Conditionally pathogenic bacteria include: Opportunistic microflora

Veillonella, their properties and role in pathology.

PEPTOSTREPTOCOCCI, their properties and role in pathology.

PEPTOCOCCAS, their properties and role in pathology.

PLAN

1 .General characteristics of opportunistic microorganisms.

2 .PROTEAS:

prevention.

3.PSEUDOMONADS: taxonomy, morphology, cultural,

enzymatic properties, resistance, toxin formation,

antigenic structure. Pathogenesis of diseases caused by them

microbiological diagnostic methods, treatment and

prevention.

4. KLEBSIELLA: taxonomy, morphology, cultural,

enzymatic properties, resistance, toxin formation,

antigenic structure. Pathogenesis of diseases caused by them

microbiological diagnostic methods, treatment and

prevention.

5. bacteroids: taxonomy, morphology, cultural, enzymatic properties. Diseases caused by them, the material being studied and its transportation to the laboratory. Laboratory diagnosis, treatment and prevention.

UPM (opportunistic, potentially pathogenic) – a large group of microbes heterogeneous in their systematic position that enter into relationships with the human body in some cases of symbiosis, commensalism or neutralism, and in others into competitive relationships, often leading to the development of disease.

UPMs are found among all groups of microbes: bacteria, fungi, protozoa and, probably, viruses. In modern human pathology, representatives of the genera Escherichia, Proteus, Klebsiella, Enterobacter, Serratia, Staphylicoccus, Streptococcus, Peptococcus, Haemophilus, Vibrio, Bacillus, Bacteroides, Clostridium, Mycobacterium, Treponema, Candida and others are of great importance.

Most types of UPM are normal inhabitants of the skin and mucous membranes of the human body, without exerting a pathogenic effect on a healthy body. They are often found in water, soil, food products, on objects and other objects of the external environment, which is associated with their massive release from the host’s body, their ability to survive for a relatively long time in the external environment, and under certain conditions, to reproduce in it. UPM have a pathogenic effect on the human body under conditions of passive penetration into the internal environment in large quantities, or a sharp decrease in general and local human immunity.

They have a pathogenic effect on the body with the help of endotoxin and toxin enzymes.

Diseases caused by UPM differ in many ways from those caused by obligate pathogenic microorganisms:

· UPM do not have a strictly defined organ localization: the same type can cause damage to many organs;

· opportunistic infections are polyetiological; the same clinical form can be caused by essentially any UPM;

· the clinical picture of opportunistic infections is not very specific: their semiotics depends more on the affected organ than on the etiological agent;

· opportunistic infections often occur as mixed infections. They often overlap existing infectious and non-infectious diseases, i.e. they are secondary infections and are caused by a combination of pathogens;

· opportunistic infections tend to have an acute-chronic or chronic course, which is associated with a weakened elimination ability of the human body;

· although opportunistic infections begin as local, local processes, they always retain the potential for the development of septicopyemia and metastasis;

· effectiveness of therapy, including antimicrobial, in many forms

opportunistic infections are small, which is due to the high resistance of UPM to antimicrobial drugs and the reduced ability of the body to develop an effective immune response to Ag from UPM.

Opportunistic infections are widespread in healthcare facilities. With them, the contagiousness of patients and carriers is relatively low, and the susceptibility of healthy people is low.

Diagnosis of opportunistic infections is very difficult; it is necessary to use an effective set of differential diagnostic media to identify microbes with the establishment of their generic, species and variant affiliation.

A huge number of harmful and beneficial microorganisms live on and inside the human body. There is also an intermediate variant called opportunistic flora (OPF). These microorganisms are so named because they do not harm the body under normal conditions. But under certain circumstances, representatives of opportunistic flora living on the mucous membranes of the nasopharynx, intestines, genitals, skin and other organs can unexpectedly become active and transform into harmful microorganisms. For example, soor in a smear on the flora indicates the development of candidal stomatitis, in other words, thrush; detritus in the smear indicates the death of epithelial cells due to the proliferation of one of the varieties of pathogenic flora.

