Distribution of enrofloxacin in intestinal tissue and contents of healthy pigs after oral and intramuscular administrations

Selective and Concentrative Enteropancreatic Recirculation of Antibiotics by Pigs

Antibiotics that are efficacious for infectious pancreatitis are present in pancreatic exocrine secretion (PES) after intravenous administration and above minimal inhibitory concentrations. We measured concentrations of four antibiotics by tandem liquid chromatography-mass spectroscopy in plasma and PES after enteral administration to juvenile pigs with jugular catheters and re-entrant pancreatic-duodenal catheters. Nystatin, which is not absorbed by the intestine nor used for infectious pancreatitis (negative control), was not detected in plasma or PES. Concentrations of amoxicillin increased in plasma after administration (p = 0.035), but not in PES (p = 0.51). Metronidazole and enrofloxacin that are used for infectious pancreatitis increased in plasma after enteral administration and even more so in PES, with concentrations in PES averaging 3.1 (±0.5)- and 2.3 (±0.6)-fold higher than in plasma, respectively (p's < 0.001). The increase in enrofloxacin in PES relative to plasma was lower after intramuscular administration (1.8 ± 0.5; p = 0.001). The present results demonstrate the presence of a selective and concentrative enteropancreatic pathway of secretion for some antibiotics. Unlike the regulated secretion of bile, the constitutive secretion of PES and intestinal reabsorption may provide a continuous exposure of pancreas tissue and the small intestine to recirculated antibiotics and potentially other therapeutic molecules. There is a need to better understand the enteropancreatic recirculation of antibiotics and the associated mechanisms.

Occupational exposure to veterinary antibiotics: Pharmacokinetics of enrofloxacin in humans after dermal, inhalation and oral uptake - A clinical study

Occupational exposure to veterinary antibiotics in hen houses at poultry feeding farms was demonstrated by biomonitoring campaigns in the past. The objective of this study was to investigate pharmacokinetics of three uptake routes: dermal, oral and inhaled. In an open-label cross-over study, six healthy volunteers were exposed to single occupational relevant doses of enrofloxacin. Plasma and urine samples were analysed for enrofloxacin and ciprofloxacin. Physiologically based pharmacokinetic (PBPK) modelling based on bioanalysis data showed underestimation for the elimination rate in comparison to experimental data pointing towards a lack of sufficient ADME information and limitations of available physico-chemical properties of the parent drug. The data obtained in this study indicate that oral uptake with its various sources, e.g. airborne enrofloxacin, direct hand-mouth contact, is the major source for occupational exposure to enrofloxacin in hen houses. Dermal exposure was considered negligible.

PBPK Model To Predict Marbofloxacin Distribution in Edible Tissues and Intestinal Exposure in Pigs

Marbofloxacin (MAR) is a fluoroquinolone antibiotic used in food-producing animals in European Union, especially in pigs. In this study, MAR concentrations in plasma, comestible tissues, and intestinal segments were determined in pigs injected with MAR. Based on these data and the literature, a flow-limited PBPK model was developed to predict the tissue distribution of MAR and estimate the withdrawal period after label-use in Europe. A submodel describing the different segments of the intestinal lumen was also developed to assess the intestinal exposure of MAR for the commensal bacteria. During model calibration, only four parameters were estimated. Then, Monte Carlo simulations were performed to generate a virtual population of pigs. The simulation results were compared with the observations from an independent data set during the validation step. A global sensitivity analysis was also carried out to identify the most influential parameters. Overall, the PBPK model was able to adequately predict the MAR kinetics in plasma and edible tissues, as well as in small intestines. However, the simulated concentrations in the large intestine were mostly underestimated, highlighting the need for improvements in the field of PBPK modeling to assess the intestinal exposure of antimicrobials in food animals.

Recovery of the Structure and Function of the Pig Manure Bacterial Community after Enrofloxacin Exposure

A stable intestinal bacterial community balance is beneficial for animal health. Enrofloxacin is widely used in animal husbandry as a therapeutic drug, but it can cause intestinal environmental imbalance.

Effect of Intramuscularly Administered Oxytetracycline or Enrofloxacin on Vancomycin-Resistant Enterococci, Extended Spectrum Beta-Lactamase- and Carbapenemase-Producing Enterobacteriaceae in Pigs

Simple Summary

Nowadays, there is great concern about the prevalence of multidrug resistant bacteria in food-producing animals since they are potential sources of transmission to humans. The aim of this work was to evaluate the effect of two antibiotics (oxytetracycline and enrofloxacin) treatments in pigs on resistant bacteria that are considered a threat to public health. This study highlights that the use of oxytetracycline or enrofloxacin in food-producing animals could select resistant bacteria in pig faeces. Special care should be taken to avoid faecal contamination of carcasses during slaughter.

Abstract

Nowadays, there is a great concern about the prevalence of multidrug resistant Enterococcus spp. and Enterobacteriaceae in food-producing animals. The aim of this work was to evaluate the effect of oxytetracycline or enrofloxacin treatment on vancomycin-resistant enterococci (VRE), extended spectrum β-lactamase (ESBL) and carbapenemase-producing Enterobacteriaceae in pigs. A total of 26 piglets were received and distributed in three groups. Group 1 was treated with enrofloxacin (N = 12), group 2 with oxytetracycline (N = 10) and group 3 did not receive any treatment (control group) (N = 4). A higher number of vancomycin-resistant E. faecium were recovered compared to E. faecalis. In the pigs treated with enrofloxacin, vancomycin resistant E. faecium was found in a higher percentage of animals than in the control group. ESBL-producing E. coli was not detected in rectal samples from control animals. However, it was detected in 17–20% of animals treated with oxytetracycline on days 6 to 17 and in 17–50% of the animals treated with enrofloxacin. Carbapenemase-producing E. coli was isolated in animals treated with oxytetracycline, but not in animals treated with enrofloxacin or in the control group. This study highlights that the use of oxytetracycline or enrofloxacin in food-producing animals could select ESBL and carbapenemase-producing E. coli. Further studies shall be needed to validate the results obtained, considering a more robust and extended experimental design.

Antibiotic Resistance in Escherichia coli from Broiler Chickens After Amoxicillin Treatment in an Experimental Environment

Groupwise antibiotic treatments are common in broiler chicken production. They induce selection for antibiotic resistance in commensal Escherichia coli. This study aimed to investigate antibiotic resistance after individual (I, drenching) or groupwise treatment (G, by water) with amoxicillin, and after contact with I or G (KI or KG), compared with untreated broilers without contact with treated broilers (C), and pretreatment values. Finally, we compared antibiotic resistance from broilers (G) after a second treatment, with a treatment in the contact animals (KG), and a first treatment in the control animals (C). Resistance to ampicillin and other antibiotics was significantly increased in groups G and I within 2 days, suggesting (co-)selection of resistance. The increase was lower in groups KI, KG, and C during the first treatment (days 1-5). The increased resistance in group C was interpreted as a change in the microbiota after initial moving and first feeding. After treatment, resistance rates decreased to initial or lower values in all groups. During the second treatment period (days 34-38), all three groups' (G, KG, and C) resistance levels increased to equally high levels. Cephalosporin resistance was low, and did not change over the experimental period. On days 3 and 38, resistance rates of E. coli from duodenum, jejunum, and cecum did not differ between segments and treatment routes. Overall, the baseline levels of antibiotic resistance in E. coli were high. Amoxicillin triggered an increase in resistance levels, irrespective of the mode of treatment. Substantial resistance dynamics in untreated controls warrant further investigation.

