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2.2 Microbiology > Denise - Anaerobes (Clostridioides) > Flashcards

Denise - Anaerobes (Clostridioides) Flashcards

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1
Q

What is an obligate aerobe

A

Acquire energy ONLY by respiration
They cannot survive without oxygen

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2
Q

Give two examples of obligate aerobes

A

Mycobacterium tuberculosis
Pseudomonas aeruginosa

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3
Q

What is an obligate anaerobe

A

Acquire energy ONLY by fermentation
Most cannot survive in oxygen

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4
Q

Give two examples of obligate anaerobes

A

Clostridioides perfringes
Bacteroides fragilia

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5
Q

What is a facultative anaerobe

A

Most bacteria
Acquire energy be either respiration or fermentation
Can survive with or without oxygen

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6
Q

Give two examples of obligate anaerobes

A

E. Coli
Staphylococcus aureus

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7
Q

What is the physiology behind aerobes

A

Inhibited or damaged by oxygen gas
Lack the enzymes that allow aerobes to detoxify free oxygen radicals
- peroxidase
- catalase
- superoxide dismutase

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8
Q

What are the main reservoirs for obligate anaerobes

A

Endogenous
- GIT of animals
- Gingival crevices around teeth
- Skin glands and hair follicles

Exogenous
- soil
- sewage
- aquatic setting

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9
Q

Write about anaerobic infections

A

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

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10
Q

What are are the most important clostridioides species

A

C. perfringens
C. tetani
C. botulinum
C. difficile
C. histolyticum

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11
Q

What are the two different types of infection caused by clostridioides

A

Invasive clostridioides infection
Toxigenic infection

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12
Q

Give some exmaples of invaside clostridioides infections

A

Gas gangrene/ myonecrosis
Would infection/abscess
Food poisoning

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13
Q

What species of Clostridioides causes gas gangrene/myonecrosis and food poisoning

A

C. perfringens

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14
Q

What species of Clostridioides causes wound infection/abscess

A

C. histolyticum

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15
Q

What are three examples of toxigenic infections by clostridioides

A

Tetanus
Botulism
Antibiotic-associated colitis

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16
Q

What Clostridioides causes tetanus?

A

C. tetani

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17
Q

What Clostridioides causes botulism?

A

Botulinum

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18
Q

What Clostridioides causes antibiotic-associated colitis?

A

C. difficile

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19
Q

What are clostridioides species

A

Gram positive, spore-forming bacilli

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20
Q

Write about Clostridioides spores

A

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

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21
Q

Write about the process of sporulation

A

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

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22
Q

What are the three different types of spore positions

A

Terminal spore
Central spore
Subterminal spore

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23
Q

What species has terminal spores

A

C. tetani

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24
Q

What species has central spores

A

C. perfringens

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25
What species has subterminal spores
C. difficile
26
What are the two main types of infections caused by C. perfringens
Wound and soft tissue infections Foodborne infections
27
What four wound and soft tissue infections are caused by C. perfringens
Myonecrosis - gas gangrene Anaerobic cellulitis Necrotic enteritis Clostridial endometriosis
28
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
29
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
30
Why does C. perfringens require tissue damage
Anaerobic conditions Impaired blood supply Complex nutrients Ca++ ions
31
What is the main toxin produced by C. perfringens
a-toxin (lecithinase)
32
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
33
Write about anaerobic cellulitis caused by C. perfringens
Connective tissue infection No muscle involvement
34
Write about necrotic enteritis caused by C. perf
Outbreaks reported Rare
35
Write about endometriosis caused by C. perf
Complication of incomplete abortion Inadequately sterilised instruments Gangrenous uterine tissue Toxins and BSI
36
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
37
Is C. perfringens food poisoning caused by enterotoxins or exotoxins
Enterotoxins - spore forming
38
List the C. perfringens toxins (7)
a toxin B toxin E toxin I toxin Net B a- haemolysin Enterotoxin
39
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
40
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
41
Write about E toxin of C. perf
Epsilon pore forming toxin Produced only by type B and D isolates
42
Write about I-toxin of C. perf
Iota toxin A binary toxin produced only by C. perf type E strains ADP-ribosyltransferase activity
43
What is Net B also called
Necrotic enteritis B-like toxin
44
Write about CPE
C. perfringens Enterotoxin CPE A heat labile toxin produced in colon- causes food poisoning
45
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
46
What are some risk factors for C. difficile infection
Old Age humoral Ab response to gut micro Hospitilasation Antimicrobials
47
What are three antimicrobials known to cause C. diff infection
Cephalosporins Clindamycin Fluoroquinolones
48
What are the clinical manifestations of CDI
Mild - asymptomatic colonisation Moderate - diarrhoeal illness - recurrent diarrheae - abdominal pain - fever Severe - toxic megacolon - life threatening
49
Write about C. diff infection
Asymptomatic carriage Watery diarrhea Psudomembranous colitis Recurrent infection Outbreaks in hospitals - cross infection - infection control important
50
How is C. diff treated
Antimicrobials: Probiotics Faecal transplantation
51
What antimicrobials are used for C. diff
Metranidazole Vancomycin Fidoxamycin
52
What are the virulence factors of C. diff
A and B toxins Binary toxin
53
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
54
Write about C. Botulinum
Causes botulism One of the most potent neurotoxins known Divided into two groups: - mesophilic - psycrotolerant Several different clinical forms
55
What are the two groups of C. botulinum
Mesophilic Psycrotolerant
56
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
57
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
58
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
59
What does C. botulinum toxins cause
Prevents contraction of muscle Causes flaccid paralysis
60
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
61
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
62
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
63
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
64
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
65
What is done on day 1 isolation
Blood agar + metranidazole Selective media - Cycloserine-cefoxitin-egg yolk agar for C. difficile
66
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'
67
What are the basic characteristics of Clostridioides
Beta haemolysis GPBs Spores Catalase negative
68
What identification tests are there for Clostridioides
Anaerobic growth Lactose gelatin test Lipase/lecithinase activity on egg yolk agar Toxin detection/neutralisation tests
69
What are the biochemical results for C. perf
Glucose + Maltose + Sucrose + Lactose + Gelatin + Lipase - Lecithinase +
70
What is the C. perfringens toxin confirmation test
Nagler reaction
71
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
72
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
73
What are the basic characteristics of C. tetani
Swarming growth on blood agar GPBs Catalase negative
74
What are the biochemical test results for Clostridioides
Lactose negative Gelatin positive Lipase positive Lecithinase negative
75
What are the basic characteristics of C. botulinum
Haemolysis on blood agar GPBs Catalase negative
76
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
77
What is done on the day 1 investigation of C. difficile
Direct detection of toxin gene Direct detection of organism (C. Diff Complete)
78
How is direct detection carried out for C. difficile
Real Time PCR EntericBio BD Max Syndromic testing Biofire GI panel
79
What are the basic characteristics of C. difficile
Haemolysis on blood agar Stable horse manure smell GBP Catalase negative

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