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Eric Huynh, Phat Tran, Patrick Pham, Abdul Hamood, Kelly Mitchell, Ted W Reid; 5% Betadine solution in not effective in inhibiting the growth of different Gram Negative and Gram Positive Pathogens in vitro. Invest. Ophthalmol. Vis. Sci. 2014;55(13):5787.
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© ARVO (1962-2015); The Authors (2016-present)
Injections of intravitreal medications has become routine care in ophthalmology offices throughout the world for the treatment of several retinal diseases. Studies estimate that the rate of endophthalmitis form intraocular injections range from 1.67% to 0.006%. Currently, 5% providone-iodine (Betadine) is widely accepted as the main antisepsis used to decrease this risk. Thus, the present study was undertaken to measure the effectiveness of 5% Betadine in inhibiting the growth of both Gram negative and Gram positive bacteria.
Betadine disks were prepared by adding 20 μl of 5% Betadine solution onto each 6 mm diameter BBL blank paper disk. LB Agar plates were inoculated with a confluent lawn of bacteria, made on each plate using cotton swabs dipped into 107 CFU/ml of the bacterial suspensions. Within 15 min after the plates were inoculated, Betadine disks were distributed evenly onto the LB Agar surface, with at least 24 mm (center to center) between them. The plates were incubated at 37oC for 24 h before results were read. The diameters of the zones of complete inhibition, including the diameter of the disk, were measured to the nearest millimeter with a ruler. In addition, the remaining microorganisms on the disks were quantified by the CFU assay. All experiments were done in triplicate, and all measurements were repeated three times. The bacteria tested were Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, Streptococcus salivarius, Streptococcus mutans, Staphylococcus epidermidis, and Serratia marcescens.
All the bacteria, except Pseudomonas aeruginosa, showed zones of inhibition against the lawns of bacteria. However, when the disks were tested for bacteria after the zone of inhibition study was completed, only three of the eight different bacteria showed killing of the bacteria on the disk. These were, one gram negative bacteria, Serratia marcescens, and two gram positive bacteria, Streptococcus salivarius, and Streptococcus mutans.
The two main conclusions are: 1) the zone of inhibition assay does not give a realistic assessment of the ability of an antimicrobial to kill bacteria; and 2) In vitro, 5% Betadine does not appear to be effective at killing the bacterial species associated with post procedure endophthalmitis.
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