What is a bacterium? These are microorganisms that consist of one single cell, the structure of which can be very complex. Depending on the variety, they have very different capabilities. For example, there are bacteria that can live in conditions above the boiling point and below the freezing point. These microorganisms are also capable of processing everything from sugar and carbohydrates to seemingly “indigestible” substances such as sunlight, sulfur and iron.

According to scientific classification, bacteria belong to living beings called “prokaryotes”. A special feature of prokaryotes is that their genetic material (DNA) is not limited to the nucleus shell. Bacteria, like their closest “relatives”, archaea, are one of the earliest forms of life that arose on Earth. They played a key role in shaping the appearance of the planet, contributing to the emergence of more advanced forms of life through the emergence of the process of photosynthesis.

To survive, polymorphic bacteria settle on various organisms of the plant and animal world. Humans are no exception; bacteria that have settled in the body are often called flora.

Why are lactobacilli needed?

One of the most common tests to determine the balance between beneficial and opportunistic flora is a flora smear in women. Most microorganisms found in the vagina can be harmful to the vaginal environment. Exceptions include Lactobacillus species.

The microbes most often found in the vaginal flora include Lactobacillus bacteria, which are responsible for the health of the vagina. In addition to healthy lactobacilli, the most common pathogens found in the vagina include Gardenerella vaginalis and Streptococcuus, which infect the vagina. But this is only a small part of the flora that can be present in the vagina, both in a healthy and infected state.

Lactobacilli are one of the types of microorganisms that support a healthy vaginal microbiome. There are different species of Lactobacillus that can colonize the vaginal flora, but the most common species found in the vaginal mucosa is Lactobacillus acidophilus. This type of lactobacilli helps prevent bacterial vaginosis by producing hydrogen peroxide. During this disease, with a lack of lactobacilli, various microorganisms are able to colonize the vaginal area, which can lead to complications such as inflammatory diseases of the pelvic cavity, as well as sexually transmitted diseases, including HIV.

Research is currently underway to determine which Lactobacillus species has the strongest "decolonizing" ability (that is, preventing other bacteria from colonizing the vagina) in women with bacterial vaginosis. Currently, two varieties have been found that have these properties. To successfully cope with their task, they perform the following tasks:

• have the ability to produce sufficient amounts of hydrogen peroxide to have an inhibitory effect against the causative agents of bacterial vaginosis;
• produce sufficient amounts of lactic acid;
• have good ability to attach to the vaginal mucosa.

Studies show that the causative agents of bacterial vaginosis are able to activate HIV, while lactobacilli delay it. A species such as Lactobacillus acidophilus helps inhibit sexually transmitted diseases. The acid produced by lactobacilli also kills viruses.

Features of the study of lactobacilli

It should be noted that “healthy” vaginal microflora is a loose concept. As recent studies show, at what level of a certain type of flora a person is considered healthy depends greatly on the specific organism.

For example, every gynecologist will say that increased levels of lactobacilli are a necessity for every woman to maintain healthy microflora. The reason for this is the production of lactic acid by lactobacilli, which protects the flora from harmful microorganisms, the absence of which indicates the norm.

But according to recent research, some women can have lower levels of lactobacilli in their vaginas and still be completely healthy. In addition, the composition of the vaginal microflora detected in a smear in healthy women can vary greatly over short periods of time, while in others it remains constant. Research shows that changes in the vaginal microflora that put some women at risk for infection are completely normal and acceptable for other women. The continuation of these tests may greatly change the traditional point of view and reconsider the procedure for diagnosing and treating diseases such as vaginosis and vaginitis, in which the vaginal flora is considered to be conditionally disturbed.

This explains the need for multiple testing, when not one smear is performed on the flora, but a whole series of tests that will help the doctor determine what changes in the vaginal microflora occur over time. It often happens that doctors “play it safe,” deciphering just in case that the result is positive and diagnosing bacterial vaginosis. The new approach could significantly reduce the unnecessary prescription of antibiotics, which have various side effects, including the destruction of beneficial flora, which can be replaced by pathogenic microorganisms.

