Enterobacteriaceae family contains a large number of bacterial genera that are biochemically and genetically related to one another. Bacteria in this family include: Escherichia, Shigella, Salmonella, Enterobacter, Proteus, and Yersinia.
Common characteristics of Enterobacteriaceae
Members of the Enterobacteriaceae family posses the following characteristics:
- They are Gram negative, short rods
- They are non-sporulating, facultative anaerobes
- They have simple nutritional requirements. MacConkey (MAC) agar is used to isolate and differentiate organisms of Enterobacteriaceae family. Lactose fermenters (LFs) form pink-red colonies on MAC while non-lactose fermenters (NLFs) form pale colored colonies on MAC. LFs include Citrobacter, Escherichia, Enterobacter, and Klebsiella. NLFs include Shigella, Yersinia, Proteus, Salmonella.
- Motility if present is by means of peritrichous (lateral) Shigella and Klebsiella are non-motile.
- They are catalase positive
- They are Cytochrome C oxidase negative
- They reduce nitrate to nitrite
- They have antigenic cell wall that aid in their identification in the laboratory. The antigens of Enterobacteriaceae are: O:Outer membrane; H: Flagella, K: Capsule; and Vi antigen: Capsule of Salmonella
- They produce acid from glucose
Tests for identification of members of Enterobacteriaceae family
Member of the Enterobacteriaceae family are identified based on their biochemical properties. The ommonly used biochemical tests to identify them are:
- Citrate utilization Test
- Indole Test
- Motility Test
- Methyl Red (MR) Test
- Voges–Proskauer (VP) Test
- Triple Sugar Iron (TSI) Agar Test
- Urease Test
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