Is Candida orthopsilosis recognized as a human pathogen?

Candida orthopsilosis as a Human Pathogen

Candida orthopsilosis is definitively recognized as a human pathogen that belongs to the Candida parapsilosis complex and causes a range of clinical infections, though it is less frequently isolated than its sister species C. parapsilosis.

Taxonomic Classification and Pathogenic Status

Candida orthopsilosis is one of three species in the Candida parapsilosis sensu lato complex, alongside C. parapsilosis (the most common) and C. metapsilosis 1. This taxonomic distinction is important as these were previously considered a single species but are now recognized as separate pathogens with different clinical profiles.

The pathogenic status of C. orthopsilosis is well-established:

• It has been documented to cause invasive infections in humans 2, 1
• It possesses virulence factors including adhesins that facilitate attachment to human epithelial cells 3
• It has been isolated from clinical specimens in cases of human disease 1

Clinical Significance and Epidemiology

While C. orthopsilosis is less frequently isolated than C. parapsilosis, it remains clinically significant:

• It is capable of causing candidemia and invasive candidiasis, particularly in immunocompromised patients 1
• It is more prevalent in certain geographic regions including Asia, Southern Europe, and Latin America 2
• High-risk populations include:
  • Neonates with low birth weight
  • Immunocompromised individuals
  • Patients with indwelling medical devices 2, 1

Virulence Factors

C. orthopsilosis possesses several virulence mechanisms:

• Adhesion to human cells: The CORT0C04210 gene (CoALS4210) has been specifically identified as important for adhesion to human buccal epithelial cells 3
• Biofilm formation capability, though less robust than C. parapsilosis 2
• Secretion of hydrolytic enzymes that contribute to tissue invasion 4

Antifungal Susceptibility

C. orthopsilosis has distinct antifungal susceptibility patterns:

• Like other members of the C. parapsilosis complex, it shows higher minimum inhibitory concentrations for echinocandins compared to other Candida species due to a naturally occurring FKS1 polymorphism 1
• It may develop resistance to fluconazole, particularly in healthcare settings where clonal outbreaks have been reported 1

Genomic Features

The C. orthopsilosis genome has been fully sequenced and analyzed:

• It contains approximately 12.6 Mb organized on 8 chromosomes 5
• It has 5,700 protein-coding genes, of which 5,570 have orthologs in C. parapsilosis 5
• Genomic differences between C. orthopsilosis and C. parapsilosis may explain their different virulence profiles, including expansions of certain gene families in C. parapsilosis 5

Clinical Management

When C. orthopsilosis is identified in clinical specimens:

• It should be considered a true pathogen rather than a contaminant, particularly in high-risk patients 6
• Treatment follows similar guidelines to other invasive Candida infections:
  • Echinocandins are recommended as first-line therapy for invasive disease, despite higher MICs 6
  • Fluconazole remains an option for susceptible isolates in stable patients 6
  • Removal of infected indwelling devices is crucial when possible 6

Diagnostic Considerations

Accurate identification of C. orthopsilosis requires:

• Modern molecular methods, as traditional phenotypic methods cannot reliably distinguish between members of the C. parapsilosis complex 1
• Species-level identification is important for epidemiological tracking and may have therapeutic implications 1

In conclusion, C. orthopsilosis is an established human pathogen with documented virulence factors and clinical significance. While less common than C. parapsilosis, it should be considered in the differential diagnosis of invasive candidiasis, particularly in high-risk populations.