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Akash Desai, Phat Tran, Abdul Hamood, Kelly Thrush Mitchell, Ted W Reid; 2.5, 5, and 10% Betadine solution is not effective in inhibiting the growth of different Gram Negative and Gram Positive Pathogens in vitro. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):285.
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© ARVO (1962-2015); The Authors (2016-present)
Injections of intravitreal medications have become routine care in ophthalmology officies throughout the world for the treatment of several retinal diseases. Studies estimate that the rate of endophthalmitis from intraocular injections ranges from .006% to 1.67%. Providone-iodine (Betadine) is widely accepted as the main antiseptic to decrease this risk. This study was undertaken to measure the effectiveness of different Betadine concentrations in inhibiting the growth of both Gram negative and Gram positive bacteria.
The bacteria tested were laboratory strains of Staphylococcus aureus GFP and Pseudomonas aeruginosa GFP, clinical isolates of Staphylococcus aureus and Pseudomonas aeruginosa, and two strains of Methicillin-resistant Staphylococcus aureus (MRSA). Betadine disks were prepared by adding 20 μl of 2.5, 5, or 10% Betadine solution onto 6 mm diameter BBL blank paper disks. Disks were allowed to dry before use, and three disks were distributed evenly onto a lawn of bacteria on the LB Agar surface. The plates were incubated at 37oC for 24 h. The diameters of the zones of inhibition were measured to the nearest millimeter with a ruler. Moreover, the disks from the S. aureus GFP and P. aeruginosa GFP plates were examined under the Confocal Laser Scanning Microscopy (CLSM). In addition, the remaining microorganisms on the disks were quantified by the colony forming unit (CFU) assay. All experiments were done at least in triplicate.
All the bacteria except P. aeruginosa GFP laboratory strain showed zones of inhibition when using 2.5% Betadine. At 5 and 10% Betadine concentrations, all bacteria showed zones of inhibition. However, when the disks were tested for bacteria after the zone of inhibition study using CFU assays, only Gram positive bacteria showed killing at 10% Betadine. The CLSM confirmed the CFU results for S. aureus GFP AH133 and P. aeruginosa GFP.
The three main conclusions are: 1) the zone of inhibition assay does not give a realistic assessment of the ability of an antimicrobial to kill bacteria; 2) In vitro, 2.5 and 5% Betadine are not effective at killing all the bacterial species associated with post procedure endophthalmitis; and 3) In vitro, 10% Betadine is only effective against the Gram positive bacteria tested.
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