Antibacterial activity of isopropoxy benzene guanidine against Riemerella anatipestifer

Introduction: Riemerella anatipestifer (R. anatipestifer) is an important pathogen in waterfowl, leading to substantial economic losses. In recent years, there has been a notable escalation in the drug resistance rate of R. anatipestifer. Consequently, there is an imperative need to expedite the development of novel antibacterial medications to effectively manage the infection caused by R. anatipestifer. Methods: This study investigated the in vitro and in vivo antibacterial activities of a novel substituted benzene guanidine analog, namely, isopropoxy benzene guanidine (IBG), against R. anatipestifer by using the microdilution method, time-killing curve, and a pericarditis model. The possible mechanisms of these activities were explored. Results and Discussion: The minimal inhibitory concentration (MIC) range of IBG for R. anatipestifer was 0.5-2 μg/mL. Time-killing curves showed a concentration-dependent antibacterial effect. IBG alone or in combination with gentamicin significantly reduced the bacterial load of R. anatipestifer in the pericarditis model. Serial-passage mutagenicity assays showed a low probability for developing IBG resistance. Mechanistic studies suggested that IBG induced membrane damage by binding to phosphatidylglycerol and cardiolipin, leading to an imbalance in membrane potential and the transmembrane proton gradient, as well as the decreased of intracellular adenosine triphosphate. In summary, IBG is a potential antibacterial for controlling R. anatipestifer infections.

PK/PD integration of florfenicol alone and in combination with doxycycline against Riemerella anatipestifer

Riemerella anatipestifer (RA) is an important pathogen found in poultry. RA infection can kill ducks and lead to significant economic losses. Seven RA strains with different susceptibility phenotypes were chosen to study the pharmacokinetic/pharmacodynamic (PK/PD) integration of florfenicol (FF) alone and in combination with doxycycline (DOX). The checkerboard assay indicated that synergy [fractional inhibitory concentration index (FICI) ≤ 0.5] was detected in the CVCC3952 strain of RA and that additivity (FICI >0.5 to ≤ 1) was observed in other strains. Static time–kill curves showed that the bactericidal effect of FF against RA was produced at a FF concentration ≥4 MIC, and the antibacterial activity of FF against RA was enhanced from the aspects of efficacy and efficacy in combination with DOX. Dynamic time–kill curves indicated that FF elicited bactericidal activity against the CVCC3857 strain with a reduction ≥4.88 log₁₀CFU/ml when the dose was ≥8 mg/L. However, a bactericidal effect was not achieved at the maximum administered dose of FF monotherapy (20 mg/L) for isolates with a MIC ≥4 μg/ml. The effect of FF against RA was enhanced upon combination with DOX. The combination of FF with DOX reduced the bacterial burden ≥4.53 log₁₀CFU/ml for all strains with a MIC ≥4 μg/ml. Data were fitted to a sigmoidal E_max model. The PK/PD parameters of AUC_24h/MIC (the area under the concentration–time curve over 24 h divided by the MIC) and %T >MIC (the cumulative percentage of time over a 24-h period at which the concentration exceeded the MIC) of FF for eliciting a reduction of 3 log₁₀CFU/ml was 40.10 h and 58.71, respectively. For strains with a MIC ≤ 16 μg/ml, the magnitude of the AUC_24h/MIC and C_max/MIC required for a 3 log₁₀CFU/ml of bacterial killing was 34.84 h and 4.74 in the presence of DOX at 0.5 MIC, respectively. These data suggest that combination of FF with DOX enhanced the activity against RA strains with various susceptibilities to FF and DOX.

Comparative pharmacokinetics of intravenous and intramuscular cefquinome sulfate administration in ducklings and goslings

OBJECTIVE

To compare the pharmacokinetics of cefquinome sulfate in ducklings and goslings after IV or IM administration of a single dose.

ANIMALS

216 healthy Muscovy ducklings (Cairina moschata) and 216 healthy Sichuan white goslings (Anser cygnoides).

PROCEDURES

Ducklings and goslings were each randomly assigned to 3 groups (n = 72/group) that received a single dose (2 mg/kg) of injectable cefquinome sulfate administered IV or IM or of injectable cefquinome sulfate suspension administered IM. Blood samples were collected at various points after drug administration (n = 6 birds/time point). Plasma cefquinome concentrations were measured by high-performance liquid chromatography with UV detection, and pharmacokinetic parameters were calculated with a 2-compartment model method.

