Background The emergence, resurgence and spread of human food-borne pathogenic Vibrios are one of the major contributors to disease burden and mortality particularly in developing countries with disputable sanitary conditions. Previous research on pathogenic Vibrio cholerae and Vibrio parahaemolitycus derived from clinical samples has proposed links between acquisition of virulence and multiple drug resistance traits and intercellular transmissibility of mobile genetic elements in the environment. To date, very few information is available on environmental Vibrio isolates. In this study, we characterized eleven Vibrio strains bearing the SXT/R391-like integrative and conjugative elements (ICEs) derived from aquatic products and environment in the Yangtze River Estuary, China. Results The eleven Vibrio strains were isolated in 2010 to 2011, and taxonomically identified, which included six Vibrio cholerae , three Vibrio parahaemolyticus , one Vibrio alginolyticus and one Vibrio natriegens . Most of the strains displayed strong resistance phenotypes to ampicillin, mercury and chromium. The majority of their ICEs, which belong to S and R exclusion system groups, contain ICEs-chromosome junction sequences and highly conserved core-genes required for ICE transfer. However, comparative sequence analysis uncovered interesting diversity in their mosaic accessory gene structures, which carry many novel genes that have not been described in any known ICEs to date. In addition, antibiotic resistance was transmitted by ICE Vch Chn6 and ICE Vpa Chn1 from V. cholerae , V. parahaemolyticus to E. coli MG1655 via conjugation, respectively. Our data also revealed that the ICEs characterized in this study are phylogenetically distant from most of the SXT/R391 ICEs reported previously, which may represent a novel cluster likely shaped by the ecological environment in the Yangtze River Estuary, China. Conclusions This study constitutes the first investigation of ICEs-positive Vibrio spp. in the Yangze River Estuary, China. The newly identified ICEs were characterized with mosaic accessory gene structures and many novel genes. The results demonstrated self-transmissibility of antibiotic resistance mediated by two of the ICEs from V. cholerae , V. parahaemolyticus to E. coli via conjugation, respectively. Our results also revealed that the ICEs examined in this study may represent a novel cluster in the SXT/R391 family.

The aim of this study was to investigate virulence and drug resistant mechanism of multidrug resistant Pseudomonas aeruginosa(PA) isolated from water sample of fishery pond,in order to provide scientific support for practical aquaculture disease treatment,effective management of aquaculture environment and aquatic food safety control.Antimicrobial susceptibility of PA isolates under this study were examined by using standard Kirby Bauer disk diffusion method according to the Clinical and Laboratory Standards Institute(USA,2010 Edition),showing distinct susceptibility to nine antimicrobial agents belonging to six drug classes tested.All PA isolates were resistant to trimethoprim and rifampin,of which,90% were to ampicilin and kanamycin,and 10% were to gentamycin.The genes involved in pathogenicity,intrinsic and transferred antibiotic resistance were detected by polymerase chain reaction(PCR).The toxA and exoU genes were absent from the PA isolates tested,50% of which were exoS+/exoU-infectious genetype,and none of which were exoS-/exoU+ cell toxic genetype that usually existed in clinical PA isolates.Subsequent analysis revealed that the multidrug efflux pumps including MexAB-OprM,MexXY-OprM and MexVW-OprM were present in all PA isolates,20% of which were positive for ampC gene,whereas the other four efflux pumps including MexEF-OprN,MexJK-OprM,MexCD-OprJ and MexGHI-OpmD were fully or partially deficient.In addition,the comINT gene of class Ⅰ-Ⅲ integrons was negative in the PA isolates,however,the functional genes(int,soj,pilS2,pilD)of conserved module structures of integrative conjugative elements(ICEs) were detected positive,suggesting possible transfer activity of the ICEs detected in the PA isolates.This study revealed the major mechanism under multidrug resistance of the PA isolates mediated by efflux pumps encoded by chromosome genes,and constituted the first evidence for mobile genetic element ICEs in PA isolates of environmental origin.