Classification of spore forming bacilli
Spore forming bacilli (rods) are important gram positive bacteria
2 main genera based on oxygen requirements:
1. Bacillus aerobic spore forming rods
2. Clostridium anaerobic spore forming rods
Important properties
They have the ability to form highly resilient structures called spores in
response to adverse environmental conditions.
1. Structure and composition
a. Spore forms inside bacterial cell
b. It contains complete bacterial DNA genome, some cytoplasm,
cell membrane, peptidoglycan and very little water.
2. Extreme resistance
a. Spores are surrounded by a thick, keratin-like coat
b. It makes them resistant to heat, dehydration, radiation and
chemicals.
c. Resistance is also mediated by dipicolinic acid(calcium ion
chelator).
3. Dormancy and germination
a. Spores are metabolically inactive
b. Survive in a dormant state for years in soil
c. Exposure to water and nutrients enzymes degrade the thick
coat.
d. The spore then germinates into a single, pathogenic,
metabolically active bacterial cell
e. This is a means of survival, not reproduction.
4. Medical and sterilization implications
a. Spores exhibit no measurable metabolic activity and possess
impermeable coat
b. Thus antibiotics are completely ineffective
c. Spores are not killed by boiling at 100 degrees Celsius.
d. Spores must be subjected to autoclaving for true
sterilization steam heating under pressure at 121 degrees
Celsius for 15-30 minutes.
Important properties of specific spore forming bacilli
1. Genus bacillus
, a. Bacillus anthracis
i. Causative agent of anthrax
ii. Large, nonmotile, gram-positive rod with square ends
that is frequently found in chains.
iii. Unique as its antiphagocytic capsule is made of poly-D-
glutamic acid instead of polysaccharides.
iv. Its exotoxin has 3 features:
1. Protective antigen
2. Edema factor
3. Lethal factor
b. Bacillus cereus
i. Common cause of food poisoning
ii. May survive initial boiling of foods like rice, germinate in
warm food.
iii. Produce enterotoxins that cause diarrhea and vomiting.
2. Genus clostridium
a. Clostridium tetani
i. Causative agent of tetanus
1. Forms terminal spore (at end of rod)
2. Gives it a tennis racket appearance
3. spores from the soil enter wounds germinate in
anaerobic conditions
4. exotoxin tetanospasmin produced
5. This exotoxin blocks release of neurotransmitters
and causes spastic paralysis
b. Clostridium botulinum
i. Causes botulism
ii. Spores are widespread in soil, contaminate vegetables and
meats.
iii. Germinate in anaerobic environment of canned food.
iv. Produce botulinum toxin
v. Cause flaccid paralysis by blocking Ach release.
c. Clostridium perfringens
i. Cause gas gangrene (myonecrosis) and food poisoning
ii. Spores from soil or feces contaminate traumatized
tissue.
iii. Upon germination, spores produce toxins, mainly alpha
toxin (lecithinase) which damages cell membranes.
d. Clostridium difficile
i. Causes antibiotic-associated pseudomembranous colitis
Spore forming bacilli (rods) are important gram positive bacteria
2 main genera based on oxygen requirements:
1. Bacillus aerobic spore forming rods
2. Clostridium anaerobic spore forming rods
Important properties
They have the ability to form highly resilient structures called spores in
response to adverse environmental conditions.
1. Structure and composition
a. Spore forms inside bacterial cell
b. It contains complete bacterial DNA genome, some cytoplasm,
cell membrane, peptidoglycan and very little water.
2. Extreme resistance
a. Spores are surrounded by a thick, keratin-like coat
b. It makes them resistant to heat, dehydration, radiation and
chemicals.
c. Resistance is also mediated by dipicolinic acid(calcium ion
chelator).
3. Dormancy and germination
a. Spores are metabolically inactive
b. Survive in a dormant state for years in soil
c. Exposure to water and nutrients enzymes degrade the thick
coat.
d. The spore then germinates into a single, pathogenic,
metabolically active bacterial cell
e. This is a means of survival, not reproduction.
4. Medical and sterilization implications
a. Spores exhibit no measurable metabolic activity and possess
impermeable coat
b. Thus antibiotics are completely ineffective
c. Spores are not killed by boiling at 100 degrees Celsius.
d. Spores must be subjected to autoclaving for true
sterilization steam heating under pressure at 121 degrees
Celsius for 15-30 minutes.
Important properties of specific spore forming bacilli
1. Genus bacillus
, a. Bacillus anthracis
i. Causative agent of anthrax
ii. Large, nonmotile, gram-positive rod with square ends
that is frequently found in chains.
iii. Unique as its antiphagocytic capsule is made of poly-D-
glutamic acid instead of polysaccharides.
iv. Its exotoxin has 3 features:
1. Protective antigen
2. Edema factor
3. Lethal factor
b. Bacillus cereus
i. Common cause of food poisoning
ii. May survive initial boiling of foods like rice, germinate in
warm food.
iii. Produce enterotoxins that cause diarrhea and vomiting.
2. Genus clostridium
a. Clostridium tetani
i. Causative agent of tetanus
1. Forms terminal spore (at end of rod)
2. Gives it a tennis racket appearance
3. spores from the soil enter wounds germinate in
anaerobic conditions
4. exotoxin tetanospasmin produced
5. This exotoxin blocks release of neurotransmitters
and causes spastic paralysis
b. Clostridium botulinum
i. Causes botulism
ii. Spores are widespread in soil, contaminate vegetables and
meats.
iii. Germinate in anaerobic environment of canned food.
iv. Produce botulinum toxin
v. Cause flaccid paralysis by blocking Ach release.
c. Clostridium perfringens
i. Cause gas gangrene (myonecrosis) and food poisoning
ii. Spores from soil or feces contaminate traumatized
tissue.
iii. Upon germination, spores produce toxins, mainly alpha
toxin (lecithinase) which damages cell membranes.
d. Clostridium difficile
i. Causes antibiotic-associated pseudomembranous colitis
