Lecture 6- Bacillus Flashcards
What phylogenetic branch does bacillus belong to
Firmicutes (based on 16S rRNA sequencing)
Is bacillus a spore former
Yes it sporulates
Bacillus is gram negative - true or false
FALSE
Bacillus is gram positive
What shape is bacillus
Rod
Is bacillus catalase positive or negative
Catalase positive
Is bacillus aerobic or anaerobic
Aerobic
Where are the spores of bacillus found
Oval/central spores (no distension of sporgangium)
Spore fit within cell - no swelling
Bacillus is considered motile except for one species - which is it
Anthrax
What is specific about bacillus metabolism
It is very diverse - no typical bacillus
What are the three key species of bacillus
MESOPHILES - B.cereus, B. Anthracis and B.subtilis
INSECT PATHOGEN - B. Thuringiensis - toxic to insects so use as pesticide. Also in GM crops
What are the paenibacillus
Almost bacillus.
Reclassified 1993
Which did ferdinand cohn do in 1872
Work in spores of b. Subtilis and prove spores move transiently from spore to bacteria (spore and germination life cycle)
What fundamental work did r. Koch do in 1876 with a bacillus species
Linked b. Anthracis with disease. Looked at anthrax in mice
How many species are there in bacillus genus and nested genera
266 species
Where is bacillus cereus most commonly found
Ubiquitous
Typical soil and dust
Name two types of food b.cerus is associated with and why
Rice (associated starchy foods)
Herbs and spices
Dry foods e.g. Pot noodle
What are the two distinct foodborne intoxications of bacillus cereus
Emetic - vomiting
Diarrhoea
( different toxins)
Describe the incubation form and duration of EMETIC b.cereus and explain why it is this length
Onset 1-6 hours (short incubation)
Duration - up to 24 hours
Preformed toxin all have to do is eat - short incubation, as physical toxin clear form gut quicker henc 24 hr
What is the emetic toxin produced by b.cereus and what are key characteristics of this toxin
CEREULIDE
- heat stable - hence cannot reheat
- preformed
- resistant to proteolytic cleavage - pepsin and trypsin in stomach will not denature toxin
What does the emetic toxin CEREULIDE do
Once in stomach directly activate vagal neural system and lead to release of SEROTONIN (activate serotonin receptor) - increased stimulation of enteric NS lead to nausea and vomiting.
Gut has lots of neural connections - toxin attack this
Describe onset and duration of b.cereus diarrhoea form
Onset 8-16 hours
Duration 24 hours but has been seen to go on for 4-5 days
What is the pore forming complex of b.cereus diahorreal form made up of and why is it pore forming (shape)
Haemolysin BL (Hbl) Nonhaemolytic enterotoxin (Nhe) Cytotoxon K (Cytk)
Produced in intestine
BETA barrel confirmation THROUGH membrane so form a barrel hole in membrane - cell death. Lose structure of intestine wall so lose function - cannot absorb water so lose in faeces.
What is differnt about diahorreal toxin to emetic form
Emetic - heat stabile, preformed
Diahorreal - heat LABILE (sensitive to gut acids and heat - if reheat this then safe as not heat stable).
Organism produce toxin in gut (organism must be live in food and eaten rather than toxin eaten) - not preformed like emetic form.
