COLIFORMS: CHARACTERISTICS, TYPES, GENERA, DISEASES - BIOLOGY - 2025

The coliforms are a group of bacteria that a number of features grouped together. They all belong to the Enterobacteriaceae family and are generally part of the normal bacterial flora of the digestive tract of some animals.

It owes its name to the best known member of this group, the Escherichia coli bacteria. However, coliform bacteria group four bacterial genera: Escherichia, Enterobacter, Klebsiella, and Citrobacter.

Escherichia coli, the best known coliform bacteria. Source: IDKlab

From an ecological point of view, these bacteria are important because they constitute an indicator of the levels of contamination in water bodies. The presence of these bacteria indicates that the water is contaminated with fecal matter. Likewise, some are important pathogens for man.

Taxonomy

The taxonomic classification of coliform bacteria is as follows:

• Domain: Bacteria
• Kingdom: Monera
• Phylum: Proteobacteria
• Class: Gammaproteobacteria
• Order: Enterobacteriales
• Family: Enterobacteriaceae.
• Genres: Escherichia, Enterobacter, Citrobacter, Kleibsella

characteristics

Despite the fact that coliform bacteria are made up of several genera, they have certain characteristics that they share.

Shape

This group of bacteria are characterized by having a rod shape, which is why they are known as bacilli. They are elongated, measuring approximately 3 to 6 microns, and some have rounded edges, while others have curved edges.

Habitat

These bacteria are found throughout the world geography, mainly in soils. Some grow on decaying organic matter.

Likewise, they are an integral part of the bacterial flora of the intestine of some warm-blooded animals such as humans.

They are gram negative

Coliform bacteria are gram negative. This means that when they are subjected to the Gram staining process, they do not acquire the typical violet color, but rather a fuchsia hue.

This is due to the configuration of its cell wall, which is made up of peptidoglycan and is very thin. Being thin, it is not able to retain the gram dye particles.

They are aerobic or facultative anaerobes

An aerobic organism is one that must be in an oxygen-rich environment in order to develop. Likewise, facultative anaerobes can develop in environments in which there is oxygen availability, or lack of it. Some of the coliform bacteria are strictly aerobic, while others are facultative anaerobic.

They are oxidase negative

Coliform bacteria do not have the ability to synthesize any of the enzymes of the group of cytochrome c oxidases. This means that they cannot use oxygen as an acceptor in the electron transport chain.

They are not sporogenic

Gram negative bacteria, including coliforms, are characterized by not producing spores. In this way they lack that protection mechanism when environmental conditions turn hostile.

Ferment lactose

One of the most distinctive characteristics of coliform bacteria is that they have the ability to ferment lactose, generating gas in the process within 48 hours at average temperatures of 37 ° C. However, there is another group of bacteria within coliforms, which can carry out the process at much higher temperatures of between 42 and 45 ° C.

Types

Many people tend to think that coliform bacteria are all fecal in origin. However, this thinking is wrong, since there are some members of this group of bacteria that do not meet this characteristic.

This is why specialists have decided to classify coliform organisms into two large groups: total and thermotolerant.

Total coliforms

The group of total coliform bacteria is made up of a wide variety of bacteria that have a bacillary shape and are gram-negative, in addition to being facultative anaerobes, which means that they can develop both in the presence and in the absence of oxygen.

Total coliforms encompass all coliform bacteria, within which there are genera that can be pathogenic for humans, as well as others that are totally innocuous.

These bacteria are quite useful as indicators of the levels of contamination or cleanliness of the waters. Taking into account that many of the coliform bacteria proliferate and develop in fecal matter, they are an excellent indicator of water contamination by fecal matter. The more coliforms there are in the water, the more serious and intense is its contamination.

Thermotolerant or fecal coliforms

This is a subgroup within the total coliform bacteria. They are known as thermotolerant because they have the peculiarity of being able to ferment lactose at extremely high temperatures, between 44 and 45 ° C.

These bacteria are also known as fecal coliforms because they generally have their origin in the intestines of some animals. Because of this, they are contained in fecal matter.

The genera that make up the group of thermotolerant bacteria are Escherichia, Enterobacter and Klebsiella, being the most representative of all the bacteria Escherichia coli.

