Enterobacteriaciae Flashcards
List the pathogenic organisms
Bacteria
Viruses
Parasites
Fungi
Classification of bacteria according to gram staining
Gram positive (aerobic and anaerobic)
Gram negative (aerobic and anaerobic)
Examples of pathogenic gram positive bacteria
Staphylococcus
Streptococcus & Enterococcus
Micrococcus
Shapes of gram-postive bacteria and examples
Cocci:
Staphylococcus
Streptococcus
Enterococcus
Bacilli:
Bacillus
Clostridium
Listeria
Cornyebacterium
Nocardia
Actinomyces
Shapes and examples of gram negative bacteria
Cocci:
Neisseria
Bacilli:
Enterobacteriacea
Pseudomonas
Acinetobacter
Enterobacteriaceae habitat
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!)
What is the commonest agent of nosocomial infection?
enterobacteriaceae
enterobacteriaceae is also known as?
Enteric bacteria
Enterics
Feacal coliforms
Enteric gram negative rods
General Characteristic of enterobacteriaceae
- Ferment glucose with acid production
* Ferment glucose by the mixed acid pathway
* Klebsiella, Enterobacter & Serratia utilize the butanediol pathway - Reduce nitrates (NO3 to NO2 or all the way to N2)
- Oxidase negative
Properties of enterobacteriaceae
- 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)
- Catalase positive (and oxidase negative)
- G + C content of DNA usually 39-59%
- Motile with peritrichous flagellation except Klebsiella, Shigella & Yesinia
- Gram negative, non-sporing bacilli
Most UTI’s are caused by which family of bacteria?
enterobacteriaceae (particularly E.coli)
What preferred agar do enterobacteriaceae grow on?
MacConkey agar (only for gram negative bacilli (rods))
What signifies the enterobacteriaceae as lactose fermentors on agar?
Pink colonies on MacConkey
What signifies non-lactose fermentors on agar?
Clear & Colourless colonies on MacConkey
What test can be used to differentiate pseudomonas and Enterobacteriacea (seeing as they’re both gram negative, catalase positive bacteria)?
Oxidase test
Pseudomonas is oxidase positive whilst Enterobacteriacea is oxidase negative
What is the classification of Enterobacteriacea?
- 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 - 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 - 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
Discuss the Antigenic Structure Enterobacteriacea (for serological identification)
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)
- K (capsular) antigens: capsular polysaccharide, particularly heavy in Klebsiella
- H (flagellar) antigens: flagellar proteins of motile genera and species; used for typing; absent in nonmotile genera (Shigella, Klebsiella & Yesinia)
- O (somatic) antigens: O-specific polysaccharide side chain of lipopolysaccharide; used for typing
(Most pathogenic species are associated with O & H antigens)
What is a cross reaction
Cross-reactivity between antigens occurs when an antibody directed against one specific antigen is successful in binding with another, different antigen
What are Virulence factors?
Virulence factors are molecules or structures produced by pathogens (bacteria, viruses, fungi, or parasites) that enhance their ability to cause disease.
Virulence Factors
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
Additional Virulence Factors
- 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)
- Sequestration of nutritional factors:
Fe chelating in particular by production of siderophores which are extracellular iron-chelating compounds (e.g., enterobactin, aerobactin) - 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
Difference between exotoxins and endotoxins
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
Sites and types of infection
- CNS
- Lower respiratory tract
- Bloodstream
- GIT
- Urinary tract
Modes of Transmission of Infection
- 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) - Endogenous- UTI, Spontaneous bacterial peritonitis
- Nosocomial
- Insect vector (Fleas- Yesinia pestis)
Laboratory Diagnosis of Enterics
- 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 - Microscopy
- Culture
- Identification
Biochemical test
Serology
Antigen test
Molecular assay - Antibiotic sensitivity testing
