title: Production of 2-aminophenoxazin-3-one by Staphylococcus aureus causes false-positive results in β-galactosidase assays.
abstract: Staphylococcus aureus can be distinguished from similar coagulase-positive staphylococci by its absence of β-galactosidase activity. This is commonly tested using o-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.
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong.
authors.forename: Herman
authors.initials: H
authors.lastname: Tse
authors.forename: Elaine
authors.initials: E
authors.lastname: Chan
authors.forename: Ching-Wan
authors.initials: CW
authors.lastname: Lam
authors.forename: Ka-Fai
authors.initials: KF
authors.lastname: Leung
authors.forename: Pat
authors.initials: P
authors.lastname: Chow
authors.forename: Kim-Chung
authors.initials: KC
authors.lastname: Lee
authors.forename: Kong-Hung
authors.initials: KH
authors.lastname: Sze
authors.forename: Stanley K K
authors.initials: SK
authors.lastname: Cheung
authors.forename: Man-Kit
authors.initials: MK
authors.lastname: Tse
authors.forename: Pak-Leung
authors.initials: PL
authors.lastname: Ho
authors.forename: Sze-Pui
authors.initials: SP
authors.lastname: Leung
authors.forename: Susanna K P
authors.initials: SK
authors.lastname: Lau
authors.forename: Patrick C Y
authors.initials: PC
authors.lastname: Woo
authors.forename: Kwok-Yung
authors.initials: KY
authors.lastname: Yuen
mesh_terms: D000818:Animals; D005189:False Positive Reactions; D005697:Galactosides / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000378:metabolism; D009598:Nitrophenylgalactosides / Q000378:metabolism; D010078:Oxazines / Q000378:metabolism*; D013203:Staphylococcal Infections / Q000175:diagnosis / Q000662:veterinary; D013211:Staphylococcus aureus / Q000201:enzymology* / Q000302:isolation & purification / Q000378:metabolism*; D001616:beta-Galactosidase / Q000032:analysis*
chemical_list: D005697:Galactosides; D007211:Indoles; D010078:Oxazines; C005512:3-aminophenoxazone; C055012:2-nitrophenylgalactoside; D009598:Nitrophenylgalactosides; D001616:beta-Galactosidase; C044888:5-bromo-4-chloro-3-indolyl beta-galactoside