Bacillus

1. Bacillus

2. Bacillus • Classification • All are large Gram-positive bacilli • Are aerobic • Form endospores • Most are found in dust and soil • Bacillus anthracis is the major pathogen in the group • Morphology and Cultural Characteristics (Bacillus anthracis)

3. Bacillus anthracis • G+B with square cut ends • Form endospores • Non-motile • Capsule made of glutamic acid (a polypeptide). • The capsule is not found in cultured bacteria unless the bacteria are grown on bicarbonate containing media and in the presence of increased CO² concentrations.

4. Gram stain of Bacillus sp.

5. Endospores of Bacillus sp.

6. Bacillus anthracis • Grow well on ordinary lab media producing large granular colonies with a coarse texture.

7. B. anthracis • Virulence factors • Capsule­ helps organism to resist phagocytosis but antibodies are not protective. • Exotoxin­ is very complex and is produced only when the bacteria is growing in animal tissues. • Toxin production is mediated by a temperature sensitive plasmid. • The toxin consists of three protein components (maximum toxicity occurs when all three components are present).

8. Bacillus anthracis • Protective antigen (PA) ­ reacts with host cell tissue receptors where it is proteolytically activated so that it binds LF and EF to allow entry of LF and EF into the host cells via endocytosis. • Injection of PA will result in the production of antibody against PA that provides short term immunity. • Lethal factor (LF)­ Both PA and LF are required for lethal activity. • Edema factor (EF) ­ Both PA and EF are required for edema to occur. • EF has adenylate cyclase activity and it becomes active when it enters eucaryotic cells. • This results in an increase of cAMP and resulting edema.

9. Bacillus anthracis

10. Bacillus anthracis • Clinical significance  • Anthrax which is the disease caused by B. anthracis is essentially a disease of animals who acquire the organism by ingestion or inhalation of spores. • The spores are extremely resistant to adverse chemicals and physical environments. • They may remain a source of infection in soil for 20-30 years. • Man acquires anthrax usually from contact with animal products; less commonly from working in an agricultural setting with infected animals.

11. Bacillus anthracis • Man may acquire the organism through skin abrasions, by inhalation of spores, or by ingestion. The disease that develops depends upon the mode of transmission: • Pulmonary (Woolsorter‘s disease)­ Spores are inhaled and germinate in the lungs where they multiply and spread to cause a fatal septicemia or meningitis. • This is the most serious form of the disease. •  Intestinal anthrax­ results from ingestion of spores.

12. Pulmonary anthrax

13. Bacillus anthracis • Cutaneous anthrax­ when organism comes in through skin abrasions; • Most common form; • most damage comes from the invasion but the toxin may play a role; • Spores enter through a cut, germinate, and vegetative cells multiply; • There is an acute host inflammatory response, but the capsule probably prevents phagocytosis; • Exotoxin release and invasive damage result in rapid development of a malignant pustule; • Occasionally, without treatment, the organism will disseminate to cause septicemia and death in a few days (rare because of B-lysin activity in the bloodstream that kills the bacteria); • Vascular injury with edema, hemorrhage, and thrombosis may occur; • Death results from respiratory failure and anoxia caused by actions of the toxin on the central nervous system (toxemic degeneration).

14. Cutaneous Anthrax

15. Bacillus • Antibiotic susceptibility and treatment • Penicillin or tetracycline • A short-term PA vaccine is available for industrial workers and others at high risk. • Other Bacillus species • Bacillus subtilis, and occasional other species may occasionally cause opportunistic infections. • Bacillus cereus is a major cause of enterotoxin food poisoning; • The toxin is protein in nature and can be destroyed by heating; • Food poisoning occurs after ingestion of pre-formed toxin; • Vomiting occurs 1-5 hours after ingestion

16. Bacillus • B. cereus is also an opportunistic pathogen that has been cultured from cases of septicemia, endocarditis, meningitis, wound infections, pneumonia, and fulminant eye infections • In addition to the enterotoxin that bacteria may produce, a dermonecrotic and a lethal toxin, hemolysins, lecithinase, proteases, and nucleases may be involved in its pathogenesis • Clindamycin with or without gentamycin may be used for treatment of infections