Neglected in diagnostic labs- but they
outnumber the aerobic bacteria including
most sites of human and animal body.
Mouth and skin -10-30 times more frequent
than aerobic bacteria.
The numbers of anaerobes have been
estimated to be 10 4-10 5/ml in small
intestine,10 8/ml in saliva and 10 11/g in the
reactions and antibiotic sensitivity pattern.
Current classification-based on DNA base
composition and analysis of fatty acids, end
products of metabolism
Aerobes and facultative anaerobes have
metabolic systems listed below, whereas
anaerobic bacteria do not
▪ Cytochrome system of metabolism of oxygen.
▪ Superoxide dismutase, which catalyses the following
▪ Catalase, which catalyses the following reaction.
▪ 2H2O2----2H2O+O2 (gas bubbles).
Anaerobic bacteria do not have cytochrome
systems for metabolism.
Less fastidious anaerobes have low levels of
superoxide dismutase and may not have
Obligate anaerobes usually lack superoxide
dismutase and catalase and are susceptible to
lethal effects of oxygen radicals.
Most human infections are caused by
moderately obligate anaerobes.
Ability to tolerate oxygen varies from species to
They cause following infections
Divided into Graminfections,wound
Genital positive and Gram
size 0.2-2.5 µ. Many aerotolerent.
Normal flora of vagina,intestinesand mouth.
ess in the brain,lungs and
other internal anaerobicuspuerperal sepsis.
GNC of varying sizes occurring as
diplococci,short chains or groups
They are normal inhabitants of
mouth,intestinal and genital tract
All anaerobic cocci are generally sensitive to
metronidazole and resistant to streptomycin
POLYMICROBIAL INFECTION OF
Lactobacillus usually non CHARACTERIZED BY THIN
VAGINAL PH IS MORE THAN 4.5
CLUE CELL SEEN
IN FRAM STAINED SMEARSMobiluncus-M.mulieris,M.curtisii-Bacterial
What is bacterial vaginosis?
Large group of GNB appear as slender rods or
Normal commensal of intestine.
Normal stool-1011 B.fragilis/gram.
thetaiotamicron and others.
Contamination by contents of colon where
they may cause suppuration-perotinitis
Constitutes less than 10% of Bacteroides species
in the normal colon, however, is the most
common isolate of anaerobes.
Major virulence factor: capsular
polysaccharides, which may cause abscess
formation when injected into the rat abdomen.
Resistant to penicillin.
Classification is based on colonial and
biochemical features and characteristic short
chain fatty acid patterns in gas liquid
Associated with anaerobic coccipeptostreptococci and others.
GNB-slender rods and cocobacilli
Found in lung and brain abscess,in empyema
and in pelvic inflammatory diseases,and
Often polymicrobial –
peptostreptococci,anaerobic gram positive
rods and fusobacterium species.
Black colonies produced by this.
Colonies show-red fluorescence in UV rays
Normal oral commensal.
Gingival, periapical tooth infections.
More commonly-breast,axillary,perianal and
male genital infections
Most species produce butyric acid and
convert threonine to propionic acid.
Isolated from mixed bacterial infections-oral
infection pleuropulmonary sepsis.
Now-a-days techniques are simplified for
their isolation & identification.
Precipitating factors are there.
Site and type of infection
Bacteria commonly responsible
Central nervous system-brain abscess
Mouth and jaw-ulcerative gingivitis,dental
abscess,cellulitis,abscess or sinus of jaw
tal abscess,wound infection after
Female genitialia-purperal sepsis etc
Skin and soft tissue
Interpretation should be done cautiously.
Avoid resident flora contamination.
Avoid or minimise the exposure with oxygen.
In laboratory exposure should me limited to
Gram staining shows large variety of different
organisms and numerous pus cells
Occasionally-brain abscess-single organism.
UV examination-bright red fluorescence?
Gas liquid chromatography
Freshly prepared blood agar with
neomycin,yeast extract,hemin and vitamin K
Incubated at 37oC with 10%CO2.
Gas pak Jar is used
Examine plates after 24-48 hrs
Parallel aerobic cultures shd. Be always put.
Methods for excluding oxygen
1. Fluid media containing
fresh animal tissue or 0.1%
agar containing a reducing
2. Anaerobic jar
3. Anaerobic glove chamber