Phenotype Analysis And Drug Resistance Characteristics Against Vancomycin And Fidaxomicin Of 131 C. Difficile Strains

Part one Phenotype Analysis of 131 Clostridium difficile strainsObjective:Clostridi difficile is the principle pathogen causing nosocomial infection.Ribotype 027 is the most epidemic clone in North America and Europe,and had contributed to a outbreak.However,sequence type(ST)37C.difficile,identified by PCR ribotyping as type 017,is the predominant genotypes in China and Asia,but study about ST37 is extremely limited.Whether ST37 can become a major epidemic strainsrelated to its higher virulence phenotype is unknown.131 C.difficile strains was selected and analyzed at resistance rates,biofilm and Sporulationcapacity to investigate why ST37 is a major epidemic strains in China and Asia.Methods:Antimicrobial susceptibility testing was performed using t he agar dilution method.fourteen antibiotics involved were metronidazole,vancomycin,tigecycline and so on.Biofilm formation was calculated by CrystalViolet staining.Sporulation capacity was calculated by spore forma tion test.Results:1.Minimal inhibitory concentration(MIC)of 14 antibiotics to 131 C.difficile showed that all the isolates were highly susceptible to metronid azole,vancomycin,fidaxomicin and tigecycline.While the resistance rat e of levofloxacin,ciprofloxacin,tetracycline,erythromycin,ceftazidime,clinda mycin is 61.8%,99.2%,38.2%,85.5%,96.2%,91.6%,respectively.C.difficile were more resistant to ciprofloxacin than levofloxacin although both of t hem are quinolones(99.2%vs61.8%).All strains were more resistant to c eftazidime than ceftriaxone although both of them are cephalosporin(96.2%vs30.5%).it is worthy to notice that 121 C.difficile exhibited multi-d rug resistance.2.ST37 have higher resistance rate to levofloxacin,meropenem,tetracy cline,ceftriaxone,erythromycin,rifaximin,clindamycin(P<0.05).All ST37 sh owed multi-drug resistance,and the multi-drug resistance rate were signifi cantly higher than other ST types(P<0.05).Strains resistanted to rifamx imin were derived from ST37.Among 6 meropenem-resistant isolates,83%belongs to ST37.3.ST37 had similar biofilm formation amounts(0.82±0.03vs0.74±0.02)with others ST types(P>0.05).but showed lower spore numbers than ST3?ST2?ST35 and others(P<0.001).Conclusions:1.ST37 Clostridium difficile has high resistance to various antibiotic s,which may be the main reason for its spread in China and Asia.2.Resistance of ST37 C.difficile is serious,so antibiotics usage shou ld be strictly controlled in clinical practice,especially quinolones,cephal osporins and rifamycin.Metronidazole,vancomycin,fidaxomicin,and tetr acycline can be used as treatment drugs.Meanwhile,we should trengthen the surveillance of ST37 infection and drug resistance.Part two Resistance analysis of Clostridium difficile to Vancomycin and FidaxomycinObjective:Vancomycin and fidaxomicin is the main choice for C.dif ficile infection.So far,A few report about the resistance of this two dru gs to C.difficile was reported,but in the long run,antibiotic resistancei s still a problem which can not be ignored.So Multi-step induction was conducted with 15 C.difficile isolates and 5 reference strains to explore stability of antimicrobial activity of vancomycin and fidaxomicin against C.difficile in vitro.Methods:Multi-step induction was conducted with 15 C.difficile iso lates and 5 reference strains,followed by agar dilution method to detect change of MIC.Results:When passaged on vancomycin,before induction,the MICrange of the vancomycin was between 0.125 and 0.5 ug/ml,after 20 pa ssages,it was between 0.5 and 2 ug/ml.Three isolates displayed an 4-fol d increase,Seventeen isolates displayed no changes or a 2-foldincrease in susceptibility following the 20 th passage.When passages on fidaxomicin,before induction,the MIC range of fidaxomicin was between 0.015 and0.5 ug/ml,after 20 passages,it was between 0.0075 and 0.5 ug/ml.8-fold increase of three strains,4-fold increase of four strains were observed f ollowing the 20 th passage.Conclusions:Vancomycin and fidaxomicin are of good stability of antimicrobial activity against Clostridium difficile in vitro.It is not easy to make secondary resistance.