<i>ErmF</i> and <i>ereD</i> Are Responsible for Erythromycin Resistance in <i>Riemerella anatipestifer</i>

<div><p>To investigate the genetic basis of erythromycin resistance in <i>Riemerella anatipestifer</i>, the MIC to erythromycin of 79 <i>R</i>. <i>anatipestifer</i> isolates from China and one typed strain, ATCC11845, were evaluated. The results showed that 43 of 80 (53.8%) of the tested <i>R</i>. <i>anatipestifer</i> strains showed resistance to erythromycin, and 30 of 43 erythromycin-resistant <i>R</i>. <i>anatipestifer</i> strains carried <i>ermF</i> or <i>ermFU</i> with an MIC in the range of 32–2048 μg/ml, while the other 13 strains carrying the <i>ereD</i> gene exhibited an MIC of 4–16 μg/ml. Of 30 <i>ermF</i> + <i>R</i>. <i>anatipestifer</i> strains, 27 (90.0%) carried the <i>ermFU</i> gene which may have been derived from the CTnDOT-like element, while three other strains carried <i>ermF</i> from transposon Tn4351. Moreover, sequence analysis revealed that <i>ermF</i>, <i>ermFU</i>, and <i>ereD</i> were located within the multiresistance region of the <i>R</i>. <i>anatipestifer</i> genome.</p></div

Distribution of <i>R</i>. <i>anatipestifer</i> strains with different MICs for erythromycin.

<p>Distribution of <i>R</i>. <i>anatipestifer</i> strains with different MICs for erythromycin.</p

Clustal W alignment of the upstream sequences from the <i>ermF</i> / <i>ermFU</i> genes from CTnDOT, Tn4351, and different <i>R</i>. <i>anatipestifer</i> strains.

<p>The start codon ATG of <i>ermFU</i>/<i>ermF</i> gene was underlined.</p