Staphylococcus aureus serodiagnosis

Infection with S. aureus effects the production of specific antibodies against extracellular products,the most important of which is the alpha haemolysin (staphylolysin O). In parallel, testing is also performed to detect antibodies to the nuclease enzyme which is produced by most strains of S. aureus.
Under normal circumstances, serum samples are processed once weekly (usually Mondays) and the turnaround time is 7 working days.
A volume of 200ul serum is required; please do not send whole blood. Contaminated, fatty and/or haemolysed samples give erroneous results and will not be assayed. Samples should be sealed with parafilm not sellotape, securely wrapped in cotton wool, placed in a plastic bag and packaged in a box according to the Post Office regulations.

Anti-staphylolysin Test

Basis: Inhibition by anti-staphylolysin of the haemolysis of erythrocytes by staphylolysin.

Clinical usefulness and limitations.
The detection of antibodies to S. aureus in patients suspected of having a staphylococcal infection is problematic and no single test is satisfactory.
The anti-staphylolysin test has mainly been used for the diagnosis of chronic osteomyelitis where about 65% of cases give raised titres. Elevated titres are also evident in joint infections (Taylor et al. J. Clin. Pathol. (1975; 28; 284-288).
The normal range is up to and including 2 units/ml. A titre of 2-4 units/ml indicates that further testing is required. Titres of 4 and 4-6 units /ml are suggestive of staphylococcal infection. Titres of 8 and >8 units/ml are indicative of infection.
A single determination may be of little significance. Serial titrations at bi-weekly intervals 4-6 weeks following infection yield more pertinent information.

Anti-nuclease Test

Basis: The anti-nuclease test measures antibody to nucleases common to all strains of S. aureus. Nuclease deploymerises DNA; patient's antibody inhibits activity of the enzyme.

Clinical usefulness and limitations.
Anti-nuclease titres are generally raised in staphylococcal osteomyelitis, and the test gives fewer false positives in bone TB than the alpha-lysin (Taylor et al, 1975).
The normal range is up to and including 4 unit/ml. Titres of 8 and 16 indicate that further testing is required. A titre of 32 units/ml is suggestive of staphylococcal infection. Titres of 64 and 128 units/ml are indicative of infection.

Last reviewed: 23 July 2009