Survival of Streptococcus pneumoniae in corneal storage media

The Cincinnati Eye Bank had six corneoscleral rims in which Streptococcus pneumoniae was cultured after preservation in corneal storage media. To determine the survival of this organism under conditions common for corneal storage, gentamicin-supplemented McCarey-Kaufman (M-K) medium and chondroitin sulfate/Dextran medium (Dexsol, Ciron Ophthalmics, Irvine, CA, U.S.A.) were inoculated with S. pneumoniae and kept at 4 degrees C. Thioglycollate broth plus 10% rabbit serum (Thio-S) and tryptic soy broth (TSB) served as growth controls. At day 14 after inoculation of 10(5) colony-forming units (CFU)/ml, Dexsol showed a 1-log decrease in bacterial concentration, the M-K medium a 2-log decrease and Thio-S a 4-log decrease, whereas TSB showed no detectable organisms. By day 21 Dexsol had only a 2-log decrease in bacteria. These data suggest that corneal storage medium supplemented with gentamicin does not exert bactericidal activity against S. pneumoniae and may actually support its survival at 4 degrees C.