Bacterial Toxins and Anaerobes Flashcards
4 properties of a successful pathogen
- Gain access into host: correct portal of entry
- Colonize host tissue: Attachment to specific host tissue
- Resist host-defense mechanism: Non-specific (TLR and cytokines and macrophage) or specific (Aquired T and B cell mediated)
- Damage host: Pathogens
two mechanisms of pathogenicity
- Invasiveness: ability to enter host (and replicate in it)
2. Toxigenicity (ability to produce a toxin)
Where is anaerobic bacteria usually located
hundred of species of anaerobes on mucosal surfaces
How many anaerobic species are important in human pathogens
only a few
Describe the composition of infection by anaerobes
mixed, opportunistic infections. Include either/both aerobic or anaerobic bacteria
Describe how anaerobes are sensitive to O2 intermediates
- they have little superoxide dismutase to remove O2 radicals
- they have low amounts of catalase to remove H2O2
- they often lack cytochromes so usually metabolize via fermentation
Site of infections for anaerobic gram negative pathogens
colon ( intra-abdominal abscess) mouth and skin
infections by anaerobic gram negative pathogens are often foul smelling-why?
due to short chain fatty acids produced during fermentations
anaerobic gram negative pathogens do fermentation metabolism and therefore are often
gas producing
Describe the Poly-microbial nature of the anaerobic infection
infections often due to the contamination of tissue by
normal flora
How do you isolate isolate anaerobic pathogens
culture techniques
anaerobic gram negative pathogens are often void of pathogens
aerobic bacteria (anoxic environment)
Common gram negativ anaerobic pathogen
Bacteriodes fragilis
Most intra-abdominal infections are due to
Bacteriodes fragilis
-common inhbaitant of bowel
Virulence factor for Bacteriodes fragilis
-polysaccharide capsule (anti-phagocytic)
-Bacteroides are aerotolerant anaerobes able to tolerate
atmospheric concentrations of oxygen.
-Bacteroides encode two major oxidative stress
response genes, catalase and superoxide dismutase.
•B. fragilis often isolated in mixed bacterial infection with;
- other anaerobes
- with facultative anaerobes (often Peptostreptococcus (gram positive anaerobic cocci) in intra-abdominal abscess
Describe the structure of Bacteriodes fragilis
pleomorphic often bacilli
What should you grow bacteria in if you want to see if it is Bacteriodes fragilis
bile salts ans gentamicin
most aerobic and anaerobic bacteria are inhibited by bile salts and gentamicinexcept for Bacteriodes fragilis.
While Bacteriodes fragilis are the most intra-abdominal infections, the types of pathogens isolated in other surgical sites differ:
- sites of infection are pathogen-specific
- mixed infections are common
Surgical site infections in cardiac surgery patients
gram-positive organisms 48%
gram negative organisms 40%
fungi 12%
Clostridia
Anaerobic gram positive, spore forming bacili
obligate anaerobes or aerotolerant
Pathogenesis of clostridia
-due invasiveness or an exotoxin
Physiology of clostridia
either saccharolytic – sugars
or
proteolytic – amino acid
Where doe sclostridia live
soil inhabitant or inhabitant of intestinal tract
Invasive clostridia
histotoxic: C. perfringens
produces alpha toxin (pholpholipase) causes tissue damage
Toxin producing clostridia: gastrointestinal disease:
C. difficile (Toxin A and Toxin B)
Toxin producing clostridia: tetanus:
C. tetani, (tetanus toxin)
Toxin producing clostridia : botulism, food poisoning:
C. bolulinum, botulinum toxin
Histotoxic clostridia
-invasive and cause extensive destruction of muscle and connective tissue
-characterized by the formation of gas.
-Invasive C. perfringens (alpha toxin):-cause most clostridial-mediated
myonecrosis
-pathology: A deep wound to muscle predisposes infection
-gas gangrene
Steps of infection by C. perfringens (alpha toxin)
- reduction of tissue redox potential leading to host cell death. It turns pyruvate into lactate which decreases the pH
- host proteases release the nutrient from the host tissues and the clostridia grow
- C. perfringens releases an alpha toxin which is a phospholipase and cases tissue damage
C. perfringens toxin
alpha toxin. It is a phospholipase and causes tissue damage
What does a C. perfringens infection cause adn how do you treat it
gas gangrene- treatment is antibiotic and often excision with amputation
4 types of bacterial infection
- surface acting toxin
- pore forming toxin
- A/B toxin (extreme potency)
- Type II and IV toxin (injects it toxin and produces 100os of molecules to inject into host and paralyze neutrophils) (Mortal Combat)
Each bacterial toxin has what two components
catalytic component and a host cell binding component
Catalytic component of bacterial toxin
modifies specific host macromolecules (post-translational modification)
Host cell binding component
may be tissue specific (clostridial neurotoxin) or not tissue specific ( diptheria toxin)
Diphtheria toxin and Pseudomonas aeruginosa exotoxin A
ADP-ribosylate EF2(elongation factor 2 of the host) : inhibits proteins synthesis
Botulinum toxin & Tetanus toxin:
Protease for SNARE proteins: inhibits neurotransmittor vesicle fusion to the cell membrane
Large Clostridium difficile toxins:
Glucosylate Rho proteins: inhibits cell motility and
ultrastructure, via active modification
Shiga toxin:
- a little unusual bc although it is a protein toxin its targets RNA
- Deadenylates a adenine on RNA: inhibits protein synthesis
How do we vaccinate for bacteria that produce toxins
lot of times we use an inactive component of their toxin called a toxoid
DT/ TT vaccine
formalin inactivated diphtheria/tetanus toxins
Conjugate vaccines
Hib polysaccharide conjugated to diphtheria
toxoid, making a T cell-dependent immune response (IgM IgG
and memory)
Antibiotic-associated diarrhea (gastrointestinal colitis) Causative agent: and what toxins does it produce
C. difficile
A and B toxins
because
AB CD
Antibiotic therapies may be associated with C. difficile infections where the normal floral are reduced allowing endogenous and ingested C. difficile to expand and produce Toxin A and Toxin B, which contribute to diarrhea and inflammation.