Distribution of Flumequine in Intestinal Contents and Colon Tissue in Pigs after Its Therapeutic Use in the Drinking Water

Flumequine concentrations in plasma, colon tissue and intestinal contents were evaluated in 12 healthy pigs after oral administration (12 mg/kg every 24 h for 5 consecutive days in drinking water). Plasma, colon tissue and intestinal content samples were collected from animals sacrificed on days 3, 6 and 7. Concentrations were measured by high performance liquid chromatography after having validated the method, following the European Medicines Agency (EMA) requirements. The drug was not detected in any plasma sample. In colon tissue, concentrations were higher on day 3 (0.230 ± 0.033 µg/g, descending colon; 0.156 ± 0.093 µg/g, ascending colon) than on day 6 (0.187 ± 0.123 µg/g, descending colon; 0.107 ± 0.007 µg/g, ascending colon). Concentrations were considerably higher in intestinal contents, again on day 3 (1.349 ± 1.401 µg/g, descending colon; 0.591 ± 0.209 µg/g, ascending colon) than on days 6 (0.979 ± 0.346 µg/g, descending colon; 0.595 ± 0.075 µg/g, ascending colon) and 7 (0.247 ± 0.172 µg/g, descending colon; 0.172 ± 0.086 µg/g, ascending colon). Measured concentrations were lower than those effective against the most common intestinal pathogenic microorganisms in swine and, more specifically, Brachyspira hyodysenteriae.

Occurrence of Escherichia coli non-susceptible to quinolones in faecal samples from fluoroquinolone-treated, contact and control pigs of different ages from 24 Swiss pig farms

BACKGROUND

Despite their indispensability in human medicine, fluoroquinolones (FQ) are used for the treatment of bacterial infections in farm animals which increases the risk of transferring FQ-resistant bacteria into the environment and via the food chain to humans. The objectives of this observational study were to follow-up of the presence of quinolone non-susceptible Escherichia coli (QNSE) qualitatively and quantitatively in faecal samples of pigs at four time points (2 weeks old, 4 weeks old, 2 weeks post weaning and during fattening period). Moreover differences between groups of FQ-treated pigs, pigs with contact to treated pigs and control pigs were investigated. Additionally, quinolone and FQ resistance of Escherichia coli isolates of the faecal samples were investigated by determining minimum inhibitory concentrations (MICs).

RESULTS

40.9% of 621 fecal samples contained QNSE. Proportion of samples with detectable QNSE from treated and contact pigs did not differ significantly and were highest in piglets of 2 and 4 weeks of age. However, the proportions of samples with QNSE were significantly lowest in control pigs (7/90; 7.8%; CI = 3.5-14.7%) among all groups. Also, the number of colony-forming units was lowest in both weaners and fattening pigs of the control group compared to treated and contact groups. Following CLSI human breakpoints, in total, 50.4% out of 254 isolates in faecal samples were intermediate or resistant to ciprofloxacin.

CONCLUSIONS

QNSE were present in faeces of pigs independent of age or FQ background but significantly less were found in pigs from farms without FQ usage. Due to the long half-life of FQ, it is likely that only a prolonged absence of fluoroquinolone treatments in pig farming will lead to a reduced frequency of QNSE in the farm environment. Solutions need to be found to minimise the emergence and transfer of quinolone and FQ-resistant bacteria from treated pigs to contact pigs and to farms without FQ usage.

Comparative Study on Pharmacokinetics of Four Long-Acting Injectable Formulations of Enrofloxacin in Pigs

A comparative study on pharmacokinetics of four long-acting enrofloxacin injectable formulations was investigated in 36 healthy pigs after intramuscular injection according to the recommended single dose @ 2.5 mg/kg body weight. The drug concentrations in the plasma were computed using high-performance liquid chromatography (HPLC) with fluorescence detection. WinNonLin5.2.1 software was used to analyze the experimental data and compared it under one-way ANOVA using SPSS software with a 95% confidence interval (CI). The main pharmacokinetic parameters, that is, the maximum plasma concentrations (C_max), the time to maximum concentration (T_max), area under the time curve concentration (AUC_all) and Terminal half-life (T_1/2) were 733.84 ± 129.87, 917.00 ± 240.13, 694.84 ± 163.49, 621.98 ± 227.25 ng/ml, 2.19 ± 0.0.66, 1.50 ± 0.37, 2.89 ± 0.24, 0.34 ± 0.13 h, 7754.43 ± 2887.16, 8084.11 ± 1543.98, 7369.42 ± 2334.99, 4194.10 ± 1186.62 ng h/ml, 10.48 ± 2.72, 10.37 ± 2.38, 10.20 ± 2.81, and 10.61 ± 0.86 h for 10% enrofloxacin (Alkali), 20% enrofloxacin (Acidic), Yangkang and control drug Nuokang® respectively. There were significant differences among C_max, T_max, and AUC_all of three formulations compare with that of the reference formulation. No significant differences were observed among the T_1/2 for tested formulations compare with the reference formulation. The pharmacokinetic parameters showed that the tested formulations were somewhat better compared to the reference one. The calculated PK/PD indices were effective for bacteria such as Actinobacillus pleuropneumoniae and Pasteurella multocida with values higher than the cut-off points (C_max/MIC₉₀≥10–12 and AUC/MIC₉₀ ≥ 125). However, they were not effective against bacteria like Haemophilus parasuis, Streptococcus suis, E. coli, and Bordetella bronchiseptica where lower values were obtained.

The impact of therapeutic-dose induced intestinal enrofloxacin concentrations in healthy pigs on fecal Escherichia coli populations

BACKGROUND

Knowledge of therapy-induced intestinal tract concentrations of antimicrobials allows for interpretation and prediction of antimicrobial resistance selection within the intestinal microbiota. This study describes the impact of three different doses of enrofloxacin (ENR) and two different administration routes on the intestinal concentration of ENR and on the fecal Escherichia coli populations in pigs. Enrofloxacin was administered on three consecutive days to four different treatment groups. The groups either received an oral bolus administration of ENR (conventional or half dose) or an intramuscular administration (conventional or double dose).

RESULTS

Quantitative analysis of fecal samples showed high ENR concentrations in all groups, ranging from 5.114 ± 1.272 μg/g up to 39.54 ± 10.43 μg/g at the end of the treatment period. In addition, analysis of the luminal intestinal content revealed an increase of ENR concentration from the proximal to the distal intestinal tract segments, with no significant effect of administration route. Fecal samples were also screened for resistance in E. coli isolates against ENR. Wild-type (MIC≤0.125 μg/mL) and non-wild-type (0.125 < MIC≤2 μg/mL) E. coli isolates were found at time 0 h. At the end of treatment (3 days) only non-wild-type isolates (MIC≥32 μg/mL) were found.

