Genus Bacillus
Classification of Gram-PositiveGram-positive bacilli
Aerobic
Anaerobic
Non spore forming
Spore forming
Spore forming
Corynebacterium
Bacillus
Clostridium
THE MOST IMPORTANT SPECIES: 1. Bacillus anthracis 2. Bacillus cereus 1. Gram-positive bacilli 2. Spore former 3. Aerobic
*
Microscopical Appearance: 1. Large gram positive bacilli. 2. Non-motile. 3. Found singly, in pairs or in long chains. 4. Capsulate in both tissues and body fluids of the infected host. 5. Spores are formed in culture, dead animal's tissue . 6. Spores are oval ,central and non projecting .
* Bacillus anthracis
When describing spore-forming bacteria, the location of the endospore is usually stated as central, terminal, or subterminal.
* Gram stain of Bacillus anthracis showing Gram-positive rods
Cultural Characteristics: large ,white - gray colonies with irregular borders ,opaque and are non-hemolytic on blood agar plates .*
Under the low power microscope, the edge of the colony is composed of long , interlacing chain of bacilli resembling locks of matted hair. This is called the ”Medusa head appearance”
Morphology:Motile.Non Capsulated . 3. Spores may be central ,terminal or subterminal located.4. -hemolysis . * Bacillus cereus
Catalase Test
Bacillus spp. ( + )Principle Nutrient Agar containing 1% Starch + M.O Glucose Starch + Iodine blue, purple, or black Glucose + Iodine No reaction Procedure Inoculate nutrient agar plate containing 1% Starch with the M.O. Incubate the plate at 37 for overnight After incubation, flood the plate with Iodine solution Result Activity of amylase is indicated by a clear zone around the growth while the rest of the plate gives blue color after addition of iodine solution.
Starch Hydrolysis
AmylaseBacillus spp. ( + )
(depending on the concentration of iodine)
Gelatin Liquefaction
Gelatin is a simple protein. When in solution, will be a solid at a temperature of 25oC or lower. Gelatin will be a liquid at a temperature of 26oC or higher. Some microorganisms can liquefy gelatin by producing the extracellular enzyme called “Gelatinase”. When bacteria that produce the enzyme gelatinase are grown in a gelatin medium, the enzyme breaks up the gelatin molecule and the medium cannot solidify even at cold temperatures.Procedures
Inoculate gelatin deeps and incubate for up 2 days. To determine whether liquefaction has occurred place the tube in the refrigerator for 30 minutes Remove and check the tube for liquefaction. if negative, continue incubation until liquefaction occur.B.cereus ( + ) B.antracis ( - )