Enterobacteriaceae Family

By Acharya Tankeshwar •  Updated: 06/12/22 •  4 min read

The Enterobacteriaceae family contains a large number of genera that are biochemically and genetically related to one another. Taxonomically, the Enterobacteriaceae family currently has 53 genera and over 170 named species, of these 26 genera are known to be associated with infections in humans. Many of the familiar bacteria are found in this family e.g. Escherichia coli, Shigella, Salmonella, Enterobacter, Proteus, Yersinia, etc.

LF and NLF colonies in MacConkey Agar
LF and NLF colonies in MacConkey Agar

Common Characteristics

  • 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.
  • Most of the species are catalase-positive (there are few exceptions that can be utilized for the identification/differentiation of organisms)
  • 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 family
Antigens of the Enterobacteriaceae family

Antigens of Enterobacteriaceae are:

  1. O: Outer membrane
  2. H: Flagella
  3. K: Capsule
  4. Vi: Capsule of Salmonella

Medically Important Genera

  1. Citrobacter species
  2. Enterobacter species
  3. Escherichia species
  4. Hafnia species
  5. Klebsiella species
  6. Morganella species
  7. Plesiomonas shigelloides
  8. Proteus species
  9. Providencia species
  10. Salmonella species
  11. Serratia species
  12. Shigella species
  13. Yersinia species

List of lactose fermenter and non-lactose fermenter

Lactose fermenters: (CEEK)

Mnemonic Lactose Fermenter and NLF
  1. Citrobacter
  2. Escherichia
  3. Enterobacter
  4. Klebsiella

Non lactose fermenter (ShYPS)

  1. Shigella
  2. Yersinia
  3. Proteus
  4. Salmonella

Primary Isolation Media

  1. Blood Agar (BA)
  2. MacConkey (MAC) agar
  3. Cystine-lactose-electrolyte deficient (CLED) agar
  4. Desoxycholate citrate agar (DCA)
  5. Xylose-lysine-desoxycholate agar (XLD)
  6. Brilliant Green Agar (BGA)
  7. Cefixime-tellurite-sorbitol-MacConkey (CT-SMAC) agar
  8. Thiosulphate-citrate-bile salt (TCBS) agar
  9. Cefsulodin-Irgasan-novobiocin (CIN) agar
  10. Chromogenic media

Colonial Appearance

Name of the culture mediaColony morphology
Blood agarColonies are 2-3 mm in diameter, low, convex, grey, smooth, or mucoid, and may be hemolytic or swarming.
MACColonies may appear pink (lactose fermenting) or colorless (lactose non fermenting), size and shape vary with individual species
CLEDColonies may appear yellow (lactose fermenting) or blue (lactose nonfermenting), size and shape vary with individual species.
DCAColonies may appear pink (lactose fermenting) or colorless (lactose nonfermenting) and may have a black center (H2S producers).
XLDColonies may appear yellow (xylose, lactose, or sucrose fermenting) or pink (non-fermenting) and may have a black center (H2S producers).
BGAColonies appear as red-pink, 1-3mm in diameter, surrounded by brilliant red zones in the agar.
CT-SMACColonies may appear pink (sorbitol fermenting) or colorless (sorbitol nonfermenting).
TCBSColonies may appear yellow (sucrose fermenting) or blue-green (sucrose nonfermenting).
CINColonies may have deep-red centers (mannitol fermenting) surrounded by a translucent border giving the appearance of a “bull’s eye”.

Tests for the Identification of Enterobacteriaceae Family 

Members of the Enterobacteriaceae family are identified based on their biochemical properties. Commonly used biochemical tests are;

  1. Citrate utilization Test
  2. Indole Test
  3. Motility Test
  4. Methyl Red (MR) Test
  5. Voges–Proskauer (VP) Test
  6. Triple Sugar Iron (TSI) Agar Test
  7. Urease Test

Summary of biochemical reactions of Enterobacteriaceae

 TSIIndoleMRVPCitrateUreaseMotility
E.coliA/A, Gas+ve+ve-ve-ve-veMotile
Citrobacter freundiiA/A or K/A, Gas, H2S+ve+ve+ve-ve-veMotile
Klebsiella pneumoniaeA/A, Gas (++), H2S-ve-ve+ve+ve+veNon-motile
Enterobacter cloacaeA/A, Gas (++)-ve-ve+ve+ve+veMotile
Salmonella Typhik/A, H2S (weak)-ve+ve-ve+ve-veMotile
Shigella boydiiK/A, No Gas, No H2S-ve+ve-ve-ve-veNon-motile
Proteus mirabilisK/A, Gas, H2S-ve+ve-ve+ve+veMotile (swarming)

Antimicrobial Resistance

Certain members of the Enterobacteriaceae possess chromosomally determined inducible AmpC beta-lactamases. These include the so-called MYSPACE organisms: Morganella morgannii, Yersinia enterocolitica, Serratia marcescens, Providencia spp., Aeromonas spp. Citrobacter freundii complex, and Enterobacter spp.

