Abstract
To investigate the genetic basis of erythromycin resistance in Riemerella anatipestifer, the MIC to erythromycin of 79 R. anatipestifer isolates from China and one typed strain, ATCC11845, were evaluated. The results showed that 43 of 80 (53.8%) of the tested R. anatipestifer strains showed resistance to erythromycin, and 30 of 43 erythromycin-resistant R. anatipestifer strains carried ermF or ermFU with an MIC in the range of 32–2048 μg/ml, while the other 13 strains carrying the ereD gene exhibited an MIC of 4–16 μg/ml. Of 30 ermF + R. anatipestifer strains, 27 (90.0%) carried the ermFU gene which may have been derived from the CTnDOT-like element, while three other strains carried ermF from transposon Tn4351. Moreover, sequence analysis revealed that ermF, ermFU, and ereD were located within the multiresistance region of the R. anatipestifer genome.
Highlights
Riemerella anatipestifer is one of two species in the genus Riemerella within the family Flavobacteriaceae, which is one of the largest branches in the phylum Bacteroidetes [1, 2]
2 (8.3%) of 24 R. anatipestifer strains, which were isolated from sick ducklings in China between 1996 and 2004, were resistant to erythromycin, while 41 (77.4%) of 56 R. anatipestifer isolates obtained from 2005 to 2014 exhibited erythromycin resistance
The increased use of erythromycin and other macrolides may have increased the selective pressure on bacterial populations [16], the percentage of erythromycin-resistant R. anatipestifer isolates may vary among different duck farms in different regions in China
Summary
Riemerella anatipestifer is one of two species in the genus Riemerella within the family Flavobacteriaceae, which is one of the largest branches in the phylum Bacteroidetes [1, 2]. For the first time, our results showed that erythromycin resistance in R. anatipestifer was due to the presence of the ermF, ermFU, and ereD genes in the bacterial genome. To determine the type of ermF carried by different ermF+ R. anatipestifer strains, the upstream sequence of ermF gene was PCR-amplified using primers ermFU P1 plus ermFU P2 for ermFU, and ermF P1' plus ermFU for ermF, respectively.
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