Anaerobic Infection Flashcards
Require complete absence of oxygen is?
Obligate/ strict anaerobe
Classification of anaerobes?
- Spore forming anaerobes
- Non-spore-forming anaerobes
- Spirochaetes
Predisposing factors for Anaerobic Infections?
- Trauma
- Impaired blood supply
- Presence of other organisms
- Foreign bodies
- Disruption of barriers
Features of anaerobic infections?
- Production of a large amount of foul-smelling pus.
- Proximity of lesions to mucosal surface or portal of entry. 3. Failure to isolate organisms from pus by the usual aerobic methods (sterile pus).
- Infection associated with necrotic tissue, deep seated abscesses or closed space , e.g. brain
abscess. - Gas formation in the surrounding tissues detected as crepitations.
- Failure to respond to conventional antimicrobial therapy. 7. Presence of special character, e.g. Sulphur granules seen by the naked eye in the pus in case of actinomycosis
anaerobic infections Presence of special character?
Sulphur granules seen by the naked eye in the pus in case of actinomycosis
Common types of anaerobic infections?
Respiratory tract infections
Central nervous system infections
Intra-abdominal and pelvic infection
Wounds and soft tissue infections
Bacteremia and endocarditis
Laboratory diagnosis of Anaerobic Infections?
- Specimen
II. Macroscopic examination
III. Microscopic examination
IV. Culture
Laboratory diagnosis of Anaerobic Infections
I. Specimen?
Adequate clinical specimens are collected and transported, as soon as
possible, to the laboratory, preferably before antibiotic therapy.
Best samples are taken by disposable closed syringe or on swab with
reduced transport media.
The samples should be taken, as deep as possible , away from atmospheric
oxygen and as much sample as possible.
Treatment of anaerobic infections
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Surgical treatment:
Antimicrobial therapy:
3. Treatment of the aerobic organisms accompanying anaerobes, in a
mixed infection, is also necessary.
drainage of pus from abscesses, debridement, and
removal of necrotic tissues may be sufficient. ?
Treatment of anaerobic infections
1. Surgical treatment
Spore-forming Anaerobes ?
Clostridia
•Large, Gram-positive, spore-forming bacilli.
•The position of the spore within the vegetative cells is useful
in identifying the species
Clostridium
Microbiological features:
Morphology:
Clostridium Microbiological features?
-Morphology:
•Large, Gram-positive, spore-forming bacilli.
•The position of the spore within the vegetative cells is useful
in identifying the species
- Culture characteristics:
• Anaerobic
Clostridium Natural habitat ?
Soil Intestinal tract of animals & humans
Clostridium Important species?
Clostridium perfringens: Gas gangrene & Food poisoning
Clostridium tetani: Tetanus
Clostridium botulinum: Botulism
Clostridium difficile: (superinfection).
Gram positive large rectangular bacilli
Oval sub-terminal non bulging spores
Spores are rarely seen
Clostridium perfringens Morphology
Clostridium perfringens
Culture?
Anaerobic organism.
Colonies on blood agar are surrounded by complete haemolysis
Biochemical reactions Clostridium perfringens
?
Ferments sugars with production of acid & gas.
Clostridium perfringens
Virulence factors?
Alpha-toxin: lecithinase
Theta-toxin: cytolysin
Others
Clostridium perfringens Virulence factors:
Alpha-toxin: lecithinase? Theta-toxin: cytolysin
? Others?
Alpha-toxin: lecithinase
= It lyses cell membrane lecithin
Theta-toxin: cytolysin
= direct vascular injury
Others
= Haemolysins, collagenases, proteases, lipases
Pathogenesis of Clostridium perfringens
?
All clostridial wound infections occur in an anaerobic tissue environment caused by
an impaired blood supply secondary to trauma, surgery, foreign bodies,
malignancy
Usually polymicrobic because the source of wound contamination (faeces, soil) is
polymicrobic.
Clostridium perfringens
Clinical findings
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A- Gas Gangrene (Clostridial myonecrosis)
B- Anaerobic Cellulitis
Symptoms of Clostridium perfringens
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As the clostridia multiply → exotoxins are liberated into the surrounding
tissue → more local tissue necrosis & systemic toxemia . Infected muscle is discolored (purple mottling) & edematous & produces a
foul-smelling exudate & gas bubbles which cause crepitations. Severe shock with massive hemolysis & renal failure is usually the ultimate
cause of death.
Clostridium perfringens Diagnosis ?
Specimen: taken from the depth of the wound & examined rapidly.
Clostridium perfringens Treatment & prevention:
?>
Correction of the anaerobic conditions:
• Drainage & Surgical removal of dead tissues
Penicillin is the drug of choice
Hyperbaric oxygen therapy may limit the spread of infection.
Gram positive rod Bulging terminal spore (drumstick appearance ) Most strains are motile
Clostridium tetani
Morphology
Strict anaerobe
Grows well on ordinary & cooked meat media.
On blood agar, → swarm with surrounding zones of β-
hemolysis
Culture of Clostridium tetani
Clostridium tetani
Virulence factors:
Tetanospasmin toxin”
Tetanus Pathogenesis?
Most cases result from lacerations or small puncture
wounds, contaminated with Cl. tetani spores.
Ingestion of tetanus toxin does not produce the disease.
The spores germinate , in the traumatized tissue, (the
blood supply is cut off & ischemia results, producing an anoxic
anaerobic environment, with low redox potential).
A puncture wound can also cause spores to be injected
deeply into the tissue, offering anaerobic medium.
The vegetative cells of Cl. tetani grow locally in the
necrotic tissue → release of tetanospasmin toxin.
Tetanus Neonatal tetanus ?
mother lacks
immunity & the umbilical stump becomes
contaminated with Cl. tetani spores
Tetanus Prevention?
I. Active immunization:
Toxoid is given to infants in the first year of life: the triple
vaccine (DPT) is given at the age of 2, 4 & 6 months by IM injection.
II. Passive immunization Human tetanus immunoglobulin (HTIG)
Non-spore-forming anaerobes
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Bacteroides
Gram-ve bacilli, highly pleomorphic Capsulated (virulence factor)→ antiphagocytic.
Bacteroides
The commonest pathogen among Bacteroides species
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B. fragilis
released from the colon into blood → multiplies rapidly →
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Bacteroides
bacteremia
If introduced into the abdominal cavity →
Bacteroides
abdominal abscess
Drug resistance is common (beta lactamase production) Preoperative antibiotics are given to prevent surgical wound
contamination with ?.
Bacteroides
Gram+ve bacilli, having the typical morphology of diphtheroides. Their metabolic products include propionic acid from which the
genus name is derived. ?
Propionibacterium Morphology
Normally present in human skin, hair, oropharynx & GIT . It is the major contributor to the complex pathogenesis of acne vulgaris.
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P. acne
