Anaerobic Bacteria Flashcards
What do anaerobic organisms not require?
Anaerobic organisms do not require oxygen
What are the main categories of anaerobic microorganisms?
Obligate anaerobes = harmed by presence of oxygen
Facultative anaerobes = can grow without oxygen but use oxygen if it’s present
Microaerophiles = grow in atmosphere of low oxygen <5%
Features of anaerobiosis?
Anaerobic respiration/fermentation
- Produce energy without oxygen
- May use fermentation or anaerobic respiration
- In presence of oxygen = faculative anaerobes can use aerobic respiration
What occurs in anaerobic fermentation?
Organic electron acceptor in the absence of oxygen
Glucose - pyruvate (organic e receptors, 2ATP plus acids > incomplete breakdown products) - TCA cycle
What are the fermentation products?
Lactic acid
Acetic acid
= streptococcus, lactobacillus
H2, CO2, acetic acid, ethanol, lactic acid, propionic acid
= Enteric bac (E.coli)
H2, CO2, Ethanol, butanol, acetone
= Clostridium
= Live in mouth
How much glucose is produced by aerobic respiration?
38/mol glucose
What is respiration?
Converting energy from e.g. glucose into a usable form
What is aerobic respiration?
ATP is released as electrons are transported along chain to final acceptor O2 (forms water)
What is 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+)
Allows growth in low O2 environs
Drawbacks for obligate anaerobes; no ability to resist presence O2 or other radicals that are by-products of aerobic life
Inefficient process
Anaerobes often slower growing
How are anaerobes diagnosed/studied?
Jars/cabinets to exclude O2 subculture
Gram stain, spore stain, anaerobes = sensitivity to metronidazole
Sugar fermentation
Toxin production - Clostridia
Gas-liquid chromatography - fatty acid end products
16s RNA sequencing
Give examples of major anaerobic bac in humans?
Clostridia Bacteriodes Fusobacterium Porphyromonas and black pigmented Gardnerella
Features of clostridium species?
Large, straight, gram pos bacilli Produce endospores and exo-toxins Cl.perfringens - food poisoning Cl.botulinum = botulism (food) Cl.tetani - tetanus Cl.difficile - pseudomembranous colitis
Cl. perfringens features?
Capsulated, non-motile, gram pos rod
Polysaccharide capsule, repeating units of 6 sugars
Fast growing, spread, BETA hemolytic colonies on BA
Exo-toxins are differentiated based on? What are the types of exo-toxins?
Differentiated based on production of major lethal toxins
5 toxigenic types; A-E
Features of the major exo-toxin?
When are enterotoxins formed? Features?
Alpha-toxins;
- Phospholipase C
- Luses RBCs, platelets, leukocytes, endothelial cells
- Inflam and major swelling
- Oedema, bleeding
- Haemolysis
- Kidney damage - renal failure
- Myocardial dysfunction
Other VFs; proteases and hyaluronidase - destroy tissue
Enterotoxin - pore forming, heat labile - produced upon sporulation of ingested bac in stomach acid secretion
How to test for toxins?
Nagler test - half plate infiltrated with antitoxin, rxn = fuzzy area, no rxn = colonies grown
clowdiness on side without alpha antitoxin
Name the diseases caused by Cl.perfringens? Treatment?
Gas gangrene
- Spore contamination of wounds - source - soil, animal and human excreta
- Oedema, gas formation, necrosis, toxaemia, cellulitis
- Treatment - surgery (amputation), antibiotics
Features of food poisoning?
Incubation 10-12hrs
Abdominal cramps, diarrhoea
Resolves in 24hrs
How is diarrhoea from food poisoning caused?
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
Tatanus features? What causes it?
Acute spastic paralysis caused by potent bacterial neuro-exotoxin
Trismus, rictus grin
Caused by uncontrolled contraction of muscles - mostly in CNS
Cl.tetani features?
Incubation 10-14 days
Enters body through wounds, splinters, cuts
Spores ubiquitous in environment
Spores in soil, contaminates wounds
Grows in wounds, toxin released into bloodstream
Motile - thin spreading film on agar (drumstick)
Name the tetanus toxins and their features? (How does Cl.tenani cause disease)
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 (muscle relaxant) Absorbed from infectious focus - Travels along alpha fibres to CNS -2.5ng/kg kills a human
What treats tetanus?
