AUTHOR=Huang Li , Yuan Hui , Liu Ma-Feng , Zhao Xin-Xin , Wang Ming-Shu , Jia Ren-Yong , Chen Shun , Sun Kun-Feng , Yang Qiao , Wu Ying , Chen Xiao-Yue , Cheng An-Chun , Zhu De-Kang 

TITLE=Type B Chloramphenicol Acetyltransferases Are Responsible for Chloramphenicol Resistance in Riemerella anatipestifer, China

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.00297

DOI=10.3389/fmicb.2017.00297

ISSN=1664-302X

ABSTRACT=<p><italic>Riemerella anatipestifer</italic> causes serositis and septicaemia in domestic ducks, geese, and turkeys. Traditionally, the antibiotics were used to treat this disease. Currently, our understanding of <italic>R. anatipestifer</italic> susceptibility to chloramphenicol and the underlying resistance mechanism is limited. In this study, the <italic>cat</italic> gene was identified in 69/192 (36%) <italic>R. anatipestifer</italic> isolated from different regions in China, including <italic>R. anatipestifer</italic> CH-2 that has been sequenced in previous study. Sequence analysis suggested that there are two copies of <italic>cat</italic> gene in this strain. Only both two copies of the <italic>cat</italic> mutant strain showed a significant decrease in resistance to chloramphenicol, exhibiting 4 μg/ml in the minimum inhibitory concentration for this antibiotic, but not for the single <italic>cat</italic> gene deletion strains. Functional analysis of the <italic>cat</italic> gene via expression in <italic>Escherichia coli</italic> BL21 (DE3) cells and <italic>in vitro</italic> site-directed mutagenesis indicated that His79 is the main catalytic residue of CAT in <italic>R. anatipestifer</italic>. These results suggested that chloramphenicol resistance of <italic>R. anatipestifer</italic> CH-2 is mediated by the <italic>cat</italic> genes. Finally, homology analysis of types A and B CATs indicate that <italic>R. anatipestifer</italic> comprises type B3 CATs.</p>