Anaerobic Non-spore Forming Bacteria Flashcards
General characteristics
Anaerobic bacteria:
1) Non-spore forming anaerobic bacteria
2) Spore- forming anaerobic bacteria
- metabolically inefficient
- produce energy by fermentation
- require certain growth factors
> grow symbiotically - lack of superoxide dismutase and catalase
> die in air atmosphere
Classification
- undergoes continuous changes
- more than 50 genera
Major non-spore forming anaerobic bacteria of clinical significance:
1) Gram-negative rods
2) Gram-positive rods
3) Gram-positive cocci
4) Gram-negative cocci
1) Gram-negative rods
- Genus Bacteroides
- Genus Prevotella
- Genus Porphyromonas
- Genus Fusobacterium
2) Gram-positive Rods
GENUS
Actinomyces Propionibacterium Mobiluncus Lactobacillus Eubacterium Bifidobacterium
3) Gram-positive cocci
GENUS
Peptostreptococcus Anaerococcus Finegoldia Micromonas Schleiferella
4) Gram-negative cocci
Genus Veillonella
Morphology
- more pleomorphic in appearance than aerobic bacteria
- a variety of morphological types;
Bacilli
Cocci
Comma-shaped
Spiral-shaped (rarely) - stain poorly and may be gram-variable
Growth characteristics
Oxygen intolerant
- lack of catalase and superoxide dismutase -> H2O2 and free radicals kill anaerobic bacteria
- very fastidious organisms
- requirement for growth:
Reduced O2 tension
Elevated CO2 levels (10-30%)
Special enriched media for anaerobes
Virulence factors
- weak pathogenicity
- no toxins produced
- virulence factors found particularly in gram-negative bacilli:
Polysaccharide capsule
Lipopolysaccharide
Enzymes
Metabolic end products
Anaerobic infections
- anaerobic infections are always polymicrobial
Mixed anaerobic infections:
- with a variety of anaerobic species (only)
- with a combination of anaerobic and obligate aerobic/facultatively anaerobic (most commonly) bacteria
- typically multiple of 5 to 6 or more species are found
Ecology
- anaerobic bacteria are part of the normal flora
- the number of anaerobes exceeds the number of aerobes:
> 10 - 100 folds in the oral cavity
> 1000 folds in the large intestine
Epidemiology
Endogenous spread from adjacent mucosal surfaces after:
- trauma
- surgery (especially, abdominal and gynecological surgery)
- perforation
Disease
1) intra-abdominal infections (IAIs)
- derived from spillage of fecal matter into the peritoneal cavity
2) Obstetric and gynecological infections
- derived from contamination with vaginal and endocervical flora
3) Pleuropulmonary infections
- derived from mouth aspiration
4) Oropharyngeal infections
5) Soft tissue infections
- usually from:
Traumatic injury
Surgery
Ischemia
6) Septicemia
- evolve from:
Abdominal infections
Pelvic infections
Microbiological diagnosis
1) Specimen:
Aspirates or tissue specimens are preferable to swabs:
- better survival of anaerobes
- greater quantity of specimen
- less contamination
!! Specimen for anaerobic culture should be placed in an anaerobic transport device !!
2) Microscopic examination
- gram stain shows different morphocytes
3) Culture
- innoculation on special enriched media for anaerobes
- anaerobic incubation by:
Sealed jars
Sealed plastic pouches
- incubation at 37oC for 3 - 5 days
4) identification
- gram stain
- culture: colonies appearance
- oxygen tolerance
- biochemical characteristics
- susceptibility to antibiotics
5) antimicrobial susceptibility testing
- not performed routinely (very complex process -> only in reference hospitals/labs)
- disk-diffusion method is not reliable
- dilution tests for determination or MIC of antimicrobials are used
Treatment
- many anaerobic gram (-) rods produce beta lactamases
I.e.
fusobacterium spp.
Bacteroides fragilis group
Resistance to:
- penicillin
- cephalosporins
> surgical drainage and resection of necrotic tissue (obligatory!)
active drugs (also obligatory!)
Metronidazole
Carbapenems:
- Imipenem
- Metropenem
Clindamycin (20 - 30% resistant to B.fragilis -> not good for abdominal infections)
Beta-lactamases inhibitors/ Beta-lactams
