TABLE 2.

Oxacillin, nafcillin, and cefoxitin MICs for wild-type and mutant strainsa

StrainPFGE serotypeMIC (μg/ml)
OXANAFFOX
MW2 (USA400) (wild type)USA400641664
MW2 Δpbp3USA400641664
MW2 Δpbp4cUSA400 4 1 64
MW2 Δpbp3/4cUSA400 4 1 64
MW2 Δpbp4::pbp4USA400641664
MW2 exbUSA4001281616
MW2 ex Δpbp3USA4001281632
MW2 ex Δpbp4cUSA400 2 1 16
MW2 ex Δpbp3/4cUSA400 1 1 32
USA300 (wild type)USA300641664
USA300 Δpbp4USA300 4 1 64
USA300 Δpbp4::pbp4cUSA300641664
COL wild-typeUSA50025664128
COL Δpbp3USA50025664128
COL Δpbp4USA50025664128
COL Δpbp3/4USA50025664128
N315 (wild type)USA1002566464
N315 Δpbp4USA1001286464
Mu50 (wild type)USA100256256256
Mu50Δpbp4USA100256256256
  • a Determinations of MICs of oxacillin, nafcillin, and cefoxitin for parental and isogenic pbp mutants were performed according to CLSI (formerly NCCLS) protocols. Bacteria, grown to an OD650 of 1, were added to CSMHB to a final concentration of 5 × 105 CFU/ml.

  • b MW2 ex, MW2 cured of plasmid pMW2.

  • c pbp4 is essential for β-lactam resistance in CA-MRSA strains MW2 and USA300 but not in HA-MRSA COL, N315, and Mu50 (MRSA/VISA) (as shown bolded and highlighted).