In vitro analysis of interactions between Pseudomonas aeruginosa and Candida albicans treated with silver sulfadiazine in wound infections.

Background: Microorganisms tend to rely on close relationships with other species to survive. Consequently, biofilms formed by interactions of different species have been shown to delay the wound healing process. Studies suggest these mixed-population infections contribute to the development of drug resistance and inhibition of host immune response. Silver sulfadiazine (SSD) has been shown to effectively decrease the risk of infection in an open wound. Typically, these are bacterial wound infections; however, the role of fungal species needs further attention.

Objectives: The purpose of this in vitro study was to determine the effect of SSD on interactions between Pseudomonas aeruginosa 09-009 (PA1) or P. aeruginosa 09-010 (PA2) and Candida albicans ATTC 64550 (CA).

Methods: A mixture of 4 mL of tryptic soy broth (TSB) and 100 µL of CA and/or PA1 or PA2 (∼10⁶ log cfu/mL) inoculums were deposited into either wells or vials. The wells or vials were then sonicated (50 W for 10 s) to separate microorganisms attached to the walls. After incubation, cell counts were performed at 24 and 48 h for each microorganism using specific media.

Results: Our results show that without SSD treatment, P. aeruginosa exhibits an inhibitory effect on C. albicans. Treatment with SSD demonstrated significant reduction of P. aeruginosa; however, C. albicans persisted. This experiment demonstrates that SSD was effective in reducing the bioburden of both P. aeruginosa strains after 24 and 48 h; however, it was not as effective in reducing C. albicans.

Conclusions: The data suggest that for polymicrobial mixed infections containing Pseudomonas spp. and C. albicans, treatment with SSD may be beneficial but does not provide adequate microorganism eradication. As such, added treatments that provide coverage for Candida infection are necessary. Additional in vivo studies are needed to obtain a better understanding of the complex interactions between these organisms.