1.5 Streptococcus Pyogenes Flashcards
What is the Normal Flora?
The population of microorganisms routinely found growing on the body of a healthy individual
What are the two types of natural flora?
Resident (inhabit for extended periods of time)
Transient (inhabit for shorter periods of time)
What are Endogenous Pathogens?
Part of the resident or transient normal flora that under certain conditions may become pathogenic. Related to organism and host factors.
What are Exogenous Pathogens?
Never part of the normal or commensal flora. When present, are always pathogenic.
Why is knowing the normal flora important?
In interpreting the significance of microbiological culture results.
What are some of the Normal Flora of the NOSE?
Staphylococcus Aureus
Staphylococcus Epidermidis
Diptheroids
Streptococci
What are some of the Normal Flora of the Teeth?
Streptococcus mutans Bