Which species of Candida and other fungi are there?

What is Candida?

Candida is a type of yeast. Many Candida species can be present naturally in the body, especially in the gastrointestinal tract, oral cavity, genital area and on the skin. In normal amounts, Candida does not have to be harmful. Problems can arise when the fungus gets the opportunity to grow too much or invade tissues where it does not belong.

A Candida infection can be superficial, for example a genital yeast infection, oral thrush or skin fungus. It can also be invasive, which means the fungus spreads to the blood or internal organs. Invasive candidiasis is less common but significantly more serious and is seen mainly in people who are severely ill, immunosuppressed or have medical lines such as catheters.

Common factors that can contribute to Candida overgrowth

• Antibiotic treatment that affects the bacterial flora
• Weakened immune system
• Diabetes or high blood sugar
• Pregnancy or hormonal changes
• Moist skin folds and impaired skin barrier
• Catheters, implants or prolonged hospital care
• Cortisone or other immunosuppressive therapy
• Poor diet over time

The key Candida species

Different Candida species have different characteristics. Some mainly cause local infections, while others are more associated with hospital care, drug resistance or invasive infections.

Candida albicans – the most common pathogenic species

Candida albicans is the best-known and most common Candida species in human infection. It occurs naturally in the gut, mouth, genital area and on the skin, but can cause problems when the balance of the microbiome is disrupted.

This species is particularly adaptable. It can switch between yeast form and hyphal form, which helps it adhere to tissues and form biofilms. A biofilm is a protective structure in which microorganisms can be harder for the immune system and treatment to reach.

Common associations:

• Yeast infection in the genital area
• Oral thrush
• Skin infections in moist skin folds
• Gastrointestinal symptoms with suspected overgrowth
• Invasive candidiasis in at-risk patients

Candida glabrata – more challenging to treat

Candida glabrata is an important Candida species because it is often less sensitive to some common antifungals than Candida albicans. It occurs particularly in older adults, people with weakened immune systems and patients with recurrent or complicated infections.

It is often linked to urinary tract infections, genital symptoms and invasive infections. Because drug susceptibility can vary, species identification is important in more severe or recurrent infections.

Candida parapsilosis – common on skin and in catheter-related infections

Candida parapsilosis is often found on the skin and nails. It is particularly relevant in healthcare settings because it can spread via hands, surfaces and medical equipment.

The species is associated with infections related to catheters, implants and other medical lines. It can also form biofilms on foreign materials, which makes it important to know about in healthcare-associated infections.

Candida tropicalis – often more invasive in vulnerable groups

Candida tropicalis is a Candida species that can be more invasive, especially in people with weakened immune systems, blood disorders or cancer treatment. It can occur in the gut and is sometimes linked to gastrointestinal symptoms, but is primarily clinically important when it causes bloodstream infection or dissemination in the body.

If an invasive infection is suspected, medical assessment, laboratory diagnosis and targeted treatment are always required.

Candida krusei – naturally resistant to certain antifungals

Candida krusei is less common than Candida albicans, but important because it is naturally resistant to certain antifungals, especially fluconazole. This makes accurate species identification crucial in more serious infections.

The species is seen mainly in people with severely weakened immune systems, such as patients with cancer, blood disorders or prolonged hospitalization.

Candida auris – multidrug-resistant fungus of global significance

Candida auris is a relatively new and highly publicized Candida species. It differs from many other Candida species because it spreads more easily in healthcare settings, survives on surfaces and can be resistant to several classes of antifungals.

It is particularly problematic in hospitals and care facilities where it can cause outbreaks. Healthy people usually have a low risk of becoming seriously ill, but in patients with weakened immune systems, catheters, intensive care or severe underlying disease, the infection can become serious.

Candida auris can also be difficult to identify with older laboratory methods, which makes modern diagnostics and infection control measures important.

Candida lusitaniae – rarer but important in the context of resistance

Candida lusitaniae is a rarer Candida species, but it is clinically relevant because it can cause opportunistic infections in people with weakened immune systems, for example in hematologic diseases, neutropenia or after transplantation.

The species is particularly known for being able to develop resistance during ongoing treatment, especially to amphotericin B. It can cause candidemia, i.e., Candida in the blood, and other systemic infections. Because drug susceptibility can vary, species identification and susceptibility testing are important in serious infections.

Other fungi that can affect humans

Candida is only part of the larger group of fungi that can affect human health. Some fungi naturally live on the body, while others come from the environment, soil, plants, animals or damp buildings.

Dermatophytes – fungi of the skin, hair and nails

Dermatophytes are fungi that attack keratin, a protein found in skin, hair and nails. They are common causes of athletes foot, nail fungus and ringworm.

