Methods for optimal recovery of Malassezia furfur from blood culture

Abstract

Malassezia furfur, a recently described agent of catheter-associated sepsis, requires long-chained fatty acids for in vitro growth. To determine optimum conditions for recovery of the organism from blood culture, we compared a radiometric (BACTEC) with a lysis centrifugation-direct agar plating (Isolator) blood culture method. When blood culture isolates of M. furfur were suspended in phosphate-buffered saline and used as inocula, the BACTEC system detected the organisms radiometrically only when bottles were supplemented with lipid compounds; detection was often delayed (greater than or equal to 72 h) when small inoculum sizes were tested. The Isolator pediatric tube system detected growth of M. furfur within 48 h of plating onto a lipid-supplemented agar medium. Simulated blood culture experiments showed that the addition of whole human blood and Intralipid to the BACTEC 6B bottle was associated with rapid lysis of erythrocytes, accumulation of a chocolate brown sediment in the bottles, and fungicidal activity to the M. furfur isolates. In contrast, suspensions of M. furfur in whole human blood were stable for at least 8 h in Isolator tubes and quantitatively recoverable after plating onto agar. Of the two systems studied, the Isolator tube system provided a more suitable procedure for isolation of M. furfur from blood culture.