Enterobacteriaceae: Introduction, Phenotypic Features, Keynotes, and Related photos

Introduction of Enterobacteriaceae

The family Enterobacteriaceae was first proposed by Rahn in 1936 and it is a very large group of gram-negative bacteria that possess a number of common morphological and biochemical properties and similar DNA base compositions. The widely used systems for the classification of Enterobacteriaceae are-

1. Bergey’s manual
2. Kauffmann and
3. Edward -Ewing.

Even having certain differences, the general approach is the same. A family is a group of subdivisions or tribes and each tribe consists of one or more genera. Similarly, each genus consists of one or more subgenera and species. The species are classified into types like biotypes, serotypes, bacteriophage types, and colicin types.

This family has the following tribes

Tribe 1: Escherichiae

Genus 

1. Escherichia
2. Edwardsiella
3. Citrobacter
4. Salmonella
5. Shigella

Tribe 2: Klebsiellae

Genus

1. Klebsiella
2. Enterobacter
3. Hafnia
4. Serratia

Tribe 3: Proteeae

Genus

1. Proteus
2. Morgenella
3. Providencia

Tribe 4: Erwinieae

Genus

1. Erwinia

Phenotypic Features

The family Enterobacteriaceae has the following general phenotypic features-

1. They are small gram-negative rods (GNRs).
2. Having usual cell structure (non sporulated)
3. Motile by peritrichous flagella
4. Grow on ordinary medium (nutrient agar)
5. Grow both aerobically and anaerobically.
6. Grow without the addition of sodium chloride or other supplements.
7. Grow well on MacConkey agar.
8. Active biochemically
9. Ferments D-glucose and other sugar, often with gas production.
10. Catalase test positive
11. Oxidase test negative
12. Reduce nitrate to nitrite
13. Contain the enterobacterial  common antigen (ECA) and
14. They have a 39-59% guanine plus cytosine (G+C) content of DNA.

Keynotes

1. All the members of the family Enterobacteriaceae are catalase-positive except Shigella dysentery type 1.
2. All the members of the family Enterobacteriaceae are oxidase negative except Plesiomonas shigelloides which is oxidase test positive.
3. All oxidase-positive bacteria are catalase test positive except Kingella, Eikenella, and Cardiobacterium those are catalase test negative.

Photos of bacteria related to Enterobacteriaceae

Escherichia coli Gram negative rods in Gram staining of culture

Proteus in Gram staining of culture showing swarm and vegetative cells

Gram-negative bacilli of Salmonella in Gram staining

Gram-negative rods of Klebsiella pneumoniae in Gram staining of culture

Klebsiella pneumoniae colony morphology on nutrient agar

E. coli Colony Characteristics on MacConkey medium

Klebsiella mucoid lactose fermenter colony on MacConkey agar demonstration

Proteus non-lactose fermenter colony on MacConkey agar

Shigella non-lactose fermenter colony on MacConkey agar

E. coli in thioglycollate broth

Further Readings

1. Cowan & Steel’s Manual for identification of Medical Bacteria. Editors: G.I. Barron & R.K. Felthani, 3rd ed 1993, Publisher Cambridge University press.
2. Clinical Microbiology Procedure Handbook, Chief in editor H.D. Isenberg, Albert Einstein College of Medicine, New York, Publisher ASM (American Society for Microbiology), Washington DC.
3. Bailey & Scott’s Diagnostic Microbiology. Editors: Bettey A. Forbes, Daniel F. Sahm & Alice S. Weissfeld, 12th ed 2007, Publisher Elsevier.
4. Colour Atlas and Textbook of Diagnostic Microbiology. Editors: Koneman E.W., Allen D.D., Dowell V.R. Jr, and Sommers H.M.
5. Mackie and Mc Cartney Practical Medical Microbiology. Editors: J.G. Colle, A.G. Fraser, B.P. Marmion, A. Simmous, 4th ed, Publisher Churchill Living Stone, New York, Melborne, Sans Franscisco 1996.
6. Textbook of Diagnostic Microbiology. Editors: Connie R. Mahon, Donald G. Lehman & George Manuselis, 3rd edition2007, Publisher Elsevier.
7. Jawetz, Melnick and Adelberg’s Medical Microbiology. Editors: Geo. F. Brook, Janet S. Butel & Stephen A. Morse, 21st ed 1998, Publisher Appleton & Lance, Co Stamford Connecticut.