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Anaerobic Bacteria

Fundamentals IIStephen 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· Culture

Sample collection and transport are critical

Require 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.