Anaerobic bacteria Flashcards
What are anaerobic organisms
Do not require oxygen
2 main categories of anaerobic micro-organism
Obligate anaerobes, which are harmed by the presence of oxygen
Facultative anaerobes, which can grow without oxygen but use oxygen if it is present
(Microaerophiles- grow in atmosphere of low oxygen <5%)
Anaerobosis
Anaerobic respiration/ fermentation
- production of energy (ATP) without involvement of oxygen
- anaerobes may use fermentation or anaerobic respiration
- in presence of oxygen, facultative anaerobes can use aerobic respiration
Aerobic respiration
Glucose comes in –> glycolysis –> acetyl CoA –> TCA cycle –> electron transport chain
Max ATP = 38/mol glucose
Anaerobic fermentation mechanism
Organic electron acceptor in the absence of oxygen
-e.g. lactic acid/ lactate
2ATP + acids (VFAs) /alcohols > incomplete breakdown products
-less energy
Fermentation products
Lactic acid -degrades enamel over time Acetic acid Enteric bacteria (propionic acid) Butyric acid (produced by many oral anaerobes e.g. Clostridium)
Propionic acid
Propionibacterium first isolated from Emmentaler cheese
Fermentative production of CO2 creates holes
Propionic acid adds to the flavour!
Aerobic respiration
Converting energy from, e.g., glucose, into a ‘usable form’
Aerobic respiration - ATP is released as electrons are transported along chain to final acceptor O2 (forms water)
Anaerobic respiration uses electron transport chain but the final electron acceptor is not O2
-nitrate (NO3- reduced to nitrite NO2-, or N2)
-ferric iron (Fe3+ reduced to Fe2+)
Anaerobic respiration - energy available = less
Inefficient process e.g. Sulphate:
glucose + 3SO42- + 3H+ 6HCO3- + 3SH-, ΔG0’ = -453 kJ
ΔG0’ of aerobic respiration of glucose is -2844 kJ
Anaerobes often slower growth
Anaerobic lifestyle - WHY
Allow growth in low O2 tension environments…. E.g. Gut/ sub-gingival biofilm plaque
Drawbacks for obligate anaerobes: no ability to resist presence O2 or other radicals that are by-products of aerobic life
Lab diagnosis/ study of anaerobes
Special culture methods to exclude O2 - Jars, cabinets
Gram stain, spore stain, sensitivity to metronidazole
-only obligate anaerobes sensitive to metronidazole
Sugar fermentation- species specific?
Toxin production- Clostridia
Gas-liquid chromatography
- fatty acid end products (VFAs)
16s RNA sequencing
Maldi-TOF
Major anaerobic bacteria in humans
Clostridia Bacteroides Fusobacterium Porphyromonas and Black-Pigmenters Gerdnerella and GPACs
Clostridium species
Large, straight, gram-positive bacilli Produce endospores Produce endospores Produce exo-toxins Important species in prominent diseases -Cl. perfringens - gas gangrene, food poisoning -Cl. botulinum - botulism (food) -Cl. tetani - tetanus (environmental) -Cl. difficile - pseudomembranous colitis
Cl. perfringens
Capsulate, non-motile, Gram positive Rod
-polysaccharide capsule, repeating units of 6 sugars:
[→ 4)Glc pβ(1 → 3)Gal pNAcβ(1 → 4)Glc pAβ(1 → 3)Glc pNAcβ(1 → 2)Gal pα(1 → 3)Man pβ(1 →)]n)
-spreading, fast growing, BETA hemolytic colonies on BA
5 types of exo-toxins (Cl. perfringens)
A-E
Differentiated based on production of ‘major lethal’ toxins
Major exo-toxin (Cl. perfringens)
alpha-toxin: Phospholipase C/ lecithinase Lyses RBCs, platelets, Leukocytes and endothelial cells Inflammation & major swelling oedema, bleeding (anti-platelet activity) Haemolysis Kidney damage- renal failure Myocardial dysfunction
Other VFs (Cl. perfringens)
Proteases and hyaluronidase destroy tissue
Enterotoxin - pore forming, heat labile
-produced upon sporulation of ingested bacteria in stomach acid reaction
Toxin detection (Cl. perfringens)
Nagler reaction/ plate
- opacification due to phospholipase activity of alpha toxin (no anti-toxin)
- clostridial innoculation where alpha toxin on other half of plate
Diseases caused by Cl. perfringens
Gas gangrene (Clostridial myonecrosis) Food poisoning
Gas gangrene (clostridial myonecrosis)
Spore contamination of wounds
-source – soil, animal & human excreta
Oedema, gas formation, necrosis, toxaemia, cellulitis
-treatment: surgery (amputation), antibiotics
Food poisoning (Cl. perfringens)
2nd/3rd most common cause of food poisoning
Incubation 10-12 h.
