Presence and mechanisms of acquired antimicrobial resistance in Belgian Brachyspira hyodysenteriae isolates belonging to different clonal complexes.

Swine dysentery (SD) is an economically important disease for which antimicrobial treatment still occupies an important place to control outbreaks. However, acquired antimicrobial resistance is increasingly observed in Brachyspira hyodysenteriae. In this study, the Minimal Inhibitory Concentrations (MIC) of six antimicrobial compounds for 30 recent Belgian B. hyodysenteriae isolates were determined using a broth microdilution method. In addition, relevant regions of the 16S rRNA, 23S rRNA and the L3 protein encoding genes were sequenced to reveal mutations associated with acquired resistance. Finally, a phylogeny was reconstructed using minimal spanning tree analysis of multi locus sequence typing of the isolates. For lincomycin, doxycycline, tylosin and tylvalosin, at least 70% of the isolates did not belong to the wild-type population and were considered to have acquired resistance. For valnemulin and tiamulin, this was over 50%. In all isolates with acquired resistance to doxycycline, the G1058C mutation was present in their 16S rRNA gene. All isolates showing acquired resistance to lincomycin and both macrolides displayed the A2058T mutation in their 23S rRNA gene. Other mutations in this gene and the N148S mutation in the L3 protein were present in both wild-type isolates and isolates considered to have acquired resistance. Multi locus sequence analysis revealed a previously undescribed clonal complex, with 4 novel sequence types in which the majority of isolates showed acquired resistance to all tested antimicrobial products. In conclusion, acquired antimicrobial resistance is widespread among Belgian B. hyodysenteriae isolates. The emergence of multi-resistant clonal complexes can pose a threat to swine industry.

In vitro sensitivity of poultry Brachyspira intermedia isolates to essential oil components and in vivo reduction of Brachyspira intermedia in rearing pullets with cinnamaldehyde feed supplementation.

Cecal enteritis due to Brachyspira infections tends to be chronic in laying hens. Limited availability of antimicrobial drugs for use in laying hens emphasizes the need for alternative control measures. A broth microdilution method was used to determine the antimicrobial susceptibility of 20 Brachyspira intermedia field isolates from laying hen flocks to components of essential oils (EO). Minimal inhibitory concentration (MIC) distributions, obtained for 8 EO components, were all monomodal. Cinnamaldehyde had the lowest MIC values (40 to 80 mg/L), followed by nerolidol, capsaicin, carvacrol, and thymol (80 to 320 mg/L), eugenol (160 to 640 mg/L), and linalool (320 to 1,280 mg/L). The MIC ranges of piperine were mostly above the test range of 1,280 mg/L. In an in vivo experiment, coated trans-cinnamaldehyde was supplemented to the feed of rearing pullets. A completely randomized experimental design with 4 treatments and 3 replicates each (replicate = group of seven 1-d-old laying hen chickens) was applied. The negative and positive controls received a conventional feed during the whole trial. The positive controls were orally inoculated on 3 consecutive days (d 22, 23, and 24) with 1 mL of 1.0 × 10(8) cfu/mL of a B. intermedia field isolate. Two treatment groups (preventive and curative), identically inoculated, received the coated trans-cinnamaldehyde-supplemented feed (500 mg/kg of trans-cinnamaldehyde), the preventive group from d 1, the curative from d 25. On d 32, ceca were collected for bacteriologic Brachyspira enumeration. The mean enumeration of Brachyspira cells was decreased (P < 0.05) in the curative treated group versus the positive control group. The in vitro results of the present study demonstrate the potential of EO components as antimicrobials against poultry Brachyspira isolates, including isolates with acquired resistance for classic antimicrobial drugs. Reduction of Brachyspira colonization in young pullets was obtained, in a curative way, in an in vivo study using feed supplemented with coated trans-cinnamaldehyde. Further studies are necessary to investigate the mode of action of the coated trans-cinnamaldehyde in reducing Brachyspira colonization of the ceca.