Infectious Disease and Microbiology – Geotrichum candidum

Overview

Geotrichum candidum is a filamentous fungus with septate hyphae that can produce arthroconidia in infected tissue. Human infection, sometimes referred to as geotrichosis, is rare but occurs worldwide.

The most important severe manifestation is disseminated infection in profoundly immunocompromised patients, particularly those with neutropenia.

Microbiologic Characteristics

Geotrichum candidum is characterized by:

• Filamentous fungal growth

• Septate hyphae

• Hyaline rather than pigmented hyphae

• Formation of arthroconidia (arthrospores)

In tissue, the characteristic appearance is:

Septate hyaline hyphae + arthroconidia

Arthroconidia

Arthroconidia are produced by fragmentation of fungal hyphae into individual rectangular or barrel-shaped cells.

Recognition of arthroconidia can provide an important clue to the identity of an arthroconidial fungus.

However, this morphology is not unique to Geotrichum, so culture and definitive organism identification remain important.

Epidemiology

Human infection is:

Rare

but has been reported worldwide.

Geotrichum organisms can be encountered in the environment, and colonization of human mucosal surfaces may occur without invasive disease.

Therefore, isolation of the organism does not automatically prove invasive infection.

Risk Factors

The most important risk factor for severe invasive disease is:

Profound neutropenia

Other states of significant immunosuppression may also increase the risk of invasive fungal disease.

Disseminated Geotrichosis

The major invasive manifestation described in the source is:

Disseminated disease in neutropenic patients

Once invasive infection develops, organisms may spread hematogenously and involve multiple organs.

This is a serious opportunistic fungal infection.

Clinical Pattern

The typical high-risk setting is:

Severely immunocompromised patient

• ●

Prolonged neutropenia

• ●

Persistent systemic illness despite antibacterial therapy

• ●

Evidence of invasive fungal infection

→ Consider an opportunistic mold or yeast-like fungus, including Geotrichum candidum

Diagnosis

Diagnosis is based on:

Identification of the fungus in tissue biopsy

and

Fungal culture

Demonstration of fungal invasion within tissue is particularly valuable because Geotrichum may occasionally represent colonization rather than invasive disease.

Histopathology

Tissue examination may demonstrate:

Hyaline septate hyphae

with

Arthroconidia

This appearance should prompt consideration of an arthroconidial fungus.

Culture

Culture allows the organism to be isolated and identified.

Because several fungi can produce arthroconidia, accurate laboratory identification is important for distinguishing Geotrichum from other morphologically similar fungi.

Important Differential Diagnosis

Arthroconidia may also be encountered with other fungi, making differentiation important.

For example:

Geotrichum

→ Hyaline septate hyphae with arthroconidia

Coccidioides

→ Produces arthroconidia environmentally, but spherules containing endospores are the characteristic tissue form

Thus:

Arthroconidia seen in tissue

→ favors an organism such as Geotrichum rather than Coccidioides.

Treatment

The source emphasizes that there are limited clinical data regarding optimal antifungal therapy for G. candidum infection.

It describes:

Intravenous amphotericin B

as having been used with moderate success.

Treatment Considerations

Because invasive geotrichosis is uncommon, management should take into account:

• Severity and extent of infection

• Antifungal susceptibility when available

• Underlying immune status

• Degree and duration of neutropenia

• Potential need for source control

Treatment of invasive disease should be individualized.

Importance of Immune Recovery

As with many opportunistic mold infections, improvement in host immune function can be extremely important.

In neutropenic patients:

Antifungal therapy

• ●

Recovery from neutropenia

→ improves the likelihood of controlling invasive fungal infection.

Persistent profound neutropenia can make disseminated disease particularly difficult to treat.

High-Yield Clinical Pattern

Profoundly neutropenic patient

• ●

Disseminated fungal infection

• ●

Tissue biopsy showing septate hyaline hyphae with arthroconidia

→ Think Geotrichum candidum

Exam Essentials

Organism: Geotrichum candidum

Disease: Geotrichosis

Type: Filamentous fungus / mold-like fungus

Hyphae: Septate and hyaline

Characteristic structure: Arthroconidia

Distribution: Worldwide

Frequency: Rare

Major risk factor: Neutropenia

Major severe manifestation: Disseminated infection

Diagnosis: Tissue biopsy + fungal culture

Tissue morphology: Septate hyaline hyphae with arthroconidia

Treatment in source: IV amphotericin B

Evidence base: Limited

Important management factor: Recovery of immune function/neutrophils

Key clinical pearl: Geotrichum candidum is a rare opportunistic fungus characterized by septate hyaline hyphae and arthroconidia in tissue. The classic severe presentation is disseminated infection in a profoundly neutropenic patient.