In vitro efficacy of a povidone-iodine 0.4% and dexamethasone 0.1% suspension against ocular pathogens

Purpose: To assess the efficacy of a povidone-iodine 0.4%-dexamethasone 0.1% suspension against bacterial, fungal, and Acanthamoeba clinical isolates. Setting: Bascom Palmer Eye Institute, McKnight Research Building, Miami, Florida, USA. Design: Experimental study. Methods: One hundred milliliters of 10⁴ colony-forming units/mL of ocular isolates of methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, Serratia marcescens, Candida albicans, Fusarium solani, and Acanthamoeba castellanii were inoculated into 100 μL of a povidone-iodine 0.4%-dexamethasone 0.1% suspension in a 96-well microtiter plate incubated at room temperature. Organism viability was assessed at 15, 30, and 60 seconds by removing 10 μL aliquots and streaking onto a 5.0% sheep blood agar plate (fungi and bacteria) and agar-agar (Acanthamoeba) using a 0.001 calibrated loop. The plates were then incubated at 35°C and monitored for up to 7 days. Isolates were inoculated into 200 μL of trypticase soy broth as controls. The number of colonies was counted and compared with controls to determine the kill rate. Results: A 99.9% kill was observed for MRSA, P aeruginosa, S marcescens, and C albicans after 15 seconds of exposure and for F solani after 60 seconds. Acanthamoeba castellanii cyst viability was not inhibited by exposure to the povidone-iodine and dexamethasone suspension. Organism growth was achieved on all control broth. Conclusions: Povidone-iodine 0.4%-dexamethasone 0.1% suspension killed all bacterial and candida isolates within 15 seconds of exposure. It killed Fusarium isolates at 60 seconds but was ineffective against Acanthamoeba cysts. Financial Disclosure: Drs. Pelletier and Miller have no financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.