Microbial colonization of an in vitro model of a tissue engineered human skin equivalent--a novel approach

This was a preliminary investigation to define the conditions of colonization of a human skin equivalent (SE) model with cutaneous microorganisms. SEs of 24 mm diameter were constructed with a dermal matrix of fibrin containing fibroblasts and a stratified epidermis. Microbial colonization of the SEs was carried out in a dry environment, comparable to 'in vivo' skin, using a blotting technique to remove inoculation fluid. The microbial communities were sampled by scrub washing and viable cells enumerated on selective growth medium. Staphylococcus epidermidis, Propionibacterium acnes and Malassezia furfur (human skin commensals) and Staphylococcus aureus (transient pathogen) were colonized at inoculum densities of 10(2)-10(6) CFU SE(-1) on the surface of replicate SEs. Growth of all species was supported for upto 72-120 h, with recovery densities of between 10(4)-10(9) CFU SE(-1). A novel, real-time growth monitoring method was also developed, using S. aureus containing a lux cassette. Light output increased from 20 to 95 h, and colonization increased from 10(2) to 10(8) CFU SE(-1), as confirmed by conventional recovery. Thus, the SE model has potential to investigate interactions between resident and transient microbial communities with themselves and their habitat, and for testing treatments to control pathogen colonization of human skin.