Various pAQU plasmids possibly contribute to disseminate tetracycline resistance gene tet(M) among marine bacterial community.

Lisa Nonaka,Takeshi Kobayashi,Tetsuya Hayashi,Yuki Onishi,Satoru Suzuki,Yoshitoshi Ogura,Fumito Maruyama,Michiaki Masuda

doi:10.3389/fmicb.2014.00152

Abstract

Emergence of antibiotic-resistant bacteria in the aquaculture environment is a significant problem for disease control of cultured fish as well as in human public health. Conjugative mobile genetic elements (MGEs) are involved in dissemination of antibiotic resistance genes (ARGs) among marine bacteria. In the present study, we first designed a PCR targeting traI gene encoding essential relaxase for conjugation. By this new PCR, we demonstrated that five of 83 strains isolated from a coastal aquaculture site had traI-positive MGEs. While one of the five strains that belonged to Shewanella sp. was shown to have an integrative conjugative element of the SXT/R391 family (ICEVchMex-like), the MGEs of the other four strains of Vibrio spp. were shown to have the backbone structure similar to that of previously described in pAQU1. The backbone structure shared by the pAQU1-like plasmids in the four strains corresponded to a ~100-kbp highly conserved region required for replication, partition and conjugative transfer, suggesting that these plasmids constituted “pAQU group.” The pAQU group plasmids were shown to be capable of conjugative transfer of tet(M) and other ARGs from the Vibrio strains to E. coli. The pAQU group plasmid in one of the examined strains was designated as pAQU2, and its complete nucleotide sequence was determined and compared with that of pAQU1. The results revealed that pAQU2 contained fewer ARGs than pAQU1 did, and most of the ARGs in both of these plasmids were located in the similar region where multiple transposases were found, suggesting that the ARGs were introduced by several events of DNA transposition into an ancestral plasmid followed by drug selection in the aquaculture site. The results of the present study indicate that the “pAQU group” plasmids may play an important role in dissemination of ARGs in the marine environment.

Highlights

Wide ranges of antimicrobial agents have been used for treatment of human infectious diseases and in the fish farming industry for therapeutic and prophylactic purposes (Cabello et al, 2013)
The results revealed that pAQU2 contained fewer antibiotics resistance genes (ARGs) than pAQU1 did, and most of the ARGs in both of these plasmids were located in the similar region where multiple transposases were found, suggesting that the ARGs were introduced by several events of DNA transposition into an ancestral plasmid followed by drug selection in the aquaculture site
SCREENING BY PCR DETECTION AND SEQUENCING OF traI GENE FOR THE MARINE BACTERIAL STRAINS WHICH HARBOR tet (M)-BEARING pAQU1-LIKE PLASMID OR ICEVchMEX-LIKE mobile genetic elements (MGEs) For screening for the bacterial strains carrying the pAQU1-like plasmids, we designed degenerate primers, MOBH1_traI062-1F and MOBH1_traI062-2R, based on the traI nucleotide sequences of pAQU1 (GenBank accession number AB571865), five of IncA/C plasmids (Welch et al, 2007; Fricke et al, 2009) and seven of SXT/R391 ICEs (Wozniak et al, 2009) which belong to the MOBH12 clade of the MOBH family (Table 1)

Summary

Introduction

Wide ranges of antimicrobial agents have been used for treatment of human infectious diseases and in the fish farming industry for therapeutic and prophylactic purposes (Cabello et al, 2013). When the antibiotics are used in the aquaculture, they are usually mixed with feed and administered to fish, and the extensive use of TCs has led emergence of resistant bacteria (Nonaka et al, 2007). Emergence and dissemination of drug resistance in the marine environment have a large impact on the fish farming industry. It is an important issue for clinical medicine because a number of antibiotics resistance genes (ARGs) are shared between marine bacteria and human pathogens (Cabello et al, 2013) and the gene flow between these environments has been suggested. Transfer of opportunistic human pathogen from aquatic environments possible to generate antimicrobial resistance infections (Cabello et al, 2013)

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