Spore-forming Gram-positive rods Flashcards
What are the spore-forming bacteria of clinical interest?
- Bacillus anthracis
- Bacillus cereus
- Clostridium difficile
- Clostridium tetani
- Clostridium botulinum
- Clostridium perfringens (rarely)
What are the morphologic features of bacterial spores?
- Contain a complete copy of the chromosome
- Contain minimum concentrations of essential proteins and ribosomes
- Have a high concentration of calcium bound to dipicolinic acid
- The spore has an inner membrane, two peptidoglycan layers, and an outer keratin–like protein coat
What are the growth requirements of Bacillus spp.?
Aerobic or facultative anaerobic
What is the morphology of Bacillus spp.?
- Large, Gram-positive rods
- Occur in chains, single or paired rods, or as long, serpentine chains
How is human anthrax acquired?
- Inoculation: the main natural route. Inoculation of Bacillus spores through exposed skin from contaminated soil or infected animal products
- Ingestion
- Inhalation
What are the virulence factors of anthrax?
- Capsule: inhibits phagocytosis; made up of poly-ᴅ-glutamic acid
- Edema toxin: has adenylate cyclase activity, leading to fluid accumulation
- Lethal toxin: a zinc MMP that stimulates macrohphages to release TNF-α, IL-1β, and other pro-inflammatory cytokines leading to a cytotoxic effect
What are the types of anthrax disease?
- Cutaneous anthrax
- Gastrointestinal anthrax
- Inhalation anthrax
What are the features of cutaneous anthrax?
- Starts with development of a painless papule at the site of inoculation
- Rapidly progresses to an ulcer surrounded by vesicles and then a necrotic eschar
- Systemic signs, painful lymphadenopathy, and massive edema may develop
What are the features of gastrointestinal anthrax?
- Infection of upper GI tract: ulcers form in the mouth or esophagus, leading to regional lymphadenopathy, edema, and sepsis
- infection of cecum/terminal ileum: nausea, vomiting, and malaise, which rapidly progress to systemic disease
What are the features of inhalation anthrax?
- Associated with a prolonged latent period (2+ months) in which spores remain latent in the nasal passages
- In active disease, the spores reach the lower airways, in which alveolar macrophages ingest the spores and transport them to the mediastinal lymph nodes
- The initial symptoms are fever, myalgias, nonproductive cough, and malaise
- Later, there is rapid worsening of fever, edema, massive lymphadenopathy, respiratory failure, and sepsis
- Almost all cases progress to shock and death within 3 days of initial symptoms unless specific treatment is given
When were the anthrax attacks?
2001
What are the diseases associated with Bacillus cereus?
- Vomiting disease (emetic food poisoning)
- Diarrheal disease (diarrheal food poisoning)
- Ocular diseases
How is emetic form B. cereus food poisoning acquired?
Consumption of contaminated rice, in which heat-resistant spores survive. If the cooked rice is not refrigerated, the spores germinate and the bacteria multiply rapidly. The heat-stable enterotoxin is not destroyed when the rice is reheated
What are the features of emetic form B. cereus food poisoning?
- Intoxication, not infection
- Short incubation period (1–6 hours)
- Short duration of illness (<24 hours)
- Nausea, vomiting, and abdominal cramps
How is diarrheal form B. cereus food poisoning acquired?
Ingestion of the bacteria in contaminated meat, vegetables, or sauces
What are the features of diarrheal form B. cereus food poisoning?
- True infection with a longer incubation period
- Release of heat-labile enterotoxin follows, which is responsible for diarrhea, nausea, and abdominal cramps
- Course of 1 day or longer
How are ocular infections with B. cereus acquired?
Traumatic, penetrating injuries of the eye with a soil-contaminated object
What are the clostridia of clinical significance?
- C. tetani
- C. botulinum
- C. difficle
- C. perfringens
What are the morphologic and growth features of clostridia?
