Anaerobic Bacteria

Question 1

Anaerobic organisms are ones which

2 main categories

sub category

Answer 1

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

Question 2

Anaerobiosis

anaerobes may

Answer 2

Anaerobic respiration/fermentation

• Produces ATP without O2 involvement
• Use fermentation or anaerobic respiration

Question 3

Anaerobic fermentation/respiration

Involves and results in
Purpose
Mechanism

Answer 3

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

Question 4

Fermentation products

Answer 4

Lactic acid
Created to reproduce NAD
Fed back into glycolysis

Question 5

Anaerobic respiration in yeast

Answer 5

Ethanol production

Question 6

Aerobic respiration - normal mechanism

Answer 6

ATP released along electron transport chain

O2 is final electron acceptor –> water

Question 7

Purpose of anaerobic lifestyle

Disadvantages

Answer 7

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

Question 8

Study of anaerobes

Answer 8

Special culture methods to exclude O2

Sensitive to metronidazole
Produce toxins

Question 9

major bacteria in humans

Answer 9

Clostridium
Bacteroides - commensal –> abdominal and gut infections Fusobacterium - oral cavity + perio
Porphyromonas and black pigments - perio and pulp infections
Gardnerella - bacterial vaginosis

Question 10

Clostridium
Characteristics
Produce
Important species

Answer 10

Large, straight, gram +ve bacilli
Produce endospores which become encapsulates in part of the cell to grow again
Endotoxins

1. Cl. perfringens - gas gangrene, food poisoning
2. Cl. botulinum - food botulism
3. Cl. tetani - tetanus
4. Cl. difficile - pseudomembranous colitis

Question 11

Cl. perfringens

Answer 11

Capsulate, non-motile, gram +ve rod
Polysaccharide capsule
Repeating units of 6 sugars
Spreading, fast growing, double BETA haemolytic colonies on BA

Question 12

Cl. perfringens exo-toxins

Specific toxin?

Answer 12

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

Question 13

Diseases caused by Cl. Perfringens

main

Source

Tx

Other diseases

Answer 13

Gas gangrene aka clostridial myonecrosis

1. spore contamination of open wounds
2. 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

Question 14

Cl. tetanus

Symptoms

Incubation period
Source
Mechanism
Characteristic

Answer 14

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

Question 15

Tetanus toxin mechanism

GABA

Answer 15

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

Question 16

Tetanus treatment

Answer 16

Anti-toxin/immunoglobulin
Penicillin and metronidazole

Tetanus toxoid vaccination

Question 17

Botulism

Cause

Symptoms

Answer 17

Contaminated food containing bacteria 
Flaccid paralysis 
Facial paralysis 
Dizziness, resp and cardiac failure 
Continuous relaxation

Question 18

Cl. Botulinum

Characteristics

Causes

Mechanism

Treatment

Answer 18

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

Question 19

Botox

Answer 19

Can weaken muscles temporarily - spasms and dystonias

• strabismic
• bruxism
• torticolis - neck spasms
• cerebral palsy

Question 20

C. difficile

Causes

Answer 20

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

Question 21

Pseudomembranous colitis

Answer 21

Bowel disease which can lead to rupture

Antibiotic associated diarrhoea
Adherent membrane of inflammatory cells and necrotic debris

Question 22

C. difficile toxin

Answer 22

Causes diarrhoea and electrolyte imbalance

Question 23

C. difficile treatment

Common in

Answer 23

In faeces of neonates

vancomycin or metronidazole
remove offending selective antibiotic

limit use of antibiotics

removal of broad spectrum antibiotics

Question 24

Other anaerobes

Gram? and what do they cause

Answer 24

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

Question 25

Black pigmented anaerobe examples

Answer 25

Prevotella
Gram -ve, non-motile
Lives in oral cavity
Colonise by binding to other bacteria in addition to epithelial cells
Abscesses, bacteraemia, wound infection, bite infections, genital tract infections and periodontitis

Porphyromonas

Gram -ve, non motile, rod shaped
Periodontal disease
P. gingivalis, T. denticola, T. forsythia form red complex

Question 26

Fusobacterium

Nature

Mechanism

Treatment

Answer 26

Long rod shaped spindle shaped bacilli

Gram -ve

Perio disease, skin ulcers, respiratory infections

highly effective at biofilm formation

Antibiotics