MESOPHILES: CHARACTERISTICS, TYPES, HABITAT, DISEASES, EXAMPLES - BIOLOGY - 2024

The term mesophiles is used to refer to organisms that reach their optimal development at temperatures ranging between 20 and 45 ° C. Although all organisms that grow in this temperature range are mesophilic, the term is used primarily to speak of microorganisms.

Living things can grow in a relatively small range of temperatures, ranging from -5 ° C to just over 80 ° C. Growth below -5 ° C is restricted due to freezing of the cytoplasm and other organic fluids.

Bacillus megaterium. A species of mesophilic bacteria that develops between 3 and 45 ° C, but its development is more optimal at 30 ° C. Taken and edited from: Osmoregulator at English Wikipedia.

Very high temperatures, on the other hand, restrict growth due to the thermolability of cellular proteins.

Mesophilic microorganisms are very diverse and can be prokaryotes or even belong to the Fungi kingdom of the Eucarya. However, the term is more commonly used for bacteria. The latter can be in the form of a coconut, a bacillus or have a spiral shape.

Classification of microorganisms according to their development temperature

Prokaryotes can be classified into three groups depending on the growth interval where their development occurs: thermophiles, mesophiles and psychrophiles.

Thermophiles

Its optimum temperature range for growth is between 55 and 75 ° C, while its minimum temperature is never lower than 35 ° C.

Mesophiles

Their optimum growth temperature is 30 to 45 ° C (20 - 50 ° C according to some authors) and they do not thrive below 10 ° C.

Psychrophiles

They can be facultative or obligate psychrophiles. In the case of facultative psychrophiles, their optimum temperature is the same as for mesophiles, but the minimum is close to 0 ° C. While the obligors have an optimal temperature of 15 to 18 ° C, a minimum temperature of 0 ° C and a maximum of 20 ° C.

characteristics

Because it is a purely ecological and functional term, the variability in organisms that it includes is quite large and it is difficult to make generalizations. Perhaps the only characteristic in common is the temperature range in which they develop.

In the case of mesophilic bacteria, these can be Gram positive or Gram negative. There are also no limitations in terms of the oxygen requirements for its metabolism, being able to be aerobic, anaerobic or facultative. In terms of shape, they can be cocci, bacilli, or spiral in shape.

Even temperature, the factor that defines them, is not a strict tool to separate bacteria into groups, since not all bacteria can thrive in the entire temperature range that defines their group. Even pH can affect the resistance of bacteria to temperature.

Another possible common characteristic among all of them may be the presence of peptidoglycans in their cell wall; but in the case of Gram positive ones, they have a thicker layer of peptidoglycans than Gram negative ones.

Types

Mesophiles, as already indicated, are a type of bacteria, according to their optimum development temperature.

But since most bacteria belong to this group, it can be subdivided based on different criteria, such as the response to vital dyes (Gram + or Gram -) or their shape (cocci, bacilli, coccobacilli, spirilli and vibrios).

Because some mesophilic bacteria, under environmental conditions, can contaminate food and cause its decomposition, or diseases (if ingested), it is common then to speak of aerobic mesophiles. In this case, a subdivision would be made based on the oxygen requirements. In this way we would obtain the following groups:

Aerobic mesophiles

Mesophilic bacteria that require oxygen for their metabolic processes.

Anaerobic Mesophiles

Those that live and develop in environments lacking oxygen and at medium temperatures. Many of them perish, or do not prosper, in the presence of oxygen, while others (aerotolerant) can grow in the presence of oxygen, but do not use it for their vital processes.

Facultative mesophiles

Bacteria that live and develop indistinctly in anaerobic or aerobic environments; that is, they can live in the presence (and use it) or absence of oxygen.

Habitat

Provided that the temperatures are adequate, mesophilic bacteria can be found in any habitat, be it marine waters, rivers, soils, on other organisms, or inside them.

Since most warm-blooded organisms have a body temperature close to 35 ° C, the bacteria that live inside them are mesophilic. These bacteria can establish mutually beneficial symbiotic relationships with their hosts, or they can act as parasites causing various diseases.

Diseases

The normal temperature of the human being is 37 ° C, so the pathogenic bacteria that affect the human being are mesophilic. Some of the most important Foodborne Illnesses (ATE) are due to mesophilic aerobic bacteria.

Due to this, one of the hygiene and safety measures followed in the food industry is the counting of this type of bacteria in food to determine whether or not they are suitable for consumption. Additionally, some bacteria that are not pathogenic under normal conditions can occasionally act as such (opportunistic pathogens).

Diseases caused by mesophiles can have different medical relevance, from self-limited diarrhea to fatal diseases, some of them of intrahospital origin.

Among the diseases caused by mesophiles are for example: bacterial diarrhea, endophthalmitis, meningitis, diphtheria, peritonitis, prostatitis, pneumonia and septicemia. Some species of mesophiles, additionally, can develop drug resistance, which complicates their treatment.

Examples

Listeria monocytogenes

It is a Gram-positive, facultative anaerobic bacillus, capable of moving thanks to the presence of peritrichous flagella. This bacterium is mesophilic; however, it is capable of surviving temperatures of 0 ° C. It is the cause of the disease known as listeriasis.

