Microbiological virulence factors

Question 1

What are the classical characteristics of viruses?

Answer 1

Obligate intracellular parasites
Smaller, DNA or RNA
Metabolically inert
Use host cell synthetic machinery

Question 2

What are the classical characteristics of bacteria?

Answer 2

Unicellular
Prokaryotic- nucleus not organised, double stranded circular DNA in cytoplasm
Rigid peptidoglycan cell wall
Binary fission

Question 3

What are the classical features of fungi?

Answer 3

Eukaryotic
Rigid cell wall
Sexual and asexual replication
Unicellular yeast like or filamentous conidia/spore bearing forms

Question 4

What are the classical features of parasites?

Answer 4

Eukaryotic
Unicellular protozoa or multicellular helminths
Many with intermediate hosts in complex life cycle

Question 5

What is the cytoplasmic membrane of bacteria made of?

Answer 5

Proteins and phospholipids

Question 6

What does the cytoplasmic membrane of bacteria not contain?

Answer 6

Sterols (only found in eukaryotes)

Question 7

What is the function of the bacterial cell membrane?

Answer 7

Synthesise and export cell wall components
Respiration
Secretion of extracellular enzymes and toxins
Uptake of nutrients by active transport mechanisms

Question 8

What is the function of bacterial cell wall?

Answer 8

Protective- rigid so can withstand osmotic and mechanical stress + provides barrier against certain toxic chemical and biological agents
Gives shape to the bacterium
Firm base for pili, fimbriae and flagella
Contains antigens- important in virulence and in host antibody production

Question 9

What are the 2 different types of bacterial cell wall?

Answer 9

Gram positive

Gram negative

Question 10

What are gram positive cell walls like?

Answer 10

2 layers
Peptidoglycan and teichoic acids
Inner plasma membrane and outer thick peptidoglycan layer

Question 11

What are Gram negative cell walls like?

Answer 11

3 layers
Thin peptidoglycan layer
Outer plasma membrane containing lipopolysaccharide (LPS) and outer membrane proteins (OMP)

Question 12

What is the bacterial capsule?

Answer 12

Mucoid polysaccharide layer

Consists of polymerised d-glutamic acid

Question 13

What is the function of the bacterial capsule?

Answer 13

Anti-phagocytic activity anf prevents attack by complement

Adhesion

Question 14

What is the capsule used for?

Answer 14

Laboratory diagnostic tests and used in vaccines

Question 15

What are 2 of the main types of pili and what do they do?

Answer 15

Sex pili- transfer DNA by conjugation

Common pili- for attachment

Question 16

What is the function of pili?

Answer 16

They are important in adhesion and anti-phagocytic activity

Question 17

What is the function of flagella?

Answer 17

Motility

Question 18

Give example of intracellular structures in bacteria?

Answer 18

Nucleoid
Ribosomes
Inclusion granules
Endospores

Question 19

What are the basic requirements for bacteria in terms of nutrition?

Answer 19

Basic requirements- carbon, nitrogen, water and a source of energy

Question 20

How is the fact that some bacteria require specific gases and growth factors used diagnostically?

Answer 20

Media can be developed for selective isolation and identification of particular bacteria

Question 21

What are the classifying features of bacteria?

Answer 21

Shape- round, long, curved, pairs, clusters, chains etc
Atmospheric requirement- requires oxygen, increased co2 and oxygen toxic
Spore production (dangerous feature)

Question 22

What are the main bacteria identification tests?

Answer 22

Enzyme production- Testing to see whether they produce certain enzymes such as:
Urease
Catalase
Coagulase
Oxidase

Toxin production:
Protein synthesis inhibitors
Haemolysins
Superantigens

Question 23

What are the components of the Gram stain?

Answer 23

Stain 1= Methyl violet and lugol’s iodine (violet-blue)

Stain 2= Methyl red (pale pink-red)

Question 24

What component of the Gram stain does both Gram positive and Gram negative bacteria take?

Answer 24

Gram positive- Stain 1 (violet blue)

Gram negative- Stain 2 (pale pink red)

Question 25

How are Gram positive first classified?

Answer 25

Based on shape- rods or cocci

Question 26

What are Gram positive bacteria differentiated based on after their shape?

Answer 26

How they aggregate and other biochemical test results

Question 27

How do staphylococcus aggregate and how do they respond to catalase test?

Answer 27

``` In clusters (grapes) Catalase positive ```

Question 28

How do streptococcus aggregate and how do they respond to catalase test?

Answer 28

In pairs/chains | Catalse negative

Question 29

How are staphylococci differentiated?

Answer 29

Based on coagulase test Positive- s.aureus Negative- s.epidermidis and s.saprophyticus and others

Question 30

What are streptococci differentiated based on?

Answer 30

Extent of haemolysis that they cause: Alpha haemolytic- (must be further differentiated using optochin- toxic chemical) Optochin sensitive- s.pneumoniae Optochin resistant- viridans group Beta haemolytic- Group A- s. pyogenes Group B- s.agalactiae Group D- enterococci Non-haemolytic Streptococcus milleri Anaerobic streptococci

Question 31

What types of infection are caused by staphylococci?

Answer 31

Staphylococcus aureus- severe infection e.g. skin/soft tissue, endocarditis and osteomyelitis Coagulase negative staphylococci- Skin commensals of low pathogenic potential and can infect prosthetic material causing line, pacemaker infections and endocarditis

Question 32

What type of infection do group B strep tend to be associated with?

Answer 32

Neonatal infection because 1/3 of healthy women carry B strep in genital tracts and can be transferred to baby during delivery

Question 33

What are the two groups of spore forming bacteria?

Answer 33

Bacillus sp.- bacillus cereus and bacillus anthracis | Clostridia sp.- clostridium perfringens, clostridium tetani, clostridium botulinum and clostridium difficile

Question 34

What do endospores contain?

Answer 34

Bacterial DNA, cytoplasm, plasma membrane, peptidoglycan, little water, dipicolinic acid and keratin like coat

Question 35

When are endospores formed?

Answer 35

In response to adverse environmental conditions

Question 36

What are endospores resistant to?

Answer 36

Chemical inactivation

Question 37

What is the function of endospores?

Answer 37

Protective- Survive drying, heat, dehydration and radiation

Question 38

What is anthrax used as?

Answer 38

Chemical weapon

Question 39

How is anthrax treated?

Answer 39

Ciprofloxacin

Question 40

What is Hide Porter's disease?

Answer 40

Cutaneous anthrax carried in contaminated animal hides, an occupational disease Characterised by black eschars, oedema and swelling

Question 41

What does the periplasm of gram-negative bacteria contain?

Answer 41

Enzymes with hydrolytic function Enzymes that inactivate antibiotics Oligosaccharides

Question 42

What is haemophillus influenzae?

Answer 42

Gram negative cocco bacilli found in the nasal cavity that doesn't cause much of a problem as most people are vaccinated

Question 43

What does Gram negative outermembrane contain?

Answer 43

``` Phospholipids Lipopolysaccharide (LPS) ```

Question 44

What is important about lipopolysaccharide?

Answer 44

It is toxic to humans and can cause fever and shock (endotoxin shock)

Question 45

What does LPS consist of?

Answer 45

``` Lipid A (toxic component of endotoxin) Core polysaccharide O antigen (major surface antigen of Gram-negative cells) ```

Question 46

How are a lot of gram negative bacteria differentiated?

Answer 46

``` Using another test- oxidase Oxidase negative- Coliforms e.g. E.coli, Klebsiella spp, Enterobacter spp, Seratia spp. Proteus spp. Oxidase positive- Pseudomonas spp. ```