Generality
Yeasts, from those with pathogenic properties to harmless ones, are eukaryotic-type microorganisms consisting of only one cell and belonging to the kingdom of fungi.
Under certain environmental conditions, many yeasts can become molds; this ability takes the name of dimorphism and the fungi that are protagonists take the name of dimorphic fungi.
There are numerous species of yeasts with pathogenic properties, ie with the ability to cause disease (infections) in humans and other animals.
The main yeasts with pathogenic properties include: Cryptococcus neoformans, Cryptococcus gattoi, Pneumocystis carinii, Penicillium marneffei, Candida albicans And Histoplasma capsulatum.
Brief reminder on mushrooms
Fungi constitute a kingdom of living organisms of the eukaryotic type, whose cells have some characteristics of animal cells (mitochondria, heterotrophy, etc.), some characteristics of plant cells (cell wall and vacuole) and some characteristics of bacterial cells (self-synthesis of "amino acid L-lysine).
There are many types of fungi, from unicellular ones - that is composed of only one cell - to multicellular ones - that is, formed by more than one cell; from the saprophytic ones to the parasitic ones, from the edible ones to the pathogenic ones for the human being and not only etc.
Their history is very ancient; according to some studies, in fact, the first fungi would have been present on Earth as early as 3.5 billion years ago.
What are yeasts?
Yeasts are unicellular organisms - therefore microorganisms - belonging to the kingdom of fungi.
Appeared on Earth several hundreds of millions of years ago, they represent about 1% of all known mushroom species.
In this article, the yeasts that are the subject of the most attention are yeasts with pathogenic properties.
Yeasts with pathogenic properties are a particular category of fungi, capable of causing disease in humans or other living beings.
Other fungi with pathogenic properties are molds. Unlike yeasts, molds are multicellular organisms.
Table showing the scientific classification of yeasts
Domain:
Eukaryote
Kingdom:
Mushrooms
Phylum And subphylum:
Ascomycetes (Ascomycota)
- Saccharomycotina
- Taphrinomycotina
Basidiomycetes (Basidiomycota)
- Agaricomycotina
- Pucciniomycotina
WHO IS CAREFUL IN THE STUDY OF PATHOGENIC YEAST?
Pathogenic yeasts and, in general, all fungi capable of causing disease in humans (and not only), are the subject of study by the branch of medicine known as medical mycology.
Mycology is the term that indicates the biomedical discipline that studies fungi in general.
WHAT KIND OF DISEASES DO YEASTS CAUSE?
Diseases caused by pathogenic yeasts (and in general by all fungi with pathogenic properties) are infectious diseases or infections.
In specialist jargon, yeast and pathogenic fungal infections take the general name of mycosis.
The mycoses are many; to simplify the study, the doctors decided to classify them according to the site of infection. It turned out that mycoses can be divided into 5 large groups (or types): superficial mycoses, cutaneous lemicoses, subcutaneous mycoses (or subcutaneous mycoses ), systemic mycoses due to primary pathogens and systemic mycoses due to opportunistic pathogens.
The most famous pathogenic yeasts are usually responsible for systemic mycoses (of both types).
Biology
Being fungi, yeasts are eukaryotic organisms.
A eukaryotic organism is a living being whose cells possess:
- A specialized compartment, which takes the name of nucleus and which is the seat of DNA (or genetic material);
- A DNA organized into chromosomes;
- A series of organelles and
- A complex system of intracellular phospholipid membranes.
Generally, yeasts have a diameter between 3 and 5 micrometers and a thick cell wall, formed by: glucans for 60%, mannan for 25%, proteins / lipids for 10% and chitin for 5%.
THEY ARE HETEROTROPHIC ORGANISMS
Yeasts and fungi in general are heterotrophic organisms.
A heterotrophic organism is a living being unable to synthesize the organic substances, necessary for life, starting from inorganic substances; in order to survive, heterotrophic organisms must feed on the organic substances produced by other organisms.
Living beings capable of synthesizing organic substances from inorganic substances are called autotrophic organisms. In nature, the autotrophic organisms par excellence are plants, which produce organic substances starting from inorganic substances through the process of photosynthesis.
