Clostridia and Bacillus Flashcards
General characteristics of Bacillus species
gram positive large rods (largest bacteria morphologically)
produce resistant spores-spore is infectious form
aerobes or facultative anaerobes
grow very fast- large colonies at 24 hours
biochemically active
majority are non-pathogenic environmental organisms
Species of bacillus of veterinary importance
B. anthracis- ANTHRAX
B. cereus- food poisoning (rice borne outbreaks- spores survive heating) , eye and soft tissue infection (man), mastitis in cattle (rare)
B. licheniformis- sporadic abortion in cattle and sheep (also food poisoning-like symptoms in man)
General characteristics of anthrax (who it effects)
serious disease affects virtually all mammalian species. worldwide, endemic or in defined regions. ruminants are highly susceptible- develop rapidly fatal septicemia
Pigs, horses moderately susceptible
Carnivores moderately resistant
Birds almost totally resistant to infection
NB: the more spores you get, the more severe the dz.
Epidemiology of Anthrax
endospore formation is the most important factor regarding persistence in the environment and spread. endospores can survive for decades in the soil. outbreaks occur in herbivores when pasture contaminated by spores. infection acquired by ingestion of spores (inhalation, skin abrasion more common in man)
Epidemiology of anthrax continued
Spores ingested–> germination and multiplication in lymphatics and spleen, vegetative forms release in massive numbers into the blood in final hours of life–>veg. forms shed at death in hemorrhagic exudate–> sporulate on exposure to O2. Man can inhale spores, eat infected meat or contaminated vegetables, or can acquire cutaneously via lesion from handling infected meat/vegetables/contaminated materials.
Anthrax pathogenesis- virulence factors
Poly-D-glutamic acid capsule and a complex toxin. both virulence factors encoded on plasmids. Expression is regulated by host temp. and CO2.
Capsule- inhibits phagocytosis- upregulated in presence of CO2.
Toxin- consists of 3 antigenic components 1)protective antigen 2) oedema factor 3) lethal factor
Virulence factors of anthrax continued
Oedema factor: calmodulin dependent adenylate cyclase- increases cAMP–> oedema in tissue and inhibits neutrophil function
Protective antigen: binds to host cell surface receptor, and an enzyme cleaves the antigen, allowing OF and LF to enter the cell
Lethal factor: zinc-metalloprotease which stimulates macs to release IL-1 and TNF alpha and cleaves MAP kinase. MAP kinase is responsible for the host inflammatory response. Cytokine release–> shock.
Local effects of anthrax
Swelling and oedema, darkening of tissue, necrosis
Septicemia, leads to increased vascular permeability, hemorrhage, shock and death.
Clinical presentation of anthrax
Incubation: hours-days
Cattle and sheep show rapidly fatal septicemia- NO rigor mortis seen
Anthrax bacilli can occlude the lumen of blood capillaries, resulting in a massive bacteremia in the last hours of life.
Diagnosis of Anthrax (B. anthracis)
Carcasses are bloated, putrified and don’t exhibit rigor mortis. Bleeding from nose, mouth and anus.
Blood of animal stained with polychrome methylene blue- blue bacteria with pink capsules- McFadyean’s capsule stain
Characteristic colonial morphology
Any holes seen on the stain are spores, which don’t gram stain.
B. anthracis culture is very characteristic: medusa-head colonies- serpentine cords of b. anthracis. Colonies are large and gray
Non-hemolytic.
Human anthrax (3 forms)
1) cutaneous- malignant pustule- endospores enter abraded skin- septicemia if untreated
2) pulmonary-“wool-sorters disease”- inhalation of spores- 80% mortality if no tx
3) intestinal- ingestion of infected material
Control of anthrax
Don’t open carcass!–> this facilitates spore formation and environmental contamination
Report to regulatory authority
Annual vaccine (live spore vax, capsule minus toxin)
Chemoprophylaxis in outbreaks
Carcasses should be incinerated or buried away from water courses.
Contaminated material disinfected in 10% formalin or if appropriate, incinerated.
Clostridium Species- major characteristics
Gram positive large rods
STRICT anaerobes
resistant spores
Grow very fast
Biochemically active
produce VFAs
enzymes including proteases and saccharases
Produce toxins: tetanus toxin on plasmid, botulism toxin on lysogenic phage
Antimicrobial sensitive but resistance my occur
Clostridia- where it’s found and what types of disease does it cause
Clostridia is ubiquitous: found in soil, alimentary tract of animals and in feces (normal flora). There are many species and not all of them are pathogens.
Pathogens are grouped according to the mode and sites of action of their potent toxins
1) neurotoxic 2) histotoxic- severe soft tissue infxn
3)enteropathogenic and enterotoxemia producing clostridia- produce diarrheal disease but also produces toxins.
Neurotoxic clostridia
C. tetani and C. botulinum
C. tetani (tetanus)- general characteristics
Potentially fatal intoxication affecting many species. Horses and humans are highly susceptible. ruminants and pigs are moderately susceptible. carnivores comparatively resistant. poultry are resistant.
Results in spastic paralysis