Objective—To determine the disposition of gamithromycin in plasma, pulmonary epithelial lining fluid (PELF), bronchoalveolar lavage (BAL) cells, and lung tissue homogenate in cattle.
Animals—33 healthy Angus calves approximately 7 to 8 months of age.
Procedures—Calves were randomly assigned to 1 of 11 groups consisting of 3 calves each, which differed with respect to sample collection times. In 10 groups, 1 dose of gamithromycin (6 mg/kg) was administered SC in the neck of each calf (0 hours). The remaining 3 calves were not treated. Gamithromycin concentrations in plasma, PELF, lung tissue homogenate, and BAL cells (matrix) were measured at various points by means of high-performance liquid chromatography with tandem mass spectrometry.
Results—Time to maximum gamithromycin concentration was achieved at 1 hour for plasma, 12 hours for lung tissue, and 24 hours for PELF and BAL cells. Maximum gamithromycin concentration was 27.8 μg/g, 17.8 μg/mL, 4.61 μg/mL, and 0.433 μg/mL in lung tissue, BAL cells, PELF, and plasma, respectively. Terminal half-life was longer in BAL cells (125.0 hours) than in lung tissue (93.0 hours), plasma (62.0 hours), and PELF (50.6 hours). The ratio of matrix to plasma concentrations ranged between 4.7 and 127 for PELF, 16 and 650 for lung tissue, and 3.2 and 2,135 for BAL cells.
Conclusions and Clinical Relevance—Gamithromycin was rapidly absorbed after SC administration. Potentially therapeutic concentrations were achieved in PELF, BAL cells, and lung tissue within 30 minutes after administration and persisted for 7 (PELF) to > 15 (BAL cells and lung tissue) days after administration of a single dose.
Objective—To determine antimicrobial effects of caprylic acid and its derivatives, monocaprylin and sodium caprylate, on Dermatophilus congolensis and to determine effects of caprylic acid on the ultrastructure of D congolensis by use of transmission electron microscopy (TEM).
Sample—3 strains of D congolensis (33411, 33413, and 14639).
Procedures—Strains of D congolensis were incubated separately under anaerobic conditions at 37°C for up to 48 hours in brain heart infusion (BHI) broth that was supplemented with various concentrations of caprylic acid (7.5, 12.5, 15, 17.5, or 20mM), monocaprylin (2.5, 5, 7.5, or 10mM), or sodium caprylate (15, 50, 60, 70, 100, or 120mM) or contained no antimicrobial treatment. After incubation, bacterial counts were determined by means of plating in triplicate on BHI-agar plates. Caprylic acid-treated or untreated D congolensis samples were embedded in epoxide resin for TEM; cross sections were examined for structural damage.
Results—Minimum inhibitory concentrations of caprylic acid, monocaprylin, and sodium caprylate against D congolensis were 7.5, 2.5, and 15mM, respectively. Minimum bactericidal concentrations of caprylic acid, monocaprylin, and sodium caprylate against D congolensis were 15, 5, and 70mM, respectively. Examination via TEM revealed that a 15-mM concentration of caprylic acid disintegrated the plasma membrane of D congolensis.
Conclusions and Clinical Relevance—Results indicated that caprylic acid, monocaprylin, and sodium caprylate could potentially be used to treat D congolensis infections. However, in vivo studies should be undertaken to determine whether these compounds can be considered as treatment options.
Objective—To investigate the contribution of gyrA mutation and efflux pumps to fluoroquinolone resistance and multidrug resistance among Escherichia coli isolates from dogs and cats.
Sample Population—536 clinical isolates of E coli.
Procedures—Minimum inhibitory concentrations (MICs) were determined for enrofloxacin and 6 other drug classes by use of broth microdilution techniques. Real-time PCR assay was used to determine the mutation in gyrA; Phe-Arg-β-naphthylamide, an efflux pump inhibitor, was used to examine the contribution of efflux pump overexpression.
