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Antimicrobial susceptibility and molecular typing of MRSA in cystic fibrosis

E A Champion1, M B Miller, E B Popowitch

  • 1Division of Pediatric Pulmonology, Department of Pediatrics, University of North Carolina, Chapel Hill, North Carolina.

Pediatric Pulmonology
|June 15, 2013
PubMed
Abstract

Insights

Most methicillin-resistant Staphylococcus aureus (MRSA) in U.S. pediatric cystic fibrosis (CF) patients are hospital-associated strains (SCCmec II). Antimicrobial resistance rates were low, even for oral antibiotics like trimethoprim-sulfamethoxazole.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Genetics

Background:

  • Methicillin-resistant Staphylococcus aureus (MRSA) is a significant pathogen in cystic fibrosis (CF) patients.
  • Understanding the genetic characteristics and antimicrobial susceptibility of MRSA strains in CF populations is crucial for effective treatment.
  • The relative proportion of hospital-associated versus community-associated MRSA strains in pediatric CF patients in the U.S. remains unclear.

Purpose of the Study:

  • To investigate the clonal distribution, including staphylococcal chromosomal cassette mec (SCCmec) types and Panton-Valentine leukocidin (PVL) presence, of MRSA isolates from pediatric CF patients in the U.S.
  • To compare the antimicrobial susceptibility profiles of different MRSA types found in this population.
  • To determine if community-associated MRSA strains are more resistant than hospital-associated strains in pediatric CF patients.

Main Methods:

  • Analysis of 277 MRSA isolates from seven U.S. pediatric CF centers.
  • Staphylococcal protein A gene sequencing (spa typing) for clonal distribution.
  • Determination of SCCmec types and PVL presence.
  • Antimicrobial susceptibility testing against various systemic and topical antibiotics.

Main Results:

  • The majority of MRSA isolates (70%) were SCCmec II, predominantly PVL negative, consistent with hospital-associated strains.
  • A smaller proportion (30%) were SCCmec IV, with 17% of all strains being PVL positive (all SCCmec IV).
  • Overall antimicrobial resistance rates were low, including to trimethoprim-sulfamethoxazole, tetracycline, tigecycline, linezolid, fosfomycin, fusidic acid, and mupirocin. No vancomycin resistance was observed. SCCmec II strains showed higher resistance to ciprofloxacin and clindamycin compared to SCCmec IV strains.

Conclusions:

  • The predominant MRSA strains in U.S. pediatric CF patients are hospital-associated SCCmec II PVL-negative types.
  • Antimicrobial resistance rates in this population are generally low, even for older, orally available antibiotics.
  • These findings have implications for treatment strategies and infection control in CF centers.
Keywords:
Panton-Valentine leukocidincommunity MRSAhospital MRSAmulti-center studyspa-typingstaphylococcal cassette chromosome mec

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