Glutamicibacter nicotianae AT6: A new strain for the efficient biodegradation of tilmicosin

The degradation of tilmicosin (TLM), a semi-synthetic 16-membered macrolide antibiotic, has been receiving increasing attention. Conventionally, there are three tilmicosin degradation methods, and among them microbial degradation is considered the best due to its high efficiency, eco-friendliness, and low cost. Coincidently, we found a new strain, Glutamicibacter nicotianae sp. AT6, capable of degrading high-concentration TLM at 100 mg/L with a 97% removal efficiency. The role of tryptone was as well investigated, and the results revealed that the loading of tryptone had a significant influence on TLM removals. The toxicity assessment indicated that strain AT6 could efficiently convert TLM into less-toxic substances. Based on the identified intermediates, the degradation of TLM by AT6 processing through two distinct pathways was then proposed.

Potential inhibitory effect of geraniol isolated from lemongrass (Cymbopogon commutatus Stapf) on tilmicosin-induced oxidative stress in cardiac tissue

An experimental study has been conducted to investigate the efficacy of geraniol (GNL) isolated from lemomgrass in protecting against cardiac toxicity induced by tilmicosin (TIL) in albino mice. Compared to TIL-treated mice, those supplemented with GNL had a thicker left ventricular wall and a smaller ventricular cavity. Studies of TIL animals treated with GNL showed that their cardiomyocytes had markedly changed in diameter and volume, along with a reduction in numerical density. After TIL induction, animals showed a significant increase in the protein expression of TGF-β1, TNF-α, nuclear factor kappa B (NF-kB), by 81.81, 73.75 and 66.67%, respectively, and hypertrophy marker proteins ANP, BNP, and calcineurin with respective percentages of 40, 33.34 and 42.34%. Interestingly, GNL significantly decreased the TGF-β1, TNF-α, NF-kB, ANP, BNP, and calcineurin levels by 60.94, 65.13, 52.37, 49.73, 44.18 and 36.84%, respectively. As observed from histopathology and Masson's trichrome staining, supplementation with GNL could rescue TIL-induced cardiac hypertrophy. According to these results, GNL may protect the heart by reducing hypertrophy in mice and modulating biomarkers of fibrosis and apoptosis.

Efflux pump inhibitor, phenylalanine-arginine beta-naphthylamide analog potentiates the activity of 5-O-mycaminosyltylonolide for multi-drug resistant Pseudomonas aeruginosa

The emergence and spread of antimicrobial resistance are global threats. Pseudomonas aeruginosa (P. aeruginosa) is responsible for a substantial proportion of this global health issue because of its intrinsic resistance to many antibiotics due to the impermeability of its outer membrane and its multidrug efflux pump systems. Therefore, therapeutic drugs are limited, and the development of new drugs is extremely challenging. As an alternative approach, we focused on a combinational treatment strategy and found that 5-O-mycaminosyltylonolide (OMT) showed potent antibacterial activity against P. aeruginosa in the presence of an efflux pump inhibitor, phenylalanine-arginine beta-naphthylamide (PAβN). In this report, we prepared a PAβN derivative and compared the potentiation activity of OMT by PAβNs against multidrug-resistant P. aeruginosa clinical isolates.

Enhanced Cellular Delivery of Tildipirosin by Xanthan Gum-Gelatin Composite Nanogels

Tildipirosin has no significant inhibitory effect on intracellular bacteria because of its poor membrane permeability. To this end, tildipirosin-loaded xanthan gum-gelatin composite nanogels were innovatively prepared to improve the cellular uptake efficiency. The formation of the nanogels via interactions between the positively charged gelatin and the negatively charged xanthan gum was confirmed by powder X-ray diffraction and Fourier transform infrared. The results indicate that the optimal tildipirosin composite nanogels possessed a 3D network structure and were shaped like a uniformly dispersed ellipse, and the particle size, PDI, and ζ potential were 229.4 ± 1.5 nm, 0.26 ± 0.04, and -33.2 ± 2.2 mV, respectively. Interestingly, the nanogels exhibited gelatinase-responsive characteristics, robust cellular uptake via clathrin-mediated endocytosis, and excellent sustained release. With those pharmaceutical properties provided by xanthan gum-gelatin composite nanogels, the anti-Staphylococcus aureus activity of tildipirosin was remarkably amplified. Further, tildipirosin composite nanogels demonstrated good biocompatibility and low in vivo and in vitro toxicities. Therefore, we concluded that tildipirosin-loaded xanthan gum-gelatin composite nanogels might be employed as a potentially effective gelatinase-responsive drug delivery for intracellular bacterial infection.

Depletion of tilmicosin residue in Gushi chickens following oral administration via drinking water

This study aimed to examine the depletion of tilmicosin residues in Gushi chickens following the administration at a concentration of 75 mg/L in their drinking water for three consecutive days. Plasma, liver, kidney, lung, muscle, and skin + fat samples were collected from 6 chickens at 6 h, 1, 3, 5, and 7 days after the treatment. Tilmicosin concentrations in the samples were determined using a high-performance liquid chromatography (HPLC) method. The findings revealed that the highest tilmicosin residues were detected in the liver, followed by the kidney, lung, skin + fat, muscle, and plasma. Notably, at 7 days post-treatment, no drug residue was detected in all samples except for the liver and kidney. The non-compartmental model was employed to calculate relevant pharmacokinetic parameters. The elimination half-lives (t1/2λz ) of tilmicosin were as follows, ranked from long to short: skin + fat (45.42 h), liver (44.17 h), kidney (40.06 h), plasma (37.64 h), lung (31.39 h), and muscle (30.05 h). Considering the current residue depletion and the maximum residue limits (MRLs) set by Chinese regulatory authorities, the withdrawal times for tilmicosin were estimated as 18.91, 10.81, and 8.58 days in the kidney, liver, and skin + fat, respectively. A rounded-up value of 19 days was selected as the conclusive withdrawal time. Furthermore, based on the observed tilmicosin concentrations in plasma and lung, combined with previously reported minimum inhibitory concentration (MIC) values against Mycoplasma gallisepticum, the current dosing regimen was deemed adequate for treating Mycoplasma gallisepticum infections in Gushi chickens.

In vitro susceptibility of Brachyspira hyodysenteriae strains isolated in pigs in northern Italy between 2005 and 2022

Pleuromutilins (tiamulin and valnemulin) are often used to treat swine dysentery due to recurrent resistance to macrolides and lincosamides. Recently, reduced susceptibility of B. hyodysenteriae to pleuromutilin has been reported. 536 strains of B. hyodysenteriae were isolated from symptomatic pigs weighing 30-150 kg in northern Italy between 2005 and 2022. B. hyodysenteriae was isolated by standard methods and confirmed by PCR. The minimum inhibitory concentration (MIC) to doxycycline, lincomycin, tiamulin, tylosin, tylvalosine and valnemulin was evaluated according to CLSI procedures and MIC data were reported as MIC 50 and MIC 90. The temporal trend of the MIC values was evaluated by dividing the data into two groups (2005-2013 and 2014-2022). Comparison of the distribution in frequency classes in the two periods was performed using Pearson's chi-squared test (p < 0.01). MIC 50 was close to the highest values tested for lincomycin and tylosin, while MIC 90 was close to the highest values tested for all antibiotics. 71.7% of the strains were susceptible to tylvalosin, while 75%-80.4% had reduced susceptibility to valnemulin and tiamulin, respectively. The difference in the distribution of MIC classes was statistically significant in the two periods for doxycycline, tiamulin, tylvalosin and valnemulin, and more MIC classes above the epidemiological cut-off were observed in 2014-2022 compared with 2005-2013. The evaluation of the trends during the period considered shows a decreasing rate of wild-type strains with MIC values below the epidemiological cut-off over time and confirms the presence of resistant strains in northern Italy.

Veterinary consumption of highest priority critically important antimicrobials and various growth promoters based on import data in Pakistan

Background

Antimicrobial resistance (AMR) is a global public health emergency driven by the indiscriminate use of antimicrobial agents in humans and animals. Antimicrobial consumption surveillance guides its containment efforts. In this study, we estimated, for the first time, veterinary consumption of Critically Important Antimicrobials with Highest Priority (CIA-HtP) for Pakistan.

Methods

The study used an export/import database which provided imports data collected from the Pakistan Customs Authority. We investigated imports of 7 CIA-HtP and various poultry feed additives/growth promoters (FAs/GPs) identified from a survey of 10 poultry and dairy farms in Punjab province in Pakistan and a previously published study, over a three-year period of 2017–2019. Antimicrobial consumption was estimated in mg/kg of country’s animal biomass.

