Blood culture procedures and diagnosis of Malassezia furfur bloodstream infections: Strength and weakness

The occurrence of Malassezia spp. bloodstream infections (BSIs) in neonatal intensive care unit was evaluated by using pediatric Isolator, BacT/Alert systems and central venous catheter (CVC) culture. The efficacy of BacT/Alert system in detecting Malassezia was assessed by conventional procedures, culturing 1 ml of bottle content before incubation and by studying the survival of Malassezia spp. strains in BacT/Alert bottles. Of the 492 neonates enrolled, blood was collected by pediatric Isolator (290 patients; group I) or by BacT/Alert bottles (202 patients; group II). The survival of Malassezia furfur and Malassezia pachydermatis in BacT/Alert bottles was evaluated by culturing the inoculum suspension (from 106 to 10 colony-forming units, cfu/ml) and assessing the cfu/ml for 15 days. In total, 15 Malassezia BSIs were detected, of which six (2.1%) from both blood and CVC culture in Dixon agar (DixA) in patients belong to group I (blood collected by paediatric Isolator tube) and nine (4.4%) only from CVC culture in DixA in patients of group II (blood collected by BacT/Alert bottle). Only one patient (0.5%) from group II scored positive for M. furfur also by culturing in DixA 1 ml blood content of BacT/Alert bottle before incubation in BacT/Alert system. M. furfur population size in BacT/Alert bottles decreased during the incubation time, whereas that of M. pachydermatis increased. The BacT/Alert system detected M. pachydermatis even at very low concentration (i. e., 10 cfu/ml) but not any positive blood culture for M. furfur. For a correct diagnosis of Malassezia furfur BSI, the blood should be culture in lipid-enriched fungal medium, and the BacT/Alert system implemented by adding lipid substrates to increase the method sensibility. Finally, CVC cultures on lipid-supplemented media may be proposed as a routine procedure to diagnose the Malassezia fungemia.