Shigella
INTRODUCTION:
- Shigella is an enterobacteriaceae
- Gram negative, Non motile
- Facultative anaerobes, Non spore forming, Non capsulated
- Non lactose fermenting except S. sonnei.
- Catalase positive except S. dysenteriae type1 and Oxidase negative.
- People with blood group O has increased susceptibility to shigella
CULTURAL CHARACTERISTIC:
Culture media:
- Non Selective
- Bromocresolpurpe lactose agar
- Low selective
- MacConkey agar
- High selective
- Deoxycholate citrate agar
- Hektoen agar/SS agar
- Temperature range for growth 10-40°C(Optimum temp 37 °C)
- In Nutrient Agar (After overnight culture)
- 2 mm in diameter, circular, convex, smooth and translucent.
In MacConkey agar:
- Colorless Colony except S. sonnei (Pink colony)
In Shigella-Salmonella agar:
- Colorless Colony
- Viability: Death point (56°C for 1 hour), 1% phenol for 30 min,
- Viable in water for days and in ice for 1-6 months, In faeces it dies within few hour due to acidity produced by growth of coliform.
BIOCHEMICAL REACTION:
- Catalase positive except S. dysenteriae type 1.
- Methyl red positive
- VP negative
- Urease negative
- Mannitol ferment
- Citrate negative
- Oxidase negative
- No production of H2S
- S. sonnei is a late lactose fermenter.
CLASSIFICATION:
Based on biochemical (fermentation of mannitol)and antigenic characteristics.
- Subgroup A: S. dysenteriae: 15 serotypes
- Subgroup B: S. flexneri: 8 serotypes.
- Subgroup C: S. boydii: 19 serotypes
- Subgroup D: S. sonnei: only one serotypes(lactose non-fermeter)
TOXONOMY:
Family Enterobacteriaceae
- Shigella dysenteriae: most serious form of bacillary dysentery (Shiga toxin)
- Shigella flexneri: shigellosis in underdeveloped countries
- Shigella sonnei: shigellosis in developed countries
- Shigella boydii : Less frequently isolated from dysentry patients.
Exam Question
INTRODUCTION:
- Shigella is an enterobacteriaceae
- Gram negative, Non motile
- Non lactose fermenting except S. sonnei.
- Catalase positive except S. dysenteriae type1 and Oxidase negative.
- People with blood group O has increased susceptibility to shigella
CULTURAL CHARACTERISTIC:
Culture media:
- High selective
- Deoxycholate citrate agar
- Hektoen agar/SS agar
- Temperature range for growth 10-40°C(Optimum temp 37 °C)
- In Nutrient Agar (After overnight culture)
- 2 mm in diameter, circular, convex, smooth and translucent.
In MacConkey agar:
- Colorless Colony except S. sonnei (Pink colony)
In Shigella-Salmonella agar:
- Colorless Colony
- Viability: Death point (56°C for 1 hour), 1% phenol for 30 min,
Mannitol ferment
- Subgroup D: S. sonnei: only one serotypes(lactose non-fermeter)
- Shigella dysenteriae: most serious form of bacillary dysentery (Shiga toxin)
Don’t Forget to Solve all the previous Year Question asked on Shigella
