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Photo Quiz: Unexpected yeast in a premature infant—pathogen or passenger

Summary

A newborn baby born very prematurely developed a yeast organism called Malassezia pachydermatis in a sputum sample, which was identified in the hospital laboratory. Researchers investigated whether this yeast was causing a serious infection or was just a harmless colonizer. Follow-up testing showed no infection, and the baby improved without antifungal treatment, suggesting it was contamination rather than true disease. However, this finding is important because this yeast has been known to cause serious infections in premature babies in hospital settings.

Background

A 3-week-old premature male infant born at 24 weeks gestation with extremely low birth weight was admitted to the NICU for management of prematurity complications. The patient had an HIV-positive mother and was receiving parenteral nutrition including lipid emulsion. A sputum culture on hospital day 20 revealed unexpected yeast growth.

Objective

To identify and characterize an unexpected yeast organism isolated from sputum culture in a premature neonate and determine its clinical significance as either a pathogen or colonizing organism.

Results

The isolated organism was identified as Malassezia pachydermatis based on characteristic monopolar budding with bowling pin appearance and collarettes. The organism grew on standard media without lipid supplementation, confirming M. pachydermatis identification by MALDI-TOF MS. Follow-up respiratory cultures were negative, and the patient improved clinically without antifungal therapy.

Conclusion

Although M. pachydermatis is a known opportunistic pathogen in neonates receiving lipid-containing parenteral nutrition, in this case the isolation likely represented colonization or contamination rather than true infection. The finding serves as a microbiological alarm warranting attention in vulnerable NICU populations, particularly given the organism’s association with nosocomial outbreaks.
  • Published in:Journal of Clinical Microbiology,
  • Study Type:Case Report,
  • Source: PMID: 41060034, DOI: 10.1128/jcm.01111-25
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