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S. Thoongsuwan, V. Cevallos, A. Singh, J. M. Stewart; A Model of Bacterial Contamination From Intravitreal Injections Using Porcine Sclera and Culture Media. Invest. Ophthalmol. Vis. Sci. 2008;49(13):5533.
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To demonstrate the possibility of using pig sclera and culture broth media as an experimental model to study the risk of bacterial contamination of the eye from intravitreal injections.
Testing sterilization: Conjunctival swab and vitreous specimens from enucleated porcine eyes were cultured in blood agar and smeared for gram stain. The sclera was incised into small pieces and immersed in 5% povidone iodine solution and 70% ethanol for different times. After immersion in antiseptics, the scleral pieces were cultured on blood agar and thioglycolate broth media. The presence of bacterial colonies on blood agar plates and the cloudiness of thioglycolate broth media were identified as positive for bacteria growth.Testing experimental model: The scleral pieces were placed on small tubes filled with culture broth media. Needles of different gauges and lengths were used to pierce the sclera until the tip of the needles passed into the media.
Numerous colonies of bacteria in blood agar plates were found from conjunctiva and vitreous cultures from porcine eyes. Gram stain of vitreous showed numerous of gram negative and gram positive bacteria. After immersion of the sclera pieces in 5% povidone iodine for 1, 2 and 5 minutes, bacterial colonies were still numerous in all specimens. The bacteria were also identified after immersion in 70% ethanol for 2 and 4 hours (40% and 33% of samples were culture-positive, respectively), however, with small numbers of colonies.In the experimental model using the longer needle, the needle could be passed through sclera into the media without causing the sclera to contact the media. With the shorter needle, there was very little space between the sclera and the media because the tube had to be filled to the top with media. The sclera almost always came into contact with the media while the needle was passed through the sclera, resulting in contamination of the media by the sclera.
Enucleated porcine eyes are contaminated with numerous bacteria. Despite the usage of strong antiseptics for a long duration, the sclera still showed evidence of bacterial contamination. A very short needle is not recommended for use in this experimental model. In this model, a longer needle (0.5 inches or longer) can be used together with pig sclera and culture media if bacterial contamination of approximately 33-40% of the specimens is acceptable or if more effective decontamination techniques are used.
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