Oral Presentation Lorne Infection and Immunity 2013

Secreted scabies mite complement inhibitors promote staphylococcal evasion from phagocytosis (#14)

Pearl M Swe 1 , David J Kemp 1 , Katja Fischer 1
  1. Queensland Institute of Medical Research , HERSTON , QLD, Australia

Staphylococcus aureus  is a versatile and harmful pathogen causing infections ranging from superficial to systematic infections. The ability of S. aureus to quickly develop and maintain resistance to clinically available antibiotics has resulted in the global epidemic of multi-drug resistant strains. In the Australian Aboriginal population, extreme incidences of S. aureus infections are associated with high prevalence of superficial skin infections caused by the scabies mite, Sarcoptes scabiei. Scabies mites cause mechanical infringement by burrowing into the upper epidermis and colonisation of S. aureus in these skin burrows has been reported. The human complement system is an immediate defence against the invading pathogen. As a successful pathogen, S. aureus produces an array of complement evading molecules. Interestingly, scabies mites also produce several families of different protein classes that interfere with various host complement molecules. They are secreted into the mite gut and excreted into the epidermal burrows with the faeces. We propose that scabies mite complement inhibitors create a microenvironment that promotes bacterial survival. Such scabies mite complement inhibitors have been reported to increase the growth of Streptococcus pyogenes in vitro1. Here we investigate the effect of recombinant scabies mite complement inhibitors on staphylococcal in vitro survival. Firstly, we addressed this in whole blood bactericidal assays and showed that two mite complement inhibitors increased the survival and growth of S. aureus in a concentration dependent manner. We have data indicating that these complement inhibitors reduce the opsonisation of S. aureus. Reduced opsonisation resulted in reduced phagocytosis of S. aureus by neutrophils. We subsequently aim to develop an in vivo study in our porcine model; on the influence of scabies mites complement inhibitors on S. aureus survival. We postulate that comprehending the interactions between mite complement inhibitors, bacteria and the host immune factors will foster the development of novel interventions.

  1. Mika A. et al. 2012. PloS NDT 6, e1563