Findings

Imports, in tonnes, for these 7 CIA-HtP were for the years 2017–19: tylosin 240.84, enrofloxacin 235.14, colistin 219.73, tilmicosin 97.32, spiramycin 5.79, norfloxacin 5.55, ceftiofur 1.02 for a total 805.39 tonnes. The corresponding antimicrobial consumption was 10.05 mg/kg of animal biomass. The poultry FAs/GPs contained: zinc bacitracin, enramycin, bacitracin methylene disalicylate, tylosin, tiamulin, colistin, lincomycin, streptomycin, flavophospholipol, tilmicosin, and penicillin with a total antimicrobial chemical compound (ACC) import volume of 577.18 tonnes for the years 2017–2019; and an estimated consumption of 96.53 mg/kg of poultry biomass.

Interpretation

These antimicrobials were a mix of macrolides, quinolones, polymyxins and cephalosporins, among which are some also on the Watch or Reserve list by the WHO, indicating the need for stewardship and to conserve essential antimicrobials to contain AMR. The finding that a yearly average of 192.39 tonnes of the ACC imported were FAs/GPs further highlight the need for stronger regulation and enforcement.

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

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

Conjugates of Desmycosin with Fragments of Antimicrobial Peptide Oncocin: Synthesis, Antibacterial Activity, Interaction with Ribosome

Design and synthesis of conjugates consisting of the macrolide antibiotic desmycosin and fragments of the antibacterial peptide oncocin were performed in attempt to develop new antimicrobial compounds. New compounds were shown to bind to the E. coli 70S ribosomes, to inhibit bacterial protein synthesis in vitro, as well as to suppress bacterial growth. The conjugates of N-terminal hexa- and tripeptide fragments of oncocin and 3,2',4''-triacetyldesmycosin were found to be active against some strains of macrolide-resistant bacteria. By simulating molecular dynamics of the complexes of these compounds with the wild-type bacterial ribosomes and with ribosomes, containing A2059G 23S RNA mutation, the specific structural features of their interactions were revealed.

In Vitro and In Vivo Activities of Tilmicosin and Acetylisovaleryltylosin Tartrate against Toxoplasma gondii

Toxoplasma gondii is a widespread intracellular pathogen that infects humans and a variety of animals. The current therapeutic strategy for human toxoplasmosis is a combination of sulphadiazine and pyrimethamine. However, this combination still has a high failure rate and is ineffective against chronic infections. Therefore, it is important to discover a new anti-T. gondii drug that is safer and more effective in both humans and animals. In this study, we describe the anti-T. gondii activities of the 16-membered macrolide tilmicosin and acetylisovaleryltylosin tartrate (ATLL). Both tilmicosin and ATLL potently inhibited T. gondii with a half-maximal effective concentration (EC₅₀) of 17.96 μM and 10.67 μM, respectively. Interestingly, tilmicosin and ATLL had different effects on the parasites. ATLL exhibited a potent inhibitory effect on intracellular parasite growth, while tilmicosin suppressed parasites extracellularly. By studying the lytic cycle of T. gondii after treatment, we found that ATLL potently inhibited the intracellular proliferation of tachyzoites, while tilmicosin affected the invasion of tachyzoites. Immunofluorescence analysis using ATLL-treated T. gondii showed morphologically abnormal parasites, which may be due to the inhibition of tachyzoite proliferation and division. In addition, tilmicosin and ATLL significantly delayed the death of mice caused by acute toxoplasmosis. Our results suggest that ATLL has potent anti-Toxoplasma activity both in vitro and in vivo and may be an alternative to toxoplasmosis in the future.

Investigation of Macrolide Resistance Genotypes of Pasteurella multocida Isolates from Cattle and Small Ruminants

Macrolides are commonly used to control respiratory tract infections in ruminants, but the susceptibility of Pasteurella multocida strains has shown a decrease to macrolide antibiotics in the last decade. In this work we assessed the prevalence of macrolide resistance of 100 P. multocida isolates from ruminant hosts and studied the resistance genotypes with newly designed PCRs. Susceptibility to erythromycin and tilmicosin was tested using minimal inhibitory concentration (MIC) test strips. A newly designed PCR was used for the detection of macAB genes, and a PCR plus restriction enzyme-based technique was developed for detecting a 23S rRNA gene mutation at position 2059. Five bovine isolates with notably increased MICs (≥256 μg/mL for erythromycin and ≥32 μg/mL for tilmicosin) carried resistance genes msr(E) and mph(E) or the A2059G point mutation in the 23S rRNA gene. Over 73% strains from small ruminants and all bovine isolates were MacAB PCR positive. Bovine strains were less sensitive to macrolide antibiotics than isolates from small ruminants, and an increase in the prevalence of macrolide resistance in bovine P. multocida isolates has also been observed over time.

Dinuclear vs. Mononuclear Copper(II) Coordination Species of Tylosin and Tilmicosin in Non-Aqueous Solutions

The veterinary 16-membered macrolide antibiotics tylosin (HTyl, 1a) and tilmicosin (HTilm, 1b) react with copper(II) ions in acetone at metal-to-ligand molar ratio of 1:2 to form blue (2) or green (3) metal(II) coordination species, containing nitrate or chloride anions, respectively. The complexation processes and the properties of 2–3 were studied by an assortment of physicochemical techniques (UV-Vis, EPR, NMR, FTIR, elemental analysis). The experimental data revealed that the main portion of copper(II) ions are bound as neutral EPR-silent dinuclear complexes of composition [Cu₂(µ-NO₃)₂L₂] (2a–b) and [Cu₂(µ-Cl)₂Cl₂(HL)₂] (3a–b), containing impurities of EPR-active mono-species [Cu(NO₃)L] (2a’–b’) and [CuCl₂(HL)] (3a’–b’). The possible structural variants of the dinuclear- and mono-complexes were modeled by the DFT method, and the computed spectroscopic parameters of the optimized constructs were compared to those measured experimentally. Using such a combined approach, the main coordination unit of the macrolides, involved in the complex formation, was defined to be their mycaminosyl substituent, which acts as a terminal ligand in a bidentate mode through the tertiary nitrogen atom and the oxygen from a deprotonated (2) or non-dissociated (3) hydroxyl group, respectively.

Following the route of veterinary antibiotics tiamulin and tilmicosin from livestock farms to agricultural soils

Veterinary antibiotics (VAs) are not completely metabolized in the animal body. Hence, when animal excretes are used as soil manures, VA residues are dispersed with potential implications for environmental quality and human health. We studied the persistence of tiamulin (TIA) and tilmicosin (TLM) along their route from pig administration to fecal excretion and to agricultural soils. TLM was detected in feces at levels folds higher (4.27-749.6 μg g^-1) than TIA (0.55-5.99 μg g^-1). Different administration regimes (feed or water) showed different excretion patterns and residual levels for TIA and TLM, respectively. TIA and TLM (0.5, 5 and 50 μg g^-1) dissipated gradually from feces when stored at ambient conditions (DT₅₀ 5.85-35.9 and 23.5-49.8 days respectively), while they persisted longer during anaerobic digestion (DT₉₀ >365 days) with biomethanation being adversely affected at VA levels > 5 μg g^-1. When applied directly in soils, TLM was more persistent than TIA with soil fumigation extending their persistence suggesting microbial degradation, while soil application through feces increased their persistence, probably due to increased sorption to the fecal organic matter. The use of TIA- and TLM-contaminated feces as manures is expected to lead to VAs dispersal with unexplored consequences for the environment and human health.

Moringa oleifera ethanolic extract attenuates tilmicosin-induced renal damage in male rats via suppression of oxidative stress, inflammatory injury, and intermediate filament proteins mRNA expression

Tilmicosin (Til) is a popular macrolide antibiotic, widely used in veterinary practice. The present study was designed to address the efficacy of Moringa oleifera ethanolic extract (MOE) in protecting against Tilmicosin (Til) - induced nephrotoxicity in Sprague Dawley rats. Animals were treated once with Til (75 mg/kg bw, subcutaneously), and/or MOE for 7 days (400 or 800 mg/kg bw, by oral gavage). Til-treatment was associated with significantly increased serum levels of creatinine, urea, sodium, potassium and GGT activity, as well as decreased total protein and albumin concentrations. Renal tissue hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels were elevated, while the activities of superoxide dismutase (SOD) and glutathione peroxidase (GPx) enzymes were diminished. The levels of renal tumor necrosis factor alpha (TNF-α) and interleukin-1 beta (IL-1β) and the mRNA expression of intermediate filament protein encoding genes (desmin, nestin and vimentin) in the kidney were up- regulated with histopathological alterations in renal glomeruli, tubules and interstitial tissue. These toxic effects were markedly ameliorated by co-treatment of MOE with Til, in a dose dependent manner. Taken together, these results indicate that MO at 800 mg/kg protects against Til-induced renal injury, likely by its potent antioxidant and anti-inflammatory properties, which make it suitable to be used as a protective supplement with Til therapy.

