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

Abstract

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.

Malassezia infections with systemic involvement: Figures and facts

“…The occurrence of three cases of confirmed M. furfur bloodstream infection in a tertiary care hospital during a 2‐year period is consistent with the reported low prevalence of these invasive infections, usually confined to severely immunocompromised hosts . Concerning diagnostic accuracy, there is a need to emphasize that the number of positive cases could be underestimated, because a keen clinical acumen is crucial to suspect these potential agents of fungemia in the appropriate clinical scenario, and in particular to provide optimal Malassezia recovery conditions from blood cultures and medical indwelling devices given the special lipid requirements (which are not provided in daily routine) …”

“…9 Concerning diagnostic accuracy, there is a need to emphasize that the number of positive cases could be underestimated, because a keen clinical acumen is crucial to suspect these potential agents of fungemia in the appropriate clinical scenario, and in particular to provide optimal Malassezia recovery conditions from blood cultures and medical indwelling devices given the special lipid requirements (which are not provided in daily routine). 27 The three unrelated cases herein reported all refer to patients with central venous catheters confirming the importance of this portal of entry, 40 which were removed early and afterwards replaced. No neonatal cases were found, neither cases associated with lipid infusion and/or total parenteral nutrition.…”

“…9,26,27 Culture of indwelling medical devices such as central venous catheters also represent a critical diagnostic step. 27 Modern and reliable speciation requires the adoption of laboratory tools such as molecular biology 11,12,28 and MALDI-TOF-MS. 29,30 Although molecular tools can be performed directly on biological samples, culture is usually performed previously to enable yeast quantification, viability assessment and eventually antifungal susceptibility testing. 31 Culture media supporting Malassezia growth include modified Dixon, Leeming and Notman agar, CHROMagar Malassezia, and Sabouraud's agar with the addition of sterile olive oil.…”

“…31 Culture media supporting Malassezia growth include modified Dixon, Leeming and Notman agar, CHROMagar Malassezia, and Sabouraud's agar with the addition of sterile olive oil. 27,30,32,33 Currently, the use of MALDI-TOF-MS has been exploited for Malassezia identification, 34 although the databases differ regarding the species and strains included, which may lead to misdiagnosis. 30 Furthermore, the non-uniformity in the culture media used may be another important issue when interpreting the results.…”

Galleria mellonella as a Novelty in vivo Model of Host-Pathogen Interaction for Malassezia furfur CBS 1878 and Malassezia pachydermatis CBS 1879

“…The genus Malassezia is comprised of 18 lipophilic species characterized as commensal yeasts, which are part of the skin mycobiota of both humans and animals (Nagata et al, 2012;Cabañes, 2014;Cabañes et al, 2016;Honnavar et al, 2016;Prohic et al, 2016), and are commonly located in lipid-rich body areas, such as the scalp, face, and trunk (Gupta et al, 2004;DeAngelis et al, 2005). Some species of this genus have been associated with skin diseases (Gupta et al, 2004;Prohic et al, 2016) and systemic infections (Gaitanis et al, 2012;Kaneko et al, 2012;Nagata et al, 2012;Iatta et al, 2014Iatta et al, , 2018Roman et al, 2016;Lee et al, 2018;Theelen et al, 2018;Chen et al, 2020).…”