Clostridium botulinum Flashcards
what are the four kinds of Cb?
- intoxication - ingestion or injection of the toxin
- infant botulism - ingestion and intestinal proliferation of the organism, internal production of the toxin
- wound botulism - deep wound results in anaerobic environment
- bioterrorism - delivery of toxin to large populations
how do you define Cb as a bacterial species?
all cb strains are toxic. non-toxic variant strains, though genetically related, are assigned to different species such as C. sporogenes
explain Botulinum Toxin:
- botulinum neurotoxin (BoNT) is an A-B toxin that consists of two subunits (A and B)
- the toxin is inactive after production
- there are two types of Cb proteolytic and non-proteolytic.
- proteolytic = bacteria produce a protease that activates the neurotoxin
- nonproteolytic = host’s stomach acids cleave the toxin (activating it)
- following ingestion, the toxin molecules are absorbed by the gut and are spread via the blood to peripheral nerves
how do nerves usually work in regards to muscle contraction?
normally the axon terminal of the neuron connects with muscle tissues through SNARE proteins and releases acetylcholine into the muscle cells which causes the contraction
what protein does BoNT act like?
protease, cleaving the SNARE proteins
how are different BoNTs similar and different?
structurally similar but immunologically very distinct
how are Cb strains grouped?
grouped into 4 groups based on physiological differences, but these groupings dont correlate to which groups produce which type of toxin
which Cb groups cause human illness?
Group 1: C. botulinum A and proteolytic strains of B and F
Group 2: C. botulinum E and non-proteolytic strains of B and F
how is the Cb toxin tested in foods?
- preparing food, feces, serum or gastric contents and testing them on mice
- dispense filtrate into three tubes: no treatment tube, tube boiled for 10 min, trypsin added to tube
- boiled tube eliminates the possibility of another pathogen being responsible
- trypsin determines if the toxin is proteolytic or non-proteolytic
- inject 2 mice with each tube
- once Cb toxin is est. as the cause, the no treatment tube is taken to make three more tubes, tube 1 containing A toxin antiserum, tube 2 containing B toxin antiserum, and tube 3 containing F toxin antiserum
what are the clinical aspects of Botulism?
- hallmark is bilateral descending weakening and paralysis of skeletal muscles
- class triad of symptoms:
1. symmetric, descending flaccid paralysis with prominent bulbar palsies (difficulty swallowing, lack of gag reflex, lack of speech, drooling)
2. lack of fever
3. a clear sensorium in the patient (ability to think and concentrate) - autonomic disfunction including constipation, urine retention, and mydriasis can also occur
- muscles affecting respiration are weakened, and mechanical ventilation to prevent death by suffocation can be required
- the patients hearing is normal, consiousness is not lost, and the victim is cognizant of the progression of the disease
What is recovery from Cb like?
its a long process that usually requires weeks to months depending on the serotype of the toxin and amount ingested. complete recovery is rare
many survivors reported having difficulty lifting things, worse psychological health, fatigue, dizziness, etc
properties of Cb Group I
- A; Proteolytic B, F
- exhibits proteolysis and lipase production
- main physiological property: highly thermoresistant spores
- optimum growth temp: 37C
- minimun growth temp: 10-12C
- causes botulism in humans
properties of Cb group II
- E; non-proteolytic B, F
- does NOT exhibit proteolysis
- DOES exhibit lipase production
- main physiological property: moderately thermoresistant spores
- optimum growth temp: 25C
- minimum growth temp: 2.5-3C
- causes botulism in humans
what is the Cb’s genome composition?
consist of one circular chromosome, between 3.6-4.1 Mb, with a G+C content of 27-28%
where can the BoNT toxin be found in Cb’s genome?
can be carried either on the chromosome or on a plasmid. The genomic context in which the BoNT toxin is found matters
why is it suggested that the BoNT toxin is derived from a similar ancestor?
the similarity of different BoNTs, the ability of different species to produce BoNT, and the fact that some strains contain combinations of boNT genes
where is Cb found in the environment? more specifically, where are group I type A spores found, where are type B spores found, and type E spores?
- ubiquitously in soils
- commonly found in Northern parts of the world
- proteolytic group I Type A spores primarily found in temperate regions including soils of the Western United States, southern and eastern European countries, and China
- type B spores are more ubiquitous
- type E spores are mainly found in aquatic sediments of colder regions such as Alaska, Canada, Scandinavia, Poland, Russia, and Japan
what kind of soils are Group I type A spores found in?
neutral to alkaline soils with low organic content; they are absent from eastern USA and western European soils
what is the theory of Cb in regards to not knowing BoNT’s purpose?
Cb may be predatory in some niches and that killing the host is important for the biome of animal decomposition and the recycling of animal biomass
environmental microbiology characteristics of Cb:
- a strict anaerobe
- fermentative metabolism
- proteolytic groups prefer proteinous compounds for fermentation substrates
- many strains can use their amino acids as their sole source of carbon and nitrogen
what is Cb sensitive to?
- low pH and cannot germinate <4.6
- sensitive to high salt and cannot germinate in more than 5.5% salt
- other competitors
what are Cb spores resistant to?
highly resistant to temperature i.e. greater than 115C
what foods are Cb found in?
low acid fruits such as figs and peaches, and vegetables (green beans, corn, spinach, asparagus, peppers, and mushrooms), and fermented fish
Type E toxins generally associated with fish, A and B are associated with fruits and vegetables
what are common symptoms of Cb in infant botulism?
poor feeding and constipation
symptoms can include: poor feeding, loss of head control, visual problems, dry mouth, and generalized weakness. can lead to paralysis lasting days and weeks and respiratory failure
no fever
what strains/serotypes cause infant botulism?
nearly all cases caused by group I strains of serotypes A and B, and rare cases can be caused by type F
what condiment is a major reservoir for Cb?
honey
what causes inadvertent/wound botulism
- deep wounds i.e. stab wounds or bullet wounds
- concentration, which makes the toxin
- anaerobic growth can occur in deep wounds
what are commercial prevention methods?
- via proper food preparation, processing, formulation, and storage
- foodborne botulism from commercial foods is very rare (but outbreaks do occur)
- growth of Cb can be controlled via temperature, pH, water activity levels, redox potential, nutrient sufficiency, the presence of antimicrobial, and competitive microbiotas (pH and aw being the most important)
Home prevention of Cb:
- do not feed honey to a child less than 1 year of age
- follow recommended practices for Home Canning
- do not store beluga, seal, or walrus meat at warm temperatures or in containers that do not allow air circulation
- age narwal, seal, beluga, or walrus meat in cool places
- follow traditional methods or established methods that allow air to circulate when fermenting foods
- do not use plastic or glass container with tight fitting lids or buckets to ferment meats
Cb Key points and review:
- CB spores are found to be widespread in the environment
- they are routinely consumed by adults who are resistant to colonization due to healthy gut microbiomes
- adults must ingest BoNT to become sick, BoNT is produced in foods which become contaminated and have the right conditions for bacterial growth (anaerobic and high pH)
- infants can become colonized with Cb, BoNT is produced in the child’s gut and child displays infant botulism