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 Tankeshwar

Hello, 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.

10 responses to “Enterobacteriaceae Family”

  1. emmy says:

    Would like to give us all media that can be used in the identification of total enterobacteriaceae

  2. Dominique says:

    Rapid Lactose Fermenters:
    EKE (Escherichia, Klebsiella, Enterobacter)

    Late Lactose Fermenters:
    SHY Citro SaSh (Serratia, Hafnia, Yersinia, Citrobacter, Salmonella arizonae, Shigella sonnei)

    Non-Lactose Fermenters:
    PEMP SaSh (Proteus, Edwardsiella, Morganella, Providencia, Salmonella except arizonae, Shigella except sonnei)

    H2S Producers:
    SPACE (Salmonella, Proteus, Arizonae, Citrobacter, Erwardsiella) if in TSIA
    SACE (without Proteus) if in LIA

    Gas Producers except:
    PP SaSh (Proteus, Providencia, Salmonella, Shigella) in TSIA

    Nitrate to Nitrite Reducers except:
    Erwinia and Pantoea agglomerans

    Only DNAse + member:
    Serratia marscesens

    Only Catalase – member:
    Salmonella dysenteriae

    Lifted from Bailey and Scotts, and Mahon. Cheers!

  3. Michele Palley says:

    Hi there. Just wondering if you might be able to help me. First off, I have Systemic Mastocytosis which was diagnosed about 5 years ago after a long road to confirmed diagnosis. I’m on many meds to help control it and had the best results from Gleevec at a dose of 100mg. After about 4 months on it with success we tried 200mg and my liver decided to no longer tolerate it. Now I take Xolair along with a a bunch of other meds and it helps but not as well. Meanwhile, my health seems to be worsening. Neuro Dr. ran many tests to rule out MS and a variety of other illnesses based on my symptoms. Worst being fatigue, legs and occasionally face having pins & needles, weakness, numbness, muscle twitching, speech slur and bad brain fog, etc. – turned up positive on 2 Lyme IgM tests for bands 23 & 41. Dr. said false positives even though it came up twice months apart. Sent to an infectious disease Dr. – more tests. Again positive for IgM Lyme bands 23 & 41. Says again false positive. Then I turn up positive for the Widal Salmonella Typhi O plus H. So far I’ve been on Doxycycline for 10 days (for possible sinus infection??) with marked improvement in all my leg symptoms. Then a 10 day round of Bactrim for the Salmonella. Again felt my energy improve and symptoms lesson again after they had begun to return. Now, about four weeks out, my health is diminishing again. Belly swollen and upper abdomen pain. In San Diego at our second home and my Dr.’s are in N. CA. – Any ideas on what could be causing these positive tests? I have not travelled anywhere other than N & S. CA in the last 2 years. Only a few states years prior FL & Louisiana. Possible tick bite either 5 years ago or could have been again without the noticed rash. I have a small long hair chihuahua who I hold all the time and sleeps next to me at night. Could the two tests be a positive for anything else that we might be missing? With my weakened immune system/crazy Mast Cells could I have Lyme and my testing not show positive for IgG other than band 41? Sorry for the long winded post. Much to my story unfortunately. Thank you.

  4. rajeena says:

    Respected Sir,
    I got chitinase producing organism with gram stain negative,non motile, (Indole, MR, VP:negative), (simmon citrate is positive,lactose,urease,hydrogen sulphide, ornithine, lysine,oxidase,O/F test:negative), starch:positive:TSI,GLUCOSE,ACID AND GAS:NEGATIVE).,Nitrate is positive. Bile esculin is positive.negative for sugars.
    Can you please help me to identify this bacteria.

  5. saeed says:

    Useful information for any student or university student I hope to get more or send it to us by mail Thank you very much

  6. saeed says:

    Acientobacter bacteria to which family belong and what traits are shared with Enterobacteriaceae

    • Tankeshwar Acharya says:

      Dear Saeed,
      I have managed to write an article about Acinetobacter spp, giving highlights on the most important properties and information needed for undergraduate students. Please find it here

  7. Fareeda says:

    Please can you refer me a journal with proper referencing on microbiological evaluations of enterobacteriaceae on blood samples and susceptibility testing, thanks.

  8. Ash says:

    It would be great if you could post all of your sources.

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