P39 Bacterial colonization in ex vivo wounds showing a heterogeneous distribution pattern

Abstract Introduction and aims Human skin supports a complex ecosystem, with Staphylococcus epidermidis being the predominant commensal. The skin microbiome is gaining attention for its role in maintaining skin health, whereas its imbalance being a feature of various skin diseases, like atopic dermatitis, psoriasis and acne vulgaris. Chronic wounds are associated with reduced microbial diversity and an increase of colonization of pathogenic bacteria such as Staphylococcus aureus or Pseudomonas aeruginosa. Most studies examining the skin microbiome use swabs or tape strips followed by genetic analysis, therefore no spatial information is obtained. This study examines skin bacteria growing on human skin wounds, to better understand the localization and interaction with host tissue. Methods Human skin excised as surgical discard was used to establish ex vivo wounds, which were then incubated with commensal (S. epidermidis and Staphylococcus hominis) and pathogenic bacteria methicillin-resistant Staphylococcus aureus (MRSA) and Acinetobacter baumannii for 48 h. The tissue was analysed by scanning electron microscope (SEM) (n = 4), histology, wholemount antibody staining (n = 5) and fluorescence in situ hybridization to determine the distribution of bacteria within the wounds and interaction of bacteria with host tissue. Results The commensal strains did not form large colonies when grown in human wounds, although individual bacteria could be detected adhered to wounds. On the other hand, MRSA and A. baumannii grew readily on the wounds. The localization of pathogenic bacteria was surprisingly heterogeneous, with regions showing full colonization and other areas devoid of bacteria. Analysis by SEM revealed that the A. baumannii appears to adhere mostly to collagen fibres within the wounds. Conclusions Our data reveal an intriguing heterogeneity in the colonization of pathogens in human wounds that were infected ex vivo, although further work will be needed to identify the reasons for this, or determine whether this is replicated in vivo.