C. difficile infection range from asymptomatic to recurrent and life-
threatening
Pathology of clostridium difficile
C. difficle produces Toxin A and Toxin B which glucosylate Rho
GTPases elicit:
actin depolymerizationdisrupt gut epithelial cells diarrhea
UDP-glucose + Rho Rho-glucose (inactive) + UDP
Whats going on in Canada . with C. difficile
Emergence of a highly toxic strain of C. difficile that is resistant to fluoroquinolones has caused outbreaks in the US and Canada.
What produces the most toxic protein for humans
Clostridia
C. botulinum symptoms
is there a vaccine
- flaccid paralysis
- no vaccine
C. tetani
symptoms
is there a vaccine
- spastic paralysis (lock jaw)
- licensed vaccine
WHy is it difficult to produce a vaccine for Botulinum toxin
there are seven serotypes A,B,C,D,E,F,G defined by antiser neutralization
an effective vaccine would have to protect against all seven serotypes and that would be hard to do
Mechanism of Action of Clostridium neutotoxins
- proteases
- BoNT and TeNT have the same mechanism of action (cleave SNARE proteins)
- cleaves SNARE proteins to inhibit synaptic vesicle function
- they have the exact same catalytic activity and even cleave at the same site but they have different physiologies bc the SNARE toxin does not define the spasticity of each toxin
If the cleavage of the SNARE protein is not responsible for the pathologies what is
- intracellular trafficking
- BoNT remains in the periphery (synaptic vesicles)
- TeNT (retrograde traffice to CNS)
BoNT pathology is caused by
peripheral action at the motor neuron, yielding an inhibition of acetyl choline release at the neuromuscular junction (flaccid paralysis)
Tetanus toxin pathology is caused by
retrograde trafficking to inhibitory interneuron, stimulates acetyl choline release at the neuromuscular junction (spastic paralysis)
tetanus, C. tetani physiology
• Anaerobe
• Proteolytic (peptides & amino acids)
• Tetanus toxin responsible for the clinical
symptoms of tetanus
Determinants of Pathogenicity for C tetani
C. tetani is not invasive, remains at site of infection,
but produces tetanus toxin
Intoxication
of C. tetani
– Following injury with a mixed bacterial infection
– soil bacteria ferment to reduce redox potential
– allows limited growth of C. tetani, sufficient for toxin
production
How do we prevent tetanus infection
immunization
the preventative vaccine is made from tetanus toxin that was treated with formalin to be tetanus toxoid
Preventative vaccine
There is a vaccine to prevent tetanus, diptheria, and pertussis DTaP, Tdap, DT, Td
At what age is the DTaP vaccine given and why
5 doses given at 2, 4, 6, and 15-18 months and 4-6 years.
It is given at 2 months bc that is when you lose protection from maternal antibodies
Therapeutic vaccine
treatment in a suspected case of tetanus
Botulism is caused by
Clostridium botulinum
Botulism: Clostridium botulinum Pathogenicity
– Botulinum toxin: AB toxin
– Zinc Protease (heat labile)
– inhibits neurotransmitter release: flaccid paralysis
Seven BoNT serotypes (A, B, C, D, E, F, and G)
– Each serotype is defined by the absence of cross neutralization
by serotype specific antisera
*• For example, anti-BT/A antisera neutralizes only BT/A
BoNT serotypes A, B, E, and F most common natural forms for
humans
-so there is no licensed vaccine bc there are so many serotypes
Why is BoNT a potent human therapy for neurological diseases
-depending on the serotype it can last for up to 5 months!!!
- not contagious
- not trasnmitted from person to person
- neuronal specificity
BoNTs are clinically useful due to neuron specificity…explain
- Bind receptors on neurons
- cleave neuronal SNARE substrates
- therefore limited off targets…super specific!!
Most common use of BoNT for therapy
for bleopharospasm-absnormal contraction or twitch of eyelid neurons (functional blindness)
- BoNT cleaves the SNARE proteins in the spastic nerves relieving spasticity
- BoNT has a long half life in nerons (months long therapy per injection0
