Differentiation of Candida albicans from non-albicans yeast directly from blood cultures by Gram stain morphology

Abstract

Clusters of pseudohyphae are commonly seen on Gram stain of blood cultures from patients with Candida albicans fungemia. Whether this morphologic feature is useful for differentiating C. albicans from other yeasts has not previously been systematically evaluated. Yeast morphology on Gram stain of blood cultures from consecutive patients with fungemia detected by the Bactec automated blood culture system was prospectively assessed and correlated with the final culture-based yeast identification. The distribution of yeast in 60 consecutive patients with fungemia included Candida spp. (C. albicans 43%, Candida glabrata 28%, Candida parapsilosis 8%, Candida krusei 7%, Candida tropicalis 5%, Candida dubliniensis 2%, and Candida lusitaniae 2%), Rhodotorula mucilaginosa 2%, and Cryptococcus neoformans 3%. Upon analysis of the first positive blood culture bottle per patient, the presence of clustered pseudohyphae on Gram stain had a sensitivity, specificity, positive predictive value, and negative predictive value of 85, 97, 96, and 89%, respectively, for C. albicans. The sensitivity and specificity of aerobic vs Myco/F blood culture bottles were 96 and 95% vs 25 and 100%, p < 0.001, respectively. Inter-rater agreement for ten separate observations among five reviewers was 100%. The presence of pseudohyphae clusters by Gram stain of blood cultures is useful in distinguishing C. albicans from non-albicans yeast. Additional studies are necessary to determine the clinical impact of these findings and their validity with other blood culture systems.