domingo, 26 de octubre de 2014

Evidence for clonal expansion after antibiotic ... [J Infect Dis. 2014] - PubMed - NCBI

Evidence for clonal expansion after antibiotic ... [J Infect Dis. 2014] - PubMed - NCBI

 2014 Oct 6. pii: jiu552. [Epub ahead of print]

Evidence for clonal expansion after antibiotic selection pressure: pneumococcal multilocus sequence types before and after mass azithromycin treatments.



 A clinical trial of mass azithromycin distributions for trachoma created a convenient experiment to test the hypothesis that antibiotic use selects for clonal expansion of pre-existing resistant bacterial strains.


 Mass azithromycin was distributed to 12 communities in Ethiopia every 3 months for 1 year. A random sample of 10 children aged 0-9 years from each community was monitored with nasopharyngeal swabs before mass azithromycin distributions and after 4 mass treatments; S. pneumoniae was isolated and multilocus sequence typing performed.


 Of 82 pneumococcal isolates identified before treatment, 4 (5%) exhibited azithromycin resistance, representing 3 different sequence types (STs): 177, 6449, and 6494. The proportion of isolates that were classified as one of these 3 STs and were resistant to azithromycin increased after 4 mass azithromycin treatments (14 of 96 isolates; 15%; P=0.04). Using a classification index, we found evidence for a relationship between ST and macrolide resistance after mass treatments (P<0.0001). The diversity of STs-as calculated by the unbiased Simpson's index-decreased significantly after mass azithromycin treatment (P=0.045).


 Resistant clones present before mass azithromycin treatments increased in frequency after treatment, consistent with the theory that antibiotic selection pressure results in clonal expansion of existing resistant strains.
© The Author 2014. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail:

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