Infections caused by anaerobes L11 Flashcards
what is an anaerobe
any organism that does not require oxygen for growth OR required reduced oxygen tension and fails to grow on solid media in 10% CO2 (an equivalent of 20% molecular oxygen)
what is aerotolerance
tolerate 2-8 % oxygen
degree to which superoxide dismutase expressed
what are the anaerobes that generally cause human infection
aerotolerant (ie tolerate 2-8 % oxygen) and can survive sustained periods- but the do not replicate- in an oxygenated atmosphere
what is a feature most anaerobes do not posess
catalase
what do the anaerobes that cause human disease often have
superoxide dismutase (catalyses partitioning of O2 radical into their molecular O2 or H2O2) and in general the degree to which this enzyme is expressed dictates the aerotolerance of the organism
how are bacteria currently classified
This is the scheme that divides the medically important anaerobes by genus. In decreasing frequency we distinguish: 1. GRAM-ve RODS; 2. GRAM+ve COCCI; 3. GRAM+ve spore forming BACILLI (Clostridia) and non sporing bacilli 4. GRAM-ve COCCI (mailny Veillonella spp)
what is the cause of most anaerobic infections
endogenous microbial flora Normal flora (Skin, Upper airways, genito-urinary tract and gastro-intestinal)
what is the endogenous role in normal flora
providing colonisation resistance
Serve nutritional function
Exert effect on host immunity
how do endogenous strains of normal flora gain access to normally sterile sites
breach to anatomical barrier
what do ANA infections indicate
ANA infections are usually endogenous indicating that they originate from the hosts’s own flora
what is exogenous acquisition
relates to either contamination of wound by objects contaminated
ingestion of food containing (C. botulinum and C. perfringens)
colonisation of GIT with spores and toxin production inside host
person to person spread
what are clinical syndromes examples -main clinical features of anaerobic infection
Abscess formation/empyema
> Foul-smelling pus or discharge (eg surgical wound)
> Gas formation in tissues
Necrotising fasciitis (myofasciitis/gas gangrene)
Sepsis syndromes
Toxin-mediated disease
what are clostridia
Large Gram-positive spore-bearing bacilli
what feature varies in clostridia
Vary considerably in O2 tolerance
what are clostridia important for
Most are environmental saprophytes important in putrefaction
what does clostridia produce
exotoxins
what are exotoxins
Biologically active proteins
Antigenic in nature
Neutralised with specific antisera
Detection can be diagnostic
how many types of Clostridium perfringens are there
5
A-E
what does Clostridium perfringens make
potent toxins
α toxin = lecithinase = phospholipase C
Egg yolk medium
how is clostridium perfringens differentiated on agar
Double zone β haemolysis
Where u get precipitate there is no antitoxin
diagnostic way to see if its perfringens
what is Clostridium perfringens like
Non motile, freq non spore forming
what does Clostridium perfringens cause
gas gangreene (myonecrosis)
it is life threatening
need surgery and antibiotics
how does Clostridium perfringens cause food poisoning
enterotoxin production during sporulation
what is Clostridium tetani
Straight slender ‘drumstick’ terminal spore (spore at the terminal end)
neurotoxin
what is the Clostridium tetani gram stain feature
readily loses gram stain
what oxygen level does Clostridium tetanineed
Obligate anaerobe
what is Clostridium tetani like
motile, swarms
where is Clostridium tetani
Cattle faeces, contaminated soil
what does Clostridium tetani cause
Prevents muscle relaxation leading to spasticity = tetanus
what is the clinical diagnosis of Clostridium tetani
3 laboratory tests
Isolate organism
Detect toxin in serum (Ref lab)
Low/no ab levels supports diagnosis
how is suspected Clostridium tetani - tetanus clinically managed
Require ITU observation
Wound cleaned
Antimicrobials including metronidazole or penicillin
Anti-tetanus antibody (TIG)
Vaccination with tetanus toxoid on recovery important to prevent future episodes
what are tetanus prone wounds like
Puncture-type
Contact with soil/manure
Significant degree of devitalised tissue
Any wound with delay >6 hours before surgery
how is Clostridium tetani - tetanus prevented
Active immunisation with toxoid introduced in UK 1961 (5 doses)
what is the tetanus neurotixin
Tetanospasmin
what are the symptoms of tetanus
Symptoms involve characteristic grin of the face, spastic posture of limbs and trunk
how does tetanus neurotoxin work
binds to the resynaptic membrane of neuromuscular junction, internalized and transported retro-axonally to
the spinal cord
spastic paralysis induced by the toxin is due to the blockade of neurotransmitter release from spinal inhibitory interneurons
what is Clostridium botulinum
Motile
sub-terminal spores
where is Clostridium botulinum
always present in nature - soil
what is Clostridium botulinum known for
most powerful toxin known
what does Clostridium botulinum cause
Descending FLACCID paralysis = Blocks acetylcholine release at neuromuscular synapses
Blurred vision, difficulty swallowing, headaches and muscle weakness
