Enterobacter

Enterobacter is the genus name of the bacteria, any group of rod-shaped bacteria that falls under the family of Enterobacteriaceae, is considered as an enterobacter. These are generally found in the gut of humans, specifically the large intestine, they are ubiquitous, that is they have a diverse range of habitats for growth and reproduction. They have the characteristic feature of the flagellum, which helps to increase their mobile ability. They are gram-negative, they are not involved in spore formation. Most of the bacteria of this family are not highly pathogenic, partially due to their inability to form spores. Spore formation ensures the viability of the organism in drastic conditions. Spore is the dormant form of the organism. Most of the members of this family have flagellum, an indicator of high mobility except for some.

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Features of Enterobacter

There are the following key features that are important from biochemical and immunological points of view. They are as follows:

1. They are gram-negative families of bacteria.

2. They are fermentative, they can ferment glucose to produce organic acids. 

3. They perform nitrogen fixation. They can convert nitrate into nitrite, which is known as nitrification. It is an important state of nitrogen fixation.

4.  They are oxidase negative, that is they lack cytochrome c oxidase.

5. They are facultative anaerobes (can live in both the presence and absence of oxygen)

6. Their preferable growth media contains bile, that is they can grow in MacConkey agar media.

7. Most of them are motile except shigella and klebsiella.

8. Most of them are not encapsulated except klebsiella.

9. They are not fastidious.

10. Bacteria which are pathogenic release endotoxin, these endotoxins are responsible for toxic shock and inflammation.

Biochemical Test

Biochemical tests are done for the identification and isolation of organisms. Biochemical tests also give the idea of metabolism and specific biochemical features of the test organism. There are the following biochemical tests that are done to perform the biochemical analysis of the sample organism.

1. Phenol red test, this test is done to find out the pH at which the bacteria is most active.

2. Tryptone broth test or commonly known as the indole test. It is done to check the concentration of indole production.  This test is very helpful in the identification of enterobacter.

3. Phenylalanine agar test is used to check the presence of deaminase.

4. Oxidase test, which is done to check the presence of oxidase. The result of this test is negative for enterobacter as it lacks oxidase enzyme activity.

5. Gelatinase test along with catalase test is used to check the presence of gelatin and catalase. Catalase breaks hydrogen peroxide to produce oxygen. 

Based on the result, these enterobacteria can be classified from the mixed consortium of bacteria.

Antibiotic Resistance in Enterobacter.

Antibiotic resistance can be defined as the condition in which certain pathogens develop resistance or are not killed when a specific antibiotic is administered. Pathogenic strains of the enterobacter group have evolved antibiotic resistance over the years, which makes it more pathogenic. Some of the examples of bacteria that have developed antibiotic resistance are as follows-

1. E. cloacae (Enterococcus cloacae) have developed resistance for aminoglycosides, the reason behind this resistance has been attributed to integrons. Integrons are incorporated into the bacterial genome through recombination.

2. E. aerogenes are also a bacteria of this family that has developed multiple drug resistance (MRD), these results in the treatment of the condition. It is resistant to the most commonly used drugs such as ciprofloxacin and imipenem.

Pathogenic strains of enterobacter can cause various diseases such as meningitis, pneumonia, bacteremia, and urinary tract infection. These bacteria generally come under the class of opportunistic pathogens.

Enterobacteriaceae Classification

Enterobacteriaceae is the name of the family under which the genus enterobacter falls. Based on their biochemical nature Enterobacteriaceae can be classified namely, lactose fermenters and lactose non-fermenters.

Classification Based on Biochemical Character-  

Under the category of lactose fermenters, there are the following bacteria.

1. E.coli

2. Enterobacter

3. Klebsiella.

4. Citrobacter. 

Under the category of lactose non-fermenters, there are the following bacterias.

1. Salmonella

2. Yersinia 

3. Shigella proteus 

Taxonomic Classification of Enterobacteriaceae-

There are four tribes genera under the family of Enterobacteriaceae, under which various genus of bacteria are present. They are as follows:

Tribe- I Escherichia, under this following genus of bacteria are classified.

1. Escherichia

2. Shigella

3. Edwardsiella

4. Salmonella

5. Citrobacter

Tribe- II Klebsiella, under this tribe following genus are classified.

1. Klebsiella

2. Enterobacter

3. Hafnia

4. Serratia

Tribe- III Proteeae, following are the genus that come under this category. 

1. Proteus

2. Morganella

3. Providencia

Tribe IV Erviniaeae, under this group only one genesis present that is 

1. Ervinia

Toxins Produced By Pathogenic Strains of Bacteria

Most pathogenic strains produce toxins but the toxin produced by E.coli is the most widely studied toxin that attributes to the virulence of the strain. Toxins are the harmful chemical substance secreted by the pathogen. Toxin interacts with the host cell and causes disease. The toxin produced by E.coli is known as Shiga toxin. Shiga toxin is mainly responsible for causing diarrhoea and dehydration in humans. It binds to the ganglioside of the epithelial cell of the small intestine, where it performs ribosylation to activate adenylyl cyclase (via G-protein signalling). Activated adenylyl cyclase in turn activates cAMP. 

This increase in cAMP concentration in turn alters the activity of sodium and chloride transporters. To balance this high osmolarity water from cells moves to the bowel. This leads to an increase in the concentration of water in the bowel, this condition is known as diarrhoea. Diarrhoea ultimately leads to dehydration and electrolyte imbalance, which can be maintained by oral rehydration. 

E.coli toxin is also responsible for causing neonatal meningitis and gastroenteritis.