| Sulsulamine-resistant genes(sul)have a serious impact on the use of sulfonamides.Sul3 gene is one of the drug-resistant genes that have been found relatively late and studied less.Most of the related studies focus on the detection of positive rate,and there are few studies on positive bacteria.In order to explore the drug resistance,pathogenicity and conjugative characteristics of E.coli carrying sul3 in Nanning area,fill the research blank of E.coli carrying sul3-positive in Nanning area,and provide reference for the prevention and treatment of E.coli.This study explored the drug resistance characteristics and prevalence of sul3 positive strains by identification medium,molecular detection,MLST,phylogenetic tree construction,drug sensitivity test,drug resistance gene detection and other test methods.The virulence characteristics and toxicity of the positive strains were investigated by related factor detection,mouse toxicity test,exercise test and biofilm formation test.Then,the change of wild sul3 plasmid to strain was detected by conjugation test,resistance gene and phenotype change between receptor and transconjugant,plasmid stability test,growth curve test,in vitro competition,sports ability and biofilm formation ability test.The results are as follows:1.A total of 142 E.coli strains were identified,46 of which were sul3 positive.The positive isolates were belonge to 12 genotypes: ST641,ST457,ST350,ST950,ST2178,ST222,ST101,ST156,ST746,ST10,ST23 and one unknown ST type.ST350 was the dominant type(13 / 46).Most of the positive strains were isolated from chicken.The evolutionary tree showed no significant correlation between sul3 genetic relatability and ST type.The strains had strong resistance.And the drug resistance rate of the positive strains was 100% to penicillin,tetracycline and chloramphenicol,followed by chloramphenicol(97.8%),amoxicillin(95.7%)and doxycycline(95.7%),only was completely sensitive to meropenem.In the detection of drug resistance gene,the detection rates of rmt D(100%),tet A(96.7%),flor(89.1%)and mar A(95.7%)were high.A total of 38drug-resistant gene combinations were found.rmt D-aac(3’)-II-tet A-tet M-TEMqnr B-flor-oqx A-Sul2-mar A was the most common resistance gene pattern in the combination(6.5%).There were significant correlations between amikacin and aac(6’)-Ib,ceftriaxone and CTX-M9,cefotaxime and CTX-MU,and gatifloxacin and oqx B.2.The detection rate of virulence related factors showed that all the positive strains were extraintestinal pathogenic E.coli.The detection rates of csg A(97.8%),omp A(100%),sod A(97.8%),ibe B(95.7%),yijp(100%)and mat(100%)were higher in virulence related factors.And csg A-aat A-omp A-sod A-ibe B-yijp-mat-R2 was the most common Virulence Related factor pattern(10.9%).Thirty strains were randomly selected for toxicity test.The results showed that 13 strains were highly toxic in mice,with a mortality rate of more than 83.3%(5 / 6);3 strains could form strong biofilm;13 strains had strong athletic ability and there was no significant correlation between toxicity related factors and mouse toxicity.3.The sul3 gene of 45 positive strains were located on the plasmid.Using C600 as the acceptor,3 transconjugants were obtained.The plasmid added 3-7kinds of drug resistance genes to the transconjugants.It suggests that multiple drug-resistant genes were co transferred with sul3.The variety and size of drug resistance were related to the types and types of drug-resistant genes and other related genes,which had a great impact on the drug resistance of the strains.The plasmids carrying sul3 could be stably and continuously passaged for at least 40 generations in antibiotic free environment.Compared with the recipient bacteria,the biofilm forming ability and motility of the transconjugants increased or decreased in varying degrees,which may be related to the types of plasmids or the genes carried.The growth curves of the transconjugants are similar to that of the recipient strain,but the in vitro nutritional competitiveness is reduced by at least 17 times,which suggests that we can prevent and control sul3 positive Escherichia coli and other drug-resistant bacteria from the direction of nutritional competition.Conclusion: The sul3-positive Escherichia coli has strong resistance to a variety of antibiotics,and the pathogenic type is the extra-intestinal pathogenic type,which has different degrees of pathogenicity to mice.Wild sul3 plasmid can bring multiple influences to recipient bacteria,the influence direction and degree are uncertain,but all can reduce their in vitro competitiveness. |
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