A non-inferiority study evaluating a new extended-release preparation of tilmicosin injected subcutaneously vs. ceftiofur administered intramammary, as dry-cow therapy in Holstein Friesian cows

BACKGROUND

A new, extended long-acting tilmicosin (TLAe) preparation was tested against intramammary ceftiofur (CEF) using a non-inferiority trial model during dry-cow therapy (DCT) in a farm with high bovine population density and deficient hygiene application.

OBJECTIVES

To evaluate the possibility that TLAe administered parenterally can achieve non-inferiority status compared to CEF administered intramammary for DCT.

METHODS

Cows were randomly assigned to TLAe (20 mg/kg subcutaneous; n = 53) or CEF (CEF-HCl, 125 mg/quarter; n = 38 cows) treatment groups. California mastitis testing, colony-forming unit assessment (CFU/mL), and number of cases positive for Staphylococcus aureus were quantified before DCT and 7 d after calving. A complete cure was defined as no bacteria isolated; partial cure when CFU/mL ranged from 150 to 700, and cure-failure when CFU/mL was above 700.

RESULTS

TLAe and CEF had overall cure rates of 57% and 53% (p > 0.05) and S. aureus cure rates of 77.7% and 25%, respectively (p < 0.05). The pathogens detected at DCT and 7 days after calving were S. aureus (62.71% and 35.55%), Staphylococcus spp. (22.03% and 35.55%), Streptococcus uberis (10.16% and 13.33%), and Escherichia coli (5.08% and 15.55%). Non-inferiority and binary logistic regression analyses revealed a lack of difference in overall efficacies of TLAe and CEF. Apart from S. aureus, S. uberis was the predominant pathogen found in both groups.

CONCLUSIONS

This study is the first successful report of parenteral DCT showing comparable efficacy as CEF, the gold-standard. The extended long-term pharmacokinetic activity of TLAe explains these results.

Preparation of tilmicosin-resin complex microsphere and its Pharmacokinetics study in rat

The objective of this study is to mask the extremely bitter taste of tilmicosin, and the tilmicosin-resin complex (DRC) microsphere were prepared by entrapping tilmicosin into resins (Tulsion® 339 and Eudragit® RS/ RL 100) for further pharmacokinetics study in rat. The DRC was characterized by FTIR and X-ray diffraction, and the microsphere containing DRC and Eudragit® RS/RL 100 were characterized by scanning electron microscopy (SEM). The rats were orally administrated with tilmicosin phosphate (10 mg/kg) and the microsphere containing the same dose of tilmicosin, respectively. These microspheres do not taste bitter and the kinetics study suggests that the drug released from microsphere meet the first order kinetics (r = 0.9911). The experimental results showed that T_½ and T_max of microsphere were much longer than tilmicosin phosphate, which indicates that the oral microsphere can be a promising long-active formulation for taste masking of tilmicosin.

Preparation, characterization, and pharmacokinetics of tilmicosin taste-masked formulation via hot-melt extrusion technology

Tilmicosin (TMS) is a macrocyclic antibiotic specially used in veterinary clinics, but its extreme bitterness limits its use. This study aimed to obtain a taste-masked formulation of TMS by hot melt extrusion (HME) technology and to investigate the formulation's characterization, stability, and effects in vitro/in vivo. Eudragit® E PO was selected as the carrier, and TMS dissolution in artificial saliva was used as a reference. The HME parameters were optimized via an orthogonal design. The optimized results were as follows: 135 ℃ extrusion temperature, 100 rpm screw speed and 30 % drug load. The masking efficiency of the formulation was evaluated by both simulated oral drug release in vitro and electronic tongue tests. The release of the taste-masked formulation in artificial saliva medium was significantly reduced within 60 s (less than 2%), while the release in 0.1 M HCl buffer was fast (more than 80 %) within 30 min. As suggested by the results of the electronic tongue, the taste-masked formulation had a better taste-masked effect than the commercial premix and the commercial enteric granules. Finally, a pharmacokinetic study was performed. Analysis of variance demonstrated that the pharmacokinetic behavior of the TMS taste-masked formulation was similar to that of the commercial premix, while the absorption effect was better than that of the commercially available enteric granules. This research indicates that the taste-masked formulation has the potential for future commercialization.

Protective potency of Astragalus polysaccharides against tilmicosin- induced cardiac injury via targeting oxidative stress and cell apoptosis-encoding pathways in rat

Tilmicosin (Til) was purposed to be used in the treatment of a wide range of respiratory diseases in livestock. However, undesirable adverse effects, cardiac toxicity, in particular, may be associated with Til therapy. In the present study, the response of adult rats administered Til subcutaneously at different doses (10, 25, 50, 75, and 100 mg/kg b.w.; single injection) was evaluated. Astragalus polysaccharide (AP) at two doses (100 and 200 mg/kg b.w.; intraperitoneally) was investigated for its potential to counteract the cardiac influences, involving the oxidative stress-induced damage and apoptotic cell death, elicited by the Til treatment at a dose of 75 mg/kg b.w. in rats. Til induced mortalities and altered the levels of the biomarkers for the cardiac damage, particularly in the rats treated with the doses of 75 and 100 mg/kg b.w.; similarly, morphological alterations in cardiac tissue were seen at all studied doses. AP was found to cause a significant (P ˂ 0.05) decline in the levels of impaired cardiac injury markers (troponin, creatine phosphokinase, and creatine phosphokinase-MB), improvement in the antioxidant endpoints (total antioxidant capacity), and attenuation in the oxidative stress indices (total reactive oxygen species, 8-hydroxy-2-deoxyguanosine, lipid peroxides [malondialdehyde], and protein carbonyl), associated with a significant (P ˂ 0.05) modulation in the mRNA expression levels of the encoding genes (Bcl-2, Bax, caspase-3, P53, Apaf-1, and AIF), related to the intrinsic pathway of apoptotic cell death in the cardiac tissue. AP administration partially restored the morphological changes in the rat's heart. The highest protective efficacy of AP was recorded at a dose level of 200 mg/kg b.w. Taken together, these results indicated that AP is a promising cardioprotective compound capable of attenuating Til-induced cardiac impact by protecting the rat cardiac tissue from Til-induced apoptosis when administered concurrently with and after the Til injection.

L-Carnitine and vitamin E ameliorate cardiotoxicity induced by tilmicosin in rats

The present study aimed to investigate the possible mitigating effect of L-carnitine (LC) and/or α-tocopherol (Vit. E) administration against tilmicosin (TIL)-induced cardiotoxicity in rats. Fifty-six male albino rats were divided into seven groups according to LC, Vit. E, and/or TIL administration. Control, LC, and Vit. E groups were given saline, 150 mg LC/kg body weight (BW)/day and 100 mg Vit. E/kg BW/day, respectively, orally once daily for 15 days. The TIL group was administered saline orally once daily for 15 days and a single dose of TIL (75 mg/kg BW) subcutaneously (SC) on day 14 from the starting of the experimental period (15 days). The TIL-LC, TIL-Vit. E, and TIL-LC-Vit. E groups received 150 mg LC/kg BW/day, 100 mg Vit. E/kg BW/day, and 150 mg LC/kg BW pulse 100 mg Vit. E/kg BW, respectively, orally once daily for 15 days with TIL as described above. The results revealed that the administration of TIL significantly (P ≤ 0.05) raised serum activities of heart injury indicators, lactate dehydrogenase (LDH), creatine kinase (CK), and CK-MB with substantial increase (P ≤ 0.05) in the cardiac contents of malondialdehyde (MDA) and decreased in antioxidants. The pathological changes appeared in the form of necrotic muscle fibers and massive inflammatory cellular infiltrations in the cardiac muscle and increased the caspase-3 immunohistochemical expression in the heart tissues as well. These changes were ameliorated by LC and/or Vit. E administration. In conclusion, supplementation of LC and/or Vit. E ameliorated the cardiotoxicity of the TIL SC injection in the rat.

Design of Novel Haptens and Development of Monoclonal Antibody-Based Immunoassays for the Simultaneous Detection of Tylosin and Tilmicosin in Milk and Water Samples

In this work, a monoclonal antibody-based indirect competitive enzyme-linked immunosorbent assay (icELISA) was established to detect tylosin and tilmicosin in milk and water samples. A sensitive and specific monoclonal antibody was prepared by rational designed hapten, which was achieved by directly oxidizing the aldehyde group on the side chain of tylosin to the carboxyl group. Under the optimized conditions, the linear range of icELISA for tylosin and tilmicosin were 1.3 to 17.7 ng/mL and 2.0 to 47.4 ng/mL, with half-maximal inhibition concentration (IC₅₀) values of 4.7 and 9.6 ng/mL, respectively. The cross-reactivity with other analogues of icELISA was less than 0.1%. The average recoveries of icELISA for tylosin and tilmicosin ranged from 76.4% to 109.5% in milk and water samples. Besides, the detection results of icELISA showed good correlations with HPLC-MS/MS. The proposed icELISA was satisfied for rapid and specific screening of tylosin and tilmicosin residues in milk and water samples.

Nanostructured lipid carriers with exceptional gastrointestinal stability and inhibition of P-gp efflux for improved oral delivery of tilmicosin

Tilmicosin (TMS) is widely applied to treat porcine bacterial respiratory diseases in veterinary medicine. However, oral administration of TMS is greatly limited due to its physicochemical properties, such as poor water solubility, gastric acid sensitivity and bitterness. Therefore, nanostructured lipid carriers (NLCs) were developed as an oral delivery system for TMS by the high shear method combined with ultrasonic techniques in this study. The results showed that TMS-NLCs were approximately spherical with a hydrodynamic diameter of 283.03 nm and a zeta potential of -30.04 mV. TMS was almost entirely encapsulated in the NLCs by interacting with the lipid matrix, as characterized by differential scanning calorimetry and fourier transform infrared spectroscopy. Thus, TMS-NLCs had an excellent encapsulation efficiency and loading capacity with values of 93.46% and 9.23%, respectively. TMS-NLCs maintained good stability not only during storage at 4 ℃, 25 ℃ and 40 ℃ for 90 days but also in stimulated gastrointestinal (GI) fluids at 37 ℃ for 7 days. Therefore, TMS-NLCs displayed low and sustained release in vitro without an initial burst release in stimulated GI fluids. Furthermore, TMS-NLCs showed higher oral bioavailability in piglets compared to the API suspension. Subsequently, Caco-2 cell monolayers were utilized to analyze the mechanism of NLC-enhanced oral adsorption of TMS. The data revealed that NLCs not only increased cellular uptake of TMS but also inhibited the efflux of P-gp in Caco-2 cells. Additionally, TMS-NLCs mainly entered Caco-2 cells via the caveolae/lipid raft-mediated endocytosis pathway. Moreover, nanoparticles were transported across Caco-2 cell monolayers in the intact form to the basolateral side, as identified by transmission electron microscopy, indicating that TMS-NLCs escape lysosome degradation. Taken together, these results indicate that NLCs are a potential delivery carrier for improving the solubility, permeability and oral bioavailability of TMS.

Evaluation of Minimum Inhibitory Concentrations for 154 Mycoplasma synoviae isolates from Italy collected during 2012-2017

Mycoplasma synoviae (MS) is a highly prevalent bacterial species in poultry causing disease and severe economic losses. Antibiotic treatment is one of the control strategies that can be applied to contain clinical outbreaks in MS-free flocks, especially because this bacterium can be transmitted in ovo. It becomes, then, very important for veterinarians to know the antibiotic susceptibility of the circulating strains in order to choose the most appropriate first-line antibiotic molecule as a proactive role in fighting antibiotic resistance. We evaluated the Minimum Inhibitory Concentrations (MICs) of enrofloxacin, oxytetracycline, doxycycline, erythromycin, tylosin, tilmicosin, spiramycin, tiamulin, florfenicol and lincomycin for MS isolates collected between 2012 and 2017 in Italy. A total of 154 MS isolates from different poultry commercial categories (broiler, layer, and turkey sectors) was tested using commercial MIC plates. All MS isolates showed very high MIC values of erythromycin (MIC90 ≥8 μg/mL) and enrofloxacin (MIC90 ≥16 μg/mL). MIC values of doxycycline and oxytetracycline obtained were superimposable to each other with only a one-fold dilution difference. Discrepancies between MIC values of tylosin and tilmicosin were observed. Interestingly, seven isolates showed very high MIC values of lincomycin and tilmicosin, but not all of them showed very high MIC values of tylosin. Most of the MS isolates showed low MIC values of spiramycin, but seven strains showed a MIC ≥16 μg/mL. In the observation period, the frequency of the different MIC classes varied dependently on the tested antibiotic. Interestingly, tilmicosin MICs clearly showed a time-dependent progressive shift towards high-concentration classes, indicative of an on-going selection process among MS isolates. Until standardized breakpoints become available to facilitate data interpretation, it will be fundamental to continue studying MIC value fluctuations in the meantime in order to create a significant database that would facilitate veterinarians in selecting the proper drug for treating this impactful Mycoplasma.

Structure Elucidation of Macrolide Antibiotics Using MSn Analysis and Deuterium Labelling

The 14- and 16-membered macrolide antibiotics are an important structural class. Ubiquitously produced by a number of bacterial strains, namely actinomycetes, purification and structure elucidation of the wide array of analogs is challenging, both for discovery efforts and methodologies to monitor for byproducts, metabolites, and contaminants. Collision-induced dissociation mass spectrometry offers an attractive solution, enabling characterization of mixtures, and providing a wealth of structural information. However, interpretation of these spectra can be difficult. We present a study of 14- and 16-membered macrolide antibiotics, including MSⁿ analysis for unprecedented depth of coverage, and complimentary analysis with D₂O and H₂¹⁸O labeling to elucidate fragmentation mechanisms. These analyses contrast the behaviors of varying classes of macrolides and highlight how analogues can be identified in relation to similar structures, which will provide utility for future studies of novel macrolides, as well as impurities, metabolites, and degradation products of pharmaceuticals. Graphical Abstract.

Multicomponent synthesis of α-acylamino and α-acyloxy amide derivatives of desmycosin and their activity against gram-negative bacteria

Bacterial resistance to the existing drugs requires constant development of new antibiotics. Developing compounds active against gram-negative bacteria thereby is one of the more challenging tasks. Among the many approaches to develop successful antibacterials, medicinal chemistry driven evolution of existing successful antibiotics is considered to be the most effective one. Towards this end, the C-20 aldehyde moiety of desmycosin was modified into α-acylamino and α-acyloxy amide functionalities using isonitrile-based Ugi and Passerini reactions, aiming for enhanced antibacterial and physicochemical properties. The desired compounds were obtained in 45-93% yield under mild conditions. The antibacterial activity of the resulting conjugates was tested against gram-negative Aliivibrio fischeri. The antibiotic strength is mostly governed by the amine component introduced. Thus, methylamine derived desmycosin bis-amide 4 displayed an enhanced inhibition rate vs. desmycosin (99% vs. 83% at 1 µM). Derivatives with long acyclic or bulky amine and isocyanide Ugi components reduced potency, whereas carboxylic acid reagents with longer chain length afforded increased bioactivity. In Passerini 3-component products, the butyric ester amide 22 displayed a higher activity (90% at 1 µM) than the parent compound desmycosin (2).

Discovery of ABBV-4083, a novel analog of Tylosin A that has potent anti-Wolbachia and anti-filarial activity

There is a significant need for improved treatments for onchocerciasis and lymphatic filariasis, diseases caused by filarial worm infection. In particular, an agent able to selectively kill adult worms (macrofilaricide) would be expected to substantially augment the benefits of mass drug administration (MDA) with current microfilaricides, and to provide a solution to treatment of onchocerciasis / loiasis co-infection, where MDA is restricted. We have identified a novel macrofilaricidal agent, Tylosin A (TylA), which acts by targeting the worm-symbiont Wolbachia bacterium. Chemical modification of TylA leads to improvements in anti-Wolbachia activity and oral pharmacokinetic properties; an optimized analog (ABBV-4083) has been selected for clinical evaluation.

