ABSTRACT
Objective To explore the stability of resistant phenotypes and changes of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) gene system on four Shigella strains in the absence of antibiotics.Methods Four clinical isolated Shigella strains that resistant to different antibiotics were consecutive passaged for 90 times without antibiotics.Agar dilution method was used to determine the minimum inhibitory concentration of Shigella strains.After sequence analysis with PCR,CRISPR Finder and Clustal X 2.1 were applied to identify the changes of CRISPR loci in the Shigella strains.Results After the consecutive transfer of 90 generations,sensitivity to certain antibiotics of four Shigella strains with different drug resistant spectrums increased.Mel-sf1998024/zz resistance to ampicillin,cephalexin,cefotaxime,chloramphenicol decreased,mel-s2014026/sx resistance to norfloxacin,trimethoprim decreased,mel-sf2004004/sx drug resistance to ampicillin,cefuroxime,cefotaxime,chloramphenicol,trimethoprim decreased and mel-sf2013004/bj resistance to chloramphenicol decreased.The spacer of which matched gene codes Cas and its upstream repeat in 3'end of CRISPR3 got lost in mel-sf1998024/zz and mel-sf2013004/bj.Conclusions Shigella strains could reduce or lose their resistance to some antibiotics after consecutive transfers,without the interference of antibiotics.CRISPR3 locus had dynamic spacers in Shigella strains while CRISPR3 locus and cas genes might have been co-evolved.
ABSTRACT
Objective To explore the stability of resistant phenotypes and changes of clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated (Cas) gene system on four Shigella strains in the absence of antibiotics.Methods Four clinical isolated Shigella strains that resistant to different antibiotics were consecutive passaged for 90 times without antibiotics.Agar dilution method was used to determine the minimum inhibitory concentration of Shigella strains.After sequence analysis with PCR,CRISPR Finder and Clustal X 2.1 were applied to identify the changes of CRISPR loci in the Shigella strains.Results After the consecutive transfer of 90 generations,sensitivity to certain antibiotics of four Shigella strains with different drug resistant spectrums increased.Mel-sf1998024/zz resistance to ampicillin,cephalexin,cefotaxime,chloramphenicol decreased,mel-s2014026/sx resistance to norfloxacin,trimethoprim decreased,mel-sf2004004/sx drug resistance to ampicillin,cefuroxime,cefotaxime,chloramphenicol,trimethoprim decreased and mel-sf2013004/bj resistance to chloramphenicol decreased.The spacer of which matched gene codes Cas and its upstream repeat in 3'end of CRISPR3 got lost in mel-sf1998024/zz and mel-sf2013004/bj.Conclusions Shigella strains could reduce or lose their resistance to some antibiotics after consecutive transfers,without the interference of antibiotics.CRISPR3 locus had dynamic spacers in Shigella strains while CRISPR3 locus and cas genes might have been co-evolved.
ABSTRACT
Objective This thesis discusses the present situation of related thesises of childhood asthma.Methods The childhood asthma related thesises in Chinese Scientific Journals Database from 1999 to 2008 were collected as the basic data.Results 2 246 authors from 31 province/city/autonomous region who published 3 121 thesises in 507 periodicals were found.Conclusions The children's hospital of the capital institute of pediatrics is the authority researcher of childhood asthma.