abdominal cramps, diarrhoea, (vomiting and fever unusual); resolves within 24 hours.
many cases subclinical
-antibodies to the toxin common in the population
Food poisoning in terms of Cl. perfringens
C. perfringens/ spores in soil and animal gut
C. perfingens grows in food- meats
Spores survive cooking, germinate in food.
Food ingested
Bacteria sporulate and produce Enterotoxin in stomach
Intestinal epithelim damage, inhibition of glucose transport
Diarrhoea (self-limiting)
Tetanus
Acute spastic paralysis caused by a potent bacterial neuro-exotoxin
Only ngs needed to cause disease and death
Characterised by Lockjaw (trismus), ricus sardonicus
Caused by uncontrolled contraction of muscles- mostly in CNS
Cl. tetani
Incubation 10-14 days
Enters body through wounds, splinters, cuts
Spores ubiquitous in the environment (soil etc.)
Spores in soil, contaminates wounds
Grows in wound, toxin released into bloodstream…
Motile - thin spreading film on agar - drum stick spores
Tetanus toxin
Classic A-B neurotoxin Tetanospasmin, TeNT A domain contains active site B domain> Carbohydrate receptor binding- Sialic acid containing poly-sialic-gangliosides Zinc endopeptidase (A-domain) Breaks down synaptobrevins Prevents release of inhibitory transmitter (Gamma-aminobutyric acid- muscle relaxant) Absorbed from infectious focus Travels along a-fibres to CNS 0.1ng kills a mouse
Treatment for tetanus
Anti toxin + penicillin + metranidazole
Prevention of tetanus
Immunisation - toxoid
Tetanus worldwide
still kills 30-50% in resource poor countries
Most cases neonates, small children, post-birth mothers
15-30,000 per year
Botulism (contaminated sausage - botulus is latin for sausage)
Caused by ingestion of preformed toxin from contaminated food containing Cl. Botulinum bacteria
Mostly in food that has been heated, then cooled and stored for long-periods
Historically associated with Tinned food (home).
Flaccid paralysis
Drooping eyelids, progressive
motor loss, flaccid paralysis;
Neurological symptoms- dizziness
respiratory & cardiac failure
Cl. botulinum
Motile Gram-positive bacillus -sub-terminal spores -widely distributed saprophyte e.g. soil -optimum growth 35°C, some can grow 1-5°C Causes botulism -severe form of food poisoning -incubation 1-2 days Toxin released as Progenitor complex to protect during passage through stomach>> intestine> bloodstream
Botulinum toxin
Potent neurotoxin – BoNT, (BoTox)
-7 types A – G; A, B & E most common
-A domain contains active site
-B domain> Carbohydrate receptor binding- Sialic acid containing DI-sialic-gangliosides (
-Zinc endopeptidase
–>affects peripheral cholinergic synapses
–>blocks release of
acetylcholine
–>IRREVERSIBLE BINDING!
Botulism treatment
Remove toxin
-polyvalent anti-toxin
Bolutism outbreaks
April - May 2017
traced the outbreak to a gas station in California’s Sacramento County
1 dead, 9 sick
BUT, could have been prevented if sauce heated above 75C, 20mins…..
