Important test?

[ANDANG66]

Hi. I would like to argue that my unknown is a staphylococcus aureus. However, the test results done on sucrose is negative when S. aureus is suppose to be positive. Is this sucrose test an important test to determine that my unknown is definite S. aureus? I am already confused. Please help me.

[MichaelXY]

Don't know if this helps, but I found this.
Capsular Polysaccharide
The majority of clinical isolates of S aureus express a surface polysaccharide of either serotype 5 or 8. This has been called a microcapsule because it can be visualized only by electron microscopy unlike the true capsules of some bacteria which are readily visualized by light microscopy. S. aureus strains isolated from infections express high levels of the polysaccharide but rapidly lose the ability when cultured in the laboratory. The function of the capsule in virulence is not entirely clear. Although it does impede phagocytosis in the absence of complement, it also impedes colonization of damaged heart valves, perhaps by masking adhesins.
http://www.textbookofbacteriology.net/staph.html