Microbial Toxins

Question 0

define toxins:

Answer 0

substances of natural origin that have the potential to cause harm

Question 1

Why have microogranisms evolved an impressive arsenal of chemical weapons ?

Answer 1

they have a vast arsenal of chemical toxins due to evolutionary pressures

• some are very selective
  e. g penicillin - highly toxic to many bacteria but not to humans

Question 2

what has the discovery of the mechanisms of action of these highly toxic substances allowed ?

Answer 2

• greatly added to our knowledge of cell functions
• provided useful tools for exploring cellular events
• and some have use for therapeutic gain

Question 3

what are most toxins?

Answer 3

mainly large molecular weight proteins and enzymes- they have a catalytic ability with extraordinary potency and only a few of their molecules are needed to enter a cell and cause disruption of biology causing disastrous effects

Question 4

what are clostridia and where do they normally live ?

Answer 4

clostridia species are anaerobic spore forming bacteria

they normally inhabit the soil- the spores are very resilient and can reside in soil for many years

Question 5

what does clostridia species produce?

Answer 5

produce paralytic neurotoxins

Question 6

what does clostridia botulinum do ?

Answer 6

it releases the neurotoxin botulin

clostridia botulinum is a gram +ve anaerobic bacterium

Question 7

what does clostridia tetani do ?

Answer 7

it releases tetanospasmin which causes tetanus - this is very similar to botulin toxin but instead of targetting peripheral nerves it targets the nerves in the spinal cord

Question 8

what does clostridium perfringens do ?

Answer 8

it releases an alpha toxin - a cytotoxic lecthinase which causes cell lysis

Question 9

what are the 3 methods in which infection and exposure of a neurotoxin can occur ?

Answer 9

food borne
infant botulinism
wound botulinism

Question 10

when is botulinism caused by food borne infection ?

Answer 10

this is a classic type of botulinism
caused by ingestion of contaminated food with preformed neurotoxin
it was first recognised in germany at the end of 18th century - discovered to be due to consumption of contaminated sausages - sausage disease

Question 11

why has botulinism occurred ?

Answer 11

due to our desire to store food

Question 12

what is infant botulinism ?

Answer 12

most common form of the disease
occurs when children ingest food containing bacterial spores - germinate in the infants gastrointestinal tract producing the neurotoxin

Question 13

what is wound botulinism ?

Answer 13

spores can contaminate wounds and then they germinate and the neurotoxin released is absorbed into the body
- intravenous heroin users are at risk of this type of botulinism because injected heroin may be contaminated with bacterial spores

Question 14

what is botulins target ?

Answer 14

peripheral nerves - mainly the motor nerves- it prevents the release of ACh and this causes flaccid paralysis of skeletal muscle
- this has a characteristic descending pattern - paralysis starts at the top of the body and descends down

Question 15

how long does it take for symptoms to arise after ingestion of botulin and how long for spores ?

Answer 15

occur after a few hours after ingestion

can take several days to develop if spores have contaminated food or a wound

Question 16

what are the typical first symptoms of botulinism poisoning ?

Answer 16

weakness of the muscles innervated by the cranial nerves - patient finds it difficult to speak, swallow and their face becomes expressionless
- vision is blurred, eyelids drop (ptosis), blinking is inhibited (stare)

Question 17

what is the major dangerous symptom caused by botulinum poisoning ?

Answer 17

paralysis of the chest - there is a progressive weakness of the muscles supporting breathing and may lead to respiratory failure and death - may have to support the patients respiration for weeks

Question 18

how is botulinum poisoning treated ?

Answer 18

treatment varies depending on the type of the disease
if the neurotoxin was ingested- activated charcoal is administered to prevent absorption
antibacterial drugs can be given to treat wounds or gastrointestinal infections
antitoxin or human botulinism immune globulin can be given to inactivate absorbed neurotoxin
main priority is to maintain respiration

Question 19

what is the mortality rate for botulinum toxin ?

Answer 19

25% even with intensive care

Question 20

what is botulinum toxin described as ?

Answer 20

natures most potent chemical weapon

Question 21

what are the types of different toxins and what is the structure of botulinum toxin?

Answer 21

toxins A-G - A and B are the most lethal
it is a 150kDa single polypeptide precursor- active toxin consists of 50kDa light chain= enzyme component that has a zinc dependent protease. 100kDA heavy chain joined to the light chain by a disulphide bond and this is responsible for targetting the toxin

Question 22

botulinum toxin is a large molecular weight protein, therefore how does it enter cells ?

Answer 22

uses trafficking system in epithelial cells to enter them

- undergoes transcytosis= endocytosis + exocytosis

Question 23

for an 80kg adult how much botulinum toxin is lethal by intravenous injection ?

Answer 23

80ng

0.1 to 1ng per kg of body weight

Question 24

how much neurotoxin is required to kill an 80kg adult by inhalation ?

Answer 24

800ng

Question 25

what does the c-terminal portion of the botulinum toxin do ?

Answer 25

responsible for nerve recognition

Question 26

what is the mechanism of action of intoxication by botulinum toxin ?

