Molecular epidemiology of methicillin-resistant Staphylococcus aureus isolated in serial cultures from the respiratory tract of children with cystic fibrosis.
BACKGROUND
Little is known about strain relatedness of methicillin-resistant Staphyloccocus aureus (MRSA) isolated at serial time points from the respiratory tract of patients with cystic fibrosis (CF). The objectives are to interrogate the genetic diversity of MRSA recovered in serial cultures from children with CF and to correlate strain relatedness with clinical characteristics.


METHODS
We performed a retrospective analysis of children with CF from whom MRSA was isolated from serial respiratory cultures from 2005 to 2011. Within individual patients, relatedness of isolated strains was determined by repetitive-sequence polymerase chain reaction, and the staphylococcal cassette chromosome mec type of each isolate was characterized. Medical records corresponding to the MRSA cultures were reviewed.


RESULTS
We identified 54 CF patients with serial MRSA cultures (145 distinct cultures). Over time, 45 (83%) patients maintained the same strain type and 9 (17%) possessed at least 2 distinct strain types. A total of 91 pairs of isolates were analyzed for strain relatedness. Of these, 81 (89%) were identical and 10 (11%) were distinct strain types. About 117 (83%) isolates were staphylococcal cassette chromosome mec type II, 24 (17%) were staphylococcal cassette chromosome mec type IV and 4 were other types not resolvable with our assay. Clinical factors, including time interval and prescription of antibiotics effective against MRSA between positive cultures, did not correlate with acquisition of a distinct MRSA strain by individual patients.


CONCLUSIONS
Our data suggest that sustained presence of MRSA in CF patients is most commonly attributable to identical strain types. Acquisition of distinct MRSA strains in the airway is infrequent.
From the *Departments of Pediatrics and †Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO.
Duha
D
Al-Zubeidi
Patrick G
PG
Hogan
Mary
M
Boyle
Carey-Ann D
CA
Burnham
Stephanie A
SA
Fritz
D000293:Adolescent; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000453:epidemiology* / Q000382:microbiology*; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D012189:Retrospective Studies; D013183:Sputum / Q000382:microbiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology*
D000900:Anti-Bacterial Agents