This document provides an overview of anaerobic bacteria. It describes the characteristics of anaerobes and how they differ from aerobic bacteria in their oxygen requirements. It also outlines methods for specimen examination, culture, identification, and the major types of clinically relevant anaerobic bacteria including Bacteroides, Prevotella, Fusobacterium, Clostridium, Actinomyces, Propionibacterium, and anaerobic cocci. Key details on morphology, habitat, diseases caused, and biochemical traits are given for important bacterial genera.

1. ANAEROBES

2.  Bacteria that require a reduced oxygen tension for
growth and fail to grow on solid media in the
presence of oxygen.

3. MACROSCOPIC EXAMINATION OF
SPECIMENS
 Specimens should be inspected for characteristics
that strongly indicate the presence of anaerobes:
1. foul odor
2. sulfur granules associated with
Actinomyces, Propionibacterium,
Eubacterium
3. brick red fluorescence under long wavelength
ultraviolet light

4. DIRECT DETECTION METHOD
 ANTIGEN DETECTION
 A latex particle agglutination test or an enzyme-linked
immunosorbent assay(ELISA) to detect toxins A and/or
B

5.  GRAM STAIN
 Rapid tool for anaerobic bacteriology
 Reveals the types and relative numbers of
microorganisms and host cells present
 Serves as quality control measures for the
adequacy of anaerobic techniques.

6.  A positive gram stain with negative culture
may indicate:
Poor transport method
Excessive exposure to air during specimen
processing
Inadequate types of media or old media
Microorganisms have been killed by
antimicrobial therapy

7. ANAEROBIC MEDIA
 Primary plates should be freshly prepared
or used within two weeks of preparations
 Plates stored for longer periods accumulate
peroxides and become dehydrated which
results in growth inhibition

8.  ANAEROBIC MEDIA COMMONLY USED FOR
CULTURE:
 ANAEROBIC BLOOD AGAR
 Nonselective for all anaerobes
 ANAEROBIC PHENYLETHYL ALCOHOL BLOOD
AGAR
 Nutrient agar base
 Selective for inhibition for gram-negative enteric bacilli
 LAKED KANAMYCIN-VANCOMYCIN BLOOD AGAR
 With antibiotics; selective for Provotella & Bacteroides
 THIOGLYCOLLATE BROTH
 Nonselective for anaerobes

9.  BACTEROIDES BILE-ESCULIN
 Trypticase soy agar base
 EGG YOLK AGAR
 Nonselective for the determination of lecithinase and
lipase production by Clostridia and Fusobacteria

10. IDENTIFICATION
 Gram staining
 Colonial Morphology
 Gas liquid chromatoraphy
 Biochemical reactions
 Susceptibility patterns

11. ANAEROBIC GRAM-NEGATIVE BACILLI
 Major normal flora in the colon and of the
oral cavity
 Most common anaerobes isolated clinically
 Gold Standard for identification is Gas-
Liquid Chromatography (GLC)

12. BACTEROIDES FRAGILIS GROUP
 Non-motile
 On aerobic blood agar, colonies are non-hemolytic
and gray with an entire margin and ring-like
structures
 Saccharolytic
 Extremely virulent and can cause widespread
tissue destruction
 Has a capsule and also produces several enzymes
 No pigment or spore formation

13. PIGMENTED SACCHAROLYTIC GRAM-NEGATIVE
BACILLI
 Include: Prevotella melaninogenica, Prevotella corporis,
Prevotella denticola, Prevotella loeschii, Prevotella
intermedius
 Normal flora of the oropharynx, nose, gastrointestinal
tract and urogenital tract
 Typically slow growing, requiring up to 3 weeks to grow
 Young colonies are tan to buff in color
 An important characteristic is its brick-red fluorescence
when viewed under ultraviolet light at 365nm
 Older colonies develop a brown to black pigment
 P. denticola, P. loeschii, and P. melaninogenica ferment
lactose while the other two don’t

14. ASACCHAROLYTIC PIGMENTED GRAM-NEGATIVE
BACILLI
 Include the genus Porphyromonas
asaccharolyticus, Porphyromonas endodentalis,
Porphyromonas gingivalis
 Normal flora of the oropharynx, nose, urogenital
tract, and gastrointestinal tract
 Typically slow growing; requiring 48 hours to as
long as 2 weeks.
 Colonies characteristically show a brick-red
fluorescence when viewed under uv light
 Older colonies develop a black to brown pigment
 Do not ferment carbohydrates

15. FUSOBACTERIUM
 Found as a normal flora of the upper respiratory
tract, GI tract, and urinary tract
 Fusobacterium nucleatum:
 The specie most isolated which is associated with
pleuropulmonary infections, including lung abscesses
 Appear as spindle-shaped cells in long filaments with
tapered or pointed ends
 Colonial morphology: opalescent with speckles when
viewed under a stereoscope
 Cannot ferment glucose

16.  Fusobacterium necrophorum:
 Associated with particularly virulent infections,
including septicemia and metastatic infections
such as lung and liver abscesses, arthritis, and
osteomyelitis
 Ferment glucose

17. ANAEROBIC GRAM-POPSITIVE SPORE-
FORMING CLOSTRIDIUM
 Anaerobic or aerotolerant gram-positive bacilli that form
spores anaerobically
 Catalase negative, which is an important reaction to
differentiate these organisms from Bacillus species,
which are catalase positive and sporulate aerobically
 The sporangia of Clostridia are characteristically swollen
and may be located in a terminal, subterminal, or central
position; spores can be seen using the gram stain
technique or a special spore stain
 Produce true exotoxins
 Additional virulence factor is the production of spores