Answer 26

1- binding to target tissue 2- internalisation 3- membrane translocation 4- enzymatic modification of molecular target 1) heavy chain recognises polysialogangliosides which are prevalent in neuronal membrane particularly in nerve terminals 2) it highjacks recycling of neurotransmitter vesicles enabling it to internalise into the cell within the vesicle 3) vesicles undergo acidification - protons are pumped into them and this allows botulinus toxin to undergo conformational change and produce a pore in the vesicle so the light chain can enter into the cytosol - this means the the reduction of the disulphide bond must occur 4) the light chain is now in the cytosol and can target snare proteins involved in capturing vesicles with NT and exocytosis of them- the light chain chops up the snare proteins preventing exocytosis

Question 27

how do they know that botulinum toxin interacts with polysialogangliosides?

Answer 27

because preincubation of botulinus toxin with gangliosides prevents botulinus induced blockade of neuromuscular function and pretreatment of cells with polysialogangliosides increases their sensitivity to botulinus toxin and treatment of the membrane with neuramidase which removes sialic acid residues from gangliosides decreases membrane binding by botulinus toxin

Question 28

what is a use of botulinus toxin but it is not medicinal?

Answer 28

for cosmetic purposes to cause muscle paralysis- botox

Question 29

when is botulinus toxin used for therapeutic gain ?

Answer 29

in conditions with abnormal levels of muscle contraction or spasm = dystonias

Question 30

what is the most commonly used botulinus toxin and how is it used ?

Answer 30

A | it is injected in carefully controlled doses into the affected muscles

Question 31

what was the first dystonias that botulinus toxin was used for and what others used it ?

Answer 31

strabismus- sever squint eyes also now used for nystagmus - inability to fix gaze also used for hyperhidrosis- excessively sweaty palms due to excessive activity of the autonomic nervous system

Question 32

what are mycotoxins?

Answer 32

diverse groups of chemicals produced by filamentous fungi | e.g ergot from fungus claviceps purpurea

Question 33

what is the function of mycotoxins ?

Answer 33

uncleat but some are toxic to competing micro organisms many are toxic to mammals 25% of worlds food crops are contaminated with them - especially in developing countries

Question 34

do fungi or bacteria produce more chemically diverse toxins ?

Answer 34

fungi but few are proteins

Question 35

what does ergot alkaloid do ?

Answer 35

it grows on a variety of cereal grains especially rye warm, damp summers encourage its infestation it grows on individual cereal grains and replaces grain with a curved purple structure called SCLEROTIUM - this contains lots of pharmacologically active substances= ergot alkaloids

Question 36

what do the ergot alkaloids cause?

Answer 36

hallucinations- not really hallucinations but distorts sensory perceptions

Question 37

what are the symptoms of ergotism ?

Answer 37

``` nausea vomiting drowsiness itching twitching muscles high blood pressure - severe and long lasting vasoconstriction- this can cause an intense feeling of burning and pain hallucinations gangrene - tissue in hands, arms, feet and legs become anaerobic and this can cause bacteria like cl.perfringens to infect and cause gangrene abortion ```

Question 38

why is ergotism referred to as st.anthonys fire or holy fire ?

Answer 38

st anthony lived in eygpt (250-350AD) and he spent long times in the desert fasting and resisting satan and is said to have experienced hallucinations and visions that were similar to ergotism symptoms

Question 39

what substance are ergot alkaloids chemically related to ?

Answer 39

LSD

Question 40

when was the first pure and pharmacologically active alkaloids isolated from ergot ?

Answer 40

1920s and 1930s

Question 41

what are the most important active alkaloids present in ergot ?

Answer 41

ergotamine and ergometrine - potent vasoconstrictor agents and stimulants of uterine smooth muscle - ergotamine used to treat migraines - ergometrine- promotes parturition and stops post partum bleeding - constricts blood vessels in the uterus

Question 42

what are amatoxins ?

Answer 42

heat stable bicyclic octapeptides | - LD50 of 0.1mg/kg

Question 43

where are amatoxins found ?

Answer 43

amanita mushrooms - some have enough in them to be fatal after consumption of a single mushroom

Question 44

how do amatoxins cause their damage ?

Answer 44

absorbed from the gut and transported into hepatocytes and renal tubule cells - it inhibits RNA polymerase 2 - prevent gene transcription and halt protein synthesis - GIT, liver and kidney with high rates of protein synthesis are target organs and death results from liver or kidney failure several days after exposure

Question 45

what is the treatment for amatoxin poisoning ?

Answer 45

no antidote remove part or undigested mushrooms from stomach by gastric lavage restrict toxin absorption by activated charcoal and correctly fluids liver/kidney transplant

Question 46

what synthesises aflatoxins and what do they mainly contaminate ?

Answer 46

aspergillus species | maize, peanuts and cottonseed

Question 47

which aflatoxin are humans mainly exposed to and what produces it ?

Answer 47

aflatoxin B1 | aspergillus flavus or aspergillus parasiticus

Question 48

what are the 4 major aflatoxins ?

Answer 48

B1, B2, G1 and G2

Question 49

what does consumption of aflatoxin B1 in high doses over a short period cause ?

Answer 49

acute aflatoxicosis - acute liver damage leading to haemorrhage , jaundice and sometimes liver death

Question 50

what does consumption of low doses of aflatoxin B1 for long periods ?

Answer 50

chronic consumption causes cirrhosis and liver cancer | - malnutrition and exposure to hepatitis vviruses may promote tumour formation

Question 51

what happens to aflatoxin B1 in the body ?

Answer 51

it is oxidatively biotransformed in the liver by cytochromes P-450 to an aflatoxin b1 -8,9 expoxide - this metabolite forms covalent adducts with DNA, major one is with N7- nitrogen atoms guanine - this is thought to be the important step in carcinogenicity