Figure 1
The percentage of resistance (dark-gray bars) and susceptibility (light-gray bars) observed for 13 antibiotics by disk diffusion test
Table 1
Result of genotypic and phenotypic methods of 50 S. aureus
| Isolate no. | mecA gene | OSA test | Oxacillin MIC | Cefoxitin disk test | Oxacillin disk | β-Lactamase test |
|---|---|---|---|---|---|---|
| SA1 | + | Growth | 128 (R) | Resistant | Resistant | Positive |
| SA2 | − | No growth | 1 (S) | Susceptible | Susceptible | Negative |
| SA3 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA4 | + | Growth | 64 (R) | Resistant | Resistant | Positive |
| SA5 | + | No growth | 8 (R) | Resistant | Resistant | Positive |
| SA6 | − | No growth | 8 (R) | Susceptible | Resistant | Positive |
| SA7 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA8 | − | Growth | 64 (R) | Resistant | Resistant | Positive |
| SA9 | + | Growth | 128 (R) | Resistant | Resistant | Positive |
| SA10 | + | Growth | 36 (R) | Resistant | Resistant | Positive |
| SA11 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA12 | + | No growth | 128 (R) | Resistant | Resistant | Positive |
| SA13 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA14 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA15 | + | Growth | 4 (R) | Resistant | Susceptible | Positive |
| SA16 | + | Growth | 8 (R) | Resistant | Susceptible | Positive |
| SA17 | + | Growth | 64 (R) | Resistant | Resistant | Positive |
| SA18 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA19 | − | No growth | 32 (R) | Resistant | Resistant | Positive |
| SA20 | − | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA21 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA22 | − | Growth | 8 (R) | Susceptible | Resistant | Positive |
| SA23 | − | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA24 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA25 | − | No growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA26 | + | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA27 | − | No growth | 1 (S) | Susceptible | Resistant | Positive |
| SA28 | − | Growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA29 | − | Growth | >128 (R) | Resistant | Susceptible | Positive |
| SA30 | − | No growth | 64 (R) | Susceptible | Susceptible | Positive |
| SA31 | − | Growth | >128 (R) | Resistant | Resistant | Positive |
| SA32 | − | Growth | 32 (R) | Resistant | Resistant | Positive |
| SA33 | − | Growth | 64 (R) | Resistant | Resistant | Positive |
| SA34 | − | Growth | 2 (S) | Susceptible | Susceptible | Positive |
| SA35 | − | No growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA36 | − | No growth | 0.5 (S) | Susceptible | Susceptible | Positive |
| SA37 | + | Growth | 8 (R) | Resistant | Resistant | Positive |
| SA38 | − | No growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA39 | − | Growth | 64 (R) | Resistant | Resistant | Positive |
| SA40 | + | No growth | 16 (R) | Resistant | Susceptible | Positive |
| SA41 | − | No growth | 2 (S) | Susceptible | Susceptible | Positive |
| SA42 | − | No growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA43 | − | Growth | 1 (S) | Susceptible | Susceptible | Positive |
| SA44 | − | No growth | 0.5 (S) | Susceptible | Susceptible | Positive |
| SA45 | − | Growth | 16 (R) | Resistant | Resistant | Positive |
| SA46 | − | Growth | 8 (R) | Resistant | Resistant | Positive |
| SA47 | − | No growth | 0.5 (S) | Susceptible | Susceptible | Positive |
| SA48 | + | Growth | 8 (R) | Resistant | Resistant | Positive |
| SA49 | − | No growth | 2 (S) | Susceptible | Susceptible | Positive |
| SA50 | − | Growth | 2 (S) | Susceptible | Resistant | Positive |
[i] OSA, oxacillin screen agar; MIC, minimum inhibitory concentration; R, resistance; S, susceptible; +, positive; −, negative.
Figure 2
Receiver operating characteristics (ROCs) for (A) cefoxitin disk diffusion (CFD), (B) minimum inhibitory concentration (MIC), (C) oxacillin disk diffusion (OD), and (D) oxacillin screen agar (OSA) illustrate area under the curve (AUC) statistics
Table 2
Comparison of phenotypic methods for the detection on methicillin resistance in S. aureus
| Phenotypic methods | No. of isolates showing mecA MRSA (n = 21) | No of isolates showing non-mecA MSSA (n = 29) | Statistical analysis (%) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| No. of true positive isolates | No. of false negative isolates | No. of true negative isolates | No. of false positive isolates | SN | SP | PPV | NPV | AUC | |
| OSA | 18 | 3 | 14 | 15 | 86 | 48 | 54.54 | 83.35 | 64 |
| MIC | 21 | 0 | 15 | 14 | 100 | 52 | 60 | 100 | 72 |
| OD | 18 | 3 | 15 | 14 | 86 | 52 | 56.25 | 83.3 | 66 |
| CFD | 21 | 0 | 18 | 11 | 100 | 62 | 65.6 | 100 | 78 |