Due to their known fecal origin, thermotolerant coliform bacteria, especially Escherichia coli, are a very effective and unequivocal indicator of contamination of water bodies by fecal matter.

Genera that make up coliform bacteria

The group of coliform bacteria is made up of a total of four widely known genera: Escherichia, Enterobacter, Klebsiella and Citrobacter.

Now, despite the fact that these four genres have similar characteristics, they also present distinctive characteristics that differ from each other.

Escherichia

This is a genus of bacteria that is well known and studied, thanks to its pathogenic potential. They are bacteria that are rod-shaped with rounded edges. They measure approximately between 0.5 and 3 microns and are part of the intestinal flora of some animals, living in them as a commensal.

This is so for a large part of the species that make up this genus. However, there are species that are considered pathogens, the most representative of this group being Escherichia coli.

The pathologies caused by bacteria of the genus Escherichia are mainly focused on the digestive level, such as gastrointestinal syndromes, whose main symptoms are diarrhea and colic. Likewise, these bacteria can generate disorders in the genitourinary tract.

Enterobacter

The Enterobacter genus is very well known in the medical field, since it is the cause of a large number of opportunistic infections. They are found mainly in soils (some are decomposers of dead organic matter), in water and in some dairy products.

One of their most outstanding characteristics is that from a nutritional point of view they are very undemanding. Although this genus encompasses a large number of species, the best known and considered to be the most important are: Enetrobacter cloacae, Enterobacter sakozaki and Enterobacter aerogenes. These are those that are generally associated with pathological processes in which they are the causal agents.

Klebsiella

The bacteria belonging to this genus are bacillary in shape, thick and short, with curved edges. Likewise, they do not present any type of flagellum or appendix that helps them in locomotion, so that they are immobile bacteria. They tend to be in pairs or very short chains.

Among its characteristics it can be mentioned that its cells are surrounded by a highly resistant capsule, made up of polysaccharides. That capsule is one of its distinctive elements.

These bacteria are mainly found in aquatic habitats and tend to reproduce very quickly when the required nutrients are available.

Klebsiella specimen seen under the electron microscope. Source: NIAID

Within this genus there are approximately 13 species, however, the most important from a sanitary and health point of view are: Klebsiela pneumoniae, Klebsiella ozaenae, Klebsiella oxytoca and Klebsiella rhinoscleromatis.

These are considered pathogens and are responsible for pathologies such as urinary tract infections, infections of the digestive tract, upper respiratory tract and respiratory tract in general.

Citrobacter

This is one of the genera of coliform bacteria that causes a wide variety of pathologies in humans. These pathologies include brain abscesses and urinary tract infections.

They are mobile bacteria, rod-shaped with an average size of between 2.5 and 6 microns in length. It shares with the rest of the coliform bacteria certain characteristics such as, for example, that they are catalase positive, reduce nitrates to nitrites and are gram negative. It is also indole positive and can ferment glucose.

Some of its species are pathogenic, the best known and most studied being Citrobacter freundii.

Diseases caused

The four genera that make up the group of coliform bacteria are responsible for various pathologies in humans. Sometimes they are opportunistic infections, generated by the individual's immunosuppression.

-Urinary infection

It is the most common infection caused by coliform bacteria. Taking into account that these bacteria are regular inhabitants of the digestive tract, it is common for them to spread from the anus to the urethra. This occurs more frequently in women, since the distance between the anus and the urethral orifice is less than in men.

Symptoms

People with a UTI have the following symptoms:

• Pressure in the pelvis
• Increase in urinary frequency.
• Discomfort in the lower abdomen.
• Feeling of incomplete emptying of the bladder.
• Burning when urinating
• Blood in the urine (in some cases)

However, if these symptoms are not treated in time, the infection can spread from the lower urinary tract to the kidneys. If this occurs, the following signs and symptoms occur:

• Nausea and vomiting
• High fever
• Pain in the kidneys and in the back.
• Shaking chills.

It is important to attend to these symptoms as soon as they appear, since otherwise it can generate more serious clinical conditions, such as kidney failure.

