Table 6.

Characteristics of the four strains resistant to oxacillin but negative for mecA by PCR

StrainsOxacillin MIC (μg/ml)Nitrocefin test resultDisk diffusion test result (mm) amoxicillin with clavulanic acidablaZ (PCR detection)
S. aureusR6204+24.0+
S. aureus R6268+22.0+
S. aureus R6274+24.5+
S. aureusSTA5728+23.3+
S. aureus ATCC 43300b64+15.2+
S. aureus ATCC 25923b128.3
  • a Strains were considered β-lactamase hyperproducers when (i) the diameter of the inhibition zone with the amoxicillin-clavulanic acid (20 and 10 μg, respectively) disk exceeded 20 mm and (ii) they were resistant to oxacillin (2).

  • b S. aureus ATCC 43300 is a nonhyperproducing strain carrying mecA, while S. aureus ATCC 25923 is a β-lactamase-negative strain not carrying mecA.