In vitro antimicrobial activity against equine Lawsonia intracellularis strains

Abstract

Summary Background Lawsonia intracellularis is the aetiologic agent of equine proliferative enteropathy (EPE). This emerging equine disease leads to diarrhoea, severe protein loss and can result in death if left untreated. Timely treatment of EPE is critical for recovery from the disease, and hence, information about antimicrobial susceptibilities of equine L. intracellularis strains to antimicrobials used in horses is needed. However, L. intracellularis is an obligate intracellular bacterium and so must be isolated and maintained in cell cultures. Objectives To determine the in vitro antimicrobial activity of 14 antimicrobials against two equine L. intracellularis strains. Study design In vitro experiments. Methods This study was designed to compare the relative in vitro susceptibility of each strain of L. intracellularis to different antimicrobials which included metronidazole, minocycline hydrochloride, erythromycin, cephalothin sodium salt, combination (4:1) of sulfamethazine and trimethoprim, chloramphenicol, rifampicin, penicillin, ampicillin, doxycycline hydrochloride, cefazolin sodium salt, clarithromycin, ceftiofur hydrochloride and enrofloxacin. The minimum inhibitory concentration (MIC) was based on intracellular and extracellular activity that inhibited 99% of L. intracellularis growth in cell culture as compared to the antimicrobial‐free control. Results Rifampicin and clarithromycin were the most active antimicrobials against the two L. intracellularis strains tested, with MICs of ≤0.125 when tested both intracellularly and extracellularly. Doxycycline, minocycline, erythromycin, chloramphenicol and enrofloxacin showed intermediate to high activity, and activity was generally higher when evaluating intracellular activity. Sulfamethazine/trimethoprim showed variable results. Ampicillin, penicillin and metronidazole had low to moderate activity. L. intracellularis was resistant to cefazolin, cephalothin and ceftiofur in in vitro conditions. Main limitations Only two equine isolates of L. intracellularis were available for this study due to the difficulty in isolating this obligate intracellular species from intestinal samples. Conclusions This is the first report of antimicrobial susceptibility patterns for equine L. intracellularis strains.

Equine antimicrobial therapy: Current and past issues facing practitioners

“…In practice, rifampin is often administered at a dose of 5–10 mg/kg PO, q 12 hr. Macrolides or azalides are commonly administered along with rifampin for the treatment of Rhodococcus equi or Lawsonia intracellularis in foals (Pereira et al, 2019). There is more on R .…”

Design, Synthesis, and Dual Evaluation of Quinoline and Quinolinium Iodide Salt Derivatives as Potential Anticancer and Antibacterial Agents

“…AutoDock Vina 1.1.2. software was used to perform docking simulations . In the present study, the derivatives were designed based on the quinoline core, depending on the former studies on the mechanism of anticancer and antibacterial activity.…”

Pharmacokinetics of chloramphenicol base in horses and comparison to compounded formulations

“…isolates (0.064–2 μg/ml n = 12, with one isolate having an MIC of 8 μg/ml), and they would be considered susceptible to attainable concentrations in horses (Lawhon, Taylor, & Fajt, ). A report of the antimicrobial susceptibility of two Lawsonia intracellularis isolates demonstrated intracellular MIC values for chloramphenicol ≤2 μg/mL, and this suggests that chloramphenicol could be used to treat this infection (Pereira et al, ). Chloramphenicol should not be used to treat infections with Gram‐negative enteric bacteria, including Enterobacter, E coli, Klebsiella pneumoniae and Salmonella spp., as well as Pseudomonas aeruginosa , based on their high MIC values (Adamson et al, ; Burrows, Morton, & Fales, ).…”