Nonrandom Distribution of Pseudomonas aeruginosa and Staphylococcus aureus in Chronic Wounds

Abstract

The spatial organization of Pseudomonas aeruginosa and Staphylococcus aureus in chronic wounds was investigated in the present study. Wound biopsy specimens were obtained from patients diagnosed as having chronic venous leg ulcers, and bacterial aggregates in these wounds were detected and located by the use of peptide nucleic acid-based fluorescence in situ hybridization and confocal laser scanning microscopy (CLSM). We acquired CLSM images of multiple regions in multiple sections cut from five wounds containing P. aeruginosa and five wounds containing S. aureus and measured the distance of the bacterial aggregates to the wound surface. The distance of the P. aeruginosa aggregates to the wound surface was significantly greater than that of the S. aureus aggregates, suggesting that the distribution of the bacteria in the chronic wounds was nonrandom. The results are discussed in relation to our recent finding that swab culturing techniques may underestimate the presence of P. aeruginosa in chronic wounds and in relation to the hypothesis that P. aeruginosa bacteria located in the deeper regions of chronic wounds may play an important role in keeping the wounds arrested in a stage dominated by inflammatory processes.

The Limitations of In Vitro Experimentation in Understanding Biofilms and Chronic Infection

“…As mentioned previously, bacteria are capable of occupying different ecological niches within a wound environment [42]. Growth of different methicillin-resistant Staphylococcus aureus (MRSA) strains on porcine nasal epithelium tissue resulted in three different growth profiles, highlighting the need to select strains with clinical relevance [137].…”

“…The milieu of species within a defined space may result in cooperation and/or conflict with other community members [37][38][39]. This creates a complex environment where species align along different nutrient gradients, be those host derived or the result of species interactions, as seen between P. aeruginosa and Staphylococcus aureus in chronic wounds [40][41][42]. The complexity of interactions between species may be enhanced through the production of diverse QS signals within the infection site, which have inter-and intra-species effects, although this is yet to be demonstrated in vivo [43][44][45].…”

“…Conversely, Kirketerp-Moller and colleagues (2008) [5] struggled to identify multiple species during a venous leg ulcer study, highlighting the diversity and complexity of different types of chronic infection. For instance, P. aeruginosa is known to grow in the deeper recesses of chronic leg ulcers, compared to S. aureus, which is found on the surface [42]. This non-random distribution suggests some species, especially anaerobes in deep recesses, will be missed if the wrong sampling method is employed.…”

Influence of Microorganisms on the Healing of Skin Grafts from Chronic Venous Leg Wounds

“…1) . S. aureus was primarily located close to the wound surface while P. aeruginosa was primarily located deeper in the wound (Fazli et al, 2009). Some bacterial species were present all over the chronic venous leg ulcer while some were only present in parts of the wounds .…”

“…by Fazli et al, 2009;Kirketerp-Moller et al, 2008¸Wolcott et al, 2009. Using qPCR and FISH it has been illustrated that the number of the pathogens S. aureus and P. aeruginosa varied depending on the location and depth of the wound examined ( Fig.…”