Denise - Anaerobes (Clostridioides) Flashcards
What is an obligate aerobe
Acquire energy ONLY by respiration
They cannot survive without oxygen
Give two examples of obligate aerobes
Mycobacterium tuberculosis
Pseudomonas aeruginosa
What is an obligate anaerobe
Acquire energy ONLY by fermentation
Most cannot survive in oxygen
Give two examples of obligate anaerobes
Clostridioides perfringes
Bacteroides fragilia
What is a facultative anaerobe
Most bacteria
Acquire energy be either respiration or fermentation
Can survive with or without oxygen
Give two examples of obligate anaerobes
E. Coli
Staphylococcus aureus
What is the physiology behind aerobes
Inhibited or damaged by oxygen gas
Lack the enzymes that allow aerobes to detoxify free oxygen radicals
- peroxidase
- catalase
- superoxide dismutase
What are the main reservoirs for obligate anaerobes
Endogenous
- GIT of animals
- Gingival crevices around teeth
- Skin glands and hair follicles
Exogenous
- soil
- sewage
- aquatic setting
Write about anaerobic infections
Infections close to mucosal surfaces
Cause tissue necrosis and abscess formation
Putrid odour
Gas in tissues
Polymicrobial flora
Failure to isolate anything from specimen in the lab usually indicates an anaerobe
What are are the most important clostridioides species
C. perfringens
C. tetani
C. botulinum
C. difficile
C. histolyticum
What are the two different types of infection caused by clostridioides
Invasive clostridioides infection
Toxigenic infection
Give some exmaples of invaside clostridioides infections
Gas gangrene/ myonecrosis
Would infection/abscess
Food poisoning
What species of Clostridioides causes gas gangrene/myonecrosis and food poisoning
C. perfringens
What species of Clostridioides causes wound infection/abscess
C. histolyticum
What are three examples of toxigenic infections by clostridioides
Tetanus
Botulism
Antibiotic-associated colitis
What Clostridioides causes tetanus?
C. tetani
What Clostridioides causes botulism?
Botulinum
What Clostridioides causes antibiotic-associated colitis?
C. difficile
What are clostridioides species
Gram positive, spore-forming bacilli
Write about Clostridioides spores
Sporulation occurs in nurient-limiting conditions
Spores are resistant to extremes of dryness, heat (boiling) and many chemical disinfectants
They can persisist in the environment for weeks to months and germinate deep in the soil where conditions are anaerobic
In favourable conditions spores germinate and may produce toxins
Write about the process of sporulation
Cell in unfavourable conditions
Cell division and partitioning begins -> spore to one side containing nuclear material from division
Elaboration of a spore coat
Free spore
What are the three different types of spore positions
Terminal spore
Central spore
Subterminal spore
What species has terminal spores
C. tetani
What species has central spores
C. perfringens
What species has subterminal spores
C. difficile
What are the two main types of infections caused by C. perfringens
Wound and soft tissue infections
Foodborne infections
What four wound and soft tissue infections are caused by C. perfringens
Myonecrosis - gas gangrene
Anaerobic cellulitis
Necrotic enteritis
Clostridial endometriosis
Write about C. perfringens
C. perfringens type A is the most common invasive Clostridioides species
Ubiquitous in nature
Vegetative form in GIT and GU tract
Spores found in soil, sewage and aquatic settings
Write about the pathogenicity of C. perfringens
(4)
Organism requires damaged tissue (anaerobe, nutrients, Ca++)
Produces 12 toxins that attack membranes including a-toxin/lecithinase
Toxins destroy PMNs, produce myonecrosis
Organism produces gas when they grow = crepitance in tissue
Why does C. perfringens require tissue damage
Anaerobic conditions
Impaired blood supply
Complex nutrients
Ca++ ions
What is the main toxin produced by C. perfringens
a-toxin (lecithinase)
How is Gas Gangrene treated and symptoms
Tissue necrosis under the skin
Big black boils of infection
Tissue needs to be dissected and necrosis needs to be removed
Write about anaerobic cellulitis caused by C. perfringens
Connective tissue infection
No muscle involvement
Write about necrotic enteritis caused by C. perf
Outbreaks reported
Rare
Write about endometriosis caused by C. perf
Complication of incomplete abortion
Inadequately sterilised instruments
Gangrenous uterine tissue
Toxins and BSI
Write about C. perfringens food poisoning
(4)
Improperly-handled food is contraminated with spores, which survive cooking temperature
Spores germinate with heating (anaerobiasis) and if > 10^5/g bacteria are ingested, illness may occur
Sporulation in the small intestine releases enterotoxin CPE
Diarrhoea occurs 6-18 hours later, and resolves in 1-2 days
Is C. perfringens food poisoning caused by enterotoxins or exotoxins
Enterotoxins - spore forming
List the C. perfringens toxins
(7)
a toxin
B toxin
E toxin
I toxin
Net B
a- haemolysin
Enterotoxin
Write about C. perf a-toxin
(3)
Also called phospholipase C or lecithinase
Lyses RBCs, platelets, leucocytes and endothelial cells
Increased vascular permeability with massive haemolysis and bleeding tissue destruction
Write about B-toxin
Responsible for necrotic lesions in necrotising enterocolitis
B-pore-forming toxin (PFT) of the a-hameolysin family and AA similarity with B toxin from S. aureua
Write about E toxin of C. perf
Epsilon pore forming toxin
Produced only by type B and D isolates
Write about I-toxin of C. perf
Iota toxin
A binary toxin produced only by C. perf type E strains
ADP-ribosyltransferase activity