Preparation and evaluation of tilmicosin microspheres and lung-targeting studies in rabbits

Tilmicosin (TMS) is a macrolide used extensively for pulmonary infections in clinical veterinary medicine. However, TMS has frequent administration and short elimination half-life. Therefore, tilmicosin-gelatine microspheres (TMS-GMS) were prepared by an emulsion-chemical cross-linking technique as a sustained-release formulation to extend drug half-life. The particle size distribution, in-vitro sustained-release properties, stability, and physical characteristics, as well as pharmacokinetic (PK) characteristics, were evaluated in rabbits. TMS-GMS were spherical in shape and had a mean diameter of 11.34±1.20μm; 95.65% of the microspheres varied in size from 5.0 to 25.0μm. Light and thermal stability tests indicated no significant changes in all observed indices. Importantly, compared to crude TMS, slower release of TMS from TMS-GMS was noted in drug release studies (in vitro). Pharmacokinetic (PK) characteristics were examined in the lung, liver, heart, kidney and muscle tissue of rabbits following IM injection of TMS-GMS or TMS-injection at a dose of 10mg/kg. The elimination half-life of TMS-GMS (59.21±0.21h) was longer than that of TMS-injection (38.56±0.13h) in the lung. The ratio of peak concentration (C_e) of TMS-GMS to TMS-injection was 2.19 (>1) in the lung, demonstrating the selectivity of TMS-GMS to target the lung compared to that of other tissues (C_e<1). Interestingly, the uptake value of TMS from TMS-GMS was 8.48 times higher in the lung than that for the TMS-injection, and was slightly higher than in the liver (1.85), heart (1.72), kidney (2.44) and muscle (2.79) tissues. TMS-GMS is a sustained-release formulation of TMS with potential to be used in veterinary clinical applications; possible benefits include lung-targeting and prolonged elimination half-life.

Mutant prevention and minimum inhibitory concentration drug values for enrofloxacin, ceftiofur, florfenicol, tilmicosin and tulathromycin tested against swine pathogens Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis

Actinobacillus pleuropneumoniae, Pasteurella multocida and Streptococcus suis are prevalent bacterial causes of swine infections. Morbidity, mortality and positively impacting the financial burden of infection occurs with appropriate antimicrobial therapy. Increasing antimicrobial resistance complicates drug therapy and resistance prevention is now a necessity to optimize therapy and prolong drug life. Mutant bacterial cells are said to arise spontaneously in bacterial densities of 107-109 or greater colony forming units/ml. Antibiotic drug concentration inhibiting growth of the least susceptible cell in these high density populations has been termed the mutant prevention concentration (MPC). In this study MPC and minimum inhibitory concentration (MIC) values of ceftiofur, enrofloxacin, florfenicol, tilmicosin and tulathromycin were determined against the swine pathogens A. pleuropneumoniae, P.multocida and S. suis. The following MIC90/MPC90 values (mg/L) for 67 A. pleuropneumoniae and 73 P. multocida strains respectively were as follows: A. pleuropneumoniae 0.031/0.5, ≤0.016/0.5, 0.5/2, 4/32, 2/32; P. multocida 0.004/0.25, 0.016/0.125, 0.5/0.5, 8/16, 0.5/1. For 33 S. suis strains, MIC90 values (mg/L) respectively were as follows: 1, 0.25, 4, ≥8 and ≥8. A total of 16 S. suis strains with MIC values of 0.063-0.5 mg/L to ceftiofur and 0.25-0.5 mg/L to enrofloxacin were tested by MPC; MPC values respectively were 0.5 and 1 mg/L respectively. MPC concentrations provide a dosing target which may serve to reduce amplification of bacterial subpopulations with reduced antimicrobial susceptibility. Drug potency based on MIC90 values was ceftiofur > enrofloxacin >florfenicol = tulathromycin > tilmicosin; based on MPC90 values was enrofloxacin > ceftiofur > tulathromycin > florfenicol ≥ tilmicosin.

Noncovalent Interaction of Tilmicosin with Bovine Serum Albumin

Tilmicosin is a widely used antibiotic in veterinary applications. Its antimicrobial activity is ranged from Gram-positive and some Gram-negative bacteria towards activities against Mycoplasma and Chlamydia. Adsorption affinity of tilmicosin antibiotics towards bovine serum albumin was investigated by both spectroscopic (UV-vis, Photoluminescence) and calorimetric methods. The interaction was determined on the basis of quenching of albumin by tilmicosin. Results confirm noncovalent binding of tilmicosin on bovine serum albumin with 1:1 stoichiometry associated with pK = 4.5, highlighting possible removal of tilmicosin molecules from the albumin surface through exchange reactions by known competitor molecules. Calorimetric measurements have confirmed the weak interaction between tilmicosin and albumin and reflect enhanced denaturation of the albumin in the presence of tilmicosin antibiotic. This process is associated with the decreased activation energy of conformational transition of the albumin. It opens a new, very quick reaction pathway without any significant effect on the product by noncovalent binding the tilmicosin molecules to the protein molecules. Results highlight the medical importance of these investigations by considerable docking of the selected antibiotic molecules on serum albumins. Although the binding may cause toxic effects in living bodies, the strength of the binding is weak enough to find competitor molecules for effective removals from their surface.

Antibiotic susceptibility profiles of Mycoplasma synoviae strains originating from Central and Eastern Europe

BACKGROUND

Mycoplasma synoviae causes infectious synovitis and respiratory diseases in chickens and turkeys and may lead to egg shell apex abnormalities in chickens; hence possesses high economic impact on the poultry industry. Control of the disease consists of eradication, vaccination or medication. The aim of the present study was to determine the in vitro susceptibility to 14 different antibiotics and an antibiotic combination of M. synoviae strains originating from Hungary and other countries of Central and Eastern Europe.

RESULTS

Minimal inhibitory concentration (MIC) values of a total of 41 M. synoviae strains were determined by the microbroth dilution method. The strains were collected between 2002 and 2016 and originated from Hungary (n = 26), Austria (n = 3), the Czech Republic (n = 3), Slovenia (n = 3), Ukraine (n = 3), Russia (n = 2) and Serbia (n = 1). Tetracyclines (with MIC50 values of 0.078 μg/ml, ≤0.25 μg/ml and 0.5 μg/ml for doxycycline, oxytetracycline and chlortetracycline, respectively), macrolides (with MIC50 values of ≤0.25 μg/ml for tylvalosin, tylosin and tilmicosin), pleuromutilins (with MIC50 values of 0.078 μg/ml and ≤0.039 μg/ml for tiamulin and valnemulin) and the combination of lincomycin and spectinomycin (MIC50 1 μg/ml (0.333/0.667 μg/ml)) were found to be the most effective antibiotic agents against M. synoviae in vitro. High MIC values were detected in numerous strains for fluoroquinolones (with MIC50 values of 1.25 μg/ml and 2.5 μg/ml for enrofloxacin and difloxacin), neomycin (MIC50 32 μg/ml), spectinomycin (MIC50 2 μg/ml), lincomycin (MIC50 0.5 μg/ml) and florfenicol (MIC50 4 μg/ml). Nevertheless, strains with elevated MIC values were detected for most of the applied antibiotics.

CONCLUSIONS

In the medical control of M. synoviae infections the preliminary in vitro antibiotic susceptibility testing and the careful evaluation of the data are crucial. Based on the in vitro examinations doxycycline, oxytetracycline, tylvalosin, tylosin and pleuromutilins could be recommended for the therapy of M. synoviae infections in the region.

A mixed treatment comparison meta-analysis of metaphylaxis treatments for bovine respiratory disease in beef cattle

The objective of this project was to evaluate the effects of antimicrobials approved for parenteral metaphylactic use in feeder and stocker calves on morbidity and mortality for bovine respiratory disease with the use of a mixed treatment comparison meta-analysis. An initial literature review was conducted in April 2016 through Pubmed, Agricola, and CAB (Commonwealth Agricultural Bureau) for randomized controlled trials for metaphylaxis antimicrobial administered parentally to incoming feedlot or stocker calves within 48 h of arrival. The final list of publications included 29 studies, with a total of 37 trials. There were 8 different metaphylactic antimicrobials. Final event outcomes were categorized into bovine respiratory disease (BRD) morbidity cumulative incidence d 1 to ≤ 60 of the feeding period, BRD morbidity cumulative incidence d 1 to closeout of the feeding period, BRD mortality cumulative incidence d 1 to closeout of the feeding period, and BRD retreatment cumulative incidence morbidity d 1 to closeout of the feeding period. Network meta-analysis combined direct and indirect evidence for all the event outcomes to determine mean odds ratio (OR) with 95% credibility intervals (CrIs) for all metaphylactic antimicrobial comparisons. The "upper tier" treatment arms for morbidity d 1 to ≤ 60 included tulathromycin, gamithromycin, and tilmicosin. For BRD mortality cumulative incidence d 1 to closeout and BRD retreatment morbidity d 1 to closeout, classifying the treatment arms into tiers was not possible due to overlapping 95% CrIs. The results of this project accurately identified differences between metaphylactic antimicrobials, and metaphylactic antimicrobial options appear to offer different outcomes on BRD morbidity and mortality odds in feedlot cattle.

