| With antibacterial drugs widely used in aquaculture,bacterial drug resistance is becoming stronger,and the diversities are also increasing,and the control effect of animal bacterial diseases is deteriorated.Aeromonas is one of the main pathogens in fish,which easily lead to hemorrhagic diseases,such as blood poisoning,furunculosis and ulceration.Antibacterials are the main factors in inducing the drug resistance of Aeromonas.In this paper,we aim to investigate and analyze drug resistance,the distribution of resistance genes,transmission mechanism of resistance genes in Aeromonas spp.from aquaculture.Among the 17 kinds of antibacterial drugs,the drug resistance rate of AMX was high to 100%,and SMZ,TMP,SXT,RIF were 60%~90%,and CTX,NEO,DOX,ENR,NOR and OFL were lower than 15%.The results showed that 41 strains were resistant to more than three categories of antibacterials,among them,24 strains were resistant to 9 kinds of antimicrobial agents.The result of minimum inhibitory concentration(MIC)test showed that MIC50 of SMZ and TMP were hight to 2048 ?g/m L,which followed by STR(64 ?g/m L),CHL(32 ?g/m L),NEO(16 ?g/mL),FFL(16 ?g/m L),TET(16 ?g/mL),DOX(4 ?g/m L)and ENR(1 ?g/m L).The minimum bactericidal concentration(MBC)test showed that MBC50 of TMP,TET,SMZ,NEO and ENR were the same as MIC50,CHL,STR and DOX were 64?g/mL,256 ?g/mL,8 ?g/m L.Analyzing the result of correlation between antibacterial circle diameter and MIC value,we found they were logarithmic or exponential negative correlation.Detection of 25 different antimicrobial-resistance genes by PCR showed that blaTEM was the highest positive rate(83.7%)in the genome,followed by sul1(69.4%)and aadA(61.2%),arr2/3,aphA1,tetC,sul2,dfrA5 and floR were higher than 40%.In the plasmid,the highest rate was sul1(51%),followed by aphA1(0.8%)and aadA(38.8%).BlaTEM,tetB,qnrB,qnrS,dfrA7,cat1 and cmlA were not detected.In addition,the remaining resistance genes were below 35%.The result of PCR detection to 5 kinds mobile elements showed that IntI1 was 65.3% in the genome.Followed by IS26,ISCR2 and tnpU,which were 63.3%,57.1% and 51%,and the rest were less than 50%.In the plasmid,the rate of IntI1 was also the highest(57.1%).IS26,ISCR2 and merA was following,the detection rate were between 20%~35%,the rest were less than 15%.13 kinds of gene cassettes were found in the variable region of class 1 integron,with the highest proportion of dfrA12-orfF-aadA2.The variable regions of ISCR2 were two kinds: ISCR2+glmM +sul2(10 strains)and ISCR2-like+strB+strA+sul2(2 strains).In this study,16 strains of Escherichia coli transformants,21 strains of Aeromonas transformants and 4 strains of Escherichia coli transconjugants were obtained.Gene aadA,aphA1,sul2,tetA and floR were more easily transfer to Escherichia coli by transformation,and mostly tetA gene positive strains were resistant to tetracycline;Aeromonas veronii transformants obtained RIF resistance,and Aeromonas hydrophila transformants obtained STR,KAN,CHL resistance mainly.The 4 kinds drug resistance easily spread through transformation in the species;The results of conjugation experiments showed that only str A-B and floR can transfer to Escherichia coli through the conjugation of Aeromonas hydrophila,and all the gene positive strains showed corresponding drug resistance.Furthermore,the detection rate of ISCR2 was the highest in all transformants and transconjugants. |
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