Results—The MIC for fluoroquinolones increased in a stepwise fashion and was lowest in the absence of mutations, higher with a single point mutation, and highest with 2 point mutations. Level of resistance in the latter category was high (8 times the breakpoint), but this was associated with expression of the AcrAB efflux pump. Inhibition of the efflux pump resulted in a reduction in the MIC to less than the susceptible breakpoint for isolates with an MIC ≤ 4 mg/L, regardless of the presence of a mutation. The greatest magnitude in MIC decrease (MIC was decreased by a factor of > 67 fold) was for isolates with a single mutation but the greatest absolute decrease in MIC (124 mg/L) was for isolates with 2 mutations. Inhibition of the AcrAB efflux pump in isolates characterized by multidrug resistance decreased the MIC of drugs structurally unrelated to fluoroquinolone.
Conclusions and Clinical Relevance—Fluoroquinolone resistance in E coli appeared to be a stepwise phenomenon, with MIC increasing as the number of point mutations in gyrA increased, but high-level resistance and multidrug resistance associated with fluoroquinolone resistance reflected overexpression of the AcrAB efflux pump.
Objective—To evaluate changes in antimicrobial consumption and productivity by Danish swine farms during 1992 to 2008.
Sample Population—All Danish swine farms for antimicrobial consumption data and a representative sample of Danish swine herds for productivity data.
Procedures—Antimicrobial consumption by Danish swine farms from 1992 to 2008 was determined and evaluated in light of policies to regulate antimicrobial consumption, changes in disease patterns, and productivity data. Trend analyses of productivity data were conducted before and after a ban on use of antimicrobial growth promoters (AGPs).
Results—Antimicrobial consumption peaked at 100 mg/kg of swine produced in 1992, decreased to 31 mg/kg in 1999, and increased to 49 mg/kg in 2008. Key factors for changes were regulations banning subtherapeutic use of antimicrobials and veterinary profits from the prescription and sale of antimicrobials in 1994 and termination of AGP use by January 2000. Pig production increased from 18.4 to 271 million pigs, and the mean number of pigs per sow per year raised for slaughter increased from 21 in 1992 to 25 in 2007 Average daily gain for weaning (< 35 kg) and finishing (> 35 kg) pigs was higher in 2008 than in 1992, but mortality rates for weaning and finishing pigs were similar in 1992 and 2008.
Conclusions and Clinical Relevance—From 1992 to 2008, antimicrobial consumption per kilogram of pig produced in Denmark decreased by > 50%. Furthermore, there was improvement in productivity, suggesting that long-term swine productivity was not negatively impacted by a ban on AGP use.
Objective—To compare prevalence of tetracycline resistance genes in the fecal flora of conventionally raised feedlot steers and feedlot steers raised without antimicrobials.
Sample Population—61 fecal samples from conventionally raised steers and 61 fecal samples from steers raised without antimicrobials at a single feedlot.
Procedures—Total DNA was extracted from each fecal sample and analyzed by means of 4 multiplex PCR assays for 14 tetracycline resistance genes.
Results—At least 3 tetracycline resistance genes were identified in all 122 fecal samples. For 5 of the 14 tetracycline resistance genes, the percentage of samples in which the gene was detected was significantly higher for fecal samples from conventionally raised cattle than for fecal samples from antimicrobial-free cattle, and for 1 gene, the percent-age of samples in which the gene was detected was significantly higher for fecal samples from antimicrobial-free cattle than for fecal samples from conventionally raised cattle. The percentage of samples with r 11 tetracycline resistance genes was significantly higher for fecal samples from conventionally raised cattle (35/61 [57%]) than for fecal samples from antimicrobial-free cattle (16/61 [26%]).
Conclusions and Relevance—Results suggested that the prevalence of tetracycline resistance genes was significantly higher in the fecal flora of conventionally raised feedlot steers than in the fecal flora of feedlot steers raised without antimicrobials and that a metagenomic approach may be useful in understanding the epidemiology of antimicrobial resistance in food animals.