Chemoenzymatic Total Synthesis and Structural Diversification of Tylactone-Based Macrolide Antibiotics through Late-Stage Polyketide Assembly, Tailoring, and C-H Functionalization

Polyketide synthases (PKSs) represent a powerful catalytic platform capable of effecting multiple carbon-carbon bond forming reactions and oxidation state adjustments. We explored the functionality of two terminal PKS modules that produce the 16-membered tylosin macrocycle, using them as biocatalysts in the chemoenzymatic synthesis of tylactone and its subsequent elaboration to complete the first total synthesis of the juvenimicin, M-4365, and rosamicin classes of macrolide antibiotics via late-stage diversification. Synthetic chemistry was employed to generate the tylactone hexaketide chain elongation intermediate that was accepted by the juvenimicin (Juv) ketosynthase of the penultimate JuvEIV PKS module. The hexaketide is processed through two complete modules (JuvEIV and JuvEV) in vitro, which catalyze elongation and functionalization of two ketide units followed by cyclization of the resulting octaketide into tylactone. After macrolactonization, a combination of in vivo glycosylation, selective in vitro cytochrome P450-mediated oxidation, and chemical oxidation was used to complete the scalable construction of a series of macrolide natural products in as few as 15 linear steps (21 total) with an overall yield of 4.6%.

Microstructure and antioxidative capacity of the microalgae mutant Chlorella PY-ZU1 during tilmicosin removal from wastewater under 15% CO2

The response mechanisms of microalgal mutant Chlorella PY-ZU1 cells were investigated in their removal of antibiotic tilmicosin from wastewater under 15% CO₂. Low concentrations (0.01-2mgL^-1) of tilmicosin in wastewater stimulated the growth of microalgal cells, whereas high concentrations (5-50mgL^-1) of tilmicosin significantly inhibited cell growth. When initial tilmicosin concentration increased from 0 to 50mgL^-1, fractal dimension of microalgal cells monotonically increased from 1.36 to 1.62 and cell size monotonically decreased from 4.86 to 3.75μm. In parallel, malondialdehyde content, which represented the degree of cellular oxidative damage, monotonically increased from 1.92×10^-7 to 7.07×10^-7 nmol cell^-1. Superoxide dismutase activity that represented cellular antioxidant capacity first increased from 2.59×10^-4 to the peak of 6.60×10^-4U cell^-1, then gradually decreased to 2.39×10^-4U cell^-1. The maximum tilmicosin removal efficiency of 99.8% by Chlorella PY-ZU1 was obtained at the initial tilmicosin concentration of 50mgL^-1.

Concentrations of tilmicosin in mammary gland secretions of dairy cows following subcutaneous administration of one or two doses of an experimental preparation of tilmicosin and its efficacy against intramammary infections caused by Staphylococcus aureus

OBJECTIVE To determine the concentration of tilmicosin in mammary gland secretions of dairy cows following administration of an experimental preparation once or twice during the dry period (45-day period immediately prior to calving during which cows are not milked) and to evaluate its efficacy for the treatment of cows with intramammary infections (IMIs) caused by Staphylococcus aureus at dry off (cessation of milking; first day of dry period), compared with that of an intramammary infusion of ceftiofur. ANIMALS 172 cows. PROCEDURES Milk samples were collected for microbiological culture 5 days before dry off and at calving and 15 and 30 days after calving. Cows with Staphylococcus IMIs were randomly assigned to receive an experimental preparation of tilmicosin (20 mg/kg, SC) once at dry off (n = 58) or at dry off and again 20 days later (56) or receive a long-acting intramammary preparation of ceftiofur (500 mg/mammary gland; 56) at dry off. Mammary gland secretions were collected from 5 cows in the tilmicosin-treated groups every 5 days after dry off until calving for determination of tilmicosin concentration. RESULTS Mean maximum concentration of tilmicosin in mammary gland secretions ranged from 14.4 to 20.9 μg/mL after the first dose and was 17.1 μg/mL after the second dose. The bacteriologic cure rate was 100% for all 3 treatments. Tilmicosin was detectable for 0 and 18 days after calving in the milk of cows treated with 1 and 2 doses of tilmicosin, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Administration of an experimental preparation of tilmicosin (20 mg/kg, SC) once to dairy cows at dry off might be useful for the treatment of S aureus IMIs.

Clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni five days after metaphylactic administration of tildipirosin or tulathromycin

OBJECTIVE

To compare clinical disease and lung lesions in calves experimentally inoculated with Histophilus somni 5 days after metaphylactic administration of tildipirosin or tulathromycin. ANIMALS Twenty-four 3-month-old Holstein and Holstein-crossbreed steers.

PROCEDURES

Calves were randomly allocated to 3 groups of 8 calves. On day 0, calves in group 1 received tildipirosin (4 mg/kg, SC), calves in group 2 received tulathromycin (2.5 mg/kg, SC), and calves in group 3 received isotonic saline (0.9% NaCl) solution (1 mL/45 kg, SC; control). On day 5, calves were inoculated with 10 mL of a solution containing H somni strain 7735 (1.6 × 10(9) CFUs/mL, intrabronchially; challenge). Calves were clinically evaluated on days 5 through 8 and euthanized on day 8. The lungs were grossly evaluated for evidence of pneumonia, and bronchial secretion samples underwent bacteriologic culture.

RESULTS

The mean clinical score for each group was significantly increased 12 hours after challenge, compared with that immediately before challenge, and was significantly lower for tildipirosin-treated calves on days 6, 7, and 8, compared with those for tulathromycin-treated and control calves. The mean percentage of lung consolidation for tildipirosin-treated calves was significantly lower than those for tulathromycin-treated and control calves. Histophilus somni was isolated from the bronchial secretions of some tulathromycin-treated and control calves but was not isolated from tildipirosin-treated calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that metaphylactic administration of tildipirosin to calves 5 days prior to H somni challenge prevented subsequent culture of the pathogen from bronchial secretions and was more effective in minimizing clinical disease and lung lesions than was metaphylactic administration of tulathromycin.

Characterization of the Two Methylation Steps Involved in the Biosynthesis of Mycinose in Tylosin

The S-adenosyl-l-methionine-dependent O-methyltransferases TylE and TylF catalyze the last two methylation reactions in the tylosin biosynthetic pathway of Streptomyces fradiae. It has long been known that the TylE-catalyzed C2‴-O-methylation of the 6-deoxy-d-allose bound to demethylmacrocin or demethyllactenocin precedes the TylF-catalyzed C3‴-O-methylation of the d-javose (C2‴-O-methylated 6-deoxy-d-allose) attached to macrocin or lactenocin. This study reveals the unexpected substrate promiscuity of TylE and TylF responsible for the biosynthesis of d-mycinose (C3‴-O-methylated d-javose) in tylosin through the identification of a new minor intermediate 2‴-O-demethyldesmycosin (2; 3‴-methyl-demethyllactenocin), which lacks a 2‴-O-methyl group on the mycinose moiety of desmycosin, along with 2‴-O-demethyltylosin (1; 3‴-methyl-demethylmacrocin) that was previously detected from the S. fradiae mutant containing a mutation in the tylE gene. These results unveil the unique substrate flexibility of TylE and TylF and demonstrate their potential for the engineered biosynthesis of novel glycosylated macrolide derivatives.

Human exposures to tilmicosin reported to poison centres, Texas, 1998-2003

Tilmicosin, or 20-deoxo-20-(3,5-dimethylpiperidin-1-yl)desmycosin, is a macrolide antibiotic primarily utilized in livestock. This study examined 46 human exposure calls involving tilmicosin received by Texas poison centres during 1998 - 2003. The majority (91%) of the calls were received from northern and central Texas. All of the cases were unintentional exposures. The most frequent route of exposure was parenteral (48%). The majority of the patients were males (80%) and adults (84%). Only 46% of the patients were managed outside of health care facilities. Some sort of adverse medical outcome was reported in 93% of parenteral exposures and 54% of other-route exposures. However, only 21% of parenteral exposures and 15% of other-route exposures involved medical outcomes that were judged to be moderate or worse. No deaths were reported. The most frequently reported clinical effects among parenteral cases were dermal (79%), while only 9% of other-route exposures had dermal effects. Cardiovascular clinical effects were observed in a single case of parenteral exposure and a single case of other-route exposure. Although the majority of cases were managed with the assistance of health care facilities, the medical outcomes were usually not serious. Outcome depended on the route of exposure.

