Download Types of Anaerobes

Anaerobic Bacteria
Dr. Yasir . A. Hussein, MD, Microbiology & Pathology
Update, September 2016
Overview
1.Introduction to anaerobic bacteria.
2.Types of anaerobic bacteria.
3.Inhabitant of anaerobic bacteria.
4.Classification of anaerobic bacteria.
5.Pathogenesis of anaerobic bacteria.
6.Predisposing Factor of anaerobic bacteria.
7.Clinical feature of anaerobic bacteria.
8.Diagnosis & treatment of anaerobic bacteria.
Introduction:
 Medically important infections due to anaerobic bacteria are
common.
 Its major part of indigenous flora in human body.
 The infections are often polymicrobial that is the anaerobic bacteria
are found in mixed infections with other anaerobes, facultative
anaerobes and aerobes.
 Several important diseases are caused by anaerobic Clostridium
species from the environment or from normal flora.
Types of Anaerobes
 Anaerobes that live outside the body are called “exogenous anaerobes” (Example: Clostridium
species)
 Anaerobes that live inside the body are called “endogenous anaerobes”
◦ Advantages: barrier to colonization by pathogenic organisms, source of fatty acids, vitamins
and cofactors.
◦ Disadvantages: Opportunists for immunocompromised.
An absence of intestinal bacteria is associated with reductions in cell mucosal
muscle wall thickness, cytokine production, and digestive enzyme activity
and with defective cell-mediated immunity.
 Most anaerobic infections are from endogenous sources.
Types of Anaerobic Infections
Usually endogenous
◦ Intestinal anaerobes
◦ Oral anaerobes
Usually exogenous
◦ Clostridium tetani (tetanus)
◦ Clostridium botulinum (botulism)
◦ Clostridium difficile (colitis)
Either endogenous or exogenous
◦ Other Clostridial infections (e.g., gas gangrene)
Inhabitant of anaerobic infections:
 Today they are found in soil, fresh and salt water, and in normal flora of
humans and animals
 Mucosal surfaces such as linings of oral cavity, GI tract, and GU tract
 Respiratory Tract – 90% of bacteria in the mouth are anaerobes
 If mucosal surfaces are disturbed, infections can occur in the oral
cavity and in aspiration pneumonia
 Skin – frequently normal skin anaerobes contaminate blood cultures.
 GU Tract – anaerobes rarely cause infection.
 GI Tract – Approximately 2/3’s of all bacteria are in the stool.
Role of Endogenous Anaerobes
Role in normal host physiology
◦ Prevent colonization & infection by pathogens
◦ Interference with adhesion
◦ Essential for the development and function of the immune system
during early life.
◦ Contributes to host physiology
◦ E. coli synthesizes vitamin K and metabolize bile acids
Types of
Anaerobes
Obligate
Aero-tolerant
Facultative
Classification of Medically Important Anaerobes
Anaerobic microorganisms
Obligate (strict) anaerobes
◦ Grow ONLY in the absence of molecular oxygen
◦ Killed by exposure to air
Aerotolerate (moderate) anaerobes
Can tolerate exposure to air for several hours but perform
metabolic activities
Facultative anaerobes
◦ Do not require O2, but use it if available
Obligate anaerobes
Obligate anaerobes need an oxygen-free environment to live. They cannot
grow in places with oxygen, which can sometimes damage and destroy them.
Obligate anaerobes are major components of the normal microflora on
mucous membranes, especially of the mouth, lower GI tract, and vagina.
 These anaerobes cause disease when normal mucosal barriers break down.
Ex. Clostridium perfringens, Bacteroides fragilis
Facultative anaerobes
Facultative anaerobes use aerobic respiration in the presence of oxygen; without
oxygen, some of them ferment; some use anaerobic respiration.
Some species in the Staphylococcus genus are facultative, and are a leading cause of
blood poisoning.
One example is Staphylococcus aureus, which produces a range of infections from
common skin problems like acne, boils, and impetigo to acute conditions like
meningitis, endocarditis, and pneumonia.
It also causes toxic shock syndrome (TSS).
Another facultative anaerobe is Escherichia coli, which contains many helpful
serotypes as well as some damaging ones, such as those that cause food poisoning.
Aero-tolerant bacteria
Aero-tolerant bacteria do not use oxygen to live, but can exist in its
presence.
