In vitro susceptibility of Brachyspira hyodysenteriae to a commercial citrus fruit extract.

Brachyspira hyodysenteriae is the main etiological agent of swine dysentery (SD). Nowadays, treatment and control of SD is increasingly difficult due to the emergence of antimicrobial resistance together with the restrictions on the use of antibiotics in veterinary practice. The aim of this study was to evaluate, as an alternative in the control of this disease, the antimicrobial activity and the main mechanism of action of BIOCITRO, a citrus extract commercialized as raw material and used as feed additive, against B. hyodysenteriae. Ten isolates of B. hyodysenteriae were used to assess the minimum inhibitory and minimum bactericidal concentrations (MIC and MBC) of BIOCITRO by broth microdilution method. Moreover, stationary phase cultures of two B. hyodysenteriae strains were subjected for 90min to four different concentrations of BIOCITRO and compared with the untreated controls by flow cytometry (FC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The results showed that BIOCITRO has a relevant bacteriostatic and bactericidal effect against B. hyodysenteriae with MIC and MBC values ranging from 32 to 128partspermillion (ppm). It induces damage in at least 35% and 76% of the bacterial cells when exposed to 128 and 256ppm of BIOCITRO respectively as revealed by the intake of propidium iodide by FC. Relevant changes in the structure of the bacterial cells were observed by SEM and confirmed by FTIR. According to these results, BIOCITRO seems to be a satisfactory alternative to the use of antibiotics in the control of SD.