Rapid optical determination of β-lactamase and antibiotic activity

BMC Microbiology

Table 1 S. aureus isolates used in the study and their β-lactamase genotype and phenotype

#	S. aureusisolate	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 Robert L. Skov, Statens Serum Institut (R. L. Skov, unpublished results) and for #16 - #27 by Dr.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^$Special comment – blaZ contained Stop codon or deletion (so non-functional) (R. L. Skov, unpublished results).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.

ISSN: 1471-2180