The Enterobacteriaceae family contains a large number of genera that are biochemically and genetically related to one another. Many of the traditional or familiar bacteria are found in this family e.g. Escherichia coli, Shigella, Salmonella, Enterobacter, Proteus, Yersinia, etc.
Common characteristics of the family Enterobacteriaceae are:
- They are gram-negative, short rods
- They are non-sporulating, facultative anaerobes
- These organisms have simple nutritional requirements and MacConkey agar is used to isolate and differentiate organisms of the Enterobacteriaceae family (pink-colored colonies of lactose fermenter-coliforms and pale-colored colonies of the non-lactose fermenter)
- Motility if present is by means of peritrichous (lateral) flagella, except Shigella and Klebsiella which are non-motile.
- They are catalase-positive
- Cytochrome C oxidase negative (enteric always negative-separates enterics from oxidase-positive bacteria of genera Pseudomonas, Aeromonas, Vibrio, Alcaligenes, Achromobacter, Flavobacterium, Cardiobacterium which may have similar morphology.)
- Usually reduces nitrate to nitrite (distinguishes enteric bacteria from bacteria that reduce nitrate to nitrogen gas, such as Pseudomonas and many other oxidase-positive bacteria).
- Produces acid from glucose; ability to ferment lactose- distinguishes enteric from obligately aerobic bacteria.
- Sodium is neither required nor stimulatory for the growth
- The cell contains a characteristic antigen, called the enterobacterial common antigen.
Antigens of Enterobacteriaceae are:
- O: Outer membrane
- H: Flagella
- K: Capsule
- Vi: Capsule of Salmonella
List of lactose fermenter and non-lactose fermenter
Lactose fermenters: (CEEK)
Non lactose fermenter (ShYPS)
Tests for identification of members of the Enterobacteriaceae family
Members of the Enterobacteriaceae family are identified based on their biochemical properties. Commonly used biochemical tests to identify them are (Please click on the test name to know more about that particular test);
- Citrate utilization Test
- Indole Test
- Motility Test
- Methyl Red (MR) Test
- Voges–Proskauer (VP) Test
- Triple Sugar Iron (TSI) Agar Test
- Urease Test
Summary of biochemical reactions of Enterobacteriaceae
|Citrobacter freundii||A/A or K/A, Gas, H2S||+ve||+ve||+ve||-ve||-ve||Motile|
|Klebsiella pneumoniae||A/A, Gas (++), H2S||-ve||-ve||+ve||+ve||+ve||Non-motile|
|Enterobacter cloacae||A/A, Gas (++)||-ve||-ve||+ve||+ve||+ve||Motile|
|Salmonella Typhi||k/A, H2S (weak)||-ve||+ve||-ve||+ve||-ve||Motile|
|Shigella boydii||K/A, No Gas, No H2S||-ve||+ve||-ve||-ve||-ve||Non-motile|
|Proteus mirabilis||K/A, Gas, H2S||-ve||+ve||-ve||+ve||+ve||Motile (swarming)|
Carbapenem-resistant or carbapenamase-producing Enterobacteriaceae have been reported worldwide and are major threats to global well-being. Carbapenem-resistant Enterobacteriaceae (CRE) are usually resistant to all β-lactam agents as well as most other classes of antimicrobial agents, which limits the available treatment options.
Carbapenem resistance in Enterobacteriaceae occurs when an isolate acquires a carbapenemase or when
an isolate produces an extended-spectrum cephalosporinase, such as an AmpC-type β-lactamase, in
combination with porin loss. Klebsiella pneumoniae carbapenemase (KPC) is one of the most common mechanism of carbapenem resistance.
Modified Hodge Test (MHT) is one of the recommended tests for the detection of carbapenemase production.
Acharya TankeshwarHello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion. As an asst. professor, I am teaching microbiology and immunology to medical and nursing students at PAHS, Nepal. I have been working as a microbiologist at Patan hospital for more than 10 years.
Biochemical Tests for Bacterial Identification
Catalase test, oxidase test, MUG test, optochin sensitivity test, bacitracin sensitivity test, coagulase test, etc are some of the common biochemical tests.
Catalase test: Principle, Procedure, Results, Uses
Catalase test is used to distinguish among Gram-positive cocci. Staphylococci are catalase-positive but Streptococci are catalase-negative.