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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
Q

What species has subterminal spores

A

C. difficile

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26
Q

What are the two main types of infections caused by C. perfringens

A

Wound and soft tissue infections

Foodborne infections

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27
Q

What four wound and soft tissue infections are caused by C. perfringens

A

Myonecrosis - gas gangrene
Anaerobic cellulitis
Necrotic enteritis
Clostridial endometriosis

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28
Q

Write about C. perfringens

A

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

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29
Q

Write about the pathogenicity of C. perfringens
(4)

A

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

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30
Q

Why does C. perfringens require tissue damage

A

Anaerobic conditions
Impaired blood supply
Complex nutrients
Ca++ ions

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31
Q

What is the main toxin produced by C. perfringens

A

a-toxin (lecithinase)

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32
Q

How is Gas Gangrene treated and symptoms

A

Tissue necrosis under the skin
Big black boils of infection
Tissue needs to be dissected and necrosis needs to be removed

33
Q

Write about anaerobic cellulitis caused by C. perfringens

A

Connective tissue infection
No muscle involvement

34
Q

Write about necrotic enteritis caused by C. perf

A

Outbreaks reported
Rare

35
Q

Write about endometriosis caused by C. perf

A

Complication of incomplete abortion
Inadequately sterilised instruments
Gangrenous uterine tissue
Toxins and BSI

36
Q

Write about C. perfringens food poisoning
(4)

A

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
Q

Is C. perfringens food poisoning caused by enterotoxins or exotoxins

A

Enterotoxins - spore forming

38
Q

List the C. perfringens toxins
(7)

A

a toxin
B toxin
E toxin
I toxin
Net B
a- haemolysin
Enterotoxin

39
Q

Write about C. perf a-toxin
(3)

A

Also called phospholipase C or lecithinase

Lyses RBCs, platelets, leucocytes and endothelial cells

Increased vascular permeability with massive haemolysis and bleeding tissue destruction

40
Q

Write about B-toxin

A

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
Q

Write about E toxin of C. perf

A

Epsilon pore forming toxin
Produced only by type B and D isolates

42
Q

Write about I-toxin of C. perf

A

Iota toxin
A binary toxin produced only by C. perf type E strains
ADP-ribosyltransferase activity

43
Q

What is Net B also called

A

Necrotic enteritis B-like toxin

44
Q

Write about CPE

A

C. perfringens Enterotoxin CPE

A heat labile toxin produced in colon- causes food poisoning

45
Q

Write about C. difficile

A

Antibiotic associated diarrhoea
- caused by suppression of normal flora in the colon

Commonly seen in elderly patients and health care environments

46
Q

What are some risk factors for C. difficile infection

A

Old Age humoral Ab response to gut micro
Hospitilasation
Antimicrobials

47
Q

What are three antimicrobials known to cause C. diff infection

A

Cephalosporins
Clindamycin
Fluoroquinolones

48
Q

What are the clinical manifestations of CDI

A

Mild
- asymptomatic colonisation

Moderate
- diarrhoeal illness
- recurrent diarrheae
- abdominal pain
- fever

Severe
- toxic megacolon
- life threatening

49
Q

Write about C. diff infection

A

Asymptomatic carriage
Watery diarrhea
Psudomembranous colitis
Recurrent infection
Outbreaks in hospitals
- cross infection
- infection control important

50
Q

How is C. diff treated

A

Antimicrobials:
Probiotics
Faecal transplantation

51
Q

What antimicrobials are used for C. diff

A

Metranidazole
Vancomycin
Fidoxamycin

52
Q

What are the virulence factors of C. diff

A

A and B toxins
Binary toxin

53
Q

Write about C. diff A and B toxins

A

Both enterotoxins
Pro-inflammatory IL8 neutrophil response
Biological activity Rho GTPase
Cell death

Toxin B is a target in molecular assays

54
Q

Write about C. Botulinum

A

Causes botulism
One of the most potent neurotoxins known
Divided into two groups:
- mesophilic
- psycrotolerant
Several different clinical forms

55
Q

What are the two groups of C. botulinum

A

Mesophilic
Psycrotolerant

56
Q

What are the symptoms of Clostridioides Botulinum

A

Blurred vision
Difficulty Swallowing
Cranial Nerve Functions

5 Ds from HomeEc
- difficulty swallowing
- difficulty breathing
- double vision
- drooping eyelids
- death

57
Q

What are the virulence factors of C. botulinum

A

Eight antigenically distinct toxins: A. B. C1, D, E, F, G

All neurotoxins with similar structure and mode of action

58
Q

How do the C. botulinum toxins work

A

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
Q

What does C. botulinum toxins cause

A

Prevents contraction of muscle
Causes flaccid paralysis

60
Q

What are the three steps to botulism toxin action

A

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
Q

Write about C. tetani

A

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
Q

Write about tetanus toxin

A

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
Q

Write about the mechanism of action of tetanospasmin

A

Blocks release of inhibitory neurotransmitters such as glycine resulting in unrestrained excitation of motor neuron

Severe prolonged muscle spasms

64
Q

What samples are seen in the lab

A

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
Q

What is done on day 1 isolation

A

Blood agar + metranidazole

Selective media
- Cycloserine-cefoxitin-egg yolk agar for C. difficile

66
Q

What direct examination is done on day 1

A

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
Q

What are the basic characteristics of Clostridioides

A

Beta haemolysis
GPBs
Spores
Catalase negative

68
Q

What identification tests are there for Clostridioides

A

Anaerobic growth
Lactose gelatin test
Lipase/lecithinase activity on egg yolk agar

Toxin detection/neutralisation tests

69
Q

What are the biochemical results for C. perf

A

Glucose +
Maltose +
Sucrose +

Lactose +
Gelatin +

Lipase -
Lecithinase +

70
Q

What is the C. perfringens toxin confirmation test

A

Nagler reaction

71
Q

What is the Nagler reaction

A

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
Q

How is the Nagler test carried out

A

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
Q

What are the basic characteristics of C. tetani

A

Swarming growth on blood agar
GPBs
Catalase negative

74
Q

What are the biochemical test results for Clostridioides

A

Lactose negative
Gelatin positive
Lipase positive
Lecithinase negative

75
Q

What are the basic characteristics of C. botulinum

A

Haemolysis on blood agar
GPBs
Catalase negative

76
Q

What biochemical results are there for C. botulinum

A

Glucose positive
maltose positive
Lactose negative
Gelatin positive
Lipase positive
Lecithinase negative

Toxin detection via ELISA or PCR

77
Q

What is done on the day 1 investigation of C. difficile

A

Direct detection of toxin gene

Direct detection of organism (C. Diff Complete)

78
Q

How is direct detection carried out for C. difficile

A

Real Time PCR
EntericBio
BD Max

Syndromic testing
Biofire GI panel

79
Q

What are the basic characteristics of C. difficile

A

Haemolysis on blood agar
Stable horse manure smell
GBP
Catalase negative

2.2 Microbiology (60 decks)

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