Objective—To evaluate administration of chlortetracycline in feed of cattle as a method to select for tetracycline resistance among enteric bacteria in feedlot settings.
Procedures—Steers were randomly assigned to an exposed cohort (n = 10) or an unexposed cohort (control cohort; 10). Chlortetracycline (22 mg/kg) in cottonseed meal was administered to the exposed cohort on days 0 through 4, 6 through 10, and 12 through 16. The control cohort was administered only cottonseed meal. Fecal samples were collected from 16 steers on days −7, 0, 2, 6, 8, 12, 14, 19, 22, 26, and 33, and Escherichia coli and Enterococcus spp were isolated. Minimum inhibitory concentration (MIC) of selected antimicrobials was estimated.
Results—Overall, 56.0% and 31.4% of E coli and Enterococcus isolates, respectively, were resistant to tetracycline. Exposure to chlortetracycline was associated with a significant temporary increase in log2 MIC for both genera but returned to preexposure values by day 33. Averaged across time, the proportion of tetracycline-resistant E coli and Enterococcus isolates was significantly greater in exposed than in unexposed steers. Although all ceftiofur-resistant E coli isolates were coresistant to tetracycline, exposure to chlortetracycline led to a significant decrease in the proportion of E coli resistant to ceftiofur during exposure.
Conclusions and Clinical Relevance—Exposure to chlortetracycline was associated with a temporary increase in the likelihood of recovering resistant bacteria. Exposure to chlortetracycline decreased the likelihood of recovering ceftiofur-resistant E coli isolates, even though isolates were coresistant to tetracycline. These findings warrant further investigation.
Objective—To define the pharmacokinetics of florfenicol in synovial fluid (SYNF) and serum from central venous (CV) and digital venous (DV) blood samples following regional IV perfusion (RIVP) of the distal portion of the hind limb in cows.
Animals—6 healthy adult cows.
Procedures—In each cow, IV catheters were placed in the dorsal common digital vein (DCDV) and the plantar vein of the lateral digit, and an indwelling catheter was placed in the metatarsophalangeal joint of the left hind limb. A pneumatic tourniquet was applied to the midmetatarsal region. Florfenicol (2.2 mg/kg) was administered into the DCDV. Samples of DV blood, SYNF, and CV (jugular) blood were collected after 0.25, 0.50, and 0.75 hours, and the tourniquet was removed; additional samples were collected at intervals for 24 hours after infusion. Florfenicol analysis was performed via high-performance liquid chromatography.
Results—In DV blood, CV blood, and SYNF, mean ± SD maximum florfenicol concentration was 714.79 ± 301.93 μg/mL, 5.90 ± 1.37 μg/mL, and 39.19 ± 29.42 μg/mL, respectively; area under the concentration versus time curve was 488.14 ± 272.53 h•μg•mL−1, 23.10 ± 6.91 h•μg•mL−1, and 113.82 ± 54.71 h•μg•mL−1, respectively; and half-life was 4.09 ± 1.93 hours, 4.77 ± 0.67 hours, and 3.81 ± 0.81 hours, respectively.
Conclusions and Clinical Relevance—Following RIVP, high florfenicol concentrations were achieved in DV blood and SYNF, whereas the CV blood concentration remained low. In cattle, RIVP of florfenicol may be useful in the treatment of infectious processes involving the distal portion of limbs.
Objective—To test the life-sparing and therapeutic effect of a parenterally administered virus-specific antiviral phosphorodiamidate morpholino oligomer (PMO) for treating kittens during outbreaks of severe viral disease.
Animals—112 kittens of various sex and age in 4 trials involving 3 outbreaks of naturally developing caliciviral disease.
