1.5 Streptococcus Pyogenes

Question 1

What is the Normal Flora?

Answer 1

The population of microorganisms routinely found growing on the body of a healthy individual

Question 2

What are the two types of natural flora?

Answer 2

Resident (inhabit for extended periods of time)

Transient (inhabit for shorter periods of time)

Question 3

What are Endogenous Pathogens?

Answer 3

Part of the resident or transient normal flora that under certain conditions may become pathogenic. Related to organism and host factors.

Question 4

What are Exogenous Pathogens?

Answer 4

Never part of the normal or commensal flora. When present, are always pathogenic.

Question 5

Why is knowing the normal flora important?

Answer 5

In interpreting the significance of microbiological culture results.

Question 6

What are some of the Normal Flora of the NOSE?

Answer 6

Staphylococcus Aureus
Staphylococcus Epidermidis
Diptheroids
Streptococci

Question 7

What are some of the Normal Flora of the Teeth?

Answer 7

Streptococcus mutans
Bacteroides
Fusobacterium
Streptococci
Actinomyces

Question 8

What are some of the Normal Flora of the Mouth?

Answer 8

Streptococci mitis
Other streptococci
Trichomonas tenax
Candida sp.

Question 9

What are some of the Normal Flora of the Throat?

Answer 9

Streptococcus viridans
Streptococcus pyogenes
Streptococcus pneumoniae
Neisseria spp.
Staphylococcus epidermidis
Haemophilus influenzae

Question 10

Define: Species

Answer 10

A collection of strains that share many stable properties and differ from other groups of strains.

Question 11

What three properties are used to identify bacteria at the species level?

Answer 11

Morphology - gram stain & colony appearance
Physiology - environmental conditions under which it grows
Metabolic Activity - substances used and by-products produced

Question 12

What is an anaerobe?

Answer 12

A bacteria that requires oxygen for survival

Question 13

What is an anaerobe?

Answer 13

A bacteria that can grow in the absence of oxygen

Question 14

What is a facultative anaerobe?

Answer 14

A organism that can grow in the presence or absence of oxygen. Most medically relevant organisms are facultative anaerobes.

Question 15

What class of organisms grow at human body temperatures?

Answer 15

Mesophiles

Question 16

Describe beta haemolysis and give examples.

Answer 16

Complete lysis of RBCs by steptolysin.

Streptococcus pyogenes, strep. agalactiae. Group C & G strep.

Question 17

Descrive alpha haemolysis and give examples.

Answer 17

Hydrogen peroxide is produced by the bacterium oxidising haemoglobin to the green methaemoglobin.
Streptococcus viridans group, strep. pneumoniae.

Question 18

Describe gamma haemolysis and provide examples.

Answer 18

No haemolysis.

Some enterococcus species, streptococcus bovid. Some streptococcus viridans group.

Question 19

Where in the body are streptococcal species usually found?

Answer 19

Nose
Teeth
Mouth
Throat
Urethra and Vagina
Skin

Question 20

What are the five types of virulence factors?

Answer 20

Adhesin
Invasin
Impedin
Aggressin
Modulin

Question 21

What is an Adhesin?

Answer 21

Coordinates the binding of the organisms to a host tissue

Question 22

What is an Invasin?

Answer 22

Enables the organism to invade a host cell

Question 23

What is an Impedin?

Answer 23

Allows the organism to avoid one or more of the hosts immune responses

Question 24

What is an Aggressin?

Answer 24

Causes direct damage to the host

Question 25

What is a Modulin?

Answer 25

Induces damage in the host indirectly. E.g. molecules produced by the bacteria that promote cytokine release and subsequent damage

Question 26

What are some examples of S. pyogenes Adhesins?

Answer 26

M Protein

Lipoteichoic Acid

Question 27

What are some examples of S. pyogenes Impedins?

Answer 27

M Protein (prevents complement activation)
Hyaluronic Acid (similar to that in human connective tissue)
C5a peptidase
Mac (prevents complement activation)
Capsule

Question 28

What are some examples of S. pyogenes Aggressins?

Answer 28

Hyraluronidase - cleaves human hyaluronan in epithelial and connective tissue
Streptokinase - contributes to lysis of clots –> facilitates dissemination
DNAses - Degrade DNA in pus –> reduces viscosity –> dissemination
Streptolysins O & S - Cytotoxic to a number of cells, including RBCs, and are involved in beta haemolysis
SpeB - cysteine protease that destroys a number of human proteins

Question 29

How is the serotype of S. pyogenes determined?

Answer 29

The amino acid sequence of the hyper variable region in the N-terminal domain of the M-Protein.

Question 30

What are the steps in Phagocytosis?

Answer 30

Binding of pathogen to the phagocyte
Pathogen is internalised in the phagosome
Phagosome fused with lysosome, which contain antimicrobial factors
Microbial death

Question 31

Describe the Direct and Indirect methods of pathogen binding in phagocytosis

Answer 31

Indirect: Antibody mediated. Complement mediated following activation (phagocyte receptors bind to activated complement bound to the bacteria.)
Direct: Macrohpage cell surface receptors or pattern recognition receptors (PRRs) bind to bacterial targets or pathogen associated molecular patters (PAMPs - masked by presence of capsule) and internalise the bacteria.

Question 32

What are some examples of bacterial PAMPs?

Answer 32

Lipoteichoic Acid

Peptidoglycan

Question 33

What are some infections associated with S. pyogenes?

Answer 33

Localised or Systemic: Pharyngitis, Skin infections (Impetigo), Disseminated Infections (Bacteraemia, Post Partum Sepsis)
Toxin Mediated: Scarlet Fever, Toxic Shock Syndrome
Immune Mediated Diseases: Rheumatic Fever, Acute Glomerulonephritis

Question 34

What are some of the basic features of S. pyogenes?

Answer 34

Gram +
Cocci
Chains
Can be Capsulated
Group A Strep.
Mesophiles
Commensal
Facultative Anaerobe
Grow at slightly acidic pH
Extracellular pathogen