This document provides an overview of anaerobic bacteria. It begins by defining obligate and aerotolerant anaerobes. It then describes various types of non-sporing anaerobes that can be commensal or pathogenic, including their roles in normal flora and diseases. Key pathogenic genera discussed are Bacteroides, Prevotella, Porphyromonas, Fusobacterium, and Actinomyces. The document outlines methods for laboratory diagnosis of anaerobic infections through microscopy, culture, and identification techniques. It concludes with discussing treatment of anaerobic infections with various antibiotic classes.

2. INTRODUCTION
• Microorganisms that grow only in complete or nearly complete absence of molecular
oxygen.
• Aerobic organisms use oxygen as terminal electron acceptor and generate toxic oxygen
reduction products including H2O2,hydroxy radicals, singlet oxygen and superoxide
anions.
• Such reactive metabolites destroy the lipid components of cells and damage the DNA.
• However, aerobes and facultative anaerobes are protected from these reactive by-
products due to certain enzymes like peroxidases and superoxide dismutase.
They can be classified as follows:
• Obligate anaerobes: They cannot grow in presence of oxygen as they completely lack
superoxide dismutase and catalase enzymes and hence are susceptible to the lethal
effects of oxygen
• Aerotolerant anaerobes: They do not utilize oxygen for growth, but tolerate its presence.
This is because they possess small amounts of superoxide dismutase and peroxidase
which may neutralize the toxic oxygen radicals.

3. OBLIGATE ANAEROBES
• Spore bearing (e.g. Clostridium)
• Non-sporing anaerobes

4. NON-SPORING ANAEROBES
• Non-sporing anaerobes are often a part of normal flora of mouth, GIT
and genital tract of man and animals.
• Many of these bacteria have also been recognized as important cause
of human infections.

5. CLASSIFICATION

6. NON-SPORING ANAEROBES AS NORMAL FLORA
Most muco-cutaneous surfaces of humans harbour a rich flora of anaerobic
bacteria which varies at different anatomic sites in terms of concentrations
and microbial species.
►Upper air ways
►Saliva (approximately 108 /ml )
►Gingiva (almost 1012
/ml)
►Stomach (almost 105 /ml)
►Small intestine (104 - 105 /ml)
►Terminal ileum and colon (1011
/gm)
►Female genital tract (105
- 1011
/ml) shows shifts during various stages of
the menstrual cycle that may be hormonally influenced.

7. ROLE AS COMMENSAL
• Compete with pathogens for its nutrition
• Modulate host innate immune response.
• Bacteroides ferments carbohydrates act as an energy source.
• Produce vit K & bile acids in intestine
• Lactobacillus maintains vaginal ph
• Prevent IBS.

8. NON-SPORING ANAEROBES AS PATHOGENES
• Anaerobic infections occur when the harmonious
relationship between the host and the bacteria is
disrupted.
• Disruption of anatomical barrier (skin and mucosal
barrier) by surgery, trauma, tumor, ischemia, or
necrosis (all of which can reduce local tissue redox
potentials) allow the penetration of many anaerobes,
resulting in mixed infection.

9. ANAEROBIC GRAM-POSITIVE COCCI
• Normal flora of the bowel, female genital tract, oral cavity, skin, and respiratory
tract,
• Associated with abscess of the liver and brain and with wound infections of the
female genital tract, abdominal cavity and respiratory tract.
Peptoccus niger
• Commonly known as “anaerobic staphylococcus”
• Typically appears in clusters
• Rare cause of infection
Peptostreptococcus
• Appears as large coccobacilli in chains on gram stained.
• Causes Abscesses, Sinusitis, Diabetic foot ulcer etc.

10. ANAEROBIC GRAM-POSITIVE BACILLI
Normal flora of the human urinary tract, oral cavity, bowel and vagina.
Eubacterium
• Gram-positive, pleomorphic rods or coccobacilli
• Small, grey, transparent or translucent, raised to convex colonies on anaerobic blood agar
• Rarely isolated from wounds and abscesses in mixed infections.
Bifidobacterium
• Gram positive diphtheroid; coccoid or thin pointed shape; highly irregular; bifurcated
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.

11. Propionibacterium acnes
• Most frequent gram-positive non-spore forming 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 corynebacterial as “Chinese letters” or "picket fences”
Actinomyces
• Normal flora of mouth and urogenital tract.
• Associated with opportunistic infections of endogenous 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.