Botox
Because it can weaken muscles temporarily when injected in small amounts, used for treatment of spasms and dystonias, e.g
- strabismus (Cross-eyes)
- bruxism (tooth grinding)> linked to bone loss
- torticolis (neck spasms)
- muscle spasms in cerebral palsy
C. difficile
Antibiotic/ hospital associated diarrhoea:
Associated with broad-spectrum antibiotic use, clindamycin and ampicillin
Outcompetes rest of population after antibiotic course complete
Hospital outbreaks, risk in elderly, care homes
Spore forming- resistant to heat and disinfectants, shed in faeces
Severe diarrhoea
Two exotoxins A and B
Pseudomembranous colitis: bowel disease- can lead to rupture
Pseudomembranous colitis
Adherent membrane of inflammatory cells and necrotic debris
Antibiotic-associated diarrhoea
C. difficile toxins (skipped over in lecture)
Produces TcdA and TcdB
-glucosyltransferases
-toxin present in patient’s stool
–>primary diagnostic marker
Cell receptor for TcdA is disaccharide Galß1-4GlcNac
Inactivates Rho (family of GTPases)
-actin condensation, rounding of the cells, membrane blebbing, and apoptosis of cell
-leads to neutrophil infiltration, disruption of tight junctions, fluid accumulation
C. difficile toxin mechanism
2x toxins encoded by tcdA and tcdB A-B toxins> glycosylate G-protein Bind disaccharide receptor on intestinal cells internalised and Catalytic domain (A) released into cytoplasm Activate host neurons >>> diarrhoea Induce cytokines>>> attract PMNs >>> disrupts cell junctions>>> Tcd-B damages underlying mucosa and tissues Septicaemia and bowel damage Toxin present in patient’s stool primary diagnostic marker of infection
C. difficile treatment
Common in faeces of neonates, not adults
Antibiotic-associated diarrhoea increased
-epidemics amongst elderly (transmission of spores)
Therapy is vancomycin or metronidazole
-+ remove offending selective antibiotic e.g. clindamycin
Prevention measures: cleaning, hand-washing, quarantine
Limit use of broad-spectrum antibiotics in ‘at-risk’ patients
Treatment: - removal of broad-spectrum antibiotic
- metronidazole or vancomycin
Gram negative anaerobes
Bacteroides -abdominal wound infections -peritonitis Prevotella -oral and genital infections Porphyromonas -oral infections Fusobacterium -F.nucleatum - oral and vaginal infections -F.necrophorum - Necrobacillosis - systemic sepsis and multisystem abscesses
Gram-positive anaerobes
Peptostreptococcus (Parvimonas)
Eubacterium
Bifidobacterium
Gardnerella
Bacteroides fragilis
Most common anaerobe recovered from non-oral clinical infections -abdominal, pelvic, brain, liver -often mixed infections -involved in bacterial vaginosis Gram-negative bacillus -capsulate (CPA, LPS) Toxigenic strains- some cause diarrhoea -toxin cleaves E-cadherin Resistant to numerous antibiotics clindamycin, metronidazole (some strains)
Prevotella
Gram-negative, non-motile, rod-shaped
In the oral cavity, Prevotella colonize by binding or attaching to other bacteria in addition to epithelial cells, creating a larger infection in previously infected areas.
Abscesses, bacteraemia, wound infection, bite infections, genital tract infections, and periodontitis
Porphyromonas
Non motile, Gram negative, rod-shaped
Periodontal disease – P.gingivalis is commonly found in biofilm with other spp.
(e.g, T.forsythia, T.denticola- RED COMPLEX)
Forms black colonies on blood agar
-P.gingivalis releases cysteine proteases – ‘gingipains’ that bind and degrade erythrocytes, destroy receptors, degrade complement components, subvert cell signalling
Fusobacterium
LONG Rod shaped spindle-shaped
bacillli, Gram negative
Associated with periodontal disease (F.nucleatum), skin ulcers, respiratory infections, BV, ANUG- often in mixed infection
Highly effective at biofilm formation
Treatment – antibiotics (Clindamycin, Chloramphenicol)
main spp.
-F.nucleatum - oral and vaginal infections, PTB
-F.necrophorum - Necrobacillosis - systemic sepsis and multisystem abscesses- Lemierres syndrome- rare head and neck origin
F. nucleatum linked to
Colon cancer
-FadA adhesin stimulates oncogenic response in colon- BIG news in microbiology- READ about it….