Among the manifestations of the disease are nausea, vomiting and diarrhea, which may be the only symptoms, or it can progress to sepsis, meningitis, pneumonia, and even cervical or intrauterine infections that cause spontaneous abortions in pregnant women.

Culture of Listeria monocytogenes. Taken and edited from: James.folsom.

Listeria monocytogenes can be acquired from contaminated foods, such as raw or pasteurized milk, cheeses, ice cream, fresh and smoked fish, among others.

Stenotrophomonas maltophilia

It is a Gram negative, mobile, catalase positive and oxidase negative bacterium. This mesophyll is found in practically any aquatic environment, as well as in the soil or living on plants.

It is an opportunistic pathogen that in people with a compromised immune system can cause, although infrequently, pneumonia, urinary tract or blood system infections. However, it is increasingly common in lung infections and in individuals with cystic fibrosis.

Stenotrophomonas maltophilia is acquired in the hospital, mainly through the use of infected urinary catheters as well as mechanical ventilation tubes, suction catheters and endoscopes that are also infected.

Streptococcus pyogenes

Gram positive bacteria, non-spore forming and nonmotile. Additionally it is aerotolerant and negative calasse. This coconut-shaped bacterium is an unusual component of the skin's bacterial flora and is usually pathogenic.

Its specific epithet (pyogenes) is due to the fact that it produces a series of infections that generate pus. Among the diseases it causes are scarlet fever, strep throat, rheumatic fever, and rheumatic heart disease.

The bacteria can be transmitted in a number of ways, including inhalation of respiratory particles from an infected person, contact with contaminated skin or objects, and through contaminated food.

Streptococcus pneumoniae

It is a Gram-positive, facultative anaerobic, coconut-shaped bacterium, usually found in pairs (diplococcus). This bacterium, also known as pneumococcus, is nonmobile and does not form spores. It can be alpha or beta hemolytic in the presence or absence of oxygen, respectively.

It is the main cause of pneumonia, but it can also cause other diseases, including meningitis, sepsis, bronchitis, rhinitis, osteomyelitis, peritonitis, cellulitis and even brain access, among others.

This bacteria can reside in the skin, respiratory tract and nasal cavity of healthy people. However, in people with weakened or compromised immune systems, it can become pathogenic. The route of infection can be autoinoculation or through breath drops from infected people.

Corynebacterium diphtheriae

It is a Gram-positive, nonmotile, facultative anaerobic rod that does not produce spores. It is also characterized by having arabinose, galactose and mannose in its cell wall and by containing metachromatic granules.

It is the main causative agent of diphtheria, which can be pharyngeal, tonsillar, laryngeal, nasal or cutaneous. It can cause the appearance of a pseudomembrane in the affected area, which can cause death due to obstruction of the airways.

The form of contagion is through particles from the breath of an infected person during respiration, and it can also occur through direct contact with secretions from skin lesions.

Bacillus cereus

Gram-positive, mobile, aerobic and facultative anaerobic bacillus that sporulates in the presence of oxygen. It is a ubiquitous bacterium in all temperate zones of the world, commonly found in soil, water, and food.

This species is responsible for most outbreaks of foodborne illness, such as fried rice syndrome and diarrhea. It can also cause other diseases such as endocarditis, chronic skin infections that are difficult to eradicate, and musculoskeletal infections.

The form of contagion is by eating contaminated and poorly handled food. Bacillus cereus is capable of forming heat resistant endospores.

Other meanings

Botany

In botany, it is called the mesophyll, the tissue that grows between the epidermis of the upper face (upper surface) and lower surface (underside of the leaves). It is made up of chlorenchyma, a tissue specialized in photosynthesis, and the veins of the leaves, of vascular tissue.

This type of tissue can be made up of one or two types of cells. In the first case, it is said to be homogeneous, while if it is made up of two different types of cells, it is called heterogeneous mesophyll.

Anatomy of a leaf. Taken and edited from: the work of H McKenna..

Plant ecology

In this field, the term mesophilic is used to define plants or plant formations (mesophilic forests) that inhabit moderate environmental conditions, especially with regard to moderate humidity conditions.

References

1. EW Nester, CE Roberts, NN Pearshall & BJ McCarthy (1978). Microbiology. 2 ^nd edition. Holt, Rinehart & Winston.
2. RY Stanier, M. Doudoroff & EA Adelberg (1970). The microbial world. Prentice-Hall, Inc.
3. Mesophile. On Wikipedia. Recovered from en.wikipedia.org.
4. C. Lyre. Corynebacterium diphtheriae: general characteristics, taxonomy, morphology, culture, pathogenesis. Recovered from lifeder.com.
5. C. Lyre. Bacillus cereus: characteristics, morphology, habitat, contagion symptoms, treatment. Recovered from lifeder.com.
6. C. Lyre. Bacteria: general characteristics, morphology, types (classification), reproduction, nutrition, caused diseases. Recovered from lifeder.com.
7. Mesophilic organism. On Wikipedia. Recovered from wikipedia.org.
8. Listeria monocytogenes. On Wikipedia. Recovered from en.wikipedia.org.
9. Stenotrophomonas maltophilia. On Wikipedia. Recovered from en.wikipedia.org.
10. Streptococcus pyogenes . On Wikipedia. Recovered from en.wikipedia.org.