• Gram negative non-spore forming bacilli.• Aerobic and facultative anaerobic.• Grow easily on ordinary media.• Most are motile with peritrichous flagella .• All species ferment glucose with production of acid or acid and gas.• Catalase +ve• Oxidase –ve• Inhabit the intestinal tract of man and animals naturally.• Many species are pathogenic.• Genera have been defined on biochemical basis.
Lactose Fermenters
Late (slowly) lactose fermenters:
non lactose fermenters:
lactose fermenters
Lactose fermenter
Lactose fermenter bacteria
Late lactose fermenter bacteria
Non-Lactose fermenter bacteria
Escherichia
.
Escherichia coli: cause UTI, diarrhea, bacteremia or meningitis.
Microscopical appearance: Gram-negative short rods. Most strains are motile.
Cultural characteristics: Colonies on MacConkey agar are pink (lactose fermented with bile precipitation.
Biochemical reactions: IMViC + + - -
IMViC tests Indole
• Enterobacteraerogenes –•Escherichia coli(pink/red) +Kovac’s reagent detects if tryptophan has been hydrolyzed to indol/tryptophanase
Methyl Red (MR)
•Enterobacter aerogenes(left) –•E. coli(bright red) +•Reagent: Methyl red indicator identifies pH change due to mixed acid fermentation
Voges –Proskauer (VP) • Enterobacter aerogenes + •E. coli –(left)•Barritt’s reagent Tests for acetoin, precursor to 2,3 butanediol fermentation•Addition of alpha-naptholand KOH
Citrate
•E. coli (left green) –•Enterobacter aerogenes (right royal blue) +•Reagent: Bromothymol blue indicator tests for ability to use citrate as sole carbon source/citrate permease
Urease
E. coli–(left)Proteus vulgaris+Phenol Red a pH indicator turns tube bright pink because NH3 decreases the pH CO(NH3)2+ 2 H2O –urease → CO2+ H2O + 2 NH3
E.Coli on EMB
E.Coli on maccoky agar
Klebsiella
The most pathogenic species is K. pneumoniae that causes pneumonia.
Microscopical appearance: G _ve short rods. Non-motile. Capsulated both in tissues and on in vitro cultivation.
Cultural characteristics: Colonies on MacConkey agar, are large, mucoid and show pink color (lactose fermenter)
Biochemical reactions: IMViC - - + +,
Enterobacter
Is considered as an opportunist. They are frequently isolated from urinary tract infections, septicemia. They are found in soil, water, dairy products & animals & human intestine. The most common species: E. cloaca, E.aerogenes.
Microscopical appearance: G _ve short rods, and motile.
Cultural characteristics: Colonies on MacConkey agar, are large, pink in color (lactose fermented).
Serratia marcescens
Free living & common opportunistic pathogen in hospitalized patients. Cause pneumonia, bactermia, endocarditic, UTI, meningitis or wound infection.
Microscopical appearance: G -ve short rods and motile
Cultural characteristics: Produce a red pigment (prodigiosin) at room temp. Colonies on MacConkey agar are late lactose fermenters, i.e give pink colonies after 48 hr.
Biochemical reactions: IMViC - - + +, TSI Alkaline slant/Acid butt (K/A).
Citrobacter
Considered as an opportunist. Can cause UTI & bacteremia. G-ve short rods, motile & late lactose fermenters on MacConky agar.
Biochemical reactions: IMViC V + - +, Urease V, TSI Alkaline slant/Acid butt(K/A).
TSI medium
Oxidase test
