Introduction
Table of Contents
Blood cultures are the cornerstone for diagnosing fungemia, but while yeasts (Candida spp.) are frequently detected, molds are rarely recovered in blood culture systems. This is because most molds (Aspergillus, Mucorales) cause tissue-invasive disease without sustained fungemia. However, certain molds such as Fusarium spp. and, less commonly, Scedosporium and Lomentospora can be recovered from blood culture bottles, especially in immunocompromised patients. Identifying molds from blood cultures is clinically significant, as it often indicates severe disseminated infection with poor prognosis.
Common Molds Recovered in Blood Cultures
- Fusarium spp.
- Most frequently isolated mold in blood cultures.
- Shows septate hyphae, canoe-shaped macroconidia, and thermotolerance at 37 °C.
- Strongly associated with fungemia in neutropenic and transplant patients.
- Aspergillus spp.
- Rarely grows in blood cultures.
- Characterized by acute-angle branching septate hyphae.
- Positive blood culture for Aspergillus usually suggests contamination or overwhelming invasive disease.
- Scedosporium / Lomentospora spp.
- It can mimic Aspergillus microscopically.
- Clinically significant in CNS, pulmonary, and disseminated infections.
- Notably resistant to amphotericin B.
- Mucorales (Rhizopus, Mucor, Lichtheimia)
- Broad, aseptate hyphae with right-angle branching.
- Rarely isolated from blood culture (more commonly seen in tissue biopsy).
- Causes mucormycosis in diabetics and transplant patients.
Comparison of Blood Culture–Positive Molds
| Mold | Microscopy (LPCB) | Growth at 37 °C | Blood Culture Yield | Clinical Significance |
|---|---|---|---|---|
| Fusarium spp. | Septate hyphae, canoe-shaped macroconidia | Good growth | Fungemia, high mortality, and resistance to many antifungals | Fungemia, high mortality, resistant to many antifungals |
| Aspergillus spp. | Septate hyphae, acute-angle branching, conidiophores with vesicles | Thermotolerant | Rare in blood cultures | Invasive aspergillosis; positive culture = poor prognosis |
| Scedosporium / Lomentospora | Septate hyphae, conidia singly/clusters, no vesicles | Grows well | Rare | CNS + disseminated disease; amphotericin B resistant |
| Mucorales | Broad, aseptate hyphae, right-angle branching | Grows rapidly | Very rare in blood cultures | Mucormycosis (pulmonary, rhino-orbital, disseminated) |
No broad aseptate hyphae (like Mucorales) are seen. Morphology suggests a septate mold, possibly Aspergillus or a related opportunistic mold.
Note: “Blood culture shows cottony fungal growth. LPCB preparation reveals septate hyphae with branching, consistent with Aspergillus species (probable A. fumigatus). Further identification and antifungal susceptibility recommended.”
Keynotes
- Fusarium is the leading mold isolated in blood cultures, often representing true fungemia.
- Aspergillus and Mucorales rarely yield positive blood cultures; diagnosis usually relies on tissue biopsy and antigen testing.
- Scedosporium/Lomentospora are emerging molds in immunocompromised patients and are notable for antifungal resistance.
- A positive blood culture for mold usually signifies severe disseminated infection with high mortality.
- Final identification requires morphology, MALDI-TOF, or molecular sequencing, along with antifungal susceptibility testing.
- Aspergillus → classic septate acute-angle branching; thermotolerant.
- Fusarium → only mold that frequently gives true fungemia with positive blood cultures.
- Scedosporium/Lomentospora → mimic Aspergillus but differ in drug resistance.
- Mucorales → broad aseptate hyphae, usually not recovered in blood culture.
- Candida (not a mold) → the commonest fungus in blood cultures; budding yeast, not hyphae.
Further Readings
- https://www.sciencedirect.com/science/article/pii/S1198743X14633619
- https://www.researchgate.net/publication/282866938_Potential_Pathogens_among_Fungi_Identified_as_Nonsporulating_Molds_from_Blood_Cultures
- https://www.cdc.gov/fungal/about/about-invasive-mold-infections.html
- https://www.cdc.gov/antibiotic-use/core-elements/pdfs/fs-bloodculture-508.pdf
- https://www.scirp.org/journal/paperinformation?paperid=60198
- https://academic.oup.com/cid/article/44/8/1078/297640
- https://www.sciencedirect.com/topics/medicine-and-dentistry/fungemia
- https://pmc.ncbi.nlm.nih.gov/articles/PMC1195428/
- 20resistant.https://pmc.ncbi.nlm.nih.gov/articles/PMC4201853/
- https://academic.oup.com/ofid/article/9/Supplement_2/ofac492.428/6902334
- https://pmc.ncbi.nlm.nih.gov/articles/PMC6699810/