12. Lactobacillus
• They are non-motile gram-positive bacilli that frequently show bipolar and barred
staining
• They are ferment materials such as milk and cheese.
• They produce lactic acid from carbohydrates and grow best at pH of <5.
• They are part of normal flora of mouth, gut and vagina.
• In stomach: Lactobacilli in the stomach (e.g. L.acidophilus) synthesize vitamins, such as
biotin, vitamin B12 and vitamin K
• In the oral cavity: It may have a role in the pathogenesis of dental caries.
• In vagina: Lactobacillus species in adult vagina (known as Doderlein's bacilli) produce
lactic acid protecting from various infections.

13. 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
BACTERIAL VAGINOSIS
• Also caused by Gardnerella vaginalis
• Polymicrobial infection characterised by rotten fish, vaginal discharge
• A direct wet mount may reveal many characteristic “clue cells” desquamated epithelial
cells with attached organisms
• Gram variable organisms seen on staining

14. 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)

15. Bacteroides fragilis group
• Non-motile, Saccharolytic
• On aerobic blood agar, colonies are non-haemolytic and gray with an entire margin and
ring-like structures
• Extremely virulent.
• It causes peritonitis following bowel injury and pelvic inflammatory disease (PID).
• It is also implicated in abdominal infections, brain abscesses and in empyema producing
foul smelling pus.
Prevotella
It moderately saccharolytic and pigmented
• Pigmented (e.g. P. melaninogenica)
• Produces hemin derived black or brown colored colonies.
• Colonies produce characteristic red fluorescence when exposed to ultraviolet light
• It has been isolated from lung or liver abscess, mastoiditis, and lesions of intestine and
mouth.
• Nonpigmented (P. denlicola and P buccalis)

16. Porphyromonas
It asaccharolytic and pigmented
• P.gingivalis: is responsible for periodontal disease .
• P.endodontalis causes dental root canal infections.
Fusobacterium
• They are long, thin spindle shaped bacilli with pointed ends,
• F.nucleatum is a normal inhabitant of the mouth and is found in oral infection and
pleuropulmonary sepsis
• F.necrophorum is agent of Lemierre's syndrome
Leptotrichia buccalis
• They are long, thin spindle-shaped bacilli with pointed ends
• They are part of the normal oral flora
• They are implicated in an acute necrotizing gingivostomatitis known as Vincent's angina;
resembling diphtheria.

17. CLINICAL PRESENTATION
Anaerobic infections are associated with various clinical clues, such as:
• Infections adjacent to mucosal surfaces that bear anaerobic flora.
• Predisposing factors such as ischemia, tumor, penetrating trauma, foreign body, or
perforated viscus
• Foul smelling pus
• Abscess formation
• Failure to respond to antibiotics that do not have significant anaerobic activity
• Organisms are seen under Gram stain, but fail to grow in routine aerobic culture
• Special features like:
Gas in specimen (gas gangrene)
Black pigment that fluoresce (P melaninogenica)
Sulfur granules (Actinomyces).

18. LABORATORY DIAGONOSIS
Specimens
• All clinical specimens must be handled meticulously as brief exposure to oxygen may kill
obligate anaerobes and result in failure to isolate them in the laboratory.
• Accepted specimens: Tissue bits, necrotic materials, aspirated body fluids or pus in
syringes
• Unacceptable specimens: All swabs, sputum or voided urine
• Specimens should be immediately put into RCM broth or other anaerobic transport
media and brought to the laboratory as soon as possible.
Microscopy
• Gram stained and examined for characteristic morphology.

19. Cultural identification
Anaerobiosis
• McIntosh and Filde's anaerobic jar
• GasPak system
• Anoxomat system
• Anaerobic glove box workstation
• Pre-reduced anaerobically sterilized (PRAS) media
Culture
Various culture media can be used for isolation of anaerobes, such as:
• Anaerobic blood agar
• Neomycin blood agar
• Egg yolk agar
• Phenylethyl agar (PEA)
• BHIS agar: Brain-heart infusion agar
• Bile esculin agar (BBE agar).
Identification of anaerobes is based on:
• Biochemical tests, Susceptibility to antibiotic disks , Gas liquid chromatography.

20. TREATMENT
Common antibiotics
• Metronidazole
• Carbapenems (imipenem)
• ß-lactam/ß-lactamase inhibitor combination (ampicillin / Sulbactam)
• Chloramphenicol
Choice of antibiotics depends on
• Site of infection
• Type anaerobe involved
• Susceptibility to antibiotics.

21. THANK YOU