RESULTS

After IV injection, mean distribution half-life of cefquinome was longer in goslings (0.446 hours) than in ducklings (0.019 hours), whereas volume of distribution at steady state was greater (0.432 vs 0.042 L/kg) and elimination half-life was slower (1.737 vs 0.972 hours). After IM administration of injectable cefquinome sulfate, bioavailability of the drug was higher in goslings (113.9%) than in ducklings (67.5%). After IM administration of injectable cefquinome sulfate suspension, bioavailability was also higher in goslings (123.1%) than in ducklings (96.8%), whereas elimination half-life was slower (6.917 vs 1.895 hours, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

In goslings, IV administration of cefquinome resulted in slower distribution and metabolism of the drug than in ducklings and IM administration resulted in higher bioavailability. The delayed-release effect of the injectable cefquinome sulfate suspension when administered IM was observed only in goslings.

Effect of ketoprofen co-administration on pharmacokinetics of cefquinome following repeated administration in goats

The pharmacokinetics of cefquinome (2 mg/kg every 24 hr for 5 days) was determined following intramuscular administration alone and co-administration with ketoprofen (3 mg/kg every 24 hr for 5 days) in goats. Six goats were used for the study. In the study, the crossover pharmacokinetics design with 20-day washout period was performed in two periods. Plasma concentrations of cefquinome were assayed using high-performance liquid chromatography by ultraviolet detection. The mean terminal elimination half-life (t_1/2ʎz ), area under the concentration-time curve (AUC_0-24 ), peak concentration (C_max ), apparent volume of distribution (V_darea /F), and total body clearance (CL/F) of cefquinome after the administration alone were 4.85 hr, 11.06 hr*µg/ml, 2.37 µg/mL, 1.23 L/kg, and 0.17 L/h/kg after the first dose, and 5.88 hr, 17.01 hr*µg/mL, 3.04 µg/mL, 0.95 L/kg, and 0.11 L/h/kg after the last dose. Ketoprofen significantly prolonged t_1/2ʎz of cefquinome, increased AUC_0-24 and C_max , and decreased V_darea /F and CL/F. Cefquinome exhibited low accumulation after the administration alone and in combination with ketoprofen. These results indicated that ketoprofen prolonged the elimination of cefquinome in goats. The 24-hr dosing intervals at 2 mg/kg dose of cefquinome, which co-administered with ketoprofen, may maintain T> minimum inhibitory concentration (MIC) values above 40% in the treatment of infections caused by susceptible pathogens with the MIC value of ≤0.75 μg/ml in goats with an inflammatory condition.

Selection of DNA aptamers and establishment of an effective aptasensor for highly sensitive detection of cefquinome residues in milk

Cefquinome (CFQ), which is a fourth-generation cephalosporin approved for veterinary use only, has been widely used for treating porcine or bovine respiratory infection, bovine mastitis and other diseases. However, the antibacterial effect of CFQ is based on the duration of drug concentration remaining in excess of the minimum inhibitory concentration in serum or tissues, thereby inevitably leading to CFQ residues with high levels in animal-sourced food. In this paper, four CFQ-specific ssDNA aptamers were selected via a magnetic bead-based systematic evolution of ligands by the exponential enrichment (SELEX) method. Aptamer W1 with the lowest dissociation constant (Kd) value of 40.13 ± 22.11 nM was chosen for establishing a fluorescence aptasensor based on magnetic separation and release of molecular beacons for detection of CFQ residues. This aptasensor exhibited a high sensitivity toward CFQ with a limit of detection (LOD) of 0.09 ng mL-1 (linear range from 0.5 to 150 ng mL-1). Moreover, the present aptasensor also showed high selectivity against ampicillin and CFQ's structural analogs (i.e., cefpirome sulfate and cefixime). Finally, this aptasensor was used to detect CFQ in real spiked milk. The recovery rate of CFQ from spiked milk samples ranged from 96.6% to 103.2%. These results indicated that the developed aptasensor is a promising, highly sensitive and specific method for CFQ residue detection in animal-sourced food.

