Anaerobic Bacteria
Dental/Optometry Microbiology
Stephen A. Moser, Ph.D.
9/17/2008
1
Reading Assignment
Medical Microbiology, 5th Ed., Murray, PR, et al
Chapter 9
Chapter 41
Chapter 42
Chapter 38
2
1
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
3
Physiology And Growth
Conditions
• 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.
4
2
5
Oxidation - Reduction Potential And
Anatomic Site
Millivolts
+810
+240
+180
0
-50
-200
-300
-420
Location
Oxygen electrode
Human cell
Venous blood
Periodontal pocket
Dental plaque
Colon
Hydrogen electrode
6
3
Anaerobic Bacteria Of Clinical
Importance
Genera
Bacilli (rods)
Gram-negative
Bacteroides fragilis group
Prevotella melaninogenica grp
Fusobacterium
Gram-positive
Actinomyces
Lactobacillus
Propionibacterium
Eubacterium, Bifidobacterium,
and Arachnia
Clostridium
Anatomic Site
Colon
Mouth
Mouth, colon
Mouth
Vagina
Skin
Mouth, colon
Colon (also found in
soil)
Cocci (spheres) Gram-positive
Peptostreptococcus
Colon
Gram-negative Veillonella
Mouth, colon
7
8
4
Vincent Angina
9
Adult Periodontitis
10
5
Anaerobic Brain Abscess
11
Anaerobic Polymicrobic Cellulitis
12
6
Anaerobic Infections
Gram-negative Bacilli

Bacteroides / Prevotella / Porphyromonas species
Non-spore forming, pleomorphic rods
Normal flora of upper respiratory tract, intestinal and
female genital tract
Most important groups - Bacteroides fragilis and
Prevotella melaninogenica
Colon associated –group (fragilis)
Upper respiratory tract - P. melaninogica group
Female genital tract - P. bivia and P. disiens
Clinical disease usually abscess formation with
mixed anaerobic and facultative anaerobic bacteria.
13
Necrotizing Fasciitis
Bacteroides fragilis
14
7
Necrotizing Fasciitis
Bacteroides fragilis
15
Anaerobic Infections
Gram-negative Bacilli
• Fusobacterium
 Pleomorphic non-spore forming rods
 Usually present in mixed infections but
may be the sole agent
 Present in both upper respiratory and
intestinal tract
16
8
Pulmonary Abscess
17
Fusobacterium
18
9
Anaerobic Infections
Gram-positive Bacilli
• Actinomyces
Most common is Actinomyces israelii
Slow growing and are difficult to isolate
Cause extensive soft tissue involvement
crossing tissue plane and involving
multiple organ systems
Can result in draining sinus tracts with
“sulfur granules”
granules”
Associated with oral, respiratory and
female genital tract infections (IUD)
19
DACRYOCYSTITIS
20
10
Actinomycosis
“Lumpy Jaw”
21
Actinomycosis
22
11
“Sulfur” Granules
23
Actinomyces israelii
24
12
Anaerobic Infections
Gram-positive Bacilli
• 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
25
Anaerobic Infections
Gram-positive Bacilli
• Clostridium







The only genus of anaerobes that forms spores
Tetanus - C. tetani - in vivo toxin production
 Tetanospasmin
Botulism - C. botulinum - ingestion of preformed neurotoxin
except for wound and infant botulism
Gas gangrene - C. perfringens - H2 & CO2
 Phospholipase C (α
(α-toxin)
Food poisoning - C. perfringens
 Enterotoxin
C. septicum - associated with malignancy, neutropenia
Pseudomembranous colitis / antibiotic associated diarrhea C. difficile
26
13
Tetanus
27
Clostridium tetani
28
14
Gas Gangrene
29
Clostridium perfringens
30
15
Clostridium perfringens
Nagler Test
31
Clostridium difficle Colitis
32
16
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.
33
DIAGNOSIS OF
ANAEROBIC INFECTIONS
• Clinical signs
 Foul smelling discharge
 Proximity to a mucosal surface
 Gas in tissue
 Abscess formation
• Gram stain
 May be helpful in the establishment
of a mixed infection or the presence
clostridia in wounds
34
17
Gram Stain of Mixed Infection
35
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
36
18
Anaerobic Containers
37
Anaerobe Chamber
38
19
Bacteroides fragilis
39
Treatment Of Anaerobic
Infections
• 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.
e.G. P. melaninogenica group, B.
fragilis groups.
• Aminoglycosides not effective.
• Toxin mediated diseases - antitoxin and
antibiotics if active infection vs. Intoxication.
40
20
Etest™ Susceptibility Testing
41
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.
42
21