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Survival of Streptococcus viridans in gentamicin-supplemented McCarey-Kaufman medium
J C Baer1, V S Nirankari, D S Glaros
1Department of Ophthalmology, University of Maryland, Baltimore.
Abstract:
Our experience with three cases of Streptococcus viridans endophthalmitis, following penetrating keratoplasty, prompted us to investigate the ability of gentamicin-supplemented McCarey-Kaufman (M-K) medium to kill S. viridans contaminants. After inoculation of 20 cc of gentamicin-supplemented M-K with S. viridans, the M-K was exposed to temperature conditions similar to those that would be encountered by a donor cornea during storage (4 degrees C) and preoperative warming prior to keratoplasty (23 degrees C). Colony counts were performed at regular intervals. After 1 h of warming, no reduction in the initial inoculum had occurred. This is in contrast to results from similar experiments with Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa in which more than 1 log unit of killing occurred after 1 h. While previously reported clinical experience has demonstrated an overall low incidence of postkeratoplasty endophthalmitis using gentamicin-supplemented M-K, our own recent clinical and laboratory data suggest that additional or alternate antibiotic coverage for S. viridans may be prudent.
Insights
Gentamicin-supplemented McCarey-Kaufman medium shows limited effectiveness against Streptococcus viridans in laboratory settings. This suggests that additional antibiotics may be necessary to prevent endophthalmitis after penetrating keratoplasty.
Area of Science:
- Ophthalmology
- Microbiology
- Corneal Transplantation
Background:
- Endophthalmitis is a serious complication following penetrating keratoplasty.
- Streptococcus viridans is a potential causative agent of postkeratoplasty endophthalmitis.
- McCarey-Kaufman (M-K) medium supplemented with gentamicin is commonly used for corneal storage.
Purpose of the Study:
- To evaluate the efficacy of gentamicin-supplemented M-K medium in killing Streptococcus viridans contaminants.
- To compare the killing activity against S. viridans with that against other common ocular pathogens.
Main Methods:
- Streptococcus viridans was inoculated into gentamicin-supplemented M-K medium.
- The medium was incubated at storage (4°C) and preoperative warming (23°C) temperatures.
- Colony counts were performed at regular intervals to assess bacterial viability.
Main Results:
- No significant reduction in Streptococcus viridans inoculum was observed after 1 hour of warming at 23°C.
- This contrasts with rapid killing (>1 log unit) of Staphylococcus aureus, S. epidermidis, and Pseudomonas aeruginosa under similar conditions.
- Previous clinical data indicated a low incidence of endophthalmitis with gentamicin-supplemented M-K.
Conclusions:
- Gentamicin-supplemented M-K medium demonstrates poor bactericidal activity against Streptococcus viridans.
- Current antibiotic supplementation may be insufficient to eradicate S. viridans contamination.
- Additional or alternative antibiotic strategies should be considered to prevent S. viridans endophthalmitis after penetrating keratoplasty.