Pharmacokinetics of cefquinome after single and repeated subcutaneous administrations in sheep

The purpose of this study was to determine the pharmacokinetics of cefquinome (CFQ) following single and repeated subcutaneous (SC) administrations in sheep. Six clinically healthy, 1.5 ± 0.2 years sheep were used for the study. In pharmacokinetic study, the crossover design in three periods was performed. The withdrawal interval between the study periods was 15 days. In first period, CFQ (Cobactan, 2.5%) was administered by an intravenous (IV) bolus (3 sheep) and SC (3 sheep) injections at 2.5 mg/kg dose. In second period, the treatment administration was repeated via the opposite administration route. In third period, CFQ was administrated subcutaneously to each sheep (n = 6) at a dose of 2.5 mg/kg q. 24 hr for 5 days. Plasma concentrations of CFQ were measured using the HPLC-UV method. Pharmacokinetic parameters were calculated using non-compartmental methods. The elimination half-life and mean residence time of CFQ after the single SC administration were longer than IV administration (p < 0.05). Bioavailability (F%) of CFQ following the single SC administration was 123.51 ± 11.54%. The area under the curve (AUC_0-∞ ) and peak concentration following repeated doses (last dose) were higher than those observed after the first dose (p < 0.05). CFQ accumulated after repeated SC doses. CFQ can be given via SC at a dose of 2.5 mg/kg every 24 hr for the treatment of infections caused by susceptible pathogens, which minimum inhibitory concentration is ≤1.0 μg/ml in sheep.

Identification of the ferric iron utilization gene B739_1208 and its role in the virulence of R. anatipestifer CH-1

Riemerella anatipestifer is an important bacterial pathogen in ducks and causes heavy economic losses in the duck industry. However, the pathogensis of this bacterium is poorly understood. In this study, a putative outer membrane hemin receptor gene B739_1208 in R. anatipestifer CH-1 was deleted to determine the relationship between iron uptake and virulence. The R. anatipestifer CH-1ΔB739_1208 mutants grew significantly more slowly than the wild-type bacteria in TSB liquid medium. Further characterization revealed that the R. anatipestifer CH-1ΔB739_1208 mutants were deficient in iron uptake. Animal experiments indicated that the median lethal dose of the wild-type RA-CH-1 in ducklings was 3.89×10⁸, whereas the median lethal dose of the R. anatipestifer CH-1ΔB739_1208 mutant in ducklings was 5.68×10⁹. The median lethal dose of the complementation strain in ducklings was 9.84×10⁸. Additional analysis indicated that bacterial loads in the blood, liver, and brain tissues in the R. anatipestifer CH-1ΔB739_1208-infected ducklings were significantly decreased compared to those in the wild-type R. anatipestifer CH-1 infected ducklings. In a duck co-infection model with R. anatipestifer CH-1 and R. anatipestifer CH-1ΔB739_1208, the R. anatipestifer CH-1B739_1208 mutant was outcompeted by the wild-type R. anatipestifer CH-1 in the blood (P<0.002), livers (P<0.001) and brains (P<0.001) of infected ducks, indicating that B739_1208 gene expression provided a competitive advantage in these organs. Our results demonstrate that the B739_1208 gene is a virulence factor in R. anatipestifer CH-1.

Plasma and synovial fluid pharmacokinetics of cefquinome following the administration of multiple doses in horses

The plasma and synovial fluid pharmacokinetics and safety of cefquinome, a 2-amino-5-thiazolyl cephalosporin, were determined after multiple intravenous administrations in sixteen healthy horses. Cefquinome was administered to each horse through a slow i.v. injection over 20 min at 1, 2, 4, and 6 mg/kg (n = 4 horses per dose) every 12 h for 7 days (a total of 13 injections). Serial blood and synovial fluid samples were collected during the 12 h after the administration of the first and last doses and were analyzed by a high-performance liquid chromatography assay. The data were evaluated using noncompartmental pharmacokinetic analyses. The estimated plasma pharmacokinetic parameters were compared with the hypothetical minimum inhibitory concentration (MIC) values (0.125-2 μg/mL). The plasma and synovial fluid concentrations and area under the concentration-time curves (AUC) of cefquinome showed a dose-dependent increase. After a first dose of cefquinome, the ranges for the mean plasma half-life values (2.30-2.41 h), the mean residence time (1.77-2.25 h), the systemic clearance (158-241 mL/h/kg), and the volume of distribution at steady-state (355-431 mL/kg) were consistent across dose levels and similar to those observed after multiple doses. Cefquinome did not accumulate after multiple doses. Cefquinome penetrated the synovial fluid with AUC_{synovial fluid} /AUC_plasma ratios ranging from 0.57 to 1.37 after first and thirteenth doses, respectively. Cefquinome is well tolerated, with no adverse effects. The percentage of time for which the plasma concentrations were above the MIC was >45% for bacteria, with MIC values of ≤0.25, ≤0.5, and ≤1 μg/mL after the administration of 1, 2, and 4 or 6 mg/kg doses of CFQ at 12-h intervals, respectively. Further studies are needed to determine the optimal dosage regimes in critically ill patients.