Case study: bacillus anthracis

Describe the phenotypic characteristics of B anthracis

Gram positive, facultative anaerobe, rod shaped. Poly D glutamic acid capsule. Forms single spore

What are the three principal forms of human anthrax

Cutaneous, inhalational or ingestion. Can progress to meningitis following inhaltion or septicaemia

Describe the virulence plasmids expressed by B.anthracis

Two virulence plasmids: pX01; encoding lethal factor and Oedema factor with protective antigen with the AtxA global virulence factor. pX02; encodes the capsule operon capBCADE

How would you diagnose suspected cutaneous anthrax

Sampling of suspect skin, confirm by labroatory testing: staining polychrome methylene blue, colonial morphology white cream colonies on nutrient or blood agar

When using PCR to confirm B. anthracis which genes are used as targets

Sequences targeting lethal factor and protective antigen genes on pX01 show specificity for the anthracis species

What is the primary treatment for systemic infections

Antibiotics, typically do doxycycline, ciprofloxacin and penecillin

Which type of antimicrobials are least effective against B. anthracis

Poor sensitivity to extended spectrum cephalosporin trimethoprim-potentiated sulphonamides

Give an account of the virulence factors factors elicited by bacillus anthracis and their mode of action

The PA complexes on the host cell membrane which allows LF and EF to bind, following endocytosis by the cell PA acts as a channel to deliver LF and EF to the cytosol of the cell. LF is a zinc metalloproteinase which acts to suppress immune functions including phagocytosis. EF is an adenylyl cyclase which again suppresses immune cells functions. The toxins can also work together to have systemic effects. The capsule inhibits phagocytosis, can also interfere with the action of antimicrobials and acts to shield the bacterial cell surface antigens