CONCLUSIONS

In conclusion, the observed intestinal ENR concentrations in all groups showed to be both theoretically (based on pharmacokinetic and pharmacodynamic principles) and effectively (in vivo measurement) capable of significantly reducing the intestinal E. coli wild-type population.

Acute and long-term effects of antibiotics commonly used in laboratory animal medicine on the fecal microbiota

Biomedical research relies on the use of animal models, and the animals used in those models receive medical care, including antibiotics for brief periods of time to treat conditions such as dermatitis, fight wounds, and suspected bacterial pathogens of unknown etiology. As many mouse model phenotypes are sensitive to changes in the gut microbiota, our goal was to examine the effect of antibiotics commonly administered to mice. Therefore, four treatment groups (subcutaneous enrofloxacin for 7 days, oral enrofloxacin for 14 days, oral trimethoprim-sulfamethoxazole for 14 days, and topical triple antibiotic ointment for 14 days) alongside a fifth control group receiving no treatment (n = 12/group) were included in our study. Fecal samples were collected prior to treatment, immediately after two weeks of exposure, and four weeks after cessation of treatment, and subjected to 16S rRNA library sequencing. The entire experimental design was replicated in mice from two different suppliers. As expected, several treatments including enrofloxacin and triple antibiotic ointment substantially decreased the amount of DNA recovered from fecal material, as well as the microbial richness. Notably, many of these effects were long-lasting with diminished gut microbiota (GM) richness four weeks following exposure, in both substrains of mice. Trimethoprim-sulfamethoxazole induced minimal to no discernible changes in the taxonomic composition beyond that seen in control mice. Collectively, these data highlight the need to consider the impact on GM of brief and seemingly routine use of antibiotics in the clinical care of research animals.

Occurrence, Seasonal Variation and Risk Assessment of Antibiotics in the Surface Water of North China

In this study, the occurrence, seasonal, and spatial variations of four classes antibiotics were investigated in the surface water of North China. Water samples were taken from 24 sampling sites along rivers in May and August and antibiotics in water samples were detected by SPE-UPLC-MS/MS. The occurrence of all antibiotics except for FLO in May were higher than in August. The mean concentrations of four classes antibiotics detected in May and August were in the following order respectively: quinolones (421.23 ng/L) > tetracyclines (28.37 ng/L) > amphenicols (20.38 ng/L) > sulfonamides (5.79 ng/L) and amphenicols (284.36 ng/L) > quinolones (15.74 ng/L) > tetracyclines (3.05 ng/L) > sulfonamides (0.20 ng/L). The results showed that quinolones and amphenicols were dominant antibiotics among four classes antibiotics. To explore the source of antibiotics from the fish ponds nearby, antibiotic concentration data, which was investigated in the sediment, fish feed and fish revealed a direct relationship between the main antibiotics and fish farms along the rivers. Risk assessment data indicated enrofloxacin and florfenicol could cause higher safety risks to aquatic organisms compared to other antibiotics.

Therapeutic administration of enrofloxacin in mice does not select for fluoroquinolone resistance inCampylobacter jejuni

Enrofloxacin is registered for therapeutic use in beef cattle to treat bovine respiratory disease in Canada. A murine model was used to experimentally examine the impact of therapeutic administration of enrofloxacin on fluoroquinolone resistance development in Campylobacter jejuni. Administration of enrofloxacin to mice via subcutaneous injection or per os routes resulted in equivalent levels of bioactive enrofloxacin within the intestine, but bioactivity was short-lived (<48 h after cessation). Enrofloxacin administration did not affect densities of total bacteria, Firmicutes, or Bacteroidetes in digesta and had modest impacts on densities of Enterobacteriaceae. All mice inoculated with C. jejuni NCTC 11168 became persistently colonized by the bacterium. Enrofloxacin reduced C. jejuni cell densities within the cecal and colonic digesta for all treatments, and densities shed in feces as a function of antibiotic duration. None of the C. jejuni isolates recovered from mice after administration of enrofloxacin (n = 260) developed resistance to ciprofloxacin regardless of method or duration of administration. Furthermore, only modest shifts in the minimum inhibitory concentration of the isolates by treatment were noted. The study findings indicate that the risk posed by short-term subcutaneous administration of enrofloxacin for the development of fluoroquinolone resistance in mammals is low.

Inter-Laboratory Validation of Method to Determine Residual Enrofloxacin in Chicken Meat

An inter-laboratory study was performed to evaluate the performance of a method developed for the quantification of enrofloxacin in chicken meat. Liquid-liquid extraction combined with a clean-up procedure based on solid-phase extraction followed by a liquid chromatography-tandem mass spectrometric method was used by three individual laboratories. All the investigated results of calibration curves and limits of quantification were within the acceptable range for regulatory testing of enrofloxacin. The three laboratories received blind a certified reference material to analyze in triplicate and assess using statistical analysis. From the results, no statistical differences were found between the laboratories in the precision of the method. Additionally, all the results of the z-score, which is an indication of fixed interval bias criteria for accuracy from the laboratories, fell within the allowable limits (±2σ). Based on this proficiency testing by inter-laboratory comparisons, the analytical method including the sample preparation step was proven to be applicable.

Effects of intramuscularly administered enrofloxacin on the susceptibility of commensal intestinal Escherichia coli in pigs (sus scrofa domestica)

BACKGROUND

In the European Union, various fluoroquinolones are authorised for the treatment of food producing animals. Each administration poses an increased risk of development and spread of antimicrobial resistance. The aim of this study was to investigate the impact of parenteral administration of enrofloxacin on the prevalence of enrofloxacin and ciprofloxacin susceptibilities in the commensal intestinal E. coli population.

METHODS

E. coli isolates from faeces of twelve healthy pigs were included. Six pigs were administered enrofloxacin on day 1 to 3 and after two weeks for further three days. The other pigs formed the control group. MIC values were determined. Virulence and resistance genes were detected by PCR. Phylogenetic grouping was performed by PCR. Enrofloxacin and ciprofloxacin were analysed in sedimentation samples by HPLC.

RESULTS

Susceptibility shifts in commensal E. coli isolates were determined in both groups. Non-wildtype E. coli could be cultivated from two animals of the experimental group for the first time one week after the first administration and from one animal of the control group on day 28. The environmental load with enrofloxacin in sedimentation samples showed the highest amount between days one and five. The repeated parenteral administration of enrofloxacin to pigs resulted in rapidly increased MIC values (day 28: MIC up to 4 mg/L, day 35: MIC ≥ 32mg/L). E. coli populations of the control group in the same stable without direct contact to the experimental group were affected.

CONCLUSION

The parenteral administration of enrofloxacin to piglets considerably reduced the number of the susceptible intestinal E. coli population which was replaced by E. coli strains with increased MIC values against enrofloxacin. Subsequently also pigs of the control were affected suggesting a transferability of strains from the experimental group through the environment to the control group especially as we could isolate the same PFGE strains from both pig groups and the environment.

