TABLE 2.
Characteristics of 16 S. aureus strains misclassified as oxacillin susceptible by at least one of the susceptibility testing methods
| Isolate | Resultc of indicated reference method
|
Result of indicated oxacillin susceptibility testing method
|
|||||
|---|---|---|---|---|---|---|---|
| mecA PCR | Oxacillin agar screen | Disk diffusion | E-test (MIC [μg/ml]) | Rapid ATB Staph | ATB Staph | Vitek | |
| 7079 | R | S | Ra | 0.38 | S | S | S |
| 6710 | R | S | Ra | 1 | S | S | S |
| 5295 | R | R | Rb | 1.5 | S | S | S |
| 5401 | R | R | Rb | 4 | S | S | R |
| 7741 | R | R | Ra | 6 | S | S | R |
| 8879 | R | R | Rb | 6 | S | R | R |
| 1638 | R | R | Rb | 6 | S | R | R |
| 7394 | R | R | Rb | 8 | S | R | R |
| 6019 | R | R | R | 12 | S | S | R |
| 5839 | R | R | Ra | 16 | S | R | R |
| 2471 | R | R | R | 16 | S | R | R |
| REFd | R | R | Rb | 16 | S | R | R |
| 760 | R | R | R | 24 | S | R | R |
| 6229 | R | R | R | 24 | S | R | R |
| 3902 | R | R | R | 32 | S | R | R |
| 5490 | R | R | Rb | >256 | R | S | R |
a
Strain had a susceptible zone of inhibition (≥20 mm with the 5-μg oxacillin disk) but had colonies within the zone (heteroresistance).
b
Strain had a resistant zone of inhibition (<20 mm with the 5-μg oxacillin disk) and had colonies within the zone (heteroresistance).
c
R, resistant; S, susceptible.
d
REF, low-level-expression strain ATCC 43300.