18. CLOSTRIDIUM TETANI
 Etiologic agent of tetanus
 Tetanospasmin toxin- a potent neurotoxin that travels
along nerve fibers from the wound to the anterior horn
cells of the spinal cord.
 “lockjaw”
 Opisthotonus
 Diagnosis of tetanus is accomplished through clinical
picture and history of the injury
 Disease can be prevented by tetanus toxoid vaccination
 Identification of organisms:
 Observation of gram-positive bacillus with round, terminal
spores that resemble a drumstick
 Unable to ferment most carbohydrates
 Motile

19. CLOSTRIDIUM BOTULINUM
 Agent in food and wound botulism, as well as infant botulism
 Botulism toxin- neurotoxin
 Causes acute and flaccid paralysis
 Types of Botulism toxin: A, B, C, D, E, F, and G
 Most common types in humans: A, B, E, and F
 Food Botulism is associated with the ingestion of preformed
botulism toxin in home-canned foods
 The spores are not inactivated because of a poor incomplete
canning process and germinate under the anaerobic conditions
 Wound botulism occurs as the organism grows in the wound.
 Most Common Type: Infant botulism
 Diagnosed through clinical symptoms and patient history
 Ferments glucose
 Motile

20. CLOSTRIDIUM PERFRINGENS
 The most common species of Clostridium isolated
from clinical specimens
 Causes myonecrosis (gas gangrene), food
poisoning, post-abortion sepsis, intraabdominal and
pleuropulmonary infections, enterocolitis and
antibiotic-associated diarrhea
 It is known to produce 12 toxins
 germination occurs in deep wounds
 secretes both enzymes and enxotoxins
 The organism produces a mild and self-limiting
condition lasting 2 to 3 days.

21.  Food commonly contaminated: beef, turkey, and
chicken
 Symptoms occur 7 to 15 hours after ingestion and
include foul-smelling stools and diarrhea, but
usually no vomiting
 Also causes Necrotic Bowel Disease
 Ferments glucose, lactose, maltose, and fructose
 Spores are round and subterminal but are usually
impossible to demonstrate
 Nonmotile

22. ANAEROBIC, GRAM-POSITIVE NON-SPORE
FORMING BACILLI
 Actinomyces, Bifidobacterium, Eubacterium, anaerobic
lactobacillus, Propionibacterium, Mobiluncus
 Normal flora of the human urinary tract, oral cavity, bowel
and vagina

23. ACTINOMYCES
 Normal flora of mouth and urogenital tract
 Associated with opportunistic infections of endegenous
origin
 Actinomyces israelli is the most significant specie.
 Actinomycosis is characterized by the presence of “sulfur
granules” in the exudate of the infection
 Cells are branching and diphtheroid in appearance
 On agar the organism grows heaped, rough, and white
and the colonies are described as “molar tooth”

24. BIFIDOBACTERIUM
 Gram positive diphtheroid; coccoid or thin pointed
shape; highly irregular; bifurcated (forked) ends
(“dog bones”)
 On anaerobic blood agar: small, white, convex
shiny colonies with irregular edge
 Normal flora of the gastro intestinal tract and is a
rare cause of pulmonary infections

25. PROPIONIBACTERIUM ACNES
 The most frequent gram-positive non-sporeforming
bacillus
 Normal flora of the skin, nasopharynx, oral cavity, and GI
tract and a rare cause of endocarditis
 More often found as a skin contaminant in blood cultures
 Produces propionic acid
 Sometimes referred to as “anaerobic diphtheroids”
 Resembles the corynebacteria as “Chinese letters” or
“picket fences”

26. EUBACTERIUM
 Gram-positive, pleomorphic rods or coccobacilli
 Small, gray, transparent or translucent, raised to
convex colonies on anaerobic blood agar
 Rarely isolated from wounds and abcesses in
mixed infections

27. MOBILUNCUS
 Gram variable, small thin, curved rods
 Grows on anaerobic blood agar producing small,
low convex and translucent colonies
 Found in the vagina and have been associated with
bacterial vaginosis

28. ANAEROBIC COCCI
 Normal flora of the bowel, female genital tract, oral
cavity, skin, and respiratory tract
 Associated with abcess of the liver and brain and
with wound infectionsof the female genital tract,
abdominal cavity and respiratory tract

29. ANAEROBIC GRAM-POSITIVE COCCI
 Peptoccus niger
 Commonly known as “anaerobic staphylococcus”
 Typically appears in clusters
 Rare cause of infection
 Peptostreptococcus anaerobius
 Appears as large coccobacilli in chains on gram stained
preparation
 Peptostreptococcus tetradius
 Appears as tetrads

30. ANAEROBIC GRAM NEGATIVE COCCI
 Veilonella
 Appears as gram-negative cocci arranged in pairs, short
chains, or irregular clumps
 Rare cause of human infection
 Megasphaera
 Acidoaminococcus

31.  www.globalrph.com/bacterial-strains-anaerobic.htm
 www.wikipedia.org/wiki/Anaerobic_organism
 Dr. Lisa Young Compilations
 www.merckmanuals.com/professional/infectious_di
seases/anaerobic_bacteria/overview_of_anaerobic
_bacteria.html