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Blood culture bottles are the best test for sterility in cornea banks

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Patients having corneal transplants could be saved from serious inflammation within the eye if cornea banks switched to blood culture bottles for screening organ culture media for microbial contamination, researchers have found. This method is quicker too.

The researchers spiked sterile standard organ culture medium for storing corneas with type cultures of 14 bacterial species and three fungal species commonly associated with such infection After two days’ incubation they tested the cultures for microbial growth during 14 days by three methods: turbidity and colour change in the medium; conventional subculture in bacterial and fungal media; and subculture into blood culture bottles (one each for aerobic and anaerobic bacterial species, and one for fungi).

The original medium contained two antibacterial and one antifungal antibiotics. These effectively stopped subsequent growth on subculture in five bacterial species. Residual contamination was shown with blood culture bottles for all (30/30) 12 remaining species compared with 77% (23/30) by conventional subculture and 70% (21/30) by the visual method. Final subcultures confirmed no external contamination of the samples. Results were available in under eight hours in 40% (12/30) of samples using blood culture bottles.

Most European cornea banks use organ culture medium containing antibiotics to store corneas and have a 10–12 day quarantine time for tests to ensure sterility. Blood culture bottles are particularly suitable for testing when microbes are present in small numbers or when antibiotics are present—so it made sense to test them in this context.