What is Net B also called
Necrotic enteritis B-like toxin
Write about CPE
C. perfringens Enterotoxin CPE
A heat labile toxin produced in colon- causes food poisoning
Write about C. difficile
Antibiotic associated diarrhoea
- caused by suppression of normal flora in the colon
Commonly seen in elderly patients and health care environments
What are some risk factors for C. difficile infection
Old Age humoral Ab response to gut micro
Hospitilasation
Antimicrobials
What are three antimicrobials known to cause C. diff infection
Cephalosporins
Clindamycin
Fluoroquinolones
What are the clinical manifestations of CDI
Mild
- asymptomatic colonisation
Moderate
- diarrhoeal illness
- recurrent diarrheae
- abdominal pain
- fever
Severe
- toxic megacolon
- life threatening
Write about C. diff infection
Asymptomatic carriage
Watery diarrhea
Psudomembranous colitis
Recurrent infection
Outbreaks in hospitals
- cross infection
- infection control important
How is C. diff treated
Antimicrobials:
Probiotics
Faecal transplantation
What antimicrobials are used for C. diff
Metranidazole
Vancomycin
Fidoxamycin
What are the virulence factors of C. diff
A and B toxins
Binary toxin
Write about C. diff A and B toxins
Both enterotoxins
Pro-inflammatory IL8 neutrophil response
Biological activity Rho GTPase
Cell death
Toxin B is a target in molecular assays
Write about C. Botulinum
Causes botulism
One of the most potent neurotoxins known
Divided into two groups:
- mesophilic
- psycrotolerant
Several different clinical forms
What are the two groups of C. botulinum
Mesophilic
Psycrotolerant
What are the symptoms of Clostridioides Botulinum
Blurred vision
Difficulty Swallowing
Cranial Nerve Functions
5 Ds from HomeEc
- difficulty swallowing
- difficulty breathing
- double vision
- drooping eyelids
- death
What are the virulence factors of C. botulinum
Eight antigenically distinct toxins: A. B. C1, D, E, F, G
All neurotoxins with similar structure and mode of action
How do the C. botulinum toxins work
Mostly AB toxins
A, B and E mostly seen in humans
Neurotoxins which block neurotransmission at nerve ending by preventing acetycholine release
Does this through their action as zinc metalloproteases
Heat sensitive
What does C. botulinum toxins cause
Prevents contraction of muscle
Causes flaccid paralysis
What are the three steps to botulism toxin action
Botulinum toxin passes from the gut into the circulation
Botulinum toxin is taken up by an exon and cleaved into the A and B subunits
The A subunit of botulinum toxin interrupts signal transmission by blocking release of acetylcholine from synaptic vesicles
Write about C. tetani
Introduction of tetanus spores into small wounds e.g. puncture wounds
Rare disease
O2 sensitivity
Immunisation
Growth is local but toxin spreads to the nerves
Write about tetanus toxin
Tetanosplasmin (tetanus toxin)
Plasmic encoded by a single polypeptide
Cleaved to generate mature toxin - 2 chains held together by a disulphide bond
Heavy chain B binding
Light chain A activity
Write about the mechanism of action of tetanospasmin
Blocks release of inhibitory neurotransmitters such as glycine resulting in unrestrained excitation of motor neuron
Severe prolonged muscle spasms
What samples are seen in the lab
Wound and soft tissue infection
- pus
- tissue samples
- muscle biopsy
Food-borne infection
- faeces
- food
- gastric contents
- vomitus
- serum
Antibiotic associated diarrhoeae
- faecal specimen
What is done on day 1 isolation
Blood agar + metranidazole
Selective media
- Cycloserine-cefoxitin-egg yolk agar for C. difficile
What direct examination is done on day 1
Gram-stained smears show absence of inflammatory cells
Gram-positive rods with/without endospores
C. perf = ‘boxcar-like’ large/short/fat rods
C. tetani = ‘drumstick appearance’
What are the basic characteristics of Clostridioides
Beta haemolysis
GPBs
Spores
Catalase negative
What identification tests are there for Clostridioides
Anaerobic growth
Lactose gelatin test
Lipase/lecithinase activity on egg yolk agar
Toxin detection/neutralisation tests
What are the biochemical results for C. perf
Glucose +
Maltose +
Sucrose +
Lactose +
Gelatin +
Lipase -
Lecithinase +
What is the C. perfringens toxin confirmation test
Nagler reaction
What is the Nagler reaction
Lecithinase activity
Egg yolk agar (contains lecithin)
Anerobically incubation at 37 degrees for 24 hours
Neutralisation of lecithinase activity with C. perfringens antiserum containing alpha antitoxin is present on the medium
How is the Nagler test carried out
Cover half of plate with antiserum to alpha toxin of C. perfringens
Streak control and test strains from antiserum-free side to antiserum-covered side
What are the basic characteristics of C. tetani
Swarming growth on blood agar
GPBs
Catalase negative
What are the biochemical test results for Clostridioides
Lactose negative
Gelatin positive
Lipase positive
Lecithinase negative
What are the basic characteristics of C. botulinum
Haemolysis on blood agar
GPBs
Catalase negative
What biochemical results are there for C. botulinum
Glucose positive
maltose positive
Lactose negative
Gelatin positive
Lipase positive
Lecithinase negative
Toxin detection via ELISA or PCR
What is done on the day 1 investigation of C. difficile
Direct detection of toxin gene
Direct detection of organism (C. Diff Complete)
How is direct detection carried out for C. difficile
Real Time PCR
EntericBio
BD Max
Syndromic testing
Biofire GI panel
What are the basic characteristics of C. difficile
Haemolysis on blood agar
Stable horse manure smell
GBP
Catalase negative