Aero-tolerant organisms are strictly fermentative (lactobacillus).
Pathogenesis & Transmission
 Endogenous route:
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Hematogenous.
Direct invasion
Secretion of mucous in oral cavity
Aspiration of mucus
Penetration of organism to peritoneal cavity.
 Exogenous:
 Penetration of organism through injury
Pathogenesis of anaerobic
Attachment and adhesion
◦ Polysaccharide capsules and pili
Invasion
◦ Alteration in host tissue (trauma, surgery, disease)
Establishment of infection
◦ Polysaccharide capsule (B. fragilis)
◦ Spore formation (Clostridium)
Tissue damage
◦ Elaboration of toxins
General Features of Anaerobic Infection:
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Brain abscess.
Upper respiratory tract infection.
Retropharyngeal abscess.
Chronic otitis media
Eye infection
Dental abscess
Gingivitis.
Lower respiratory tract infection:
 Pneumonia.
Abdominal infection:
• Peritonitis
• Intraabdominal abscess
• Hepatic abscess
• Splenic abscess.
• Appendicitis
• Irritable bowel syndrome
• Diverticulitis.
• Biliary tract infection.
Female Genital tract infections:
• Perineal abscess
• Vulvar abscess
• Endometritis
• Ovarian abscess
• Pelvic inflammatory disease
Skin infections:
• Skin ulcer
• Cellulitis.
 Bone infection:
• osteomyelitis
Neonatal infection:
• Conjunctivitis,
• Aspiration pneumonia
Clinical Features of anaerobic infections
Diagnosis: Specimens for Anaerobic
Culture
Aspirates
◦Should be collected with needle and syringe
◦Excess air expressed from syringe
◦Specimen injected into oxygen-free transport tube or
vial.
Specimens for Anaerobic Culture
Tissue
◦ must be placed in an oxygen-free transport bag or vial
◦ Usually ground for best results
Blood
◦ aerobic & anaerobic bottles are collected for most blood culture
requests
◦ History & physical examination are too important
Processing Clinical Samples for Anaerobic
Culture
Must be placed in an anaerobic chamber or holding device while
awaiting processing
Procedures
◦ Macroscopic exam of specimen
◦ Foul odor
◦ Presence of “sulfur granules”
◦ Black pigmentation
◦ Gram stain
◦ Distinct morphology
Typical Anaerobic Media
Anaerobic blood agar (BRU/BA)
◦ Supports growth of all obligate and facultative anaerobes
Bacteroides bile esculin agar (BBE)
◦ Supports growth of bile-tolerant anaerobes, such as Bacteroides, Prevotella, Porphyromonas,
Fusobacterium species
Kanamycin-vancomycin-laked blood agar (KVLB)
◦ Supports growth of Bacteroides and Prevotella spp.; certain facultative gnr will also grow
Phenylethyl alcohol agar (PEA)
◦ Supports growth of all obligate and gram positive facultative anaerobes, inhibits enteric gnr
◦ Cycloserine-cefoxitin-fructose agar (CCFA)
◦ Selective for C. difficile
Anaerobic broth, such as thioglycollate (THIO) or chopped meat
◦ Supports growth of all types of bacteria; obligate aerobes near the top, obligate anaerobes at the bottom
and facultative anaerobes throughout
Anaerobic Media
Bacteroides fragilis on KVLB (left) and BBE agar (right)
Indications of Anaerobes in Cultures
Foul odor when opening anaerobic jar or bag
Colonies on anaerobically incubated media but not on aerobic media
Good growth on BBE
Colonies on KVLB that are pigmented or fluorescent
Double zone of hemolysis on blood agar
Interpretation of Cultures
Primary cultures are examined after 48 hours of incubation
If no growth, reincubate for up to 5 days before discarding.
Treatment
Surgical therapy
◦ Draining abscesses, removing dead tissue, eliminating obstructions
Hyperbaric oxygen
◦ Oxygen is forced into necrotic tissues, killing anaerobes
Antitoxins
◦ Used in cases of tetanus and botulism to neutralize the neurotoxins produced by C.
tetani and C. botulinum
◦ Metronidazole.
◦ Antibiotics (Chloramphenicol, Penicillin, Ampicillin).
◦ Ticarcillin plus clavulanate, Amoxicillin plus sulbactam, Piperacillin plus
tazobactam) and Carbapenems (imipenem, meropenem and ertapenem).
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