Candida Species as Opportunistic Pathogens: Epidemiology, Virulence, Laboratory Diagnosis, and Antifungal Resistance

Abstract

Candida species are among the most common opportunistic fungal pathogens affecting humans, particularly immunocompromised individuals. While Candida albicans has historically been the predominant etiological agent of candidiasis, recent epidemiological trends indicate a significant rise in infections caused by non-albicans Candida species, many of which exhibit intrinsic or acquired resistance to commonly used antifungal agents. These yeasts, which normally exist as commensals within the human microbiota, can transition to pathogenic forms under favourable host or environmental conditions. This review provides a comprehensive overview of the clinical and epidemiological features of Candida infections, with emphasis on laboratory diagnosis, virulence mechanisms, and antifungal resistance. Conventional and advanced diagnostic methods, including culture-based techniques, phenotypic tests, and molecular assays, are critically discussed. The growing challenge of antifungal resistance, biofilm-associated infections, and emerging multidrug-resistant species such as Candida auris is also addressed. Understanding these evolving dynamics is essential for improving patient outcomes, guiding antifungal therapy, and informing public health interventions.

Introduction

Candida species are common commensal yeasts that inhabit the skin, gastrointestinal tract, and mucosal surfaces of healthy individuals. When host immunity is compromised or the normal microbiota balance is disrupted, these organisms can become pathogenic, causing infections that range from superficial mucocutaneous disease to invasive, life-threatening systemic candidiasis. Candidiasis poses a substantial global healthcare burden, particularly among immunocompromised patients.

The epidemiology of Candida infections is shifting, with increasing involvement of non-albicans Candida (NAC) species and the emergence of multidrug-resistant pathogens such as Candida auris. These trends complicate diagnosis, treatment, and infection control. Although the genus Candida is taxonomically diverse and polyphyletic, its clinically important species share convergent pathogenic traits that enable colonisation and invasion of human hosts.

Risk factors for candidiasis include immunosuppression, HIV/AIDS, malignancy and chemotherapy, transplantation, broad-spectrum antibiotic use, indwelling medical devices, diabetes, and extremes of age. Candida virulence is mediated by multiple factors, including morphological switching, adhesion and invasion mechanisms, biofilm formation, secretion of hydrolytic enzymes, and toxins such as candidalysin.

Diagnosis relies on culture, chromogenic media, microscopy, and increasingly on molecular methods for rapid and accurate species identification, especially for resistant strains. Antifungal resistance—particularly to azoles and echinocandins—has become a major concern, necessitating routine susceptibility testing to guide therapy. Management strategies combine appropriate antifungal treatment, stewardship, infection control, and preventive measures. Ongoing research into Candida biology, resistance mechanisms, and novel therapeutic approaches remains critical to improving clinical outcomes.

Conclusion

Candida species remain among the most important opportunistic fungal pathogens worldwide. The shift towards non-albicans species, increasing antifungal resistance, and emergence of highly resistant pathogens such as Candida auris demand heightened vigilance and ongoing research. Accurate diagnosis, species-level identification, and antifungal susceptibility testing are central to effective management. Future advances in diagnostics, therapeutics, and prevention will be critical in addressing the evolving challenges posed by Candida infections.

References

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Copyright

Copyright © 2026 Jyotika Gupta, Dr. Bhavini Shah, Ankita Murnal. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.