JUL 31, 2012
This prospective study found that the addition of daptomycin to Optisol-GS donor storage medium significantly increases anti-methicillin-resistant Staphylococcus aureus (MRSA) activity without any apparent negative effects on donor corneal tissue.
The authors supplemented Optisol-GS with linezolid at 2×, 4× or 10× minimum inhibitory concentration (MIC) or daptomycin and calcium at 5× or 50× MIC. Unsupplemented control groups were also used.
Gentamicin-sensitive and gentamicin-resistant isolates of MRSA were added, and vials were refrigerated for 48 hours followed by sampling for viable colony counts immediately upon removal from refrigeration and after warming to room temperature for three hours. Central corneal thickness (CCT) and endothelial cell density (ECD) of the donor corneas were evaluated to assess the safety of Optisol-GS supplementation with 50× MIC daptomycin and calcium, and the stability of daptomycin in Optisol-GS at storage was also tested.
They found no apparent benefit from the addition of linezolid to Optisol-GS against either gentamicin-sensitive or gentamicin-resistant MRSA. Consistent more with its bacteriostatic activity, the majority of inoculated gentamicin-sensitive and gentamicin-resistant bacteria remained viable in Optisol-GS solution with linezolid during refrigeration and after three hours at room temperature.
However, viable counts of gentamicin-sensitive and gentamicin-resistant MRSA were effectively reduced with both 5× MIC and 50× MIC daptomycin supplementation. There was no appreciable effect of 50× MIC daptomycin–supplemented Optisol-GS on the CCT or ECD of the donor cornea, and it was stable at storage for 14 days. More important, there was no gross damage observed to the morphology of the endothelial cells.
The authors write that these results seem surprising in light of the clinical efficacy of linezolid against gram-positive organisms, but an in vitro antagonistic effect of linezolid on the bactericidal activity of gentamicin has been reported and may explain these observations.
They conclude that daptomycin may provide a new, safe and efficacious antimicrobial agent that can be used to further decrease the risk of post-penetrating keratoplasty infection.