Clinical Efficacy and Residue Depletion of 10% Enrofloxacin Enteric-Coated Granules in Pigs

A new, more palatable formulation of 10% enrofloxacin enteric-coated granules was investigated to evaluate the pharmacokinetic effect in plasma, the residue elimination in tissues and the clinical efficacy against Actinobacillus pleuropneumonia (APP) and Mycoplasam suis (MS) in pigs. In this study, the enrofloxacin concentrations in plasma and tissues were detected using high-performance liquid chromatography with phosphate buffer (pH = 3) and acetonitrile. The pharmacokinetics and elimination of enrofloxacin enteric-coated granules were performed after oral administration at a single dose of 10 mg/kg body weight (bw) and 5 mg/kg twice per day for 5 consecutive days, respectively. The in vivo antibacterial efficacy and clinical effectiveness of enrofloxacin enteric-coated granules against APP and MS were assayed at 2.5, 5, 10 mg/kg, compared with tiamulin (8 mg/kg) based on establishment of APP and MS infection models. 56 APP strains were selected and tested for in vitro antibacterial activity of enrofloxacin enteric-coated granules. The main parameters of elimination half-life (t_1/2β), T_max, and area under the curve (AUC) were 14.99 ± 4.19, 3.99 ± 0.10, and 38.93 ± 1.52 μg h/ml, respectively, revealing that the enrofloxacin concentration remained high and with a sustainable distribution in plasma. Moreover, the analysis on the evaluation of enrofloxacin and ciprofloxacin in muscle, fat, liver and kidney showed that the recovery were more than 84% recovery in accordance with the veterinary drug residue guidelines of United States pharmacopeia, and the withdrawal periods were 4.28, 3.81, 4.84, and 3.51 days, respectively, suggesting that the withdrawal period was 5 d after oral administration of 5 mg/kg twice per day. The optimal dosage of enrofloxacin enteric-coated granules against APP and MS was 5 mg/kg, with over 90% efficacy, which was significantly different (p < 0.05) to the 2.5 mg/kg group, but not to the 10 mg/kg group or the positive control group (tiamulin). In conclusion, 10% enrofloxacin enteric-coated granules had significant potential for treating APP and MS, and it provided an alternative enrofloxacin palatability formulation.

An update discussion on the current assessment of the safety of veterinary antimicrobial drug residues in food with regard to their impact on the human intestinal microbiome

The human gastrointestinal tract ecosystem consists of complex and diverse microbial communities that have now been collectively termed the intestinal microbiome. Recent scientific breakthroughs and research endeavours have increased our understanding of the important role the intestinal microbiome plays in human health and disease. The use of antimicrobial new animal drugs in food-producing animals may result in the presence of low levels of drug residues in edible foodstuffs. There is concern that antimicrobial new animal drugs in or on animal-derived food products at residue-level concentrations could disrupt the colonization barrier and/or modify the antimicrobial resistance profile of human intestinal bacteria. Therapeutic doses of antimicrobial drugs have been shown to promote shifts in the intestinal microbiome, and these disruptions promote the emergence of antimicrobial-resistant bacteria. To assess the effects of antimicrobial new animal drug residues in food on human intestinal bacteria, many national regulatory agencies and international committees follow a harmonized process, VICH GL36(R), which was issued by a trilateral organization of the European Union, the USA, and Japan called the International Cooperation on Harmonization of Technical Requirements for Veterinary Medicinal Products (VICH). The guidance describes a general approach currently used by national regulatory agencies and international committees to assess the effects of antimicrobial new animal drug residues in animal-derived food on human intestinal bacteria. The purpose of this review is to provide an overview of this current approach as part of the antimicrobial new animal drug approval process in participating countries, give insights on the microbiological endpoints used in this safety evaluation, and discuss the availability of new information. Copyright © 2016 John Wiley & Sons, Ltd.

Pharmacokinetic and Pharmacodynamic Integration and Modeling of Enrofloxacin in Swine for Escherichia coli

The aim of this study was to optimize the dose regimens of enrofloxacin to reduce the development of fluoroquinolone resistance in Escherichia coli (E.coli) using pharmacokinetic/pharmacodynamic (PK/PD) modeling approach. The single dose (2.5 mg/kg body weight) of enrofloxacin was administered intramuscularly (IM) to the healthy pigs. Using cannulation, the pharmacokinetic properties, including peak concentration (C max), time to reach C max (T max), and area under the curve (AUC), were determined in plasma and ileum content. The C max, T max, and AUC in the plasma were 1.09 ± 0.11 μg/mL, 1.27 ± 0.35 h, and 12.70 ± 2.72 μg·h/mL, respectively. While in ileum content, the C max, T max, and AUC were 7.07 ± 0.26 μg/mL, 5.54 ± 0.42 h, and 136.18 ± 12.50 μg·h/mL, respectively. Based on the minimum inhibitory concentration (MIC) data of 918 E. coli isolates, an E. coli O101/K99 strain (enrofloxacin MIC = 0.25 μg/mL) was selected for pharmacodynamic studies. The in vitro minimum bactericidal concentration (MBC), mutant prevention concentration (MPC), and ex vivo time-killing curves for enrofloxacin in ileum content were established against the selected E. coli O101/K99 strain. Integrating the in vivo pharmacokinetic data and ex vivo pharmacodynamic data, a sigmoid E max (Hill) equation was established to provide values for ileum content of AUC24h/MIC producing, bactericidal activity (52.65 h), and virtual eradication of bacteria (78.06 h). A dosage regimen of 1.96 mg/kg every 12 h for 3 days should be sufficient in the treatment of E. coli.

Pharmacokinetic-Pharmacodynamic Modeling of Enrofloxacin Against Escherichia coli in Broilers

The purpose of the present study was to establish a pharmacokinetic/pharmacodynamic (PK/PD) modeling approach for the dosage schedule design and decreasing the emergence of drug-resistant bacteria. The minimal inhibitory concentration (MIC) of 929 Escherichia coli isolates from broilers to enrofloxacin and ciprofloxacin was determined following CLSI guidance. The MIC50 was calculated as the populational PD parameter for enrofloxacin against E. coli in broilers. The 101 E. coli strains with MIC closest to the MIC50 (0.05 μg/mL) were submitted for serotype identification. The 13 E. coli strains with O and K serotype were further utilized for determining pathogencity in mice. Of all the strains tested, the E. coli designated strain Anhui 112 was selected for establishing the disease model and PK/PD study. The PKs of enrofloxacin after oral administration at the dose of 10 mg/kg body weights (BW) in healthy and infected broilers was evaluated with high-performance liquid chromatography (HPLC) method. For intestinal contents after oral administration, the peak concentration (C max), the time when the maximum concentration reached (T max), and the area under the concentration-time curve (AUC) were 21.69-31.69 μg/mL, 1.13-1.23 h, and 228.97-444.86 μg h/mL, respectively. The MIC and minimal bactericidal concentration (MBC) of enrofloxacin against E. coli (Anhui 112) in Mueller-Hinton (MH) broth and intestinal contents were determined to be similar, 0.25 and 0.5 μg/mL respectively. In this study, the sum of concentrations of enrofloxacin and its metabolite (ciprofloxacin) was used for the PK/PD integration and modeling. The ex vivo growth inhibition data were fitted to the sigmoid E max (Hill) equation to provide values for intestinal contents of 24 h area under concentration-time curve/MIC ratios (AUC0-24 h/MIC) producing, bacteriostasis (624.94 h), bactericidal activity (1065.93 h) and bacterial eradication (1343.81 h). PK/PD modeling was established to simulate the efficacy of enrofloxacin for different dosage regimens. By model validation, the protection rate was 83.3%, demonstrating that the dosage regimen of 11.9 mg/kg BW every 24 h during 3 days provided great therapeutic significance. In summary, the purpose of the present study was to first design a dosage regimen for the treatment E. coli in broilers by enrofloxacin using PK/PD integrate model and confirm that this dosage regimen presents less risk for emergence of floroquinolone resistance.

