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. 2020 Aug 11;20(1):247.
doi: 10.1186/s12866-020-01927-z.

A new plasmid carrying mphA causes prevalence of azithromycin resistance in enterotoxigenic Escherichia coli serogroup O6

Ying Xiang  1   2   3 , Feng Wu  1   2 , Yinghui Chai  2 , Xuebin Xu  4 , Lang Yang  1 , Sai Tian  2 , Haoran Zhang  1 , Yinxia Li  2 , Chaojie Yang  2 , Hongbo Liu  2 , Shaofu Qiu  5 , Hongbin Song  6 , Yansong Sun  7
Affiliations

A new plasmid carrying mphA causes prevalence of azithromycin resistance in enterotoxigenic Escherichia coli serogroup O6

Ying Xiang et al. BMC Microbiol. .

Abstract

Background: At present, azithromycin has become an effective treatment for severe diarrhea caused by Enterotoxigenic Escherichia coli (ETEC) infection. However, enterobacteria have begun to develop resistance to azithromycin and have attracted attention in recent years. This study conducted to described the emergence of a high proportion of azithromycin-resistant ETEC serogroup O6 strains in Shanghai and to analyzed the mechanisms of azithromycin resistance.

Results: Strains from adult diarrhea patients with ETEC serogroup O6 infections were collected by Shanghai Diarrhea Surveillance Network and the Foodborne Surveillance Network from 2016 to 2018. We tested 30 isolates of ETEC O6 serogroup, 26 of which were resistant to azithromycin. Phylogenetic analysis revealed that these ETEC serogroup O6 strains have formed an independent dominant clone. S1-PFGE and southern blotting revealed the presence of the mphA gene on the 103 kb plasmid. Illumina and Nanopore sequencing and plasmid coverage analysis further confirmed that azithromycin-resistant strains carried a novel IncFII plasmid harboring mphA and blaTEM-1 resistance genes.

Conclusions: This is the first study to report a high proportion of azithromycin resistance in a particular ETEC serogroup due to a specific plasmid carrying mphA. Our findings indicate the rapid spread of azithromycin resistance, highlighting the urgency of stringent surveillance and control measure.

Keywords: Azithromycin; Enterotoxigenic Escherichia coli; Nanopore sequencing; Plasmid; Whole-genome sequencing; mphA.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1
Phylogenetic tree of ETEC strains. Maximum likelihood phylogeny was estimated using RAxML (v8.2.4). The branch where the self-tested strains are located was marked in red color. a Complete phylogenetic tree of 392 strains. b The branch of the self-tested strains and its adjacent phylogenetic tree branch
Fig. 2
Fig. 2
AMR gene groups detected in each genome sequence at more than 70% coverage and 80% identity using BLAST (BLASTn). Presence and absence of AMR genes were represented by dark red and light grey colors, respectively. Presence of the gyrA (Ser83Leu), gyrA (Asn87Asx) and gyrA (Asn87Tyr) point mutations were represented by light blue, dark blue and dark green colors, respectively. Purple with different color depths represents the strain’s coverage of plasmid pQPES18024_1
Fig. 3
Fig. 3
Alignment of 2014EL-1343-unnamed3, pQPES18024_1, and p203740_80. Block arrows indicate confirmed or putative open reading frames (ORFs) and their orientations. Arrow size is proportional to predicted ORF length. Resistance genes are indicated by red arrows, insert sequences are indicated by green arrows and transposases are indicated by blue arrows
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