Minimum Inhibitory Concentration Breakpoints and Disk Diffusion Inhibitory Zone Interpretive Criteria for Tilmicosin Susceptibility Testing against Pasteurella Multocida and Actinobacillus Pleuropneumoniae Associated with Porcine Respiratory Disease

Tilmicosin is a novel macrolide antibiotic developed for exclusive use in veterinary medicine. Tilmicosin has been approved as a feed premix to control porcine respiratory disease associated with Pasteurella multocida and Actinobacillus pleuropneumoniae. The development of antimicrobial susceptibility testing guidelines for tilmicosin was predicated on the relationship of clinical efficacy studies that demonstrated a favorable therapeutic outcome, on pharmacokinetic data, and on in vitro test data, as recommended by the National Committee for Clinical Laboratory Standards (NCCLS). The approved breakpoints for the minimum inhibitory concentration dilution testing for both species are resistant, ≥32 μg/ml, and susceptible, ≤16 μg/ml. The zone of inhibition interpretive criteria for disk diffusion testing with a 15-μg tilmicosin disk are resistant, ≤10 mm, and susceptible, ≥11mm.

Bactericidal effects of various concentrations of enrofloxacin, florfenicol, tilmicosin phosphate, and tulathromycin on clinical isolates of Mannheimia haemolytica

OBJECTIVE

To determine bactericidal effects of enrofloxacin, florfenicol, tilmicosin, and tulathromycin on clinical isolates of Mannheimia haemolytica at various bacterial densities and drug concentrations.

SAMPLE

4 unique isolates of M haemolytica recovered from clinically infected cattle.

PROCEDURES

Minimum inhibitory concentration (MIC) and mutant prevention concentration (MPC) were determined for each drug and isolate. Mannheimia haemolytica suspensions (10(6) to 10(9) CFUs/mL) were exposed to the determined MIC and MPC and preestablished maximum serum and tissue concentrations of each drug. Log10 reduction in viable cells (percentage of cells killed) was measured at various points.

RESULTS

Bacterial killing at the MIC was slow and incomplete. After 2 hours of isolate exposure to the MPC and maximum serum and tissue concentrations of the tested drugs, 91% to almost 100% cell killing was achieved with enrofloxacin, compared with 8% growth to 93% cell killing with florfenicol, 199% growth to 63% cell killing with tilmicosin, and 128% growth to 43% cell killing with tulathromycin over the range of inoculum tested. For all drugs, killing of viable organisms was evident at all bacterial densities tested; however, killing was more substantial at the MPC and maximum serum and tissue drug concentrations than at the MIC and increased with duration of drug exposure. Rank order of drugs by killing potency was enrofloxacin, florfenicol, tilmicosin, and tulathromycin.

CONCLUSIONS AND CLINICAL RELEVANCE

Findings suggested that antimicrobial doses that equaled or exceeded the MPC provided rapid killing of M haemolytica by the tested drugs, decreasing opportunities for antimicrobial-resistant subpopulations of bacteria to develop during drug exposure.

The anti-nociceptive potential of tilmicosin against chemical-induced but not thermal-induced pain in mice

The aim of the present study was to assess the analgesic activity of the macrolide antibiotic tilmicosin at dose levels of 20 and 40 mg/kg of body weight, subcutaneously, against chemical- and thermal-induced acute pains, using acetic acid-induced writhing, formalin-induced pain, hot-plate, and tail-flick models in mice. Tilmicosin showed a dose-dependent significant decrease in the number of writhes in the acetic acid-induced writhing test and significant decrease in hind paw-licking time in the late phase of the formalin test. However, it did not cause any significant changes in the reaction times to heat stimuli in the hot-plate and tail-flick models. In chemically-induced pains, both dose levels of tilmicosin showed significant effects compared to those of the corresponding standard peripheral analgesic, acetylsalicylic acid (200 mg/kg of body weight, subcutaneously) being 26.37±2.88 and 43.64±3.85% vs. 73.35±1.44% in acetic acid test; and 19.23±3.85 and 44.90±1.80% vs. 73.63±2.39% in the late phase of formalin test, respectively. These results may indicate that tilmicosin possesses a significant peripheral but not central analgesic potential that may be beneficial in symptomatic relief of pain when it is used in therapy, in addition to its well-established antibacterial effect.

Preparation and evaluation of tilmicosin-loaded hydrogenated castor oil nanoparticle suspensions of different particle sizes

Three tilmicosin-loaded hydrogenated castor oil nanoparticle (TMS-HCO-NP) suspensions of different particle sizes were prepared with different polyvinyl alcohol surfactant concentrations using a hot homogenization and ultrasonic technique. The in vitro release, in vitro antibacterial activity, mammalian cytotoxicity, acute toxicity in mice, and stability study were conducted to evaluate the characteristics of the suspensions. The in vitro tilmicosin release rate, antibacterial activity, mammalian cytotoxicity, acute toxicity in mice, and stability of the suspensions were evaluated. When prepared with polyvinyl alcohol concentrations of 0.2%, 1%, and 5%, the mean diameters of the nanoparticles in the three suspensions were 920±35 nm, 452±10 nm, and 151±4 nm, respectively. The three suspensions displayed biphasic release profiles similar to that of freeze-dried TMS-HCO-NP powders, with the exception of having a faster initial release. Moreover, suspensions of smaller-sized particles showed faster initial release, and lower minimum inhibitory concentrations and minimum bactericidal concentrations. Time-kill curves showed that within 12 hours, the suspension with the 151 nm particles had the most potent bactericidal activity, but later, the suspensions with larger-sized particles showed increased antibacterial activity. None of the three suspensions were cytotoxic at clinical dosage levels. At higher drug concentrations, all three suspensions showed similar concentration-dependent cytotoxicity. The suspension with the smallest-sized particle showed significantly more acute toxicity in mice, perhaps due to faster drug release. All three suspensions exhibited good stability at 4°C and at room temperature for at least 6 months. These results demonstrate that TMS-HCO-NP suspensions can be a promising formulation for tilmicosin, and that nanoparticle size can be an important consideration for formulation development.

Extraction of trace tilmicosin in real water samples using ionic liquid-based aqueous two-phase systems

The effective method of ionic liquid-based aqueous two-phase extraction, which involves ionic liquid (IL) (1-butyl-3-methyllimidazolium chloride, [C4mim]Cl) and inorganic salt (K2HPO4) coupled with high-performance liquid chromatography (HPLC), has been used to extract trace tilmicosin in real water samples which were passed through a 0.45 μm filter. The effects of the different types of salts, the concentration of K2HPO4 and of ILs, the pH value and temperature of the systems on the extraction efficiencies have all been investigated. Under the optimum conditions, the average extraction efficiency is up to 95.8%. This method was feasible when applied to the analysis of tilmicosin in real water samples within the range 0.5-40 μg mL(-1). The limit of detection was found to be 0.05 μg mL(-1). The recovery rate of tilmicosin was 92.0-99.0% from the real water samples by the proposed method. This process is suggested to have important applications for the extraction of tilmicosin.

Development and validation of an indirect competitive enzyme-linked immunosorbent assay for the screening of tylosin and tilmicosin in muscle, liver, milk, honey and eggs

Incorrect use of tylosin and tilmicosin could result in allergy and select resistance. To monitor the illegal use of these antibiotics in animals, a monoclonal-based indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) has been established. Several haptens were synthesized and conjugated to carrier protein. Female Balb/c mice were inoculated with the four different conjugates to produce monoclonal antibodies according to the schemes of immunization. Aftercell fusion and culture several times, nine hybridoma cell lines were isolated. Only one, 3C4 that has isotype IgG2a, was selected for detailed study. The cross-reactivity of the monoclonal antibody 3C4 to tylosin and tilmicosin was 100% and 51% respectively. The standard curves based on the tylosin and tilmicosin matrix calibration ranged from 2.5 to 40 μg L(-1), with an IC(50) value of 6.1 μg L(-1) and 12.1 μg L(-1), respectively. The limits of detection of the ic-ELISA ranged from 5.1 μg kg(-1) to 13.8 μg kg(-1) in edible animal tissues. The recoveries were 74.1% to 120.7% with less than 18.6% of the coefficient of variation when tylosin and tilmicosin were spiked in various biological matrices with the concentrations of 25.0-200.0 μg kg(-1). Good correlations between the results of the ic-ELISA and high performance liquid chromatography were observed in the incurred tissues. These results suggest that the ic-ELISA is a sensitive, accurate and low-cost method that would be a useful tool for the screening of the residues of tylosin and tilmicosin in muscle, liver, milk, honey and eggs.

