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, Shigella, Salmonella, Enterobacter, Proteus, Yersinia etc.
Common characteristics of family Enterobacteriaceae are:
- They are gram negative, short rods (Read about Gram staining here)
- They are non-sporulating, facultative anaerobes
- These organism have simple nutritional requirements and MacConkey agar is used to isolate and differentiate organisms of Enterobacteriaceae family (Pink colored colonies of lactose fermenter-coliforms and pale colored colonies of Non lactose fermenter)
Lactose fermenters: (CEEK)
Non lactose fermenter (ShYPS)
- Motility if present is by means of peritrichous (lateral) flagella. Motile by peritrichous 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, Flavibacterium, 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).
Find out more about Nitrate Reduction Test
- Cell contain a characteristic antigen, called the enterobacterial common antigen.
Antigens of Enterobacteriaceae are:
- O:Outer membrane
- H: Flagella
- K: Capsule
- Vi: Capsule of Salmonella
- Produces acid from glucose; ability to ferment lactose- distinguishes enteric from obligately aerobic bacteria.
- Sodium neither required nor stimulatory for growth
Tests for identification of members of Enterobacteriaceae family
Member 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 for 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 test for the detection of carbapenemase production.