Research studies using genetic testing of bacteria in vaginal smears were conducted on a large group of women of different nationalities over a period of more than 4 months. At the same time, significant fluctuations were noted in some and relative constancy in others. In a small percentage of women, despite a reduced level of lactobacilli, the reproductive system was healthy, while others had problems despite an increased level of lactobacilli. As the researchers note, the factors that most strongly influence the composition of the microflora are sexual activity and menstruation (scanty blood flow may indicate problems).

Based on these studies, doctors are developing specific recommendations. In particular, a new classification of types of vaginal microflora is being carried out, and specific treatment recommendations are being developed. For example, some types of probiotics may be beneficial for some women's vaginal flora, but not for others. This also needs to be taken into account when the condition changes, for example during pregnancy, since the risk of vaginal infection in this case can have completely different consequences.

Harmful bacteria

Gardenerella vaginalis is one of the common pathogens that causes bacterial vaginosis. This microorganism changes the vaginal environment, increasing the pH level of the vagina. Because Lactobacillus produces lactic acid, which maintains natural acidity, Gardenerella vaginalis must outnumber other bacteria in order for the pH to increase and the balance necessary for health to be disrupted. In addition, Gardenerella vaginalis produces copious amounts of grey-yellow vaginal mucus with a fishy odor.

Gardenerella vaginalis is believed to be spread through sexual contact, but not only. Using showers and intrauterine devices also increases the risk of this bacteria growing and developing bacterial vaginosis. Gardenerella vaginalis, along with other bacteria, colonizes the vaginal microflora, causing a chemical imbalance. During vaginosis, the flora in the smear shows that the number of these bacteria significantly exceeds the number of lactobacilli.

Another type of opportunistic flora is group B streptococci (beta). Streptococcus agalactiae is a Gram-positive, beta-hemolytic, opportunistic pathogen. It colonizes the vaginal and gastrointestinal microflora of healthy adult women by adhering to epithelial cells.

This is a permanent inhabitant of the vaginal microflora in a healthy state, which waits for suitable conditions when the immune system weakens and the number of antibodies that prevent its reproduction and development decreases. After this, it begins to have negative and destructive effects on the vaginal environment and the body of the infected woman, which shows a bad smear.

The main method of Streptococcus agalactiae is to ferment hydrocarbons into non-gaseous products such as acetate. In addition, it has hemolytic properties that destroy blood: these microorganisms decompose red blood cells located around the colonies. This feature makes Streptococcus agalactiae especially dangerous when infecting newborns during childbirth. The hemolytic properties of Streptococcus agalactiae are facilitated by the cAMP factor, which destroys erythrocyte membranes. The pathology is not easy to identify, since genital colonization with Streptococcus agalactiae often occurs without symptoms.

The vagina is much more often colonized by Streptococcus agalactiae than the rectal areas of the intestine. Streptococcus can be transmitted to newborns from mothers through vertical transmission. This involves the mechanisms of adhesion (adhesion) to the vaginal epithelium, hemolysis (decomposition of red blood cells) and resistance to the immune defense of the vaginal mucosa. Streptococcus agalactiae is the most common cause of sepsis in newborns, pneumonia, septicemia, as well as various complications, including secondary meningitis.

It should also be noted that streptococcus agalactiae is a representative of developed bacteria with developed bacteria-host relationships. This microorganism has a priority program for influencing the pregnant woman’s body in order to ensure further colonization of the newborn’s body.

Interaction of microorganisms

Some microorganisms that live in the vagina tend to interact, while others, on the contrary, compete with each other. One striking example is the interaction of Lactobacillus acidophilus with Gardenerella vaginalis. Recent studies have shown that Lactobacillus acidophilus, Gardenerella vaginalis and Streptococcus agalactiae bind to the same epithelial cell receptor. However, Lactobacillus acidophilus has a significant advantage over competing microorganisms due to its more suitable structure. Therefore, Lactobacillus acidophilus is much more likely to establish itself and colonize the vaginal walls, displacing Gardenerella vaginalis and Streptococcus agalactiae.

