New Molecular Techniques to Study the Skin Microbiota of Diabetic Foot Ulcers

Abstract

Significance: Diabetic foot ulcers (DFU) are a major and growing public health problem. They pose difficulties in clinical practice in both diagnosis and management. Bacterial interactions on the skin surface are important in the pathophysiology of DFU and may contribute to a delay in healing. Fully identifying bacteria present in these wounds is difficult with traditional culture methods. New molecular tools, however, have greatly contributed to our understanding of the role of the cutaneous microbiota in DFU. Recent Advances: Molecular technologies revealed new information concerning how bacteria are organized in DFU. This has led to the concept of "functionally equivalent pathogroups," meaning that certain bacterial species which are usually nonpathogenic (or at least incapable of maintaining a chronic infection on their own) may coaggregate symbiotically in a pathogenic biofilm and act synergistically to cause a chronic infection. The distribution of pathogens in multispecies biofilms is nonrandom. The high bacterial diversity is probably related to the development of a microbial biofilm that is irreversibly attached to the wound matrix. Critical Issues: Using molecular techniques requires a financial outlay for high-cost equipment. They are still too time-consuming to perform and reporting is too delayed for them to be used in routine practice. Finally, they do not differentiate live from dead or pathogenic from nonpathogenic microorganisms. Future Directions: Molecular tools have better documented the composition and organization of the skin flora. Further advances are required to elucidate which among the many bacteria in the DFU flora are likely to be pathogens, rather than colonizers.

Jean-Philippe Lavigne, MD, PhD

Figure 1.

Overview of currently available techniques to characterize the skin microbiota in diabetic foot ulcers. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/wound

Figure 2.

Factors influencing delayed wound healing. The presence of biofilm and abundant leukocytes surrounding the biofilm prevent the healing of the wounds. Moreover, the balance of proteases produced by inflammatory cells also damage normal and healing tissues and immune cells, adversely affecting healing (adapted from Phillips et al.). To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/wound

Figure 3.

Displayed are the three main groups of microorganism comprising the skin flora, as demonstrated by PCA. The axes represent the values for principal components 1, 2, and 3. Points lying in the negative portion of an axis indicate a negative correlation between the principal component and the sample. Organisms found on intact skin are shown in blue, while those from wounds are shown in red. The ability to linearly separate the classes within the PCA figures indicates that bacteriology of intact skin differs from that of wounds (adapted from Gontcharova et al.). PCA, principal component analysis. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/wound

Figure 4.

The nMDS ordination plot comparing wound bacterial communities from antibiotic-treated versus untreated participants. Each data point represents the bacterial community identified from a single wound specimen. Comparison by the multiresponse permutation procedure demonstrated a significant difference in wound microbiota between antibiotic-treated and untreated patients (p=0.0069) (adapted from Price et al.). DM, diabetes mellitus; nMDS, nonmetric multidimensional scaling. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/wound

Figure 5.

Principles of wound biofilm formation and management.