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Microbiology > Enterobacteriaciae > Flashcards

Enterobacteriaciae Flashcards

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Biology 101 flashcards
1
Q

List the pathogenic organisms

A

Bacteria
Viruses
Parasites
Fungi

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2
Q

Classification of bacteria according to gram staining

A

Gram positive (aerobic and anaerobic)
Gram negative (aerobic and anaerobic)

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3
Q

Examples of pathogenic gram positive bacteria

A

Staphylococcus
Streptococcus & Enterococcus
Micrococcus

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4
Q

Shapes of gram-postive bacteria and examples

A

Cocci:
Staphylococcus
Streptococcus
Enterococcus

Bacilli:
Bacillus
Clostridium
Listeria
Cornyebacterium
Nocardia
Actinomyces

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5
Q

Shapes and examples of gram negative bacteria

A

Cocci:
Neisseria

Bacilli:
Enterobacteriacea
Pseudomonas
Acinetobacter

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6
Q

Enterobacteriaceae habitat

A

Heterogeneous group of bacteria whose natural habitat is the intestine of animals including man

Few members however inhabit the environment (water, soil and sewage)

Members second most common isolate from clinical specimen

(They can be found alomst anywhere!)

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7
Q

What is the commonest agent of nosocomial infection?

A

enterobacteriaceae

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8
Q

enterobacteriaceae is also known as?

A

Enteric bacteria
Enterics
Feacal coliforms
Enteric gram negative rods

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9
Q

General Characteristic of enterobacteriaceae

A
  1. Ferment glucose with acid production
    * Ferment glucose by the mixed acid pathway
    * Klebsiella, Enterobacter & Serratia utilize the butanediol pathway
  2. Reduce nitrates (NO3 to NO2 or all the way to N2)
  3. Oxidase negative
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10
Q

Properties of enterobacteriaceae

A
  1. Facultative anaerobes/ aerobes (A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent)
  2. Catalase positive (and oxidase negative)
  3. G + C content of DNA usually 39-59%
  4. Motile with peritrichous flagellation except Klebsiella, Shigella & Yesinia
  5. Gram negative, non-sporing bacilli
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11
Q

Most UTI’s are caused by which family of bacteria?

A

enterobacteriaceae (particularly E.coli)

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12
Q

What preferred agar do enterobacteriaceae grow on?

A

MacConkey agar (only for gram negative bacilli (rods))

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13
Q

What signifies the enterobacteriaceae as lactose fermentors on agar?

A

Pink colonies on MacConkey

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14
Q

What signifies non-lactose fermentors on agar?

A

Clear & Colourless colonies on MacConkey

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15
Q

What test can be used to differentiate pseudomonas and Enterobacteriacea (seeing as they’re both gram negative, catalase positive bacteria)?

A

Oxidase test
Pseudomonas is oxidase positive whilst Enterobacteriacea is oxidase negative

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16
Q

What is the classification of Enterobacteriacea?

A
  1. Infection type:
    a. Opportunistic/ Non- Opportunistic
    * All opportunistic except Salmonella, Shigella & Yesinia –(Primary intestinal Pathogens)
    b. Infection site:
    * Intestinal
    * Extra-intestinal
    c. Endogenous/ Exogenous
    * All could cause both types of infections except Salmonella, Shigella & Yesinia which cause exogenous infections always
  2. Lactose fermentation:
    a. Lactose fermenters:
    * Fast fermenter- E. coli, Klebsiella, Enterobacter
    * Slow fermenters- Edwardsiella, Serratia, Citrobacter, Arizona, Providentia, Erwinia
    b. Non-lactose fermenters- Shigella, Salmonella
  3. Taxonomic
    * Complex & evolving,
    * based on biochemical rxn, nucleic acid structure, antigenic composition (O, H & K)
    * Over 30 genera and 120 species
    * More than 95% are clinically significant strains
    * clinically significant strains falls into not less than 10 genera & 25 species
17
Q

Discuss the Antigenic Structure Enterobacteriacea (for serological identification)

A

Antigen types (serological identification):
(different types of antigens on the Enterobacteriacea that ellict an antiobdy response but cann also be used to help identify strains)

  1. K (capsular) antigens: capsular polysaccharide, particularly heavy in Klebsiella
  2. H (flagellar) antigens: flagellar proteins of motile genera and species; used for typing; absent in nonmotile genera (Shigella, Klebsiella & Yesinia)
  3. O (somatic) antigens: O-specific polysaccharide side chain of lipopolysaccharide; used for typing

(Most pathogenic species are associated with O & H antigens)

18
Q

What is a cross reaction

A

Cross-reactivity between antigens occurs when an antibody directed against one specific antigen is successful in binding with another, different antigen

19
Q

What are Virulence factors?

A

Virulence factors are molecules or structures produced by pathogens (bacteria, viruses, fungi, or parasites) that enhance their ability to cause disease.

20
Q

Virulence Factors

A

i. Endotoxin: Lipopolysaccharide (LPS)
* Lipid A: toxigenic component (causes inflammatory effects and fixes/activates complement)
* Polysaccharide: antigenic component

ii. Exotoxin: Enterotoxins
* E.coli causing diarrhoea.

iii. Capsule – antiphagocytic

iv. Pili-for attachment (K88 of E.coli→dirrhoea/infant)

v. Cell envelope & surface appendages
Ability to colonize, adhere and invade tissues

vi. Plasmids - mediate resistance to antibiotics

21
Q

Additional Virulence Factors

A
  1. Antigenic phase variation: capability to alternately express or not express either capsule or flagella and thus avoid host immunity (harder for the immjne system to respond to so many variations)
  2. Sequestration of nutritional factors:
    Fe chelating in particular by production of siderophores which are extracellular iron-chelating compounds (e.g., enterobactin, aerobactin)
  3. Resistance to serum killing: many bacteria are inherently sensitive to nonspecific bloodborne components and to circulating complement and the resultant complement-mediated clearance, but Enterobacteriaceae and other bloodborne pathogens can resist such killing
22
Q

Difference between exotoxins and endotoxins

A

EXOTOXIN
1. Released from the cell before or after lysis
2. Protein
3. Heat labile
4. Antigenic and immunogenic
5. Toxoids can be produced
6. Specific in effect on host
7. Produced by gram-positive and gram-negative organisms

ENDOTOXIN
1. Integral part of cell wall
2. Endotoxin is LPS; Lipid A is toxic component
3. Heat stable
4. Antigenic; ??immunogenicity
5. Toxoids cannot be produced
6. Many effects on host
7. Produced by gram-negative organisms only

23
Q

Sites and types of infection

A
  1. CNS
  2. Lower respiratory tract
  3. Bloodstream
  4. GIT
  5. Urinary tract
24
Q

Modes of Transmission of Infection

A
  1. Contaminated food & water
    Salmonella, Shigella & Yesinia enterolitica, Escherichia coli O157:H7 (a particular strain of E. coli that causes a severe intestinal infection in humans. It is the most common strain to cause illness in people)
  2. Endogenous- UTI, Spontaneous bacterial peritonitis
  3. Nosocomial
  4. Insect vector (Fleas- Yesinia pestis)
25
Q

Laboratory Diagnosis of Enterics

A
  1. Specimens: pus, tissue, sputum, fluids, rectal swabs, faeces e.t.c
    If not processed quickly, should be collected and transported in Cary-Blair, Amies, or Stuart media
  2. Microscopy
  3. Culture
  4. Identification
    Biochemical test
    Serology
    Antigen test
    Molecular assay
  5. Antibiotic sensitivity testing

Microbiology (18 decks)

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