NONCYTOTOXIC COMBINATIONS OF TOPICAL ANTIMICROBIAL AGENTS WITH CULTURED SKIN SUBSTITUTES

Cultured skin grafts are destroyed more easily than split-thickness sk in grafts by common burn wound organisms, including gram-negative and gram-positive bacteria and fungi. To increase the survival and engraft ment of cultured skin grafts, formulations of antimicrobial agents wer e tested for cytotoxicity to cultured human keratinocytes and fibrobla sts and for activity against common organisms from burn wounds. On the basis of previous studies, a base formulation containing neomycin (40 mu g/ml), polymyxin B (700 U/ml), and mupirocin (40 mu g/ml) was prep ared, to which ciprofloxacin (20 mu g/ml) or norfloxacin (20 mu g/ml) and amphotericin B (0.25 mu g/ml) or nystatin (100 U/ml) were added. T oxicity to cultured human cells was determined by the growth response of cell cultures (n = 6) to each drug combination over 4 days. Activit y against clinical isolates (n = 40) of Staphylococcus aureus, Pseudom onas aeruginosa, other gram-negative bacteria, and Candida spp. was de termined by the wet disc assay. Analysis of variance testing showed no significant differences in the growth of keratinocytes or fibroblasts under control or experimental conditions. Medium without antimicrobia l agents was not effective against any of the 40 microbial strains tes ted. The base formulation was effective against all bacterial strains tested but against none of the fungi, while all experimental formulati ons were effective against all microbial strains tested. These finding s suggest that neomycin, mupirocin, and polymyxin B may be combined wi th a quinolone and an antimycotic agent to provide broad antimicrobial activity for a formulation for topical use with cultured skin on burn s. However, the formulations described here are strictly experimental and are not recommended for clinical use without further evaluation.