Effect of administration route and dose escalation on plasma and intestinal concentrations of enrofloxacin and ciprofloxacin in broiler chickens

Background

The (mis)use of fluoroquinolones in the fowl industry has led to an alarming incidence of fluoroquinolone resistance in pathogenic as well as commensal bacteria. Next to simply reducing antimicrobial consumption, optimizing dosage regimens can be regarded as a suitable strategy to reduce antimicrobial resistance development without jeopardizing therapy efficacy and outcome. A first step in order to limit antimicrobial resistance is to assess the exposure of the intestinal microbiota to enrofloxacin after different treatment strategies. Therefore, a study was conducted in broiler chickens to assess the effect of route of administration (oral versus intramuscular) and dose escalation (10 and 50 mg/kg body weight) on plasma and intestinal concentrations of enrofloxacin and its main metabolite ciprofloxacin after treatment with enrofloxacin once daily for five consecutive days. Four different parts of the intestinal tract were sampled: ileum, cecum, colon and cloaca. A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to quantify both analytes in plasma and intestinal content. Sample preparation prior to LC-MS/MS analysis consisted of extraction with ethyl acetate. For intestinal content samples PBS buffer was added before extraction. The supernatant was evaporated to dryness and resuspended in water prior to analysis.

Results

The results in plasma and intestinal content demonstrated that biotransformation of enro- to ciprofloxacin in broiler chickens is limited. In general, the intestinal microbiota in cecum and colon is exposed to significant levels of enrofloxacin after conventional treatment (21–130 μg/g). A clear increase of intestinal concentrations was demonstrated after administration of a five-fold higher dose (31–454 μg/g). After intramuscular administration, intestinal concentrations were comparable, except for the higher levels in cloaca due to the complete bioavailability and urinary excretion.

Conclusions

The intestinal microbiota is exposed to high levels of the antimicrobial, after oral as well as parenteral therapy. Furthermore, a dose and time dependent correlation was observed. The impact of the detected intestinal levels on resistance selection in the intestinal microbiota has to be further investigated.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-014-0289-1) contains supplementary material, which is available to authorized users.

Effect of on-farm use of antimicrobial drugs on resistance in fecal Escherichia coli of preweaned dairy calves

Respiratory disease and diarrhea are the 2 most common diseases that result in the use of antimicrobial drugs in preweaned calves. Because the use of drugs in food animals, including dairy calves, has the potential for generating cross-resistance to drugs used in human medicine, it is vital to propose farm practices that foster the judicious use of antimicrobials while assuring animal health and productivity. The objective of this study was to use dairy farm calf treatment records to identify antimicrobial drug treatments in calves and to evaluate their effects on the prevalence of antimicrobial-resistant Escherichia coli from rectal swabs of preweaned dairy calves. Eight farms from central New York participated in the study, 3 farms using individual pen housing management and 5 farms using group pen housing management. Eligible study farms could not add antimicrobial drugs to the milk fed to preweaned calves and were required to have farm records documenting antimicrobial drug treatment of calves from birth to weaning. Three fecal E. coli isolates per calf were tested for susceptibility to 12 antimicrobial drugs using a Kirby-Bauer disk diffusion assay. A total of 473 calves were sampled, from which 1,423 commensal E. coli isolates were tested. Of the 9 antimicrobial drugs used on study farms, only enrofloxacin was significantly associated with reduced antimicrobial susceptibility of E. coli isolates, although treatment with ceftiofur was associated with reduced susceptibility to ceftriaxone. The median numbers of days from treatment with ceftiofur and enrofloxacin to rectal swab sampling of calves were 16 d (range: 1-39) and 12 d (range: 6-44), respectively. At the isolate level, treatment with enrofloxacin resulted in odds ratios of 2 [95% confidence interval (CI): 1-4] and 3 (95% CI: 2-6), respectively, for isolation of nonsusceptible E. coli to nalidixic acid and ciprofloxacin compared with calves not treated with enrofloxacin. Treatment with ceftiofur resulted in an odds ratio of 3 (95% CI: 0.9-12) for isolation of nonsusceptible E. coli to ceftriaxone compared with calves not treated with ceftiofur. Treatment with enrofloxacin resulted in selection of isolates that presented phenotypic resistance to both ciprofloxacin and ceftriaxone. Treatment with ceftiofur resulted in a higher prevalence of isolates resistant to ≥3 antimicrobial drugs (97%) compared with no treatment with ceftiofur (73%). These findings reinforce the necessity for continued implementation of practices at the dairy farm that support the sustainable and judicious use of antimicrobial drugs in dairy calves.

Mathematical modeling of bacterial kinetics to predict the impact of antibiotic colonic exposure and treatment duration on the amount of resistant enterobacteria excreted

Fecal excretion of antibiotics and resistant bacteria in the environment are major public health threats associated with extensive farming and modern medical care. Innovative strategies that can reduce the intestinal antibiotic concentrations during treatments are in development. However, the effect of lower exposure on the amount of resistant enterobacteria excreted has not been quantified, making it difficult to anticipate the impact of these strategies. Here, we introduce a bacterial kinetic model to capture the complex relationships between drug exposure, loss of susceptible enterobacteria and growth of resistant strains in the feces of piglets receiving placebo, 1.5 or 15 mg/kg/day ciprofloxacin, a fluoroquinolone, for 5 days. The model could well describe the kinetics of drug susceptible and resistant enterobacteria observed during treatment, and up to 22 days after treatment cessation. Next, the model was used to predict the expected amount of resistant enterobacteria excreted over an average piglet's lifetime (150 days) when varying drug exposure and treatment duration. For the clinically relevant dose of 15 mg/kg/day for 5 days, the total amount of resistant enterobacteria excreted was predicted to be reduced by 75% and 98% when reducing treatment duration to 3 and 1 day treatment, respectively. Alternatively, for a fixed 5-days treatment, the level of resistance excreted could be reduced by 18%, 33%, 57.5% and 97% if 3, 5, 10 and 30 times lower levels of colonic drug concentrations were achieved, respectively. This characterization on in vivo data of the dynamics of resistance to antibiotics in the colonic flora could provide new insights into the mechanism of dissemination of resistance and can be used to design strategies aiming to reduce it.

Fecal excretion of antibiotics and resistant bacteria in the environment are major public health threats associated with extensive farming. Innovative strategies that reduce the intestinal antibiotic concentrations during treatment are in development and could help prevent the dissemination of resistance. In order to anticipate the impact of these strategies, the effect of lower exposure on the amount of resistant enterobacteria excreted needs to be quantified precisely. Here, we introduce a bacterial kinetic model to capture the complex relationships between dosage regimen, antibiotic fecal concentrations, loss of susceptible enterobacteria and growth of resistant strains in the feces of piglets receiving different doses of ciprofloxacin for 5 days. We use this model to evaluate by simulation how much it would be necessary to reduce the antibiotic colonic concentration in order to prevent the expansion of antibiotic resistance. This approach provides new insights into the mechanism of dissemination of resistance during treatments and can be used to design strategies to reduce it.

