Analysis Characterizes Common Wound Microbes in Epidermolysis Bullosa

Christine Kilgore

January 06, 2021

Wound cultures from patients with the rare disease epidermolysis bullosa (EB) were most frequently positive for Staphylococcus aureus (SA), Pseudomonas aeruginosa (PA), and Streptococcus pyogenes (GAS) — and antibiotic resistance was common — in a retrospective analysis of over 700 wound cultures from 158 patients across the United States and Canada.

The findings from the EB Clinical Characterization and Outcomes Database speak to the value of surveillance cultures with routine testing for microbial resistance – including mupirocin resistance — and to the importance of antibiotic stewardship not only for oral antibiotics but for topicals as well, according to Laura E. Levin, MD, and Kimberly D. Morel, MD, of the departments of dermatology and pediatrics, Columbia University Irving Medical Center, New York, the lead and senior authors, respectively, of the paper recently published in Pediatric Dermatology.

Almost all of the 158 patients with at least one wound culture recorded in the database from the period of 2001-2018 had one or more positive culture results. Of 152 patients with positive cultures, 131 (86%) were positive for SA and 56 (37%) and 34 (22%) were positive for PA and GAS, respectively. Other bacteria isolated included Corynebacterium spp and Proteus spp. Nearly half (47%) of patients with SA-positive cultures had methicillin-resistant SA, and 68% had methicillin-susceptible SA. (Some patients grew both MSSA and MRSA at different points in time.)

Mupirocin-susceptibility testing was performed at only some of the 13 participating centers. Of 15 patients whose cultures had recorded SA mupirocin-susceptibility testing, 11 had cultures positive for mupirocin-susceptible SA and 6 (40%) had mupirocin-resistant SA isolates (2 patients grew both). Of these six patients, half had isolates that were also methicillin-resistant.

Mupirocin, a topical antibiotic, has been a cornerstone of decolonization regimens for MSSA and MRSA, but resistance has been demonstrated in other research as well and is not specific to EB, wrote Levin, Morel, and coauthors.

"Pediatric dermatologists often rely on topical antimicrobials in the treatment of patients' open wounds to both prevent and treat infection, depending on the clinical scenario," and surveillance cultures with routine testing for mupirocin resistance can help guide antibiotic choice and management strategies, Levin said in an interview.

More broadly, she added, "it's helpful to know what bacteria are routinely colonizing wounds, not causing infection, versus those that are more likely to be associated with infection, chronic wounds, or the risk of developing skin cancer ... [to know] which wounds need to be treated more aggressively."

A subset of patients with EB have been known to be at risk for squamous cell carcinoma, and research is implicating certain bacteria "as contributing to wound inflammation," Morel said in an interview.

SCC was reported in 23 out of 717 patients in the database — but fewer than half of the patients with SCC had recorded wound cultures. The small numbers precluded the identification of microbes that may confer significant risk.

Correlating particular microbes with clinical features also will take more research. About half (57%) of the patients with recorded wound cultures had wounds with purulent exudate or other features of clinical infection. However, the presence or absence of clinical signs of infection was not temporally correlated with culture results in the database.

The 158 patients with recorded wound cultures had a mean age of 12.8 years and represented a range of EB subtypes.

PA was present in the wounds of patients as young as 1 month old, the authors noted. Investigators are "looking to further study PA and characterize clinical features ... to understand more about this microbe and its impact on patients with EB," Morel said.

In the meantime, the analysis reaffirms the importance of antibiotic stewardship. Mupirocin is labeled to be used three times a day for a short period of time, but "tends to be prescribed and used less judiciously than intended," Morel said. "It's important [not to overuse it]. We have seen that patients' culture results become sensitive to mupirocin again in the future when they avoid it for a period of time."

The work was supported by the EB Research Partnership and EB Medical Research Foundation, as well as an NIH/NCATS grant. No investigator disclosures were listed.

SOURCE: Pediatr Dermatol. 2020 Nov 28. doi: 10.1111/pde.14444.

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