Anaerobic infections Flashcards
What is an anaerobic organism?
One that cannot survive in an oxygen environment
What is a facultative anaerobe?
One that can grow partially in small levels of oxygen, so is not a true anaerobic organism
Give two gram negative anaerobic bacillus’
- Bacteriodes
- Fusobacterium
Give a gram negative anaerobic coccus
Veillonella
Give a gram positive anaerobic bacillus
Clostridium
Give a gram positive anaerobic coccus
Anaerobic streptococci
What are the clostridia species?
A spore forming Gram positive bacilli
Where are clostridia found?
In soil and water, but also ubiquitous as part of normal human microbiota
How many species of clostridia are there?
Around 80, but few that are disease causing
What does the clostridia pathophysiology involve?
Entering the anaerobic conditions as spores, germinating to form large numbers, and then releasing toxins to act as the main pathogenic factor
Where is clostridium difficile found?
In the human GI tract as microbiota
What % of the GI tract microbiota is clostridium difficle?
~3% in adults
Who has a higher % of clostridium difficile in the GI tract microbiota?
Children and neonates, and hospitalised patients
Why do hospitalised patients have more C. Difficile?
Because the use of broad-spectrum antibiotics will massively alter the GI microbiota, allowing for any endogenous C. Difficile to proliferate, or for an exogenous infection due to large numbers of patients releasing clostridium spores into the environment which can then colonise the GI tract
What does C. Difficile produce?
Two toxins;
- A
- B
What do the A and B toxins produced by C. Difficile do?
Act on the gut to cause a mass release of cytokines
What does the release of cytokines due to C. Difficile cause?
Tissue damage and death, and the subsequent formation of a pseudomembrane
Why is it not a problem for neonates to carry large amounts of C. Difficile in their gut?
Because the lack of receptors for these toxins mean they can’t take an effect
What do individuals infected with C. Difficile develop?
- C. Difficile related diarrhoea
- Abdominal pain
- Malaise
- Fever
- Nausea
What can the inflammation from C. Difficile infection cause?
The stopping of bowel peristalsis
What can the stopping of bowel peristalsis related to C. Difficile lead to?
‘Toxic megacolon’
What can toxic megacolon lead to?
Bowel perforation and septicaemia
How is diagnosis of C. Difficile made?
From a stool sample, checking for antigen detection or toxin detection
What does treatment of C. Difficile involve?
- Oral metrinidazole or vancomycinD
- iscontinuing of the current antibiotic regime if possible
What is vital to prevent the spreads of C. Difficile spores?
- Hand-washing of health care workers
- Individuals should be isolated in side rooms
Why must healthcare workers wash their hands to prevent the spread of C. Difficile?
Alcohol hand gel is ineffective against the spores
What is the main cause of gas gangrene?
Clostridium Perfringes
What kind of bacteria is clostridium perfringes?
Gram positive bacillus
Where is clostridium perfringes found?
As part of the intestinal microbiota, but its spores are found everywhere in the environment
Other than gas gangrene, what can clostridium perfringes cause?
Food poisioning
When can clostridium perfringes cause food poisioning?
When poorly cooked meats are consumed
What does gas gangrene develop from?
A devitalised wound
What is meant by a devitalised wound?
One with interruption to the blood supply
How does C. Perfringes cause gas gangrene?
The spores are taken in from the environment via the wound, and they germinate in the anaerobic wound and release toxins in the ischaemic conditions
What toxins are released by C. Perfringes?
Mainly α-toxins
What does gas gangrene cause?
Extensive damage to the surrounding soft tissue
Why is gas gangrene so named?
Gas slowly collects under the skin due to metabolising anaerobes
What does treatment of gas gangrene involve?
Debridement of the devitalised tissue and intravenous antibiotics
What antibiotics are given in gas gangrene?
Mainly penicillin
What is the causative agent for tetanus?
Colstridium tetani
What is the main symptom of tetanus?
Spastic paralysis
Where do tetanus infections occur?
In wounds deep enough to cause anaerobic conditions
What happens in a tetanus infection?
C. Tetani spores cause tetanospasmin
What does tetanospasmin do?
Prevents release of inhibitory transmitter γ-aminobutyric acid (GABA)
What is the result of tetanus induced GABA release inhibition?
Spastic paralysis at the site of injury
How can tetanus be diagnosed?
From history and clinical features
What does treatment of tetanus involve?
- Muscle relaxant
- Immunisation
- Antibiotics
What are the types of vaccine for tetanus?
- Active
- Passive
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What is given in active immunisation against tetanus?
Tetanus toxoid
What is given in passive immunisation against tetanus?
Human tetanus Ig
What causes botulism?
Clostridium botulinum
What is the main symptom of botulism?
Flaccid paralysis
Where is C. Botulinum widely distributed?
As a saprophyte in soil, food, etc
Why is C. Botulinum hard to get rid of?
Its spores resist destruction by heat
What can result in botulism poisoning?
Incomplete heating in the canning or bottling process
What is the botulism toxin?
A neurotoxin
What does the botulism toxin do?
Prevents the release of acetylcholine at the NMJ, thus preventing muscle contraction
How do patients with botulism present?
- Descending flaccid paralysis
- Dysphagia
- Blurred vision
- Eventual general paralysis
What does treatment of botulism involve?
- Antitoxins,
- Penicillin as the antibiotic
- Ventilatory support
What do non-sporing anaerobes form?
The major part of the human bacterial flora of the mouth, intestine, vagina, and skin
What kind of infections are those by non-sproring anaerobes?
Endogenous
How do infections of non-sporing anaerobes occur?
Organisms escape from the normal flora into a new sterile anaerobic site
Give an example of how an infection of a non-sporing anaerobe could occur
Perforation of the large intestine
What happens once non-sporing anaerobes are established in their infective site?
They can multiply and cause tissue damage and spread
What are the main endogenous infections caused by non-sporing anaerobes?
- Intra-abdominal abscesses
- Liver abscesses
- Lung abscesses
- Dental abscess
- Bone abscess
- Leg ulceration
How do non-sporing anaerobes cause lung abscesses?
From aspiration pneumonia and subsequent formation of anaerobic compartment
What commonly happens with infection with non-sporing anaerobes?
They mix with aerobic bacteria and produce foul-smelling pus, which is quite characteristic
How is diagnosis of infection with non-sporing anaerobes made?
From spending specimens to the laboratory in anaerobic containers, and the cultures grown in selective media and under strict anaerobic conditions. The cultures can then be stained accordingly
What are the infections caused by non-sporing anaerobes mainly susceptible do?
Metronidazole
What are the main pathogens of anaerobic sepsis?
- Bacteriodes fragilis
- Prevotella melaninogenicus
Why is bacteriodes fragilis clinically relevant?
It is the most common of serious anaerobic infections
What is bacteriodes fragilis most commonly associated with?
Post-operative sepsis in abdominal or gynacological surgery
What feature does bacteriodes fragilis have?
Antiphagocytic capsule
What is the result of bacteroides fragilis’ antiphagocytic capsule?
It inhibits phagocytosis of facultative organisms, promoting the development of synergistic infections
Where is Prevotella melaninogenicus common?
In dental abscesses and sinus infections