PLAYBACK
Like non-pathogenic yeasts, yeasts with pathogenic properties are characterized by two modes of reproduction: the so-called binary cleavage and the so-called budding.
Comparison with molds
Molds have the particularity of reproducing by sporogenesis, that is, through the production of spores.
HABITAT TYPICAL
Like habitat more suited to their survival, pathogenic and non-pathogenic yeasts prefer humid environments, where they can easily find sugars and amino acids.
Among habitat typical of yeasts include: the surface of the fruit, foods in general and the roots of plants.
DO YEASTS HAVE IFE?
Yeasts, from pathogenic to non-pathogenic ones, are the only fungi that do not give rise to the so-called hyphae (singular hypha).
The hyphae are the filamentous structures which, in all fungi (except yeasts), form the so-called mycelium (or vegetative body) and distinguish the fungal process known as vegetative growth.
YEASTS CAN ALSO BE MOLD: DIMORPHISM IN MUSHROOMS
Under particular environmental conditions or other circumstances, some yeast species can become molds. Yeasts capable of transforming into molds are organisms that from unicellular become multicellular and that acquire the ability to form hyphae, for the mycelium.
The ability of some fungi to be, on some occasions, yeasts and, on other occasions, molds is called dimorphism; fungi that can be yeasts or molds, depending on certain environmental conditions, are called dimorphic fungi.
Dimorphism is a capacity that affects numerous fungi with pathogenic properties.
In biology, the term dimorphism refers to the phenomenon whereby an individual of the same living species is capable of assuming two different aspects or forms.
A dimorphic individual, therefore, is a subject that can present itself in two different forms.
Clinic
Rarely, pathogenic yeasts and fungi in general infect people in good health. As a rule, in fact, they attack more easily individuals who:
- They suffer from diabetes. The high concentration of glucose in the blood (hyperglycemia), typical of diabetes, favors the proliferation of some particular fungi (including yeasts) that populate certain anatomical areas of the human body and which, in normal conditions (ie absence of diabetes ), are completely harmless.
- They have been subjected to inadequate antibiotic therapy or for too long periods. The prolonged and / or inadequate intake of antibiotics destroys the gastrointestinal bacterial flora. The latter has the task of controlling the proliferation of pathogenic fungi, physiologically present inside or in contact with the human organism. The compromise of the bacterial flora makes it easier for the potentially pathogenic fungi, including yeasts, to spread to the human being concerned.
- They have an ineffective immune system. The immune system is the defensive barrier of an organism against threats coming from the external environment, such as viruses, bacteria, fungi, etc., but also from the internal environment, such as cancer cells (the so-called "crazy cells" ) or malfunctioning.
To affect the efficiency of the human immune system can be morbid conditions, such as AIDS (ie HIV infection) or the intake of certain drugs, such as corticosteroids, chemotherapy or immunosuppressants.
Furthermore, it should be remembered that an inefficient immune system is typically present in very young subjects (N.B: it is not yet fully developed) and in very elderly subjects (N.B: it undergoes a physiological decrease in effectiveness).
Examples
The best known pathogenic yeasts belong to the genus Cryptococcus - In the case Cryptococcus neoformans And Cryptococcus gattoi - and the genre Candida.
However, they also deserve a mention: pathogenic yeast Pneumocystis carinii, belonging to the genus Pneumocystis; pathogenic yeast Penicillium marneffei, belonging to the genus Penicillium; finally, pathogenic yeasts Blastomyces dermatitidis, Coccidioides immitis, Coccidioides posadasii, Histoplasma capsulatum And Paracoccidioides brasiliensis.
All the aforementioned pathogenic yeasts are responsible for systemic mycoses, but:
- Cryptococcus neoformans, Cryptococcus gattoi, Pneumocystis carinii, Penicillium marneffei and yeasts like that Candida are considered opportunistic pathogens (systemic mycoses due to opportunistic pathogens)
- the dimorphic yeasts Blastomyces dermatitidis, Histoplasma capsulatum, Paracoccidioides brasiliensis, Coccidioides immitis And Coccidioides posadasii they are considered to be primary pathogens (systemic mycoses due to primary pathogens).
