ANTIMICROBIAL SENSITIVITY TEST OF BRACHYSPIRA SPP. ISOLATE FROM SWINE IN TAIWAN

Abstract

Intro: Brachyspira spp. can induce mucohemorrhagic diarrhea known as swine dysentery (SD) in weaning to finishing pigs. The brachyspira is transmitted via the fecal-oral route and causes massive economic losses due to a slower rate of pig growth. Since there is no available vaccine for SD, antibiotics such as lincosamides, macrolides, and pleuromutilins are commonly used for treatment. Recently in numerous regions, decreased susceptibility of Brachyspira hyodysenteriae to antibiotics has been reported, making prevention and treatment more challenging. Additionally, prior research has linked decreased resistance to antibiotics to Brachyspira hyodysenteriae mutations in the 23S rRNA gene and L3 ribosomal protein, but the underlying processes are still unclear. Methods: From 2019 to 2020, a total of sixty-nine samples were collected, including eleven Brachyspira hyodysenteriae, three Brachyspira murdochii, and three Brachyspira innocens by[a1] CSVR selective blood agar. The minimal inhibitory concentration for six antibiotics including tiamulin, valnemulin, tilmicosin, lincomycin, carbadox, and tylosin were determined by the broth microdilution method. In addition, genes encoding 23S rRNA and L3 ribosomal proteins were sequenced to identify mutant genes related to the detected resistance. Findings: The nucleotide base sequences of 23S rRNA gene in Brachyspira spp. mutant from adenine to thymine (A2058T) were associated with reduced susceptibility to lincomycin and tylosin.[a1] Protein L3 mutant from asparagine to serine (Asn148Ser) were found in B. hyodysentery (27.27%, 3/11).[a2] [pp3] Resistant rate of Brachyspira spp. to tylosin and valnemulin was both 100%. The MIC50 of tilmicosin, tylosin, lincomycin, valnemulin, tiamulin and carbadox were 256, 256, 16, 2, 1, 1 mg/ml, respectively. Discussion: The results suggested that lincomycin and tiamulin would be the first choice to treat Swine Dysentery in Taiwan. Conclusion: Referring to the antimicrobial drug resistant monitoring, antimicrobial drug use should be concerned on selective pressure in bacterial mutation.