Effects of fluoroquinolone treatment and group housing of pigs on the selection and spread of fluoroquinolone-resistant Campylobacter

There are concerns that the use of fluoroquinolones (FQs) and group housing of food animals may contribute to the development of bacterial FQ resistance. Here, we studied the effects of administering FQ to pigs on the selection of FQ-resistant Campylobacter. Fifteen pigs were randomly allocated to either a group treated with FQs (enrofloxacin or norfloxacin), or an untreated control group. The number of FQ-resistant Campylobacter in feces was determined using appropriate selective agar containing enrofloxacin. FQ-resistant Campylobacter from samples of both groups were observed on days 3 and 4. These bacteria persisted for up to 21 days after treatment was discontinued. To evaluate the effect of group housing on the transmission of FQ-resistant Campylobacter, five pigs infected with FQ-sensitive Campylobacter pigs and one pig infected with FQ-resistant Campylobacter were housed together. On day 3, FQ-resistant Campylobacter were isolated from all six pigs. Moreover, FQ-resistant Campylobacter were isolated from environmental samples from the pen. These results indicate that the treatment of pigs with FQs selects for and spreads FQ-resistant Campylobacter among the pen. Therefore, responsible and prudent use of FQs at pig farms is required to prevent the emergence and transmission of FQ-resistant Campylobacter.

In vitro enrofloxacin binding in human fecal slurries

Most antibiotic inactivation studies have been conducted through in vitro incubations of human use aminoglycosides, beta-lactams, and fluoroquinolones, usually at fecal concentrations expected with therapeutic dose regimens in humans and animals. Less is known about the inactivation of these molecules when ingested at concentrations consistent with residue levels present in animal-derived foods from antibiotic treated animals. In this investigation, we used the fluoroquinolone, enrofloxacin which is specifically marketed for veterinary medicine as test compound. Fecal suspensions at 10%, 25%, and 50% (w/v) were subjected to physicochemical and molecular characterization and used in the drug binding studies. The fecal binding of enrofloxacin added at concentrations of 0.06, 0.1, 1, 5, 15, 50, and 150 mg/L was determined in various fecal slurry suspensions using analytical chemistry and microbiological assay methods. There was consistent correlation between both assay methods. By the analytical chemistry assay, the 10%, 25% and 50% diluted autoclaved fecal samples dosed with enrofloxacin showed binding of 50±4.6%, 54±6.5% and 56±6.8% of the enrofloxacin, respectively. Binding of enrofloxacin to fecal contents occurred rapidly within 10 min and remained constant over the incubation period. Denaturing gradient gel electrophoreses and pyrosequencing analysis showed varied profiles of the bacterial composition of the human intestinal microbiota for fecal samples from different individuals. This study provided information on methodological questions that have concerned regulatory authorities on in vitro testing to determine if concentrations of veterinary antimicrobial agent residues entering the human colon remain microbiologically active.

Distribution of enrofloxacin and its active metabolite, using an in vivo ultrafiltration sampling technique after the injection of enrofloxacin to pigs

The objective of this study was to determine the pharmacokinetics (PK) of enrofloxacin in pigs and compare to the tissue interstitial fluid (ISF). Six healthy, young pigs were administered 7.5 mg/kg enrofloxacin subcutaneously (SC). Blood and ISF samples were collected from preplaced intravenous catheters and ultrafiltration sampling probes placed in three different tissue sites (intramuscular, subcutaneous, and intrapleural). Enrofloxacin concentrations were measured using high-pressure liquid chromatography with fluorescence detection, PK parameters were analyzed using a one-compartment model, and protein binding was determined using a microcentrifugation system. Concentrations of the active metabolite ciprofloxacin were negligible. The mean ± SD enrofloxacin plasma half-life, volume of distribution, clearance, and peak concentration were 26.6 ± 6.2 h (harmonic mean), 6.4 ± 1.2 L/kg, 0.18 ± 0.08 L/kg/h, and 1.1 ± 0.3 μg/mL, respectively. The half-life of enrofloxacin from the tissues was 23.6 h, and the maximum concentration was 1.26 μg/mL. Tissue penetration, as measured by a ratio of area-under-the-curve (AUC), was 139% (± 69%). Plasma protein binding was 31.1% and 37.13% for high and low concentrations, respectively. This study demonstrated that the concentration of biologically active enrofloxacin in tissues exceeds the concentration predicted by the unbound fraction of enrofloxacin in pig plasma. At a dose of 7.5 mg/kg SC, the high tissue concentrations and long half-life produce an AUC/MIC ratio sufficient for the pathogens that cause respiratory infections in pigs.

Nonlinear toxicokinetics of enrofloxacin in rats

The dose-dependent toxicokinetics of enrofloxacin were studied by administering various single subcutaneous doses (5, 10, 20, 40, 70, 100, 150, 200, 300 and 400 mg/kg) in male Sprague-Dawley rats. The blood samples were collected from the tail veins, and the plasma concentration of enrofloxacin was determined by an HPLC-fluorescence detection (FLD) method. The time-concentration profiles of enrofloxacin were well fitted by an one-compartmental model with first order elimination. The absorption half-lives (t₁(/)₂(abs)) ranged from 0.2-0.8 h, and the mean time to maximum plasma concentration (T(max)) ranged from 0.6-1.8 h. On the other hand, marked disproportionate increases of the area under the curve (AUC) and elimination half-lives (t₁(/)₂) were observed from the increase of the doses. This result indicates that the elimination of enrofloxacin has nonlinear pharmacokinetic properties with increasing doses. Therefore, we need to take into consideration the possible occurrence of side effects resulting from greater systemic exposure from high dose therapies.

Penetration of enrofloxacin into the nasal secretions and relationship between nasal secretions and plasma enrofloxacin concentrations after intramuscular administration in healthy pigs

The pharmacokinetic behaviour of enrofloxacin (ENRO) in plasma and nasal secretions of healthy pigs was investigated, after a single-dose intramuscular administration of 2.5 mg/kg body weight of the drug. Blood samples and nasal secretions were collected at predetermined times after drug administration. Concentrations of ENRO and its active metabolite ciprofloxacin (CIPRO) were determined in plasma and nasal secretions by high-performance liquid chromatography (HPLC). CIPRO was not detected probably because we investigated young weaned pigs. The data collected in 12 pigs for ENRO were subjected to noncompartmental analysis. In plasma, the maximum concentration of drug (C(max)), the time at which this maximum concentration of drug (T(max)) was reached, the elimination half-life (t(1/2)(beta)) and the area under the concentration vs. time curve (AUC) were, respectively, 694.7 ng/mL, 1.0 h, 9.3 h and 8903.2 ngxh/mL. In nasal secretions, C(max), T(max), t(1/2)(beta) and AUC were, respectively, 871.4 ng/mL, 2.0 h, 12.5 h and 11 198.5 ngxh/mL. In a second experiment conducted in 10 piglets, the relationship between concentrations of ENRO measured in the plasma and the nasal secretions has been determined following single-dose intramuscular administration of 2.5, 10 or 20 mg/kg body weight of the drug. It has been demonstrated that, among several variables, i.e., (1) the dose administered, (2) the time between intramuscular injection and blood sampling, (3) the age, (4) the sex, (5) the animal body weight and (6) the plasma concentration of the drug, only the latter influenced significantly the ENRO concentration in nasal secretions. Practically, using a generalized linear mixed model, ENRO concentrations in the nasal secretions (microg/mL) can be predicted taking into account the ENRO concentrations in plasma (microg/mL), according to the following equation:

