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Lab no(4): Genus : BACILLUS

Characteristics:
• Aerobic, non-motile ,spore-forming, gram-positive chain forming rods.
• Bacillus species are ubiquitous saprophytes Important human pathogen
B. anthracis
B. cereus
Bacillus anthracis
• Major agent of bioterrorism and biological warfare
• Major pathogen of domesic herbivores that come in contact with
Humans
Pathogenesis and Clinical feature:
Acquired by the entry of spores through injured skin in cutaneous anthrax, or mucus membrane in intestinal anthrax, or inhalation of spores in the lung while handling skin and hides
Laboratory diagnosis:
Specimen: Fluid or pus from skin lesion, Blood, sputum
Smear: Non-capsulated gram-positive rods with centrally
located spores from culture
Large capsulated gram-positive rods without spores from primary specimen.
Culture: Grows aerobically in ordinary media over wide range of temperature. Non-hemolytic ,large, dense, grey-white irregular colonies with colony margin of “Medussa Head” or“curled-hair lock” appearance due to composition of parallel chaining of cells
Biochemical reaction:
Gelatin-stab culture: Gelatin liquefaction. Growth along the track of the wire with lateral spikes longest near the surface Providing “inverted fur tree “appearance.
Serology: ELISA has been developed to measure antibodies to edema toxin and lethal toxin
Positive result: 4-fold change or single titer > 1:32

Bacillus cereus
General characteristics:
Exhibit motility by swarming in semisolid media Produce ? lactamase, so not sensitive to penicillin
Clinical features
. Food poisoning
Lab. Diagnosis
>105 org/gm of food. Isolation of B.cereus in stool is not diagnostic since it is present in normal stool specimen

Bacillus anthracis