what can Clostridium botulinum be used for
Relatively heat stable: bioweapon potential
Botox
what causes food-borne botulism
ingestion of preformed toxin in food that has been contaminated as a result of it being improperly canned or preserved
what causes wound botulism
wound becomes infected with botulinum spores which then germinate, reproduce and then produce toxins ie growth of the organism
what causes infant botulism
very rare. Ingestion of spores or organisms followed by colonisation and toxin production in gut. Usually only affects babies < 12 months old. After this, children develop a defence against the spores
how are botulism clinical syndromes treated
Involve ITU
Polyvalent antitoxin to neutralise unfixed toxin
Wound botulism- surgical debridement and antibiotics
how is a reference laboratory of botulism clinical syndrome done
mouse bioassay for toxin
Anaerobic culture of food/faeces
how is botulism clinical syndromes prevented
Prophylactic use of polyvalent antitoxin
Vaccine (not widely used as concerns re effectiveness and adverse effects)
Avoid home canning/adequate food preparation
Do not feed honey to infants <12 months
how do the seven serotypes of botulinum neurotoxins work
act at the periphery by inducing a flaccid paralysis due to the inhibition of acetylcholine release at the neuromuscular junction
what do tetanus and botulinum toxins have in common
have specific protease activities
act on proteins in neurones which control neurotransmitter activity
proteins included SNARE proteins
what do SNARE proteins do
facilitate fusion of vesicles with membranes to a allow delivery of molecules like neurotransmitters to control nerve function
PWID
people who inject drugs
clostridia and PWID
PWID can cause tetanus
where is Clostridium difficile present
normal flora in 3-5% adults
how does Clostridium difficile infect
administration of broad-spectrum antibiotics in vulnerable patients (e.g. elderly) allows C. diff to grow and produce TOXINS
what is Clostridium difficile the leading cause of
nosocomial diarrhoea
what does Clostridium difficile make
Toxin mediated process Exotoxin A (enterotoxin) Exotoxin B (cytotoxin)
what does infection with Clostridium difficile lead to
morbidity and mortality
mild to severe diarrhea
toxic megacolon
pseudomemranous colitis
how is Clostridium difficile treated
withholding antibiotics where possible and replacing them with fluids
Fecal bacteriotherapy, also known as a stool transplant
colectomy - section of infected bowel is removed
what are the screening methods that can be used to diagnose Clostridium difficile
ELISA
PCR
what is the problem with using plates to diagnose Clostridium difficile
is slow process and need to know ASAP if infected so not regularly used in diagnostic labs
what is the problem with using cell rounding assay
labour intensive so not ideal
how is cell rounding assay performed
Take some supernatant from patient put onto eukaryotic cells
Will stop to round up due to the toxin
what is usually done first to test for Clostridium difficile
quick test
apply sample to plate
will tell if is
- antigen positive (present)
- antigen and toxin(s) positive (present and making toxins)
- negative for antigen and toxin(s) (not present)
why does C.difficile not cause problem when there are no antibiotics present
Normally in gut with no antibiotics have a mix of different types of bacteria
These bacteria take primary bile salts will be digested into secondary bile acids
Secondary bile acids are inhibitory to C. difficile germination can’t germinate any spores so wont cause problems
where are primary bile acids made
normally produced as part of the digestive system
what is key in the break down of primary bile acids to secondary
C. scindens
why does C.difficile cause a problem when antibiotics are ingested
Take antibiotics will kill off the C. scindens
So no longer get transformation of primary bile acids to secondary
Nothing blocking the C. difficile from forming spores
what does C. difficile produce
produces two large exotoxins – TcdA and TcdB
what do the toxins C. difficile produce do
have activity against gut epithelial cell
bind to the cell surface and trigger intracellular signalling pathways that cause changes in the cell cytoskeleton
can lead to cell death
what is the effect does death of cells lining the colon
can result in changes in fluid absorption and diarrhoea
how is C. difficile treated
prevention rather than using antibiotics
isolate patient
Antibiotic therapy: Metronidazole, Vancomycin, Fidaxomicin
Some alternative treatment options fall into four main areas:
prebiotics and probiotics;
“faecal transplants” — where stools donated from a healthy donor are placed in the bowel in an attempt to restore the normal microbiota
what is metronidazole
inhibitor of DNA synthesis
what does metronidazole require, why is it only effective against anaerobic bacteria and anaerobic protozoa
At low Eh values reduced to a short-lived intermediate which causes DNA strand breakages
Because of this requirement for a low Eh value, only active against anaerobic bacteria and anaerobic protozoa