Anti-toxin/immunoglobulin plus penicillin and metronidazole
Prevention - immunisation; toxoid
What causes botulism?
Ingestion of preformed toxin from contaminated food containing Cl.Botulinum bacteria
- Mostly in foods that have been heated, then cooled and stored for long periods
Symptoms/signs of botulism?
Flaccid paralysis
Drooping eyelids, progressive motor loss, flaccid paralysis
Neurological symptoms - dizziness, resp and cardiac failure
Cl.botulinum features?
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 features?
Potent neurotoxin - BoNT
- 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
How to treat botulinum toxin?
Remove toxin
Polyvalent anti-toxin
What can botox do? How?
Can weaken muscles temporarily when injected in small amounts
Uses botulinum toxin
What can botox treat?
Used to treat spasms and dystonias e.g.
- Strabismus (cross eye)
- Bruxism = bone loss
- Toricolis (neck spasms)
- Muscle spasms in cerebral palsy
Antibiotic associated diarrhoea C.difficile features?
Associated with broad spectrum antibiotic use - clindamycin and ampicillin
Outcompetes rest of pop after antibiotic course complete
Risk in elderly
Spore forming - resistant to heat and disinfectants, shed in faeces
Severe diarrhoea
2 exotoxins A and B
Pseudomembranous colitis; bowel disease - can lead to rupture
What is Pseudomembranous colitis?
Antibiotic-associated diarrhoea
Cl. Difficile- treatment?
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
Name the other gram pos and gram neg anaerobes
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
List the black pigmented anaerobes
Prevotella
Porphyromonas
Fusobacterium
Features of prevotella? What can it cause?
Gram neg, non-motile, rod shaped
Colonise in oral cavity by binding or attaching to other bacteria in addition to epi cells = larger infection in previously infected areas
Abscesses, bacteraemia, wound infections, bite infections, periodontitis
Porphyromonas features?
Non motile, Gram negative, rod-shaped
PD - P.gingivalis = commonly found in biofil with other spp.
Forms black colonies on blood agar
What does P.gingivalis do?
Releases cysteine proteases - gigipains = bind and degrade erythrocytes, destroy receptors, degrade complement components and subvert cell signalling
Fusobacterium features? Treatment?
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
What is F. nucleatum linked to?
Colon cancer - FadA adhesin stimulates oncogenic response in colon
What is GPAC?
‘GPAC’- Peptostreptococcus-
normal flora of all mucocutaneous surfaces (inc. oral)
Often isolated from infections such as chronic deep organ abscesses, obstetric and gynecological sepsis + intraoral infections.
Not well studied: difficulties with laboratory identification, isolated from mixed infections.
Features of Eubacterium and Bifidobacterium?
Gram Positive rods, rarely isolated from abdominal infections POST oral/ genital trauma.
Features of Gardnerella and Mobilincus?
Bacterial Vaginosis in females, associated with dysbiotic communities and PreTerm Birth
Cl.difficile toxins?
Produces TcdA and TcdB
- GluActivate host neurons»_space;> diarrhoea
Induce cytokines»> attract PMNs»_space;>
disrupts cell junctions»> Tcd-B damages underlying mucosa and tissues
Septicaemia and bowel damage cosyltransferases
- Toxin present in pt’s stool (primary diagnostic marker)
Cell receptor for TcdA is disaccahride Gallß1-4GlcNac
Inactivates Rho (family of GTPases)
- Actin condensation, rounding of the cells, membrane blebbing, cell apoptosis
- Leads to neutrophil infiltration, disruption of tight junctions, fluid accumulation
Cl.difficile toxin mechanisms?
TcdA and TcdB:
- Activate host neurons»_space;> diarrhoea
- Induce cytokines»> attract PMNs»_space;>
disrupts cell junctions»> Tcd-B damages underlying mucosa and tissues
Septicaemia and bowel damage
Bacteriodes Fragilis features?
Most common anaerobe recovered from non-oral clinical infecs
- Abdominal, pelvic, brain, liver
- Involved in bacterial vaginosis
Gram neg bacillus
Toxigenic strains - some cause diarrhoea
- Toxin cleaves E-cadherin
Resistant to numerous antibiotics - clindamycin, some strains of metronidazole
