Antibiotic susceptibility patterns ofCrossiella equiandAmycolatopsisspecies causing nocardioform placentitis in horses

Abstract

Nocardioform actinomycetes are significant causes of placentitis and abortions in horses. In the current study, antimicrobial susceptibility patterns of 38 Amycolatopsis spp. and 22 Crossiella equi isolates, the most common nocardioform actinomycetes causing placentitis in horses, were evaluated. Antimicrobial susceptibilities of these isolates were tested by broth microdilution method in a commercial system, which was designed for Nocardia spp., fast-growing Mycobacterium spp., and other aerobic actinomycetes. The minimum inhibitory concentration required to inhibit the growth of 90% of organisms (MIC90) of the following antibiotics tested for Amycolatopsis spp. were: 4 µg/ml for linezolid, trimethophrim–sulfametaxazole (TMP-SMX), and ciprofloxacin; 8 µg/ml for ceftriaxone, doxycycline, and minocycline; 16 µg/ml for amoxicillin–clavulanic acid, clarithromycin, and imipenem; >16 µg/ml for tobramycin; 32 µg/ml for amikacin and cefepime; and 128 µg/ml for cefoxitin. The MIC90 levels for C. equi were 0.25 µg/ml for doxycycline; ≤1 µg/ml for minocycline; 2 µg/ml for linezolid and TMP-SMX; 4 µg/ml for ciprofloxacin; 8 µg/ml for amoxicillin–clavulanic acid, ceftriaxone, and imipenem; 16 µg/ml for clarithromycin; >16 µg/ml for tobramycin; 32 µg/ml for cefepime; >64 µg/ml for amikacin; and 128 µg/ml for cefoxitin.

Effect of Dose on Intra‐Articular Amikacin Sulfate Concentrations Following Intravenous Regional Limb Perfusion in Horses

“…Another study reported that all Gram‐negative bacterial isolates from equine neonates had an MIC 90 of 4 μg/mL. Orsini et al measured just 6 isolates that had MIC that varied from 0.5 to 128 μg/mL, and finally Erol et al reported that nocardioform actinomycetes had an MIC 90 of 32 μg/mL.…”

Attempts to induce nocardioform placentitis (Crossiela equi) experimentally in mares

“…A swab from each chorioallantois was collected and cultured according to Erol et al . . Polymerase chain reactions for C.equi and Amycolatopsis spp.…”

“…In this experiment, each inoculum contained 1 × 10 9 cfu of C. equi . Detailed explanation of the bacterial culture is described elsewhere and in the Supporting information.…”

“…Microorganisms associated with nocardioform placentitis include Amycolatopsis species ( Amycolatopsis kentuckyensis , Amycolatopsis lexingtonensis and Amycolatopsis pretoriensis ) and Crossiela equi . In 2009, 2 new species of Streptomyces ( Streptomyces atriruber and Streptomyces silaceus ) were isolated from nocardioform placentitis cases .…”

“…The definitive diagnosis of nocardioform placentitis is based on the presence of macroscopic and microscopic lesions, bacterial culture and identification of bacterial DNA by PCR of samples from the chorioallantois . A presumptive clinical diagnosis can be attained through clinical examination and ventral transabdominal ultrasonography .…”