Examples of dermatophytes:

• Trichophyton rubrum – common in athletes foot and nail fungus
• Trichophyton mentagrophytes – can cause athletes foot and skin infections
• Microsporum canis – can spread from animals to humans
• Epidermophyton floccosum – can cause skin and groin infections

Malassezia – yeast on the skin

Malassezia is a yeast that normally lives on the skin. In some people it can contribute to dandruff, seborrheic dermatitis or pityriasis versicolor, a superficial skin condition that can cause lighter or darker patches.

Aspergillus – environmental mold

Aspergillus is a genus of molds found in the environment, for example in soil, dust and organic material. Most people inhale spores without becoming ill, but people with lung disease or weakened immune systems can develop allergic reactions or invasive aspergillosis.

Cryptococcus – can cause severe infections in immunosuppressed individuals

Cryptococcus is a yeast that can cause severe infection, especially in people with severely weakened immune systems. The best-known species is Cryptococcus neoformans, which can, among other things, cause meningitis.

Candida in the gut, mouth and genital area

Candida can be present in several places in the body. Where the fungus is located affects which symptoms may occur and what kind of assessment is needed.

Candida in the gut

Candida can occur naturally in the gut. With an imbalanced gut flora, some people may suspect Candida overgrowth, especially with gas, bloating, changes in bowel movements or recurrent digestive complaints. At the same time, such symptoms are nonspecific and can have many other causes, such as IBS, food intolerances, stress, inflammation or infection.

Candida in the mouth

Oral thrush is a Candida infection in the oral cavity. It can cause white coatings, burning, taste changes and discomfort. It is seen more often in infants, older adults, people with dry mouth, diabetes, inhaled corticosteroids or weakened immune systems.

Candida in the genital area

Yeast infection in the genital area is common and is often caused by Candida albicans. Typical symptoms can include itching, burning, redness and curd-like discharge. Recurrent or severe yeast infections should be assessed by healthcare professionals because other conditions can cause similar symptoms.

Why is species identification important?

Not all Candida species behave the same way. Some species are more prone to forming biofilms, some are associated with hospital care and others can be naturally resistant to specific antifungals.

Species identification is particularly important for:

• Recurrent infections
• Difficult-to-treat fungus
• Suspected invasive candidiasis
• Infection in immunosuppressed individuals
• Infection associated with a catheter, implant or hospital care
• Suspected drug resistance

For mild and typical problems, advanced diagnostics are sometimes not needed. For prolonged, recurrent or severe symptoms, however, it is important not to guess, but to have healthcare take samples and determine which species is involved.

Biofilm and hyphae – why some Candida species are harder

An important property of several Candida species is the ability to form biofilms. A biofilm can be described as a protective layer where fungal cells adhere to each other and to a surface, for example a mucosa, catheter, implant or dental prosthesis.

Candida albicans is also known for being able to switch between yeast form and hyphal form. Hyphae are thread-like structures that can help the fungus adhere, spread out and penetrate tissue. This is one of the reasons why Candida albicans is such a successful pathogen in overgrowth and infection.

Summary

There are many species of Candida and other fungi that can affect humans. The most common pathogenic species is Candida albicans, but species such as Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida krusei, Candida auris and Candida lusitaniae are also important to know about.

Differences between species matter because they may vary in their ability to cause infection, form biofilms, spread in healthcare settings and develop resistance to antifungals. With mild and typical symptoms, treatment can often be simple, but for recurrent, severe or healthcare-associated infections, accurate diagnostics are crucial.

FAQ – common questions about Candida and fungi

Which Candida species is most common?

Candida albicans is the most common Candida species in human infections and often causes yeast infection in the genital area, oral thrush and other superficial Candida infections.

Is Candida always dangerous?

No. Candida can occur naturally in the body without causing problems. It is mainly with overgrowth, a weakened immune system or spread to the blood and organs that Candida becomes medically serious.

What is the difference between Candida albicans and Candida auris?

Candida albicans is the most common and occurs naturally in many people. Candida auris is rarer but concerning because it can be multidrug-resistant, spread in healthcare settings and be hard to identify with older laboratory methods.

Can Candida cause digestive problems?

Candida can occur in the gut, but digestive issues such as bloating, gas and changes in bowel movements can have many causes. With prolonged or severe symptoms, you should investigate the cause rather than assume Candida is the problem.

Why is Candida glabrata harder to treat?

Candida glabrata can be less sensitive to certain antifungals than Candida albicans. Therefore, sampling, species identification and susceptibility testing can be important in more severe or recurrent infections.