Procedures—Each trial provided an opportunity to investigate the disease. A calicivirus isolated from the liver of a cat that died with hemorrhage and hepatitis was sequenced, and a PMO that had sequence specificity complementary to a 5' region was synthesized. In vitro efficacy of the PMO was tested against the isolate, followed by 3 trials in outbreaks of severe caliciviral disease. The PMO was administered starting on day 1 of disease onset (0.7 to 5.0 mg/kg, SC, q 24 h) and continuing for up to 7 days. Survival time, clinical recovery, and caliciviral shedding were compared by use of various antiviral dosages. In a fourth trial involving nonfatal disease, a control treatment was administered for comparison.
Results—In vitro blockage of caliciviral replication by the PMO was dose dependent. In trials 1 to 3 in which survival was the endpoint, 47 of 59 cats receiving PMO survived but only 3 of 31 survived without PMO treatment. Antiviral treatment reduced viral shedding and hastened clinical recovery, as measured by weight gains and clinical condition.
Conclusions and Clinical Relevance—These data provided evidence that virus-specific PMOs were effective in treating kittens with severe Vesivirus disease and suggested a broader application for other viruses and species, including humans.
Objective—To evaluate antimicrobial activity of bovine bactericidal permeability–increasing protein (bBPI)–derived synthetic peptides against mastitis-causing gram-negative bacteria.
Sample Population—Bacterial isolates from the milk of cows with clinical mastitis.
Procedures—3 peptides were synthesized with sequences corresponding to amino acids 65 to 99 (bBPI65–99) or 142 to 169 (bBPI142–169) or the combination of amino acids 90 to 99 and 148 to 161 (bBPI90–99,148–161) of bBPI. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of these peptides against bacterial isolates from cows with mastitis were determined by use of a standardized broth microdilution assay. The ability of these peptides to retain their antimicrobial activity in serum and milk was also evaluated. Finally, bacterial lipopolysaccharide (LPS)-neutralizing activity of these peptides was assayed with the Limulus amebocyte lysate test.
Results—Of the 3 peptides tested, bBPI90–99,148–161 had the widest spectrum of antimicrobial activity, with MIC and MBC values ranging from 16 to 64 Mg/mL against Escherichia coli, Klebsiella pneumoniae, and Enterobacter spp and from 64 to 128 Mg/mL against Pseudomonas aeruginosa. None of the peptides had any growth-inhibitory effect on Serratia marcescens. The antimicrobial activity of bBPI90–99,148–161 was inhibited in milk, but preserved in serum. Finally, bBPI142–169 and bBPI90–99,148–161 completely neutralized LPS.
Conclusions and Clinical Relevance—bBPI90–99,148–161 is a potent neutralizer of the highly proinflammatory molecule bacterial LPS and has antimicrobial activity against a variety of gram-negative bacteria. The ability of bBPI90–99,148–161 to retain antimicrobial activity in serum suggests a potential therapeutic application for this peptide in the management of gram-negative septicemia.
Objective—To determine the pharmacokinetics of gallium maltolate (GaM) after intragastric administration in healthy foals.
Animals—6 healthy neonatal foals.
Procedures—Each foal received GaM (20 mg/kg) by intragastric administration. Blood samples were obtained before (time 0) and at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 36, and 48 hours after GaM administration for determination of serum gallium concentrations by use of inductively coupled plasma mass spectroscopy.
Results—Mean ± SD pharmacokinetic variables were as follows: peak serum gallium concentration, 1,079 ± 311 ng/mL; time to peak serum concentration, 4.3 ± 2.0 hours; area under the serum concentration versus time curve, 40,215 ± 8,420 ng/mL/h; mean residence time, 39.5 ± 17.2 hours; area under the moment curve, 1,636,554 ± 931,458 ng([h]2/mL); and terminal half-life, 26.6 ± 11.6 hours. The mean serum concentration of gallium at 12 hours was 756 ± 195 ng/mL.
Conclusions and Clinical Relevance—Gallium maltolate administered via nasogastric tube at a dose of 20 mg/kg to neonatal foals resulted in gallium serum concentrations considered sufficient to suppress growth or kill Rhodococcus equi in macrophages and other infected tissues.