A simulation model for the prediction of tissue:plasma partition coefficients for drug residues in natural casings

Tissue residues arise from the exposure of animals to undesirable substances in animal feed materials and drinking water and to the therapeutic or zootechnical use of veterinary medicinal products. In the framework of this study, an advanced toxicokinetic model was developed to predict the likelihood of residue disposition of licensed veterinary products in natural casings used as envelope for a variety of meat products, such as sausages. The model proved suitable for the calculation of drug concentrations in the muscles of pigs, cattle and sheep, the major species of which intestines are used. On the basis of drug concentrations in muscle tissue, the model allowed a prediction of intestinal concentrations and residues in the intestines that remained equal to or below the concentrations in muscle tissue, the major consumable product of slaughter animals. Subsequently, residues in intestines were found to be below the maximum residue limit value for muscle tissue when drugs were used according to prescribed procedures, including the application of appropriate withdrawal times. Considering the low consumption of natural casings (which represents only about 1-2% of the weight of a normal sausage), it was concluded that the exposure to drug residues from casings is negligible.

Analysis of veterinary antibiotic residues in swine wastewater and environmental water samples using optimized SPE-LC/MS/MS

Strategies for sample preparation, solid-phase extraction (SPE), clean-up, and detection conditions of an optimized solid-phase extraction-liquid chromatography/mass/mass spectrometry (SPE-LC/MS/MS) method for determining multi-residues of four classes of widely used antibiotics in pig farms, sulfonamides (SAs), fluoroquinolone (FQs), tetracycline (TCs) and chloramphenicol (CAP) were presented. The multi-residue analysis was used in MS analysis, selecting two precursor ions to produce ion transitions for each target compound. Samples of swine wastewater, lake water and groundwater collected from two pig farms in central China were used to test the applicability of the multi-residue analysis method. The average antibiotics concentrations in groundwater, lake water, final effluent and influent swine wastewater were, respectively, 1.6-8.6, 5.7-11.6, 7.9-1172.3 and 8.5-21692.7 ng L(-1) in summer; respectively, 2.0-7.3, 6.7-11.7, 5.8-409.5 and 32.8-11276.6 ng L(-1) in winter. The limits of quantification were 0.8-4.1, 1.4-5.5, 1.8-11.5 and 6.4-104.4 ng L(-1), respectively, in groundwater, lake water, final effluent and influent swine wastewater. Results of multi-residue analysis of antibiotics in the samples indicate that SAs, FQs and TCs were widely used veterinary medicines in the pig farms. As compared with previous studies, higher elimination rates (more than 80%) of the antibiotics (except DC) were observed in effluent in this study. More detailed work is indispensable to investigate the fate and transport of antibiotics in the environment and to find out cost-effective approaches of removing antibiotics from swine wastewater and contaminated sites.

Excretion of enrofloxacin in pigs and its effect on ecological environment

The concentration of enrofloxacin and its metabolite, ciprofloxacin, in feces and urines were investigated in healthy pigs after oral administration (p.o.) of a single dose of 5.0mg/kgbw and an indoor soil model was set to study the effects of enrofloxacin and ciprofloxacin through biological and chemical metrics including changes to edaphon, edaphic ammonification and nitrification and the soil bacterial community. The results showed that the concentrations of entofloxacin and ciprofloxacin in feces and urines fluctuated, the maximum concentrations of enrofloxacin and ciprofloxacin in the urine were 22.74 and 48.04μg/ml, respectively, 24.68 and 30.98μg/g in the feces, respectively. The effect of enrofloxacin and ciprofloxacin on edaphon, edaphic ammonification and nitrification and the soil bacterial community differed at different time points. And the model can be used to evaluate environmental safety of enrofloxacin and develop possible procedures for the safe handling and utilization of animal excrement.

In vitro antimicrobial activity of rifaximin against enteropathogens causing traveler's diarrhea

The in vitro activity of rifaximin against 84 diarrheagenic Escherichia coli and 11 Shigella sonnei causing traveler's diarrhea was evaluated. The MIC of rifaximin ranged between <0.007 and 32 mg/L; other agents tested had an MIC of >256 mg/L in most cases. The results showed the potential use of rifaximin to treat these infections.

Patterns of metabolites produced from the fluoroquinolone enrofloxacin by basidiomycetes indigenous to agricultural sites

Supernatants of mycelial cultures of seven basidiomycetous fungi indigenous to agricultural sites were evaluated for metabolites generated from the veterinary fluoroquinolone enrofloxacin (EFL) by employing high-performance liquid chromatography/high-resolution electrospray ionization mass spectrometry. From exact masses, molecular formulae were derived, and the most probable chemical structures were deduced. Patterns of major metabolites were surprisingly similar but differed greatly from that provided by Gloeophyllum striatum due to the absence of monohydroxylated EFL congeners and a greater variety of metabolites with a modified piperazine moiety. The structures of three metabolites were elucidated by 1H-nuclear magnetic resonance spectroscopy. Of 61 compounds detected, 48 were new, while 13 were known from a pattern of 87 EFL metabolites identified for G. striatum. Ethylpiperazine moieties carrying oxido, hydroxy, oxo, and acetoxy groups, or showing partial degradation, were linked to the unmodified, oxidatively decarboxylated, or multiply hydroxylated core of EFL and to isatin- and anthranilic acid-type EFL congeners. Cleavage of the fluoro-aromatic bond was observed for two, 14CO2 formation for six species. Metabolites with a hydroxylated aromatic part implied subsequent ring cleavage to be brought about by the formation of potentially four oxidizable ortho-aminophenol- and one catechol-type intermediates. EFL degradation appears to be a common activity among basidiomycetes.

Comparison of faecal and optimal growth conditions on in vitro pharmacodynamic activity of marbofloxacin against Escherichia coli

The objective of the study was to compare the in vitro activity of marbofloxacin against Escherichia coli (E. coli) strains with differing marbofloxacin susceptibility levels under optimal growth conditions and under condition mimicking faecal environment in time-kill kinetic studies. Under optimal growth conditions, marbofloxacin exerted a bactericidal concentration-dependent activity against all E. coli strains with bactericidal concentrations equal to 1 or 4 times MIC. Under faecal growth conditions, marbofloxacin maintained a bactericidal concentration-dependent activity but a 4- to 16-fold increase in bactericidal concentration was required to produce a similar magnitude of effect at 8 h. The bactericidal activity decreased between 8 and 24 h and allowed a residual bacterial population to subsist with a significant regrowth for some of them. Under no-growth conditions, marbofloxacin produced a very low decrease of non-dividing bacteria during a short time. No concentration produced a reduction > or = 3log10 in viable count excepted for two susceptible strains at concentration > or = 64 x MIC after 4 h exposure. The pharmacodynamic parameters from time-kill kinetic studies provide a useful means of studying antimicrobial activity. The importance of using different growth conditions is indicated by the difference in the killing of E. coli in the absence of active dividing cells and in the presence of autoclaved faecal content, both of which have a detrimental effect on the activity of marbofloxacin.

