MIC and MPC was ciprofloxacin = enrofloxacin ≥ marbofloxacin > difloxacin ≥ orbifloxacin. Integrating our data with reported pharmacokinetic data at the recommended dose ranges revealed that only high doses of ciprofloxacin, enrofloxacin and marbofloxacin could achieve a maximal plasma concentration (C(max)) greater than the MPC of 90% of isolates (C(max)/MPC(90)). The overall rank of potency against S. pseudintermedius, based on C(max)/MIC, C(max)/MPC, the area under concentration-time curve (AUC)/MIC and AUC/MPC values, was in decreasing order: enrofloxacin > ciprofloxacin ≥ marbofloxacin ≥ orbifloxacin = difloxacin. Sequencing of the quinolone resistant determining region of gyrA, gyrB, grlA and grlB of resistant strains showed a base-pair substitution in both gyrA and gyrB that resulted in Ser-84 to Leu and Ser-80 to Arg amino acid changes, respectively. CONCLUSIONS AND CLINICAL IMPORTANCE: High doses of ciprofloxacin, enrofloxacin and marbofloxacin could minimize the selection of resistant mutants, whereas the possibility of selecting mutants with the conventional doses of difloxacin and orbifloxacin, and low clinical doses of all fluoroquinolones, seems high.