title: Impact of strain typing methods on assessment of relationship between paired nares and wound isolates of methicillin-resistant Staphylococcus aureus.
abstract: The anterior nares are the site of choice for the Veterans Administration methicillin-resistant Staphylococcus aureus (MRSA) surveillance program; however, a correlation between nares colonization and concomitant wound infections has not been well established. The purpose of this study was 3-fold: to determine the relatedness of MRSA isolates from 40 paired wound and nares specimens by four different strain typing methods, to determine concordance of typing methods, and to establish a baseline of MRSA types at this medical center. Isolates were typed by repetitive PCR (rep-PCR) (DiversiLab System; DL) and SpectraCell Raman analysis (SCRA) (commercially available methods that can be performed within a clinical lab), pulsed-field gel electrophoresis (PFGE), and an antibiotic susceptibility profile (AB). Whole-genome optical mapping (WGM) (OpGen, Inc.) was performed on selected isolates. All methods agreed that 26 pairs were indistinguishable and four pairs were different. Discrepant results were as follows: 4 where only SCRA was discordant, 3 where only AB was discordant, 2 where both DL and AB were discordant, and 1 where both DL and SCRA were discordant. All WGM agreed with PFGE. After discrepancy resolution, 80% of the pairs were indistinguishable and 20% were different. A total of 56% of nares results were nonpredictive if negative nares and positive wound cultures are included. Methods agreed 85 to 93% of the time; however, congruence of isolates to a clade was lower. Baseline analysis of types showed that 15 pairs were unique to single patients (30 strains, 38%; 47% of the matching pairs). Twenty-five strains (30%) represented a single clade identical by PFGE, SCRA, and DL, decreasing specificity. Typing method and institutional type frequency are important in assessing MRSA strain relatedness.
authors.affiliation: Pathology and Laboratory Medicine Service, Veterans Affairs Puget Sound Health Care System, Seattle, Washington, USA. jill.clarridge@va.gov
authors.forename: Jill E
authors.initials: JE
authors.lastname: Clarridge
authors.forename: Amanda T
authors.initials: AT
authors.lastname: Harrington
authors.forename: Marilyn C
authors.initials: MC
authors.lastname: Roberts
authors.forename: Olusegun O
authors.initials: OO
authors.lastname: Soge
authors.forename: Kees
authors.initials: K
authors.lastname: Maquelin
mesh_terms: D015373:Bacterial Typing Techniques / Q000379:methods*; D006787:Hospitals, Veterans; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D017720:Molecular Epidemiology / Q000379:methods; D009666:Nose / Q000382:microbiology*; D013203:Staphylococcal Infections / Q000382:microbiology*; D014946:Wound Infection / Q000382:microbiology*; D014947:Wounds and Injuries / Q000382:microbiology*