Thus, lactobacilli not only help maintain an acidic environment in the vagina, but also ensure the constancy of the microbiome, competing with pathogenic microbes, the most common of which are Gardenerella vaginalisAndStreptococcus agalactiae. Current research is investigating the mechanisms by which Lactobacillus acidophilus inhibits the growth and development of Gardenerella vaginalis and Streptococcus agalactiae.

Researchers are studying the interactions of three representatives of lactobacilli, Lactobacillus acidophilus, Lactobacillus gasseri and Lactobacillus jensenii. These three species of lactobacilli compete for receptors in epithelial cells and use a method of aggregation (clustering of many bacteria in a small area) to slow down the growth and reproduction of competitors. This effect is enhanced by the production of antimicrobial substances, which include lactic acid and hydrogen peroxide.

Fungi and viruses

It should be noted that bacteria are not the only organisms that live in the human body. Viruses and fungi also live here, which, under favorable conditions, lead to serious diseases.

Fungi are eukaryotic organisms whose DNA is confined to the nucleus. They are similar in structure to plants, but do not use sunlight to produce energy because they are not adapted to photosynthesis. G

Fungi are extremely useful creatures for humans, since with their help they have been used to obtain antibiotics necessary to combat a huge number of dangerous bacterial infections. But fungi can also be dangerous and cause illness and infection. Fungi come in a wide variety of shapes, sizes, and types. They come in the form of giant chains of cells that can stretch in a line for several kilometers, or in the form of a single cell. An example of a fungal infection of the vagina is candida, when candidal stomatitis develops. In this case, fungi are unlikely to be absent from the smear. Their presence will help the doctor determine a treatment regimen. To monitor therapy, the analysis will need to be repeated periodically so that the doctor can be sure whether the patient has candidiasis or not.

A virus is a small clump of genetic material (DNA or RNA). This material is located in the viral envelope, which is made up of pieces of proteins called capsomeres. Viruses cannot independently process nutrients, produce and remove waste, move independently, or even reproduce. To do this, the virus requires a host cell.

Despite the fact that these creatures are not even a full-fledged cell in the normal sense of the word, they played a key role in the history of planet Earth in the process of shuffling and redistributing genes within living organisms, causing various diseases in the body of humans, animals, and plants. A good example of a common virus in the vaginal flora that causes viral vaginitis is Herpes simplex, which can be detected by opportunistic culture.

A wide variety of bacteria are constantly present in the human body. All of them are in different relationships with their carrier. Most of the human microflora is formed by microbes that are symbiotic, that is, they receive some benefit from the body and at the same time play a certain role in its functioning. In addition to them, there are so-called conditionally pathogenic microorganisms, which under normal conditions do not pose any health hazard, but in a specific situation can begin to actively multiply and provoke the development of diseases.

Proteus bacterium under a microscope

There are certain criteria under which conditionally pathogenic bacteria can become dangerous to the body. These include:

• frequent consumption of alcoholic beverages;
• smoking;
• constant stress;
• serious physical activity;
• use of antibiotics;
• past infections.

All these factors can easily contribute to disruption of the normal balance of the microflora of the whole body, as they often cause the death of beneficial bacteria. In turn, the vacated space is occupied by conditionally pathogenic flora. Most often, this occurs in the gastrointestinal tract, contributing to the development of dysbiosis, which almost everyone has encountered.

Varieties of opportunistic bacteria

All people's normal flora is highly individual, and its composition differs in each specific case. Unlike obligate pathogenic bacteria, opportunistic microbes can be beneficial. By constantly fighting their effects, microorganisms in the beneficial microflora become more resilient, and immunity gradually increases. Therefore, the role of conditionally dangerous bacteria is quite important, and if you completely get rid of them, you can harm the body, causing a general weakening of immune functions.

