Bacillus subtilis

Bacillus subtilis

• Commonly known as the “hay bacillus” or “grass bacillus”.
• It is a normal gut commensal in humans.
• The organism is found in the soil; hence it is on most vegetation.
• It is also found in the gastrointestinal tract of ruminants.
• It is spread by water, wind, and normal traffic in feeds, and is present all over the world.

History:
Bacillus subtilis was first described by Ehrenberg as Vibrio subtilis in 1938.

Morphology:
• Shape and size: Cylindrical rods. They are straight or slightly curved, with rounded ends, singly or in chains and size is 3µ-4µ.
• It is gram positive.
• The form a tough, protective endospore.
• It is a facultative anaerobe.
• They are actively motile with peritrichic flagella.
• Catalase positive bacterium.

Gowth requirements and characteristics:
• Bacillus subtilis is easily cultured on any nutrient medium.
• Surface colonies on agar are small, grayish, amoeboid with crenate margin and a wool-like edge. The surface is finely granular and dull. The growth is membranous, slightly sticky, and is emulsified with difficulty.
• In broth: A thick ring pellicle which usually sinks within 24 hours is seen.

Biochemical properties:
• Acid is formed from i.e. ferments glucose, sucrose, and maltose.
• Indole negative.
• Methyl red negative.
• Vogues – Proskauer positive.
• It reduces methylene blue.
• Nitrates are also reduced by the bacterium.

Resistance:
• The bacillus is extremely resistant to heat by the virtue of the spores. Spores remain viable for years in the dry state.
• Boiling kills it in 2 hours, or death may be brought about at 120 °C in 15 minutes.
• It is sensitive to penicillin. Ordinary chemical disinfectants kill by prolonged contact.

Antibiotic produced: Subtilin.