title: Antimicrobial susceptibility and molecular typing of MRSA in cystic fibrosis.
abstract: OBJECTIVE
  The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in cystic fibrosis (CF) patients in the United States is approximately 25%. Little is known about the relative proportion of hospital- versus community-associated strains or the antimicrobial susceptibility of MRSA in different CF centers. We hypothesized that the majority of MRSA isolates obtained from children with CF are those endemic in the hospital and that those associated with community acquisition (SCCmec IV) would be more resistant than typically seen in non-CF MRSA isolates.
  
  
  METHODS
  We studied MRSA strains from seven pediatric CF centers to determine the clonal distribution based on DNA sequencing of the staphylococcal protein A gene (spa typing), the type of staphylococcal chromosomal cassette mec (SCCmec), and the proportion of strains with Panton-Valentine leukocidin (PVL). Antimicrobial susceptibility to systemic and topical antibiotics was compared between different MRSA types.
  
  
  RESULTS
  We analyzed 277 MRSA isolates from unique patients (mean age 11.15 ± 4.77 years, 55% male). Seventy % of isolates were SCCmec II PVL negative and the remainder SCCmec IV. Overall 17% MRSA strains were PVL positive (all SCCmec IV). Spa typing of 118 isolates showed most of the SCCmec II strains being t002, while SCCmec IV PVL positive isolates were t008, and SCCmec IV PVL negative isolates represented a variety of spa-types. The proportions of SCCmec II strains and spa-types were similar among centers. Overall rates of resistance to trimethoprim-sulfamethoxazole (4%), tetracycline (7%), tigecycline (0.4%), linezolid (0.4%) as well as fosfomycin (0.4%), fusidic acid (3%), and mupirocin (1%) were low. No strains were resistant to vancomycin. SCCmec II strains had higher rates of resistance to ciprofloxacin and clindamycin (P < 0.001) than SCCmec IV strains.
  
  
  CONCLUSIONS
  In this U.S. study, most MRSA isolates in the pediatric CF population were SCCmec II PVL negative. Rates of resistance were low, including to older and orally available antibiotics such as trimethoprim-sulfamethoxazole.
authors.affiliation: Division of Pediatric Pulmonology, Department of Pediatrics, University of North Carolina, Chapel Hill, North Carolina.
authors.forename: E A
authors.initials: EA
authors.lastname: Champion
authors.forename: M B
authors.initials: MB
authors.lastname: Miller
authors.forename: E B
authors.initials: EB
authors.lastname: Popowitch
authors.forename: M M
authors.initials: MM
authors.lastname: Hobbs
authors.forename: L
authors.initials: L
authors.lastname: Saiman
authors.forename: M S
authors.initials: MS
authors.lastname: Muhlebach
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D001427:Bacterial Toxins / Q000235:genetics; D001999:Bronchoscopy; D002648:Child; D002675:Child, Preschool; D015331:Cohort Studies; D003550:Cystic Fibrosis / Q000150:complications / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics*; D005098:Exotoxins / Q000235:genetics; D005260:Female; D005578:Fosfomycin / Q000494:pharmacology; D005672:Fusidic Acid / Q000494:pharmacology; D006801:Humans; D007956:Leukocidins / Q000235:genetics; D000069349:Linezolid; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives / Q000494:pharmacology; D058889:Molecular Typing; D016712:Mupirocin / Q000494:pharmacology; D023303:Oxazolidinones / Q000494:pharmacology; D046915:Penicillin-Binding Proteins; D010614:Pharynx / Q000382:microbiology; D011023:Pneumonia, Staphylococcal / Q000150:complications / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013183:Sputum / Q000382:microbiology; D013203:Staphylococcal Infections / Q000150:complications / Q000188:drug therapy / Q000382:microbiology; D013205:Staphylococcal Protein A / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology; D000078304:Tigecycline; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology; D014481:United States
chemical_list: D000081:Acetamides; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D005098:Exotoxins; D007956:Leukocidins; D023303:Oxazolidinones; C078284:Panton-Valentine leukocidin; D046915:Penicillin-Binding Proteins; D013205:Staphylococcal Protein A; C487789:mecA protein, Staphylococcus aureus; D005578:Fosfomycin; D005672:Fusidic Acid; D000078304:Tigecycline; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D016712:Mupirocin; D013752:Tetracycline; D008911:Minocycline; D000069349:Linezolid
keywords: Panton-Valentine leukocidin; community MRSA; hospital MRSA; multi-center study; spa-typing; staphylococcal cassette chromosome mec