Klebsiella pneumonia, which causes pneumonia, under a microscope

In the gastrointestinal tract, opportunistic enterobacteria are present in considerable quantities, namely:

• Klebsiella pneumonia;
• enterobacters such as aerogenes and cloacea;
• proteas;
• Citrobacter freundi.

Potentially pathogenic microorganisms also include non-hemolytic (that is, those that are not able to dissolve red blood cells) types of staphylococcus. Quite a lot of UPM are found in the large intestine, where they actively participate in lipid metabolism. The presence of streptococci is also allowed, the functions of which include activating the body's production of immunoglobulins and combating obligate pathogenic microbes, such as salmonella and shigella.

There are potentially pathogenic microorganisms that can, in fairly rare cases, cause the development of serious infections, for example, veillonella and fusobacteria. These conditionally pathogenic bacteria are usually located in the oral cavity and do not cause harm to health. However, if they enter the intestinal area, these microbes can provoke severe inflammatory processes. But not much is known about them, therefore, when conducting various studies concerning the causes of dysbiosis and the properties that characterize intestinal infections, they are not taken into account.

Helicobacter pylori bacterium, which lives in the gastric mucosa and causes gastritis and ulcers

Much more information is available about the conditionally dangerous bacteria Helicobacter pylori. These microorganisms live primarily in the stomach and are often the cause of gastritis and peptic ulcers. It is extremely difficult to treat such diseases caused by opportunistic microbes, since this species is highly resistant to antimicrobial drugs.

Features of diseases provoked by UPM

Unlike other toxic infections, diseases caused by opportunistic microorganisms have a number of signs by which they can be recognized:

1. UPM can affect different organs, not just one specific one.
2. These infections often have a blurred clinical picture and occur as mixed diseases, often superimposing on existing infections and other diseases and thus being secondary lesions.
3. Infections that are caused by potentially pathogenic microorganisms in most cases have a chronic course.
4. With such bacterial diseases, the body’s protective functions are usually reduced and therapy is ineffective.

UPM as sources of nosocomial infections

The sources may be the patients themselves, who have characteristic signs of disease, or carriers of the infection. Often infection occurs from the external environment, since some potentially pathogenic microorganisms can only spread in this way. In addition, the cause of hospital infections can be those UPMs that thrive in a humid environment; heating and ventilation systems, air humidifiers, distillers and other similar devices are suitable for them. Therefore, their correct processing is of great importance.

Some pathogens of opportunistic infections have the ability to reproduce while in liquids that are intended for disinfection and are an antiseptic.

A conditionally dangerous microorganism, when exposed to favorable conditions, can easily cause nosocomial (hospital-acquired) diseases. The characteristics of these infections most often depend on the department in which they occur. To prevent such developments, it is necessary to take basic preventive measures. As a result of competently carried out prevention, opportunistic and obligate pathogenic microorganisms are almost completely removed from the hospital. First of all, this is disinfection and sterilization. In addition, it is necessary to minimize the risk of bacteria entering from the outside, as well as their removal outside the hospital.

Conditionally dangerous microorganisms by themselves will never cause any diseases. For this to happen, certain conditions must be met. Therefore, it is enough to lead a healthy lifestyle, avoid nervous tension, eat right and treat any infectious diseases in a timely manner.

Most of the living matter on Earth is represented by microbes. At the moment, this fact has been established precisely. A person cannot be completely isolated from them, and they have the opportunity to live in or on it without causing harm.

About microbes

On the surface of the human body, on the internal membranes of its hollow organs, there is a whole crowd of microorganisms of various types and types. Among them we can distinguish facultative (they may or may not be present) and obligate (every person must have them). What is opportunistic microflora?

The process of evolution has influenced the relationship of the organism with the microbes found in it and led to a dynamic equilibrium controlled by the human immune system and some competition between different types of microbes, which is considered the norm.

However, this community of microbes also contains those that can cause any disease under conditions often beyond their control. This is opportunistic microflora. There are quite a large number of these microorganisms, for example, they include some types of clostridia, staphylococci and Escherichia.