What conc of b.cereus required for symptoms
10^5 cfu g^-1
Above what degree is food safe to be kept
63 degrees
What risk factor is there for b.cereus
Contaminated foods subject to inadequate temp control and storage following cooking
Why is it believed b.cereus is underreported
Rapid onset of symptoms
SHORT TERM DIARRHOEAL disease - unlikely
Big outbreaks noted but otherwise not likely
What agar is used for laboratory diagnosis
b.cereus selective agar
MYP (mannitol yolk agar)
Egg yolk emulsion - look for lecithinase action (hydrolysis of lecithin)
Also bacillus cannot use mannitol so keep pH indicator a blue (bromothymol blue)
Polymixin B - inhibit gram negatives
What colourful agar can be used for b.cereus diagnosis
Brilliance b.cereus agar
Chromogenic substrate
5-broom-4-chloro-3-indoxyl-B(beta)-glycopyranoside converted via beta glucosidase to give blue green colonies
What are treatments and prevention for b.cereus
SELF LIMITING
Prevent via adequate cooking, cooling and storage of food
What is interesting about presentation of b.cereus
If 100 people had same organism at same place present differently
Depend on age, health, whether taking other drugs affecting pH of stomach
Our relationship with organism is unique to our immune system - previous exposure etc
What did rob koch grow B anthracis on
In sheep eyeballs - no agar in 1877
Is b.anthracis gram positive or negative
Gram positive
Is b.anthracis an aerobic sporeformer or anaerobic sporeformer
Aerobic sporeformer
Where are the spores of b.anthracis located
Central/oval
What is the size of b.anthracis
3-5um long (BIG)
What do b.anthracis cells look like under a microscope
Square ended cells
What flagella does b.cereus have and what type of colonies does it make
Peritchricous and form rhizoids colonies
In 1887 what organism was classed by Koch as first bacterium capable of causing disease
b.anthracis
What is schedule 5
Antiterrorism bill for microbial agents could be used as for terrorism. Even c perf on there
What species does b.anthracis primarily affect
ZOONOSIS
Primarily disease of domesticated and wild animals - herbivores
What are 3 main presentations in humans
1- cutaneous (skin)
2- inhalation into lungs
3- GI (eat spore or toxin in food)
Which type of anthrax cause 95% of anthrax but is still rare
Cutaneous anthrax
Which country is b.anthracis seen hugely
NZ and Australia
How does cutaneous anthrax enter
Via minor skin abrasions in hands, arms, neck
What does b.anthracis cutaneous develop into
Painless necrotic ulcer (lesion)
Dissemination occur which lead to septicaemia
How many % of case die if untreated
5%
Which form of anthrax is most ‘weaponised’ for dirty bomb
Inhalation anthrax
What is infectious dose of b.anthracis
Approx 10,000 to 20,0000 spores
What are the symptoms of b.anthracis inhalation
General flu like symptoms - respiratory difficulty
Dissemination in lymphatic system - shock (2-6 days)
If untreated/delayed what percentage is fatal for inhaled b.anthracis
95%
What is Gi anthrax associated with
Contaminated undercooked meat
Where does gi anthrax enter
Intestinal mucosa (similar mechanism to cutaneous)
What are primary sumoptoms of gi anthrax
Severe diarhoea
Vomit blood
Dissemination in blood - septicaemia and toxaemia
Used to get in via food industry
What is fatality percentage of gi anthrax
65%
When was largest most recent outbreak of injection anthrax
2009-2010 contaminated heroin
Spores withstand process before injected - germinate inside
7 people in UK died from it
What feature of b.anthracis is used to attach and evade immune system
Use capsule.( glycocalix) slime later around cell and protect from environmental extremes( prevent phagocytosis )
Capsule made of Poly-D-Glutamate polypeptide capsule. Indian Ink doesnt stain capsule. Flourescent show capsule can be thicker than organism
What toxins does b.anthracis release and what do they together bring about
Protective antigen (PA) Edema Factor (EF) Lethal Factor (LF)
BRING ABOUT HYPOXIA, FLUID RETENTION AND NECROSIS (BLACK LESION)
PA has two subunits a and B. Which is active and which binds
A - active
B - binding (Protective antigen PA)
Describe mechanism of action for toxins
1- binding subunit of PA (B subunit) bind to ATR (anthrax toxin receptor)
2- furin (protease) cleave off a subunit to activate PA toxin
3- cause PA to form into heptomer (7 protein ring) with 6 other PA
4- as PAs come together drag membrane with them to form membrane raft which screws up membrane
5- 7 tail ends together form receptor for either EF or /and LF (toxins)
6- PA receptor get endocytosed dragging with it either EF or LF and once in endosome EF or LF dissoiate from AP
7- EITHER EF can interact with cAMP to get water retention or get LF with MAPK to get necrosis and hypoxia (cell death)
When was last case of b.anthracis
2008
What musical instrument release toxin and why
Animal hyde on drums not cured properly.- liberate toxins and spores of anthrax into air
How do you diagnose b.anthracis in lab
Gram stain blood smear
Culture on blood agar
Non haemolytic
Ground glass colonies - medusa head
What treatment and prevention is available
Antibiotics - ciprofloxacin (but need to know anthrax early on for good survival rates)
Prevention - avoid contact with animals, Iv drug use
Vaccine - BioThrax have AVA - anthrax vaccine absorbed against all 3 types of anthrax
Can use prophylactic antibiotics for those potentially exposed individuals
