52 Developing a Topical Antibiogram in the Burn Unit

Abstract

Abstract Introduction Antibiograms display susceptibilities based on bacterial growth in response to systemic agents, utilizing automated systems performing bacterial identification and susceptibility testing. There is a paucity of literature regarding burn-specific antibiograms or susceptibility testing of organisms isolated from wound cultures against topical antimicrobials. Our goal was to create an institutional topical antimicrobial antibiogram in burn and dermatologic disorder patients. Methods Institutional topical antimicrobial agent susceptibilities were retrospectively reviewed from 1/1/18-12/31/18. Quantitative biopsies or swabs collected from patients were cultured. Susceptibility plates were prepared by wells aseptically punched into an agar plate and inoculated with antimicrobial creams. Bacterial isolates were then inoculated in melted agar, overlaid onto the susceptibility dish, and incubated. Zones of inhibition (ZOI) were reported in mm; susceptible being any measurable zone and resistant defined as a zone of 0 mm. Isolated organisms were grouped as Gram-positive cocci (GPC), Gram-negative rods (GNR), or yeast-like fungi (YLF). Results In 2018, 21 organisms were tested for susceptibility in 19 patients with positive cultures. Overall susceptibilities of isolates were 71–91%. Overall, susceptibility rates were: gentamicin 71%, mupirocin 77%, silver sulfadiazine 77%, and mafenide 91%. All C. albicans isolates were susceptible to nystatin. Excluding resistant isolates, the median (IQR) ZOI measurements were: gentamicin 10.0 (7.0, 15.0), mupirocin 12.0 (7.5, 27.0), silver sulfadiazine 8.0 (7.0, 10.5), and mafenide 14.5 (10.3, 19.8). Of organisms reported, there were 10 GNR (45%), 8 GPC (36%), and 4 YLF (18%), with P. aeruginosa, MRSA, and C. albicans being most common. For GPC, susceptibility rates were 63–88% and median (IQR) ZOI measurements were: gentamicin 16.0 (8.0, 30.0), mupirocin 27.0 (9.8, 35.5), silver sulfadiazine 10.0 (8.5, 19.0), and mafenide 15.0 (10.0, 22.0). For GNR, susceptibility rates were 70–90% and median (IQR) ZOI measurements were: gentamicin 10.0 (6.0, 11.0), mupirocin 12.0 (7.0, 18.0), silver sulfadiazine 7.5 (7.0, 9.5), and mafenide 15.0 (13.0, 19.0). Conclusions Based on susceptibility profiles of isolated organisms, mafenide appears to be an appropriate first-line empiric agent with an overall susceptibility rate greater than 90% and the largest ZOI amongst topical agents tested. When examining GPC, mupirocin demonstrated the largest ZOI and may be a more appropriate empiric choice if Gram-stain results are available. Applicability of Research to Practice To our knowledge, no previously published studies exist in burn patients examining susceptibilities to topical antimicrobials. These antibiogram-level data provide direction for empiric treatment of wound infections utilizing local susceptibilities for targeted topical coverage.