Open AccessProduction of 2-Aminophenoxazin-3-one by Staphylococcus aureus Causes False-Positive Results in β-Galactosidase Assays
Author(s) -
Herman Tse,
Elaine Chan,
Ching-Wan Lam,
Ka-Fai Leung,
Pat Chow,
Kim-Chung Lee,
KongHung Sze,
Stanley K. K. Cheung,
ManKit Tse,
PakLeung Ho,
Sze-Pui Leung,
Susanna K. P. Lau,
Patrick C. Y. Woo,
KwokYung Yuen
Publication year - 2012
Publication title -
journal of clinical microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.349
H-Index - 255
eISSN - 1070-633X
pISSN - 0095-1137
DOI - 10.1128/jcm.02299-12
Subject(s) - staphylococcus aureus , micrococcaceae , microbiology and biotechnology , coagulase , staphylococcus , biology , positive control , bacteria , medicine , genetics , traditional medicine
Staphylococcus aureus can be distinguished from similar coagulase-positive staphylococci by its absence of β-galactosidase activity. This is commonly tested usingo -nitrophenyl-β-d -galactopyranoside (ONPG) as the substrate. Unexpectedly, 111 and 58 of 123 isolates displayed apparent β-galactosidase activity in the ONPG assay and on the Vitek 2 system, respectively. Compositional analysis showed that the yellow coloration of the positive ONPG assay resulted from production of 2-aminophenoxazin-3-one. Alternative β-galactosidase substrates like X-Gal (5-bromo-4-chloro-3-indolyl-β-d -galactopyranoside) should be used for testing staphylococci.
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