Antimicrobial Susceptibility Patterns of Brachyspira Species Isolated from Swine Herds in the United States

Abstract

Outbreaks of swine dysentery, caused by Brachyspira hyodysenteriae and the recently discovered "Brachyspira hampsonii," have reoccurred in North American swine herds since the late 2000s. Additionally, multiple Brachyspira species have been increasingly isolated by North American diagnostic laboratories. In Europe, the reliance on antimicrobial therapy for control of swine dysentery has been followed by reports of antimicrobial resistance over time. The objectives of our study were to determine the antimicrobial susceptibility trends of four Brachyspira species originating from U.S. swine herds and to investigate their associations with the bacterial species, genotypes, and epidemiological origins of the isolates. We evaluated the susceptibility of B. hyodysenteriae, B. hampsonii, Brachyspira pilosicoli, and Brachyspira murdochii to tiamulin, valnemulin, doxycycline, lincomycin, and tylosin by broth microdilution and that to carbadox by agar dilution. In general, Brachyspira species showed high susceptibility to tiamulin, valnemulin, and carbadox, heterogeneous susceptibility to doxycycline, and low susceptibility to lincomycin and tylosin. A trend of decreasing antimicrobial susceptibility by species was observed (B. hampsonii > B. hyodysenteriae > B. murdochii > B. pilosicoli). In general, Brachyspira isolates from the United States were more susceptible to these antimicrobials than were isolates from other countries. Decreased antimicrobial susceptibility was associated with the genotype, stage of production, and production system from which the isolate originated, which highlights the roles of biosecurity and husbandry in disease prevention and control. Finally, this study also highlights the urgent need for Clinical and Laboratory Standards Institute-approved clinical breakpoints for Brachyspira species, to facilitate informed therapeutic and control strategies.

Minimum inhibitory concentration of Brazilian Brachyspira hyodysenteriae strains

“…For valnemulin, the results were similar to those previously reported (Karlsson et al 1999, 2002, Rohde et al 2004, Hidalgo et al 2009, 2011, Zmudzki et al 2012, Alvarez et al 2013, Mirajkar & Gebhart 2013. The MIC50 results for tiamulin were higher than those published elsewhere, but the MIC90 was similar to the results obtained by Rohde et al (2004), Hidalgo et al (2011) and by Alvarez et al (2013).…”

“…Hidalgo et al (2011) identified a mutation in the 23S gene at position 2059 associated with resistance to tylvalosin. For lincomycin, the MIC50 was higher compared with that reported in the literature (Karlsson et al 1999, Karlsson et al 2002, Karlsson et al 2003, Rohde et al 2004, Hidalgo et al 2011, Zmudzki et al 2012, Mirajkar & Gebhart 2013, however, the MIC 90 was similar to those obtained by Hidalgo et al (2009) and Alvarez et al (2013).…”

“…For doxycycline, the MIC50 values were comparable to those found by Zmudzki et al (2012) and Alvarez et al (2013), but the MIC90 was elevated compared with the previously described values (Karlsson et al 2002, Rohde et al 2004, Pringle et al 2007, Hidalgo et al 2009, 2011, Zmudzki et al 2012, Alvarez et al 2013, Mirajkar & Gebhart 2013. Decreased susceptibility to doxycycline has been associated with a mutation at position 1058 of the 16S rRNA gene for B. hyodysenteriae (Pringle et al 2007).…”

“…Identifying the sensitivity pattern of Brazilian strains is important for establishing swine dysentery control and eradication programs, mainly due to the emergence of B. hyodysenteriae strains with reduced susceptibility to multiple antimicrobials, based on microbiological cut-off points, which was observed in both the present work and other studies in different countries (Karlsson et al 2002, Rohde et al 2004, Hidalgo et al 2009, 2011, Zmudzki et al 2012, Alvarez et al 2013, Mirajkar & Gebhart 2013. In addition, low sensitivity is relevant for resistance monitoring programmes as it is an indication of early resistance and allows the implementation of measures to prevent the emergence of strains with high resistance (Pringle et al 2012).…”

“…The results for tylosin were similar to those found in the literature regarding both the MIC50 and MIC90 (Table 1). High resistance to tylosin was expected based on the selective pressure caused by the widespread use of this drug in therapeutic and prophylactic programmes in recent years (Karlsson et al 2002, Rohde et al 2004, Hidalgo et al 2009, 2011, Zmudzki et al 2012, Alvarez et al 2013, Mirajkar & Gebhart 2013. The mechanism of tylosin resistance is related to mutations in the 23S ribosomal RNA gene at position 2058, inhibiting its binding (Karlsson et al 1999(Karlsson et al , 2004.…”