Correlation of in vitro and in vivo susceptibility of Candida albicans to amphotericin B and natamycin.

The efficacy of topical 0.15% amphotericin B and 5% natamycin was examined in a model of Candida keratitis in rabbits and correlated with three tests of in vitro susceptibility: tube dilution minimal inhibitory concentration (MIC), minimal fungicidal concentration (MFC) and agar diffusion zones of inhibition. For a panel of 17 strains, the MIC classified precisely the same strains as resistant or susceptible to amphotericin B as did the in vivo response. Several strains were misclassified using the MFC and the zone of inhibition. For natamycin the MIC misclassified two strains but it was still superior to the other two tests. For all strains, amphotericin B was equal or superior in efficacy to natamycin in vivo. The tube dilution MIC for amphotericin B was a reliable indicator for natamycin efficacy in vivo.