Comparison of enrofloxacin and ceftiofur sodium for the treatment of relapse of undifferentiated fever/bovine respiratory disease in feedlot cattle

This commercial field trial compared the efficacy of enrofloxacin and ceftiofur sodium in beef cattle at high risk of developing undifferentiated fever (UF), also known as bovine respiratory disease (BRD) that received tilmicosin at feedlot arrival, were diagnosed and initially treated for UF with tilmicosin, and subsequently required a second UF treatment (first relapse). Feedlot cattle (n = 463) were randomly assigned to 2 experimental groups: ENRO or CEF. Second UF relapse, 3rd UF relapse, overall case fatality and BRD case fatality rates were lower in the ENRO group than in the CEF group (P < 0.05). There were no differences in average daily gain (allocation to re-implant date), chronicity, histophilosis case fatality or miscellaneous case fatality rates between the groups (P ≥ 0.05). A per-animal economic advantage of Can$57.08 was calculated for the ENRO group versus the CEF group. In feedlot cattle in western Canada at high risk of developing UF, it was more cost effective to administer enrofloxacin than ceftiofur sodium for treatment of UF relapse.

Immuno-modulation and anti-inflammatory benefits of antibiotics: the example of tilmicosin

Exaggerated immune responses, such as those implicated in severe inflammatory reactions, are costly to the metabolism. Inflammation and pro-inflammatory mediators negatively affect production in the food animal industry by reducing growth, feed intake, reproduction, milk production, and metabolic health. An ever-increasing number of findings have established that antibiotics, macrolides in particular, may generate anti-inflammatory effects, including the modulation of pro-inflammatory cytokines and the alteration of neutrophil function. The effects are time- and dose-dependent, and the mechanisms responsible for these phenomena remain incompletely understood. Recent studies, mostly using the veterinary macrolide tilmicosin, may have shed new light on the mode of action of some macrolides and their anti-inflammatory properties. Indeed, research findings demonstrate that this compound, amongst others, induces neutrophil apoptosis, which in turn provides anti-inflammatory benefits. Studies using tilmicosin model systems in vitro and in vivo demonstrate that this antibiotic has potent immunomodulatory effects that may explain why at least parts of its clinical benefits are independent of anti-microbial effects. More research is needed, using this antibiotic and others that may have similar properties, to clarify the biological mechanisms responsible for antibiotic-induced neutrophil apoptosis, and how this, in turn, may provide enhanced clinical benefits. Such studies may help establish a rational basis for the development of novel, efficacious, anti-microbial compounds that generate anti-inflammatory properties in addition to their antibacterial effects.

American association of poison control centers database characterization of human tilmicosin exposures, 2001-2005

BACKGROUND

Tilmicosin is a veterinary antibiotic with significant human toxicity at doses commonly used in animals, but the parenteral dose-response relationship has not been well characterized.

METHODS

Human exposures to tilmicosin in the database of the American Association of Poison Control Centers (AAPCC) from 2001 to 2005 were analyzed for demographic associations, exposure dose, clinical effects and outcomes.

RESULTS

Over the 5-year period, there were 1,291 single-substance human exposures to tilmicosin. The mean age was 39.1 years, and 80% were male. By route there were 768 (54%) parenteral exposures. Patients with parenteral exposures had a significantly increased likelihood of being seen at a healthcare facility, admission, and admission to an ICU. With nonparenteral exposure, most had no clinical effects or minor effects, and there were no major effects or deaths. With parenteral exposure, moderate effects occurred in 46 (6%), major effects in 2 (0.3%) and there were 4 (0.5%) deaths, two of which were suicides. A dose-response relationship could be demonstrated. Clinical effect durations of up to a week occurred at even the lowest dose range.

CONCLUSIONS

Over 250 cases of human tilmicosin exposure are reported to poison centers per year and over 150 of those are parenteral. Most exposures produce no or minor effects, but fatalities have occurred with parenteral exposure. The case fatality rate in parenteral exposures is 10 times the case fatality rate for all human exposures in the AAPCC database. Significant adverse and prolonged effects are reported at parenteral doses > 0.5 mL, suggesting that all parenteral exposures should be referred for healthcare facility evaluation.

Identification of the related substances of tilmicosin by liquid chromatography/ion trap mass spectrometry

Structures of seven impurities of the veterinary drug tilmicosin have been elucidated by multiple fragmentation with ion trap tandem mass spectrometry. All related compounds possess the main lactone ring of tilmicosin. The differences in their structures are due to the hydroxyl, mycaminose, 3,5-dimethylpiperidine and mycinose groups connected to C(3), C(5), C(6), C(14) of the lactone ring, respectively. The following compounds of the impurity profile of tilmicosin were identified: B - tilmicosin with a hydroxyl group at C(3); C - tilmicosin without a methyl group at the N-atom connected to C(3) of the mycaminose ring; D - tilmicosin with a hydroxyl group at C(6) of the mycaminose ring; E - tilmicosin with a methoxy group at C(3), F - desmicosin; G - 20-dihydrodesmicosin; and H - tilmicosin without a mycaminose ring. Isomers of the compounds B, C, D, E and H were identified by their mass chromatograms and retention times. The concentrations of the impurities varied in the range of 0.1% to 2.9%.

Effectiveness of tilmicosin against Paenibacillus larvae, the causal agent of American Foulbrood disease of honeybees

American Foulbrood (AFB) of honeybees (Apis mellifera L.), caused by the Gram-positive bacterium Paenibacillus larvae is one of the most serious diseases affecting the larval and pupal stages of honeybees (A. mellifera L.). The aim of the present work was to asses the response of 23 strains of P. larvae from diverse geographical origins to tilmicosin, a macrolide antibiotic developed for exclusive use in veterinary medicine, by means of the minimal inhibitory concentration (MIC) and the agar diffusion test (ADT). All the strains tested were highly susceptible to tilmicosin with MIC values ranging between 0.0625 and 0.5 microg ml(-1), and with MIC(50) and MIC(90) values of 0.250 microg ml(-1). The ADT tests results for 23 P. larvae strains tested showed that all were susceptible to tilmicosin with inhibition zones around 15 microg tilmicosin disks ranging between 21 and 50mm in diameter. Oral acute toxicity of tilmicosin was evaluated and the LD(50) values obtained demonstrated that it was virtually non-toxic for adult bees and also resulted non-toxic for larvae when compared with the normal brood mortality. Dosage of 1000 mg a.i. of tilmicosin applied in a 55 g candy resulted in a total suppression of AFB clinical signs in honeybee colonies 60 days after initial treatment. To our knowledge, this is the first report of the effectiveness of tilmicosin against P. larvae both in vitro and in vivo.

Identification of tylosin photoreaction products and comparison of ELISA and HPLC methods for their detection in water

Tylosin is a widely used macrolide antibiotic for therapeutics and growth promotion in swine, beef cattle, and poultry production. Through various routes such as manure application, emission, inappropriate disposal, etc., tylosin enters the environment. The fate of tylosin in the environment is not yet fully understood. In this study, two photoreaction products of tylosin in water were identified as isotylosin A alcohol (E,Z) and isotylosin A aldol (E,Z). Tylosin A, B, C, D, isotylosin A alcohol, and isotylosin A aldol were purified, and immunological cross-reactivities of these tylosin-related compounds were tested with a specificity of 26% for tylosin B, 19% for tylosin C, 106% for tylosin D, 121% for isotylosin A alcohol, and 46% for isotylosin A aldol, compared to 100% for tylosin A. Competitive direct enzyme-linked immunosorbent assay (ELISA) for tylosin detection in water was compared with a high-performance liquid chromatography (HPLC) method by analyzing the same water samples from a study of tylosin dissipation in water. ELISA kits detect the other tylosin-related compounds besides tylosin A, which can result in differences in tylosin determination in water.

Comparison of short-term health and performance effects related to prophylactic administration of tulathromycin versus tilmicosin in long-hauled, highly stressed beef stocker calves

Health and feed performance parameters of 293 beef stocker calves at risk for bovine respiratory disease were compared after metaphylactic administration of one of two antimicrobials (tulathromycin or tilmicosin) with different durations of activity; the antimicrobial was administered 1 day after arrival. Calves that received metaphylactic tulathromycin displayed significant improvement in morbidity, mortality, and first-treatment success rates (P<.05) compared with tilmicosin-treated calves. Tulathromycin-treated calves also showed a significantly improved average daily gain and feed:gain ratio (P<.05) compared with tilmicosin-treated calves. Under conditions of this study, calves receiving tulathromycin were healthier through a 43-day growing phase compared with calves receiving tilmicosin. This health difference likely accounted for the differences in feed performance between the treatment groups.