Staphylococcus aureus Bacteraemia: A Hidden Factor in the Pathogenesis of Human Disease

Chronic low grade inflammation is a pathogenic factor in a range of common conditions including atherosclerosis, Alzheimer’s disease, diabetes mellitus, depression and obesity. Staphylococcus aureus is a prime candidate as a causative factor of chronic inflammation because carriage is common, the organism is potentially invasive and many strains produce superantigens which induce a non-specific non-targeted inflammatory response. The majority of adults has measurable serum IgG antibodies to these common superantigens (pyrogenic toxins) and since they are only produced in significant amounts at body heat or above this indicates that invasion is common and recurrent throughout life. Staphylococcal toxins are found in the urine of some adults with chronic disease but always in association with specific anti-toxin IgG. The most likely explanation is that immune complexes form in the circulation and are actively secreted (not passively filtered) into the urine. The diagnostic approach in patients with chronic low grade inflammation should be to measure urinary IgG and quantify faecal staphylococcal carriage. Establishing a causal relationship will then depend on reducing staphylococcal carriage and noting a reduction in inflammatory markers and an improvement in clinical symptoms. There is theoretical and experimental evidence to indicate that the consumption of natural yoghurt will reduce staphylococcal carriage in the oropharynx and oesophagus, which are potential sites for amplifying nasopharyngeal carriage. Thus long term yoghurt consumption is a possible preventive factor in human disease.