title: Characterization of macrolide resistance genes in Haemophilus influenzae isolated from children with cystic fibrosis.
abstract: OBJECTIVE
  to determine the mechanism(s) of macrolide resistance in Haemophilus influenzae isolated from cystic fibrosis (CF) patients participating in a randomized placebo-controlled trial of azithromycin.
  
  
  METHODS
  macrolide susceptibility, mutations and carriage of the macrolide resistance genes erm(A), erm(B), erm(C), erm(F) and mef(A) were determined using PCR assays and sequencing or hybridization of the PCR products. H. influenzae isolates were used as donors in conjugation studies with H. influenzae and Enterococcus faecalis recipients. Transconjugant susceptibility and the macrolide resistance genes carried were determined.
  
  
  RESULTS
  of the 106 H. influenzae isolates, 27 were resistant and 78 intermediate resistant to azithromycin and/or erythromycin. All isolates carried one or more macrolide resistance gene(s), with the mef(A), erm(B) and erm(F) genes found in 74%, 31% and 29% of the isolates, respectively. None of the selected isolates had L4 or L22 mutations. Twenty-five donors, with various macrolide MICs, transferred macrolide resistance genes to H. influenzae Rd (3.5 × 10(-7)-1 × 10(-10)) and/or E. faecalis (1 × 10(-7)-1 × 10(-8)) recipients. The H. influenzae transconjugants were phenotypically resistant or intermediate to both macrolides while E. faecalis transconjugants were erythromycin resistant.
  
  
  CONCLUSIONS
  this is the first identification of erm(A), erm(C) and erm(F) genes in H. influenzae or bacteria from CF patients and the first characterization of macrolide gene transfer from H. influenzae donors. The high level of H. influenzae macrolide gene carriage suggests that the use of azithromycin in the CF population may ultimately reduce the effectiveness of continued or repeated macrolide therapy.
authors.affiliation: Department of Environmental and Occupational Health Sciences 357234, School of Public Health, University of Washington, Seattle, WA 98195-7234, USA. marilynr@u.washington.edu
authors.forename: Marilyn C
authors.initials: MC
authors.lastname: Roberts
authors.forename: Olusegun O
authors.initials: OO
authors.lastname: Soge
authors.forename: David B
authors.initials: DB
authors.lastname: No
mesh_terms: D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017963:Azithromycin / Q000494:pharmacology / Q000627:therapeutic use; D002648:Child; D003227:Conjugation, Genetic; D003550:Cystic Fibrosis / Q000150:complications*; D004269:DNA, Bacterial / Q000235:genetics; D024881:Drug Resistance, Bacterial; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D006192:Haemophilus Infections / Q000188:drug therapy / Q000382:microbiology*; D006193:Haemophilus influenzae / Q000187:drug effects* / Q000302:isolation & purification; D006801:Humans; D018942:Macrolides / Q000494:pharmacology* / Q000627:therapeutic use; D008826:Microbial Sensitivity Tests; D009693:Nucleic Acid Hybridization; D016133:Polymerase Chain Reaction; D015995:Prevalence; D016032:Randomized Controlled Trials as Topic; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D018942:Macrolides; D017963:Azithromycin