LONDON – Disrupting how microorganisms communicate with each other could be a way to overcome antibiotic resistance and to help heal chronic wounds in patients with epidermolysis bullosa (EB), according to presenters at the EB World Congress, organized by the Dystrophic Epidermolysis Bullosa Association (DEBRA).
The majority of chronic wounds in patients with EB are colonized with microorganisms, with a predominance of Staphylococcus species, said Erik Gerner, an industrial PhD student at Mölnlycke Health Care in Gothenburg, Sweden, and Gothenburg University.
Because of the growing problem of antibiotic resistance, alternative treatments are needed, and one possible alternative for treating infected wounds could be interfering with quorum sensing, the cell-to-cell communication used by bacteria, he said. He is hoping to explore this possibility as a novel treatment strategy for infected wounds.
“Quorum sensing is defined as the ability to detect and respond to population density,” Mr. Gerner said, noting that, when there is a sufficient density of bacteria, “they start to communicate with each other.” This enables them to act as a community and perform actions that they could not do as individual cells. Such actions include forming biofilms, which helps protect bacteria from their environment, such as the immune system. Other actions include collectively switching on the production of virulence factors and becoming resistant to treatments.
“Bacteria use quorum sensing to act collectively,” Mr. Gerner said. “If we could shut down this quorum sensing system, it would be very beneficial … and increase the chances to heal the wound.”
The quorum sensing system is based on the production of signaling molecules called AHL (N-acyl homoserine lactones), which are constantly produced at a low rate. This isn’t a problem until the level of bacteria increases and the level of quorum sensing breaches a threshold, he explained.
There are several benefits of inhibiting bacterial communication through disrupting quorum sensing, namely, “a low risk of resistance,” Mr. Gerner said. There is also potentially less toxin production by bacteria, and this could help the immune system in killing the invading bacteria.
One approach to disrupting quorum testing that Mr. Gerner has been investigating is the use of sodium salicylate (NaSa). So far, preclinical work shows that NaSa can reduce toxin production but not the growth rate of bacteria. The advantage of using NaSa is that it is nontoxic to human dermal fibroblasts, with similar results seen in human keratinocytes and immune cells. His work to date has shown that NaSa reduced activity of NF-kB (a proinflammatory signaling pathway) in differentiated and lipopolysaccharide-stimulated monocytes; NF-kB activated production of proinflammatory cytokines (such as interleukin-1 beta and IL-6) are elevated in EB wounds. “My studies support the bodies of evidence that bacteria use quorum sensing to coordinate … and to produce a large number of toxic factors,” Mr. Gerner concluded. Future studies will look at the potential of NaSa to disrupt this activity.
Skin microbiome of EB wounds
Liat Samuelov, MD, of the department of molecular dermatology at Tel Aviv (Israel) Sourasky Medical Center, presented data on skin microbiome characteristics in eight patients with recessive dystrophic EB (RDEB). This showed that there was reduced bacterial diversity in wounds, and a “progressive development of dysbiosis across different stages of DEB wound formation.”
The skin microbiome has been implicated in several skin diseases, Dr. Samuelov and associates observed in a poster presentation. That includes the autoimmune blistering disease bullous pemphigoid (Exp Dermatol. 2017 Dec;26[12]:1221-7). “Colonization of DEB chronic wounds may lead to systemic infections, result in delayed healing, and possibly be involved in the development of squamous cell carcinoma,” they noted in the poster, “thus accurate delineation of the dysbiotic profile … may point to corrective measures of great therapeutic potential.”
The aim was to see what microorganisms were present in the chronic wounds of the patients. To be included in the study, patients must not have had any antibiotic treatment – oral or topical – in the past 6 months. Samples were taken from an untreated wound, around the wound, and from uninvolved skin, which were compared with samples taken from similar areas in age-matched controls.
Reduced bacterial diversity was observed in RDEB wounds, compared with uninvolved or perilesional areas and the skin of control subjects, Dr. Samuelov said in an oral presentation of the study results. There was increased abundance of Staphylococcus epidermidis and decreased Cutibacterium acnes, which she noted was in contrast to other studies where S. aureus was the most common colonizer in RDEB wounds.
Bacterial composition in each group was calculated using the beta-diversity score, while control samples showed similar microbial composition, the DEB samples had no microbial similarities among different samples. These data “suggest the need to ascertain the potential therapeutic benefit of interventions aimed at restoring normal microbiome composition in DEB,” Dr. Samuelov concluded.
Wound colonization and squamous cell carcinoma
Other research on wound microbiology was presented by Laura E. Levin, MD, a dermatologist at New York–Presbyterian, and associates. “Given the potential role of bacteria-induced inflammation in the development of wound-associated SCC [squamous cell carcinoma] in a subset of patients, we sought to improve our understanding of what microbes colonize and infect the wounds of patients with epidermolysis bullosa,” they explained in their poster.
SCC survival remains poor in epidermolysis bullosa
The researchers, from New York–Presbyterian Morgan Stanley Children’s Hospital and Columbia University Irvine Medical Center, New York, presented data from a retrospective analysis of 739 wound cultures taken between 2001 and 2017 from 158 patients enrolled in the Epidermolysis Bullosa Clinical Characterization and Outcomes Database. In the analysis, just under 70% of patients had DEB, of which 90% were of the RDEB subtype; 13% had EB simplex, 14% had junctional EB, and 3% had an unknown EB subtype.
At least one organism grew in 87% of cultures, with the most common microorganism isolated being Staphylococcus aureus (84% of cultures). Other commonly isolated microbes were Pseudomonas aeruginosa in 35% of cultures, Streptococcus group A in 34% of cultures (of which 22% were Streptococcus pyogenes), Corynebacterium species in 31% of cultures, and Proteus species in 18% of cultures.
“Improved understanding of what microbes are colonizing the wounds of our patients may help improve antibiotic stewardship,” the researchers stated.
Looking at the antibiotic susceptibilities, Dr. Levin and associates found that 68% of 115 cultures were sensitive to methicillin and 60% of 15 cultures were sensitive to mupirocin. “Resistance to many systemic and topical antibiotic agents in EB patients supports surveillance cultures with routine testing for mupirocin susceptibility,” they suggested.
A total of 23 patients developed SCC of whom 10 had cultures that grew S. aureus (90%) and P. aeruginosa (50%), and Proteus species (20%). Among the patients who did not develop SCC, the respective cultures positive for each of those microorganisms were 83%, 34%, and 11%. Perhaps “gram-negative and flagellated organisms may be more common in wounds of patients at risk for SCC,” they observed, adding that further studies were needed to determine if “wound microbiome interventions inhibit the risk of development of SCC and improve outcomes.”
Mr. Gerner’s research is supported by Mölnlycke Health Care. Dr. Samuelov had no disclosures. The work by Dr. Levin and associates is supported by the Pediatric Dermatology Research Alliance, EB Research Partnership, and the Epidermolysis Bullosa Medical Research Foundation.