A multimodel regime for evaluating effectiveness of antimicrobial wound care products in microbial biofilms

Abstract

Microbial biofilms have become increasingly recognized as a cause of wound chronicity. There are several topical antimicrobial wound care products available for use; however, their effectiveness has routinely been demonstrated with planktonic microorganisms. There is no target reference value for antimicrobial effectiveness of wound care products in biofilm models. In addition, data on antimicrobial activity of products in biofilm models are scattered across many test methods in a variety of studies. The aim of this work is to directly compare commercial products containing the commonly used topical antimicrobial agents iodine, silver, polyhexamethylene biguanide, octenidine, hypochlorous acid, benzalkonium chloride, and a surfactant-based topical containing poloxamer 188. Five different in vitro biofilm models of varied complexity were used, incorporating several bacterial pathogens such as Staphylococcus, Enterococcus, Streptococcus, Pseudomonas, Acinetobacter, Klebsiella, and Enterobacter. The fungal pathogens Candida albicans and Candida auris were also evaluated. A multispecies bacterial biofilm model was also used to evaluate the products. Additionally, C. albicans was used in combination with S. aureus and P. aeruginosa in a multikingdom version of the polymicrobial biofilm model. Statistically significant differences in antimicrobial performance were observed between treatments in each model and changing microbial growth conditions or combinations of organisms resulted in significant performance differences for some treatments. The iodine and benzalkonium chloride-containing products were overall the most effective in vitro and were then selected for in vivo evaluation in an infected immunocompromised murine model. Unexpectedly, the iodine product was statistically (P > .05) no different than the untreated control, while the benzalkonium chloride containing product significantly (P < .05) reduced the biofilm compared to untreated control. This body of work demonstrates the importance of not only evaluating antimicrobial wound care products in biofilm models but also the importance of using several different models to gain a comprehensive understanding of products' effectiveness.

Figure 1

CBF Log CFU/membrane values tested at the 100% nutrient level. SA, S. aureus 15981; EF, E. faecalis 51 299; SP, S. pyogenes 49399; PA, P. aeruginosa 15442; AB, A. baumannii BAA‐747; KP, K. pneumoniae BAA‐1705; E. cloacae 35549; CAL, C. albicans 10231; CAU, C. auris B11903. Treatments that share the same letter are not significantly different (P < .05)

Figure 2

Log CFU/membrane values of SA, S. aureus 15981 and PA, P. aeruginosa 15442 tested in the modified drip flow reactor with 40% nutrient. Treatments that share the same letter are not significantly different (P < .05)

Figure 3

Log CFU/explant values of P. aeruginosa PAO1 tested in the porcine explant model. Treatments that share the same letter are not significantly different (P < .05)

Figure 4

Log CFU/biofilm values of LMBM multispecies biofilm containing SA, S. aureus HCMC 6‐1, EF, E. faecium 700 221, and PA, P. aeruginosa PAO1. Treatments that share the same letter are not significantly different (P < .05)

Figure 5

Log CFU/biofilm values of MKL multispecies biofilm containing SA ‐ S. aureus HCMC 6‐1, PA, P. aeruginosa PAO1, and CA, Candida albicans SC3514. Treatments that share the same letter are not significantly different (P < .05)

Figure 6

Log CFU/excision values of SA—S. aureus Xen29 biofilms in nude mice. For 2×, treatments were applied at T0 and T24 hours, then recovered at 48 hours. For 1×, treatments were applied at T0, then recovered at 48 hours. *Treatments are significantly different from untreated control (P < .05)