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Anaerobic Bacteria
Fundamentals II
Stephen A. Moser, Ph.D.
10/19/2011
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Categories Based Upon Gaseous Requirements
· Aerobic bacteria Require oxygen as electron acceptor
· Microaerophilic bacteria Require oxygen in reduced quantity
· Capnophilic bacteria Require carbon dioxide
· Facultative bacteria Grow either with or without oxygen
· Anaerobic bacteria Both obligate and aerotolerant
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· Both pH and oxidation-reduction potential are important.
· Cytochrome systems absent.· Most lack superoxide dismutase (SOD) and
catalase. Obligate anaerobe - lack cytochrome, SOD and
catalase. Aerotolerant anaerobe - has some SOD and or
catalase. Facultative anaerobe - grow equally well under
either aerobic or anaerobic conditions.
Physiology And Growth Conditions
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Oxidation - Reduction Potential And Anatomic Site
Millivolts Location
+810 Oxygen electrode +240 Human cell +180 Venous blood
0 -50 Periodontal pocket -200 Dental plaque -300 Colon -420 Hydrogen electrode
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Anaerobic Bacteria Of Clinical Importance
Genera Anatomic Site
Bacilli (rods) Gram-negative Bacteroides fragilis group Prevotella melaninogenica grp Fusobacterium
Colon Mouth Mouth, colon
Gram-positive Actinomyces Lactobacillus Propionibacterium Eubacterium, Bifidobacterium, and Arachnia Clostridium
Mouth Vagina Skin Mouth, colon
Colon (also found in
soil) Cocci (spheres) Gram-positive
Peptostreptococcus Colon
Gram-negative Veillonella Mouth, colon
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Conjunctivitis Keratitis
Dacryocystitis
Anaerobic Bacteria in Ocular Infections
Number of patients
Aerobic organisms onlyStaphylococcus aureus 12Streptoccoccus pneumoniae 13Haemophilus influenzae 14Haemophilus parainfluenzae 3
Anaerobic organisms onlyPeptostreptococcus spp. 7Propionibacterium acnes 6Bifidobacterium spp. 2Prevotella melaninogenica 1Bacteroides fragilis 1Fusobacterium varium 1Peptostreptococcus spp. + other anaerobic bacteria 3
Patients with mixed aerobic and anaerobic organismsPeptostreptococcus spp. + Staphylococcus spp. 6Peptostreptococcus spp. + other anaerobic and aerobic bacteria
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Propionibacterium acnes + other bacteria 12
Brook I. Anaerobic and aerobic bacterial flora of acute conjunctivitis in children. Arch Ophthalmol 1980; 98: 833–835.
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Vincent Angina
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Adult Periodontitis
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Anaerobic Brain Abscess
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Anaerobic Polymicrobic Cellulitis
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Bacteroides / Prevotella / Porphyromonas speciesNon-spore forming, pleomorphic rodsNormal flora of upper respiratory tract, intestinal and
female genital tractMost important groups - Bacteroides fragilis and
Prevotella melaninogenicaColon associated –group (fragilis)Upper respiratory tract - P. melaninogica groupFemale genital tract - P. bivia and P. disiensClinical disease usually abscess formation with
mixed anaerobic and facultative anaerobic bacteria.
Anaerobic InfectionsGram-negative Bacilli
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Necrotizing FasciitisBacteroides fragilis
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Necrotizing FasciitisBacteroides fragilis
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· FusobacteriumPleomorphic non-spore forming rodsUsually present in mixed infections but
may be the sole agentPresent in both upper respiratory and
intestinal tractF. necrophorum – Lemierre’s syndromeJugular vein thrombosis
Anaerobic InfectionsGram-negative Bacilli
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Pulmonary Abscess
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Fusobacterium
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· ActinomycesMost common is Actinomyces israeliiSlow growing and are difficult to isolateCause extensive soft tissue involvement
crossing tissue plane and involving multiple organ systems
Can result in draining sinus tracts with “sulfur granules”
Associated with oral, respiratory and female genital tract infections (IUD)
Anaerobic InfectionsGram-positive Bacilli
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DACRYOCYSTITIS
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Actinomycosis“Lumpy Jaw”
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Actinomycosis
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“Sulfur” Granules
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Actinomyces israelii
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· Propionibacterium Unusual cause of infection Normal flora of the skin May be difficult to determine the role of blood
isolates in disease
· Lactobacillus Normal flora of the vagina Rare cause of disease
· Eubacterium, Bifidobacterium, Arachnia
Anaerobic InfectionsGram-positive Bacilli
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· Clostridium The only genus of anaerobes that forms spores Tetanus - C. tetani - in vivo toxin production
Tetanospasmin – blocks inhibitory neurotransmitters Botulism - C. botulinum - ingestion of preformed neurotoxin
except for wound and infant botulism Blocks release of acetylcholine
Gas gangrene - C. perfringens - H2 & CO2 Phospholipase C (-toxin)
Food poisoning - C. perfringens Enterotoxin
C. septicum - associated with malignancy, neutropenia Pseudomembranous colitis / antibiotic associated diarrhea -
C. difficile
Anaerobic InfectionsSpore forming Gram positive Bacilli
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Tetanus
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Clostridium tetani
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Gas Gangrene
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Clostridium perfringens
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Clostridium perfringens
Nagler Test
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Clostridium difficle Colitis
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Pathogenesis
· Synergy with facultative organisms.· Facultative bacteria such as Enterobacteriaceae
function to reduce the oxygen content in the tissue.
· Beta-lactamase production.
· Capsule of Bacteroides fragilis is antiphagocytic.
· Toxin production.
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DIAGNOSIS OF ANAEROBIC INFECTIONS· Clinical signs
Foul smelling dischargeProximity to a mucosal surfaceGas in tissueAbscess formation
· Gram stainMay be helpful in the establishment
of a mixed infection or the presence clostridia in wounds
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Gram Stain of Mixed Infection
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DIAGNOSIS OF ANAEROBIC INFECTIONS
· CultureSample collection and transport are
criticalRequire complex medium supplemented
with hemin, Vit. K and or blood.Should include media containing
antibiotics (aminoglycoside) to suppress facultative anaerobes, e.g., E. coli
Incubation and work up performed in CO2 in nitrogen/ hydrogen mix
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Anaerobic Containers
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Anaerobe Chamber
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Bacteroides fragilis
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· Surgical drainage of closed abscess.· Mixed infections - cover for both aerobic and
anaerobic component.· Metronidazole, penicillin G, Clindamycin.· Penicillin resistance is common among some
species, e.G. P. melaninogenica group, B. fragilis groups.
· Aminoglycosides not effective.· Toxin mediated diseases - antitoxin and
antibiotics if active infection vs. Intoxication.
Treatment Of Anaerobic Infections
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Etest™ Susceptibility Testing
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Objectives
Know the different gaseous requirements of bacteria.
Know what special collection and diagnostics methods are required to isolate anaerobes.
Know the epidemiology of anaerobic infections. Recognize the clinical syndromes associated with
anaerobic bacteria.