Impact of Strain Typing Methods on Assessment of Relationship between Paired Nares and Wound Isolates of Methicillin-Resistant Staphylococcus aureus

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

Characterization of community-associated Staphylococcus aureus

We evaluated the epidemiological and molecular features of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and methicillin-sensitive S. aureus (MSSA) from children and adult patients with skin and soft-tissue infections (SSTIs) in China. Prospective community-acquired S. aureus SSTI surveillance was conducted in 23 hospitals over a 24-month period. Susceptibility to 16 antimicrobials was evaluated using the agar dilution method. StatApriori was used to determine statistically significant association trends. The genotypic characteristics of CA-MRSA isolates were tested by staphylococcal cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing, and multilocus sequence typing. The presence of Panton–Valentine leukocidin (pvl) genes was determined. Overall, 71.6% (1946/2716) of cases were community-associated S. aureus. CA-MRSA accounted for 2.6% (51). Out of 1895 methicillin-sensitive S. aureus strains, 97.3% were resistant to erythromycin, 96.6% to penicillin and 89.1% to clindamycin. No S. aureus strains were resistant to vancomycin. Thirteen sequence types (STs) and 17 spa types were detected among the CA-MRSA strains. The most prevalent sequence type was ST121 (19/51, 37.3%), followed by ST59 (13/51, 25.5%). In addition, t437 was predominant, accounting for 43.1% (22/51). Only five (9.8%) of the CA-MRSA strains harbored pvl genes. There were no significant differences in antibiotic sensitivity profiles between ST121 and non-ST121 MRSA isolates. However, ST121 strains tended to be more resistant to cefazolin, whereas non-ST121 strains were more resistant to chloramphenicol. In conclusion, CA-MRSA infections are rare among Chinese SSTI patients. MRSA strains in China have diverse genetic backgrounds, with ST121 being the predominant clone. Fusidic acid and mupirocin remain effective for topical treatment