A person and the bacteria living in his body have quite diverse relationships. Most of the microbiocenosis (microflora) is represented by microorganisms that coexist with humans in symbiosis. In other words, we can say that a relationship with him brings them benefits (ultraviolet protection, nutrients, constant humidity and temperature, etc.). At the same time, bacteria also bring benefits to the host body in the form of competition with pathogenic microorganisms and their survival from the territory of their existence, in the form of breakdown of proteins and synthesis of vitamins. At the same time as beneficial bacteria, humans have cohabitants that do not cause much harm in small quantities, but become pathogenic under certain circumstances. These are opportunistic microorganisms.

Definition

Opportunistic pathogens are microorganisms that represent a large group of fungi, bacteria, protozoa and viruses that live in symbiosis with humans, but under certain conditions cause a variety of pathological processes. The list of the most common and well-known includes representatives of the genera: aspergillus, proteus, candida, enterobacter, pseudomonas, streptococcus, escherichia and many others.

What else is interesting about opportunistic microflora?

Scientists cannot define a clear boundary between microbes and non-pathogenic microbes, since their pathogenicity in most cases determines the state of the body. Thus, we can say that the microflora that was identified during a study in an absolutely healthy person can cause illness in another, followed by death.

The manifestation of pathogenic properties in opportunistic microorganisms can only occur during a sharp decrease in the body’s resistance. A healthy person constantly has these microorganisms in the gastrointestinal tract, on the skin and mucous membranes, but they do not cause the development of pathological changes and inflammatory reactions in him.

For the time being, it is not dangerous to humans. But there are nuances.

Therefore, opportunistic microbes are called opportunists, since they take advantage of any favorable opportunity for intensive reproduction.

In what cases should you be afraid of such an infection?

However, we can talk about the occurrence of problems in the case when, for some reason, immunity is greatly reduced, and this was discovered during the examination. Opportunistic microflora is then truly dangerous to health.

This is possible in some situations: with a severe respiratory viral infection, acquired or congenital immunodeficiency (including HIV infection), with diseases that reduce immunity (diseases of the cardiovascular system and blood, diabetes mellitus, malignant tumors and others), taking medications , which suppress the immune system (chemotherapy for cancer, corticosteroids, cytostatics and others), during hypothermia, severe stress, extreme physical activity or other extreme environmental influences, during breastfeeding or pregnancy. Each such factor individually and in combination with several of them is especially capable of causing opportunistic bacteria to develop a fairly serious infection and become a threat to human health. When required

Staphylococcus aureus

In doctoral practice, the following situations are often encountered: when a positive test for Staphylococcus aureus is obtained on a smear from the nose, pharynx, breast milk or skin surface, an absolutely healthy person may become too worried and require a specialist to carry out therapy, including antibiotics. This concern can be easily explained, but it is often unfounded, since almost half of the people around the world have Staphylococcus aureus and do not even know it. This microorganism is an inhabitant of the mucous membrane of the upper respiratory tract and skin. This is typical for such a category as opportunistic microorganisms.

It also has phenomenal resistance to various environments: the effects of many antibiotics, treatment with antiseptics, cooling and boiling. This reason makes it almost impossible to get rid of it. All household appliances, surfaces in the house, toys and furniture are contaminated with it. And only the ability of the skin’s immunity to weaken the activity of this microorganism saves most people from death due to infectious complications. Otherwise, the growth of opportunistic microflora, and in particular staphylococcus, would be unstoppable.

We can conclude that the only factor that Staphylococcus aureus cannot cope with is human immunity. Entry into the high-risk category occurs when a person’s defenses are weakened. In this case, it can cause serious illnesses, such as pneumonia, meningitis, as well as infectious lesions of soft tissues and skin (phlegmon, abscess, felon and others), cystitis, pyelonephritis and others. The only possible treatment for staphylococcus is the use of antibiotics to which this microorganism is sensitive. What opportunistic intestinal microflora exists?