Gram-positive, spore-forming, anaerobic rods
How are C. difficile infections acquired?
Long-term use of antibiotics permits overgrowth of the C. difficile population found in the normal flora or allows for exogenous infection
How is C. difficile infection treated?
Fecal transplants from healthy donors to re-establish the normal flora
What disease is associated with C. difficile infection?
Pseudomembranous colitis: formation of whitish plaques and friable erythematous mucosa content in the large intestine
What are the morphologic features of C. tetani?
- Large, motile, spore-forming rod
- Produces round, terminal spores that give it the appearance of a drumstick
What is the epidemiology of C. tetani?
- Found in fertile soil and transiently colonizes the GI tract of humans
- The vegetative forms are extremely susceptible to oxygen toxicity
What are the toxins formed by C. tetani?
- Tetanolysin: an oxygen-labile hemolysin
- Tetanospasmin: a plasmid-encoded, heat-labile neurotoxin produced during the stationary growth phase and released when the bacterium is lysed
- Tetanospasmin inactivates proteins that regulate the release of the inhibitory NTs glycine and GABA, leading to unregulated motor excitation and spastic paralysis
What are the morphologic features of C. botulinum?
- Large, fastidious, spore-forming, anaerobic rods
- Subdivided into 4 groups based on phenotypic and genetic properties (and are technically 4 separate species)
- Seven antigenically distinct toxins; human disease is caused by types A, B, E, and F
Which types of botulism toxin cause disease in humans?
A, B, E, and F
What are the types of botulism?
- Classic/foodborne botulism: associated with consumption of home-canned foods containing toxins A and B, or contaminated preserved fish with type E toxin
- Infant botulism: associated with consumption of foods (e.g. honey, infant milk powder) contaminated with botulinum or with ingestion of spore-contaminated soil and dust
- Wound botulism
- Inhalation botulism: important in bioterrorism
What is the pathogenesis of botulism?
The botulism toxins are endopeptidases that inactivate the proteins that regulate release of ACh, blocking neurotransmission at peripheral cholinergic synapses, leading to flaccid paralysis
What are the features of foodborne botulism?
- Patients become weak and dizzy 1–3 days after consuming the contaminated food
- Initial signs include blurred vision with fixed dilated pupils, dry mouth, constipation, and abdominal pain
- Bilateral descending weakness of the peripheral muscles develops in patients progressing to flaccid paralysis
- Respiratory paralysis leads to death
What are the features of infant botulism?
- The disease is caused by production of toxins in vivo by bacteria that colonize the GI tract
- Does not occur in adults as C. botulinum cannot survive and proliferate in their intestines
What are the morphologic features of C. perfringens?
- Rectangular, Gram-positive rods
- Spores are rarely observed
- Colonies are distinctly rapid growing, with β-hemolysis
What is the epidemiology of C. perfringens?
- Type A commonly inhabits the intestines of humans and is widely distributed in nature, particularly in soil and feces-contaminated water
- Strains of types B–E do not survive in soil but colonize the intestines of animals and sometimes humans
What is the pathogenesis of C. perfringens infection?
- The bacteria produce enterotoxin, primarily type A strains, whose activity is enhanced by exposure to trypsin
- Enterotoxin is produced during the transition from vegetative cells to spores and is released in the alkaline environment of the small intestine when the cells sporulate
What are the diseases caused by C. perfringens?
- Cellulitis
- Fasciitis or suppurative myositis
- Myonecrosis with gas formation in the soft tissue (gas gangrene)
What are the features of gas gangrene?
- A life-threatening disease
- The onset of the disease, characterized by intense pain, develops within a week of infection due to trauma or surgery
- The α-toxin, which inserts into the plasma membrane and produces gaps
- Gas is produced by the metabolism of the actively dividing bacteria
What are the features of clostridial food poisoning?
- Short incubation period
- Abdominal cramps and watery diarrhea but no fever, nausea, or vomiting
- Course lasting less than 24 hours
