Decreased susceptibility to doxycycline associated with a 16S rRNA gene mutation in Brachyspira hyodysenteriae

The objective of this study was to assess whether nucleotide substitutions in the 16S rDNA sequence of selected Brachyspira hyodysenteriae isolates could explain differences in doxycycline minimal inhibitory concentrations (MICs). The main part of the 16S rRNA gene was sequenced and compared for 19 isolates with different doxycycline MICs. A mutation in the 16S rRNA gene at the position corresponding to 1058 in Escherichia coli has been shown to cause tetracycline resistance in other bacteria. In the B. hyodysenteriae sequences a G1058C mutation was found for all isolates with increased doxycycline MICs whereas all susceptible isolates had the wild type sequence.