Escherichia coli

E. coli is considered a natural inhabitant of the lower digestive tract of every person. Without it, the intestines would not be able to function fully, since it is very important for the digestion process. This microorganism also promotes the production of vitamin K, which is involved in the process of blood clotting, and prevents the overly active development of pathogenic strains of intestinal bacteria that cause very serious diseases.

Escherichia coli is not able to exist for a long time outside the host’s body, since the most comfortable conditions for it are on the surface of the intestinal mucosa. But this very useful and harmless bacterium can also serve as a source of real threat when it enters the abdominal cavity or the lumen of other organs. This becomes possible when intestinal flora is introduced into the urinary tract, vagina, or with peritonitis (the appearance of an opening that serves as an outlet for intestinal contents). This mechanism leads to the occurrence of prostatitis, vulvovaginitis, cystitis, urethritis and other diseases. Regular culture of microflora is required.

Viridans streptococcus

This also applies to opportunistic bacteria, since it is found in most people. Its favorite location is the oral cavity, or more precisely the mucous membrane that covers the gums, and tooth enamel. This microbe is also found in swabs from the nose and throat. The peculiarity of viridans streptococcus is that in saliva, with an increased glucose content, it is capable of destroying tooth enamel, causing pulpitis or caries. A smear for opportunistic microflora is carried out by a doctor.

Prevention

We can say that moderate consumption of sweets and simple oral hygiene after eating are the best prevention of these diseases. In addition, sometimes viridans streptococcus causes other ailments: tonsillitis, sinusitis, pharyngitis. The most serious diseases that viridans streptococcus can cause are meningitis, pneumonia, endocarditis and pyelonephritis. However, they only develop in a very small group of people who are considered high risk.

What if the bacterial culture is normal and opportunistic microflora is not detected? This situation happens quite often. This means a variant of the norm.

Treatment

The only correct method of treating E. coli, viridans streptococcus and staphylococcus is the use of antibiotics. But it must be accompanied by certain indications, which do not include carriage if it is asymptomatic.

Pathogenic bacteria are bacteria that can cause infection. Most bacteria are harmless or even beneficial, but some are pathogenic. One high-burden bacterial disease is tuberculosis, caused by the bacterium Mycobacterium tuberculosis, which kills about 2 million people per year, mainly in sub-Saharan Africa. Pathogenic bacteria contribute to the development of other globally significant diseases such as pneumonia, which can be caused by bacteria such as Streptococcus and Pseudomonas, and foodborne illnesses, which can be caused by bacteria such as Shigella, Campylobacter and Salmonella. Pathogenic bacteria also cause infections such as tetanus, typhoid fever, diphtheria, syphilis and leprosy. Pathogenic bacteria are also responsible for high infant mortality rates in developing countries. Koch's postulates are the standard establishing the relationship between the causative microbe and the disease.

Diseases

Each type of bacteria exhibits a specific effect and causes symptoms in infected people. Some, or even most, people infected with pathogenic bacteria have no symptoms. People with weakened immune systems are more susceptible to pathogenic bacteria.

Pathogenic susceptibility

Some pathogenic bacteria cause illness under certain conditions, such as when they enter the skin through a cut, during sexual activity, or when immune function is weakened. Streptococcus and Staphylococcus bacteria are part of the normal microflora of the skin and are usually present in healthy skin or in the nasopharyngeal area. However, these species have the potential to initiate skin infections. They can also cause sepsis, pneumonia and meningitis. These infections can become quite serious and provoke a systemic inflammatory response, leading to severe vasodilation, shock, and death. Other bacteria are opportunistic pathogens and cause disease primarily in people suffering from immunosuppression or cystic fibrosis. Examples of these opportunistic pathogens include Pseudomonas aeruginosa, Burkholderia cenocepacia, and Mycobacterium avium.

Infections in a specific tissue

Bacterial pathogens often cause infections in certain areas of the body. Other pathogens are generalists. Bacterial vaginosis is caused by bacteria that alter the vaginal flora, causing overgrowth of bacteria that crowd out the lactobacilli species that maintain a healthy vaginal microbial population. Other nonbacterial vaginal infections include: yeast infection (candidiasis) and trichomonas (trichomoniasis). Bacterial meningitis is a bacterial inflammation of the meninges, that is, the protective membranes covering the brain and spinal cord. Bacterial pneumonia is a bacterial infection of the lungs. Urinary tract infections are predominantly caused by bacteria. Symptoms include urgency and frequency to urinate, pain while urinating, and cloudy urine. The main causative agent is Escherichia coli. Urine is usually sterile, but contains many salts as well as excretory products. Bacteria can ascend to the bladder or kidneys, causing cystitis and nephritis. Bacterial gastroenteritis is caused by pathogenic intestinal bacteria. These pathogenic species typically differ from the usually harmless bacteria of normal intestinal flora. But other strains of the same species can be pathogenic. It is sometimes difficult to distinguish them, as is the case with Escherichia. Bacterial skin infections include:

Mechanisms

Nutrients

Iron is a substance essential for humans and also for the growth of most bacteria. To obtain free iron, some pathogens secrete proteins called siderophores, which remove iron from transport proteins by binding even more tightly to the iron. Once the iron-siderophore complex is formed, it is captured by siderophore receptors on the surface of the bacteria, and the iron is then introduced into the bacteria.

Direct damage

Once pathogens attach to host cells, they can cause direct damage as pathogens use host cells to obtain nutrients and produce waste products. As pathogens multiply and divide within host cells, the cells typically break down and intercellular bacteria are released. Some bacteria, such as E. coli, Shigella, Salmonella, and Neisseria gonorrhoeae, can induce uptake into host epithelial cells in a process resembling phagocytosis. The pathogens can then destroy the host cells as they pass through and are expelled from the host cells through a process of reverse phagocytosis, allowing them to enter other host cells. Some bacteria can also enter host cells by secreting enzymes and using their own motility; such penetration itself may cause damage to the host cell.

Toxin production

Toxins are poisonous substances that are produced by certain microorganisms and are often the main contributing factor to the pathogenic properties of microorganisms. Endotoxins are lipid regions of lipopolysaccharides that are part of the outer membrane of the cell walls of Gram-negative bacteria. Endotoxins are released when bacteria are lysed, which is why after treatment with antibiotics, symptoms may initially worsen as the bacteria die and release their endotoxins. Exotoxins are proteins produced within pathogenic bacteria as part of their growth and metabolism and are most common in gram-positive bacteria. Exotoxins are released when bacteria die and the cell wall breaks down. Exotoxins have very specific effects on body tissue and function, destroying specific parts of the host cell or inhibiting certain metabolic functions. Exotoxins are among the most dangerous substances known. Just 1 mg of botulinum exotoxin is enough to kill one million guinea pigs. Diseases caused in this way are often caused by small amounts of exotoxins rather than by the bacteria themselves.

Treatment

Bacterial infections can be treated with antibiotics, which are classified as bactericidal if they kill bacteria, or bacteriostatic if they only prevent the growth of bacteria. There are many types of antibiotics and each class inhibits a process whose pathogen is different from the pathogen in the host. For example, the antibiotics chloramphenicol and tetracycline inhibit the bacterial ribosome, but not the structurally different eukaryotic ribosome, so they have selective toxicity. Antibiotics are used both in the treatment of human diseases and in intensive agriculture to promote the growth of animals. Both applications can contribute to the rapid development of antibiotic resistance in bacterial populations. Phage therapy can also be used to treat some bacterial infections. Infections can be prevented by antiseptic measures such as sterilizing the skin before using a syringe needle and proper care of catheters. Surgical and dental instruments are also sterilized to prevent bacterial contamination. Disinfectants such as bleach are used to kill bacteria or other pathogens on surfaces to prevent contamination and further reduce the risk of infection. Bacteria in food are killed by cooking to temperatures above 73 °C (163 °F).

List of the most famous pathogenic bacteria

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