Anaerobic Bacteria Flashcards
Anaerobic organisms are ones which
2 main categories
sub category
Do not require oxygen
Obligate and facultative
- harmed by presence of oxygen
- can grow without but use if present - use aerobic respiration in the present of oxygen
Microaerophiles
- grow in a low oxygen <5% atmosphere e.g campylobacter
Anaerobiosis
anaerobes may
Anaerobic respiration/fermentation
- Produces ATP without O2 involvement
- Use fermentation or anaerobic respiration
Anaerobic fermentation/respiration
Involves and results in
Purpose
Mechanism
Inefficient process
Slower growth
Organic electron acceptor in absence of oxygen e.g lactic acid
- results in incomplete breakdown products and less energy
Converts energy from glucose into useable form
Uses ETC but final EA is not O2
- nitrate
- ferric iron
Fermentation products
Lactic acid
Created to reproduce NAD
Fed back into glycolysis
Anaerobic respiration in yeast
Ethanol production
Aerobic respiration - normal mechanism
ATP released along electron transport chain
O2 is final electron acceptor –> water
Purpose of anaerobic lifestyle
Disadvantages
Allows growth in low O2 tension environments e.g sub-gingival biofilm plaque
Allow them to keep living
No ability to resist oxides or aerobic bi-products
Study of anaerobes
Special culture methods to exclude O2
Sensitive to metronidazole
Produce toxins
major bacteria in humans
Clostridium
Bacteroides - commensal –> abdominal and gut infections Fusobacterium - oral cavity + perio
Porphyromonas and black pigments - perio and pulp infections
Gardnerella - bacterial vaginosis
Clostridium
Characteristics
Produce
Important species
Large, straight, gram +ve bacilli
Produce endospores which become encapsulates in part of the cell to grow again
Endotoxins
- Cl. perfringens - gas gangrene, food poisoning
- Cl. botulinum - food botulism
- Cl. tetani - tetanus
- Cl. difficile - pseudomembranous colitis
Cl. perfringens
Capsulate, non-motile, gram +ve rod
Polysaccharide capsule
Repeating units of 6 sugars
Spreading, fast growing, double BETA haemolytic colonies on BA
Cl. perfringens exo-toxins
Specific toxin?
5 types A-E
Major toxin is α-toxin
- phospholipase C/lecithinase
- lyses RBCs, platelets, leukocytes and endothelial cells
- inflammation and major swelling
- oedema, bleeding due to??
- haemolysis
- kidney damage
- myocardial dysfunction
Enterotoxin
- pore-forming
- heat labile
- produced upon sporulation upon bacterial ingestion and stomach acid exposure
Diseases caused by Cl. Perfringens
main
Source
Tx
Other diseases
Gas gangrene aka clostridial myonecrosis
- spore contamination of open wounds
- oedema, gas formation, necrosis and toxaemia and cellulitis
Soil, animal and human excrement
Surgery, amputation and antibiotics
Food poisoning
- meat products
- survive cooking
- bacteria ingested and sporulated and produce enterotoxin
- intestinal epithelial damage which inhibits glucose reabsorption –> diarrhoea
Cl. tetanus
Symptoms
Incubation period
Source
Mechanism
Characteristic
Acute spastic paralysis - potent neuro exotoxin
Lockjaw, rictus sardonicus due to uncontrolled contraction of jaw muscles
Only minute amount of toxin required
10-14 days
Wounds, splinters, cuts, ubiquitous environmental spores in soil
Enter wounds
Toxin tracks to CV
Gram +ve
Thin spreading film on agar - drum stick sports due to motility
Tetanus toxin mechanism
GABA
Classic neurotoxin - TETANOSPASMIN
- a-b
A DOMAIN has active site - zinc endopeptidase
- breaks down synaptobrevins
- prevents release of inhibitory transmitter (GABA)
- gamma aminobutyric acid
- prevents relaxation of muscle = continuous stimulation
B domain - carbohydrate receptor binding site - binds to recognition site on target cell - binds to specific lipids
Tetanus treatment
Anti-toxin/immunoglobulin
Penicillin and metronidazole
Tetanus toxoid vaccination
Botulism
Cause
Symptoms
Contaminated food containing bacteria Flaccid paralysis Facial paralysis Dizziness, resp and cardiac failure Continuous relaxation
Cl. Botulinum
Characteristics
Causes
Mechanism
Treatment
Gram +ve bacillus Motile Produces sub terminal spores Widely distributed e.g in soil Grows well in most temps
Botulism
- food poisoning
- 1-2 days
- toxin released in protected form
- Potent neurotoxin with A and B domain
- Peptidase which breaks down signal molecule
- Prevents release of acetyl choline therefore preventing contracting
- binds irreversibly
Remove toxin
Botox
Can weaken muscles temporarily - spasms and dystonias
- strabismic
- bruxism
- torticolis - neck spasms
- cerebral palsy
C. difficile
Causes
Associated with hospital acquired infection and antibiotic use
Outcompetes rest of popn after antibiotic use is over
Spore forming - heat and disinfectant resistant
Severe diarrhoea
A and B exotoxins
Pseudomembranous colitis
Pseudomembranous colitis
Bowel disease which can lead to rupture
Antibiotic associated diarrhoea
Adherent membrane of inflammatory cells and necrotic debris
C. difficile toxin
Causes diarrhoea and electrolyte imbalance
C. difficile treatment
Common in
In faeces of neonates
vancomycin or metronidazole
remove offending selective antibiotic
limit use of antibiotics
removal of broad spectrum antibiotics
Other anaerobes
Gram? and what do they cause
Gram -ve
Bacteroides - abdominal wound infections
Prevotella - oral and genital infections
Porphyromonas - oral infections
Fusobacterium - oral and vaginal, necrobacillosis
Gram +ve
Peptostreptococci
Eubacterium
Bifidobacterium
Gardnerella
