Study On Antibiotic Resistance Of Mycobacterium Abscessus

Since the rapid development of bacterial resistance against wide range of antibiotics,clinically treatment of bacterial infections is the serious challenge of present time.Research on antibiotic resistance becomes very important at both theory and clinic application,while it is increasingly difficult to develop new antibiotics.Sufficient attention needed to be paid on antibiotics resistant efflux of pump as it is the first defense line of bacterial antibiotics resistance.Through genome-wide comparative analysis,several interesting features were found among Mycobacterium.The total number of transporters decreased rapidly while Mycobacterium evolved from non-resistant Mycobacterium smegmatis to natural multi-drug resistance M.abscessus and further to multi-drug resistance M.tuberculosis.The proportion of ABC family members transporters remained stable at about 50%.The proportion of efflux pump?transport harboring NBD domain?in the ABC family was 28.0% and 29.5% respectively,which was nearly 10% higher than that in the M.smegmatis?20.1%?.Above features implied the function of ABC and its certain subfamilies in the virulence and drug resistance etc.The phylogenetic trees of M.abscessus and M.tuberculosis based on NBD domain showed that almost all the reported resistance efflux of M.tuberculosis were located three clusters.And three other clusters are mainly composed by efflux from M.abscessus.Based on the information obtained from the phylogenetic tree,we selected eight resistance candidate genes for further study.First we assayed the resistance candidate genes expression of cefoxitin resistant strains?A173?and sensitive strains?ATCC19977?after bacteria treated with cefoxitin and chromium chloride for three or six hours.Much stronger candidate gene expression changes were observed in A173 rather than in ATCC19977 after cefoxitin and chromium chloride treatment at transcript level.Among the eight candidate genes,the expression of MAB₂622c and MAB₁858 were up-regulated much more by cefoxitin than that by chromium chloride.After treated with cefoxitin for six hours,the expression of MAB₂622c was increased significantly by 10.78-fold?P<0.01?in A173,however the expression of MAB₂622c remained unchanged in ATCC19977.The expression of MAB₂622c was up-regulation by 2.71 times higher by Cefoxitin than that by chromium chloride.When MAB₂622c over-expressed in M.smegmatis MC2 155,inhibition zone of cefoxitin was significantly smaller than that of the original strain and control group?P<0.05?,and the MIC value was two fold higher than that of the original strain and control group.When MAB₂622c over-expressed in M.abscessus ATCC19977,no changed in MIC value of cefoxitin was observed,but the MIC value of clarithromycin was two times higher than that of the control group.In addition,among the three clinical strains A173,A206 and A244,A173 and A206 showed typical phenomenon of DNA Phosphorylthioate,DNA degradation,and the gene cluster of DNA Phosphorylthioate,DndABCDE,were identified in the genome of both strains.MAB₂622c and other drug-resistant efflux pumps were identified and proved preliminarily by study on the ABC family resistant efflux pumps from M.abscessus at genome level,which laid a solid foundation for further revealing the mechanism of efflux pump in drug resistance.