Table 1.
S. aureus isolates used in the study and their β-lactamase genotype and phenotype
| # | S. aureus isolate | β-lactamase genotype* & (‘ blaZ’ PCR) | β-lactamase phenotype by nitrocefin disk test |
|---|---|---|---|
| 1 |
29213 |
Positive |
+ |
| 2 |
25923 |
Negative |
- |
| 3 |
75391-09 |
Positive |
- |
| 4 |
W5337 |
Negative |
- |
| 5 |
W53156 |
Positive |
- |
| 6 |
AI5070237 |
Positive |
+ |
| 7 |
AI5081845 |
Positive |
- |
| 8 |
159570-08 |
Positive |
- |
| 9 |
H30876 |
Positive |
- |
| 10 |
32455-09 |
Positive$ |
- |
| 11 |
HIP12052 |
Positive |
- |
| 12 |
AI5090298 |
Positive |
- |
| 13 |
F33263-2 |
Positive |
- |
| 14 |
AI5090297 |
Positive |
- |
| 15 |
HIP11033 |
Positive |
- |
| 16 |
HIP11353 |
Positive$ |
- |
| 17 |
158390-08 |
Positive$ |
- |
| 18 |
F52670 |
Positive |
+ |
| 19 |
H63189 |
Positive |
+ |
| 20 |
M24125 |
Positive |
+ |
| 21 |
F20358.1 |
Negative |
- |
| 22 |
H67147.3 |
Positive |
- |
| 23 |
M60028 |
Negative |
- |
| 24 |
KI58249.2 |
Unknown |
- |
| 25 |
M69678 |
Negative |
- |
| 26 |
X33116 |
Positive |
- |
| 27 | F29916-2 | Positive | - |
S. aureus strains 29213 (#1) and 25923 (#2) were obtained from ATCC and the S. aureus clinical isolates (#3 - #27) were provided by Dr. Mary Jane Ferraro (Microbiology Labs, Massachusetts General Hospital, Boston, MA, USA). Isolate numbers (e.g. #1 for 29213, etc) are used to refer to the different isolates throughout the study.
*The β-lactamase genotype was determined by PCR to detect blaZ (staphylococcal β-lactamase gene). Genotype data for isolates #3 - #15 was kindly provided by Dr. Robert L. Skov, Statens Serum Institut (R. L. Skov, unpublished results) and for #16 - #27 by Dr. Mary Jane Ferraro.
&All isolates are MSSA.
$Special comment – blaZ contained Stop codon or deletion (so non-functional) (R. L. Skov, unpublished results).
Nitrocefin disk test to determine β-lactamase production was performed as described in Methods. Development of orange colour uniformly, similar to positive control #1, was taken as positive reaction, indicated by ‘+’ symbols. ‘-’ denotes negative result (i.e. no colour change). The results are representative of three independent experiments, which gave consistent results.