Adsorption and degradation of enrofloxacin, a veterinary antibiotic on natural zeolite

The adsorption of enrofloxacin, a veterinary antibiotic onto natural zeolite and further decontamination of zeolite was investigated in the present study. In the first part of the study, the effects of pH, temperature, and presence of ammonium ion on the adsorption process were examined and evaluated on the basis of Langmuir and Freundlich isotherms. Adsorption of enrofloxacin on natural zeolite was found to be highly pH dependent, exhibiting increases correspondent to decreases in pH. The positive value of enthalpy change showed the endothermic nature of adsorption processes. The presence of ammonium ion enhanced the adsorption of enrofloxacin. In the second part of the study, infrared (IR) spectroscopy, and scanning electron microscopy (SEM) were used for the determination of the modifications on the zeolite surfaces resulting from adsorption and ozone treatment. It was found that ozone at sufficient concentrations over specified time periods was able to decompose the enrofloxacin adsorbed on zeolite.

Seven years survey of susceptibility to marbofloxacin of bovine pathogenic strains from eight European countries

This study was conducted from 1994 to 2001 to determine the susceptibility of bovine pathogenic bacteria to marbofloxacin (a third generation fluoroquinolone used only in individual administration for animals). Strains originated in bovine diseases from eight European countries. They were isolated from gut infections (Escherichia coli, salmonellae), mastitis (E. coli, Staphylococcus aureus, Streptococcus uberis, S. agalactiae, S. dysgalactiae) and respiratory diseases (Mannheimia haemolytica, Pasteurella multocida, Haemophilus somnus). There was no change in the MIC distributions for each species after the launch of marbofloxacin in 1997. In E. coli, a resistant population was present before the use of marbofloxacin having been induced by co- or cross-resistance to other antibiotics used previously. Over this period the only a significant change seen was an increase in MIC(90) of E. coli from the gut (1.275 microg/ml in 1994/1995 to 5.098 microg/ml in 2001). All the salmonellae were susceptible to marbofloxacin with a MIC(90) = 0.073 microg/ml in 2001 without development of high level resistance. The use of marbofloxacin seems not to have favoured a significant increase and spreading of resistant bacteria.

Ciprofloxacin at low levels disrupts colonization resistance of human fecal microflora growing in chemostats

We studied the in vitro effects of a range of ciprofloxacin (CI) concentrations on the human intestinal flora's colonization resistance (CR) to Salmonella kedougou NCTC 12173. Four steady state microbial communities were established in chemostats using inocula from a single pool of human feces. Three chemostats were exposed to CI (0.1, 0.43 and 5 microg/mL, respectively); one served as a no-drug control. The CR of each community was tested by three successive daily challenges of 10(8) S. kedougou, each delivered in a 1 mL bolus. There was no colonization of the no-drug chemostat. Likewise, after exposure to only 0.1 microg/mL CI there was no loss of CR and S. kedougou did not colonize. Conversely, both the 0.43 and the 5 microg/mL-exposed floras suffered a loss of CR and these chemostats were colonized. S. kedougou overgrew faster and reached higher counts in the presence of 0.43 than it did in the presence of 5 microg/mL. One possible explanation is that CI had a dose-dependent effect on both the challenge strain and CR. Thus, at higher levels, even though CR was disrupted by CI, so too was the growth of the challenge strain. Since exposure to CI elicited a dose-dependent reduction in Escherichia coli counts [Reg. Pharmacol. Toxicol. 33 (2001) 276] our new data suggest that E. coli may contribute to the CR against salmonella. We further conclude that, even at fecal levels below those reached during therapy, CI may impact the human gut flora sufficiently to facilitate colonization by S. kedougou.

A reverse-phase HPLC assay for the simultaneous determination of enrofloxacin and ciprofloxacin in pig faeces

A reverse-phase HPLC assay is described for the simultaneous assay of enrofloxacin (ENR) and ciprofloxacin (CPX) in pig faeces. Extraction used dichloromethane, 2-propanol and 0.3M ortho-phosphoric acid (1:5:4 v/v/v). Separation was achieved using a Spherisorb S5 C8 column, heated to 50 degrees C and a mobile phase of 0.16% ortho-phosphoric acid (adjusted to pH 3.0 with tetrabutylammonium hydroxide solution) with 20 ml acetonitrile per litre solution. The method used fluorescence detection (Ex 310 nm; Em 445 nm), a flow rate of 1 ml/min and a 20 microl injection volume. Retention times were approximately 6 min for ciprofloxacin and 10 min for enrofloxacin. The linearity range for both compounds was 0-20 mg/kg, lowest limit of quantification 0.3 mg/kg and recoveries were >92%.

The effects of oral and intramuscular administration and dose escalation of enrofloxacin on the selection of quinolone resistance among Salmonella and coliforms in pigs

The effect of route of administration and dose of enrofloxacin (Baytril) on the development of fluoroquinolone resistance in Salmonella and Escherichia coli in the intestinal tract of pigs was investigated. Healthy pigs at the age of 8-10 weeks were infected with a mixture of susceptible wild-type (MICciprofloxacin = 0.03 microg/ml) and a mutant Salmonella typhimurium with reduced susceptibility to fluoroquinolones (MICciprofloxacin = 0.5 microg/ml) (in the ratio 99:1) and treated with 2.5 mg/kg bwt enrofloxacin by either intramuscular (i.m.) or oral (p.o.) administration at time points either 4 or 24 h after the infection. The treatment via the intramuscular route of administration (24 h after the infection) was carried out with elevated doses of 7.5 and 15 mg/kg bwt as well. Emergence of resistance during a 3-day treatment period and persistence up to 13 days after treatment, was monitored by counting the resistant and total number of coliforms and Salmonella in faeces of the pigs. High frequencies of fluoroquinolone resistance developed rapidly among the coliform flora independent of route of administration, dose or time of initiation of the treatment. Selection for resistance among the artificially introduced Salmonella was reduced by using the intramuscular route and by escalating the dose 3 or 6 times the recommended dose of 2.5 mg/kg bwt, which also resulted in shortening of the period, in which the pigs were shedding Salmonella. The resistance among the coliform flora persisted for at least 2 weeks. The Salmonella infection was cleared in all cases during the 2 weeks independent of frequency of resistance. The study showed that resistance is very easily selected by treatment with enrofloxacin at the recommended dose 2.5 mg/kg bwt, but also that the intensity of selection can be reduced by using intramuscular dosing (instead of oral dosing) and by escalating that i.m. dose. The results obtained with Salmonella also showed that even very small changes in the active drug concentrations might completely change the intensity of selection.