Effect of povidone–iodine concentration and exposure time on bacteria isolated from endophthalmitis cases

PURPOSE: To determine the in vitro susceptibility of post-cataract surgery endophthalmitis bacterial isolates to different concentrations of povidone-iodine at different exposure times. SETTING: Poostchi Ophthalmology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran. DESIGN: Experimental study. METHODS: Ocular-fluid samples obtained from patients diagnosed with postoperative endophthalmitis were submitted to a microbiology laboratory for culture. One milliliter of microbial isolate suspension with a McFarland standard turbidity of 0.5 was mixed with 1 mL of 1%, 2%, 5%, and 10% povidone-iodine solutions. After 1 minute, 5 minutes, and 15 minutes of exposure at 37°C, each solution was transferred to appropriate culture media and incubated at 37°C for 24 hours. RESULTS: Organisms were isolated in 30 (68%) of the 44 patients evaluated. Coagulase-negative Staphylococcus was identified in 14 cases (47%), Streptococcus species in 8 cases (27%), Staphylococcus aureus in 5 cases (17%), Bacillus cereus in 2 cases (6%), and Pseudomonas aeruginosa in 1 case (3%). Higher povidone-iodine concentrations and longer exposure times were more effective than lower povidone-iodine concentrations or shorter exposure in preventing growth of bacterial isolates. The most effective regimens were 5% povidone-iodine for 15 minutes and 10% povidone-iodine for at least 5 minutes. With a high bacterial load, 13% of bacterial isolates remain viable after exposure to 10% povidone-iodine, even with a long exposure time. CONCLUSION: Results indicate that using 5% povidone-iodine for 15 minutes or 10% povidone-iodine for 5 minutes can prevent the growth of most post-cataract surgery endophthalmitis bacterial isolates.