Diagnosis

This type of pathology can be diagnosed through several tests:

-Routine urine test: in this the specialist makes a complete study of the urine, in which he could observe some indication of urinary infection, such as traces of blood, the presence of leukocytes and even bacterial cells.

- Imaging studies: the most used methods are renal and pelvic ultrasound and tomography. Through these non-invasive medical procedures, it is possible to visualize organs such as the kidney, ureters, urethra, and bladder. In this way, it can be determined if there is any structural abnormality that may be the result of an infection.

-Uroculture: it is the most accurate test to diagnose a urinary infection caused by any of the coliform bacteria. In this, what is done is that from a urine sample, a culture is carried out in the laboratory, using the most indicated culture media. If any of the coliform bacteria are causing the infection, they will grow on the prepared culture.

Culture of the bacteria is the definitive diagnostic test. Source: Sun14916

Treatment

Taking into account that this infection is caused by bacteria, the most used therapy is antibiotics. Among the antibiotics most used to solve this infection are:

• Ceftriaxone
• Nitrofurantoin
• Sulfamethoxasol
• Fofomycin

It is important to comply with the treatment time. In the case of recurrent infections, the doctor will decide the most appropriate treatment scheme for each particular case.

-Enteric infections

They are infections that develop in the gastrointestinal tract. It is common for coliform bacteria to be responsible for these types of infections, since they are normally part of the bacterial flora of the digestive tract.

Symptoms

The most common symptoms for infections of this type are:

• Frequent stools, pasty to liquid consistency.
• Pain in the abdominal area
• Bloody stools and / or mucus
• Vomiting
• Fever
• Headache
• General discomfort.

Diagnosis

It is important that when you have an intestinal infection that causes watery stools, a stool exam is performed.

In the stool examination, the specialist will study some parameters such as the presence of hidden blood or mucus, which are unequivocal evidence of an infection.

Likewise, it is possible that a stool culture is made in which a culture is carried out with a stool sample to verify if there are any bacteria growing and developing. In the event that there are any of the coliform bacteria there, they will begin to reproduce, forming colonies and allowing their identification.

Treatment

If the symptoms are mild, the most common is that the doctor recommends that the patient increase the intake of fluids to restore those that he has lost in frequent bowel movements.

Likewise, he may prescribe some type of antibiotic to eradicate the bacteria causing the disease. However, as is due, the doctor will be the one who decides what is the treatment pattern to follow according to the patient and according to the severity of the case.

-Pneumonia

This is an infection that affects the lung tissue. Some bacteria of the genus Klebsiella are known causative agents of pneumonia. If it is not attended to in time it can be life threatening.

Symptoms

Among the most common symptoms of pneumonia are:

• Coughing up phlegm, which may be purulent or bloody.
• High fever
• Malaise and general decay
• Chest pain that may be worse with breathing movements.
• Nausea and vomiting
• Increase in heart rate and decrease in blood pressure.

Diagnosis

There are several diagnostic methods for this pathology. Among the most successful are imaging tests (X-ray or CT) and sputum culture.

In imaging studies, what is sought is to determine if at the anatomical and structural level there is any variation in the normal arrangement of the lungs that may be caused by pneumonia.

In the case of sputum culture, a sample is taken from the expectoration that is made by coughing and a bacterial culture is performed. Here, through different identification methods, we seek to determine exactly which is the microorganism causing the pathology. This is perhaps the most accurate diagnostic method, since it clearly identifies the causative agent of the disease.

Treatment

When pneumonia is of bacterial origin, the first line of treatment preferred by specialists is the use of antibiotics. Among the antibiotics most used in the treatment of pneumonia are:

• Penicillins
• Beta-lactams (Amoxicillin)
• Quinolones (Levofloxacin)
• Macrolides (Azithromycin)

Of course, the doctor will be the one to determine the best antibiotic therapy required.

Other infections

Bacteria of the coliform group can generate, in extreme cases, other infections apart from those already mentioned. These include:

• Atrophic rhinitis
• Endophthalmitis
• Osteomyelitis
• Otitis media
• Sepsis
• Cellulitis

These infections occur in a very small percentage of the population, especially in those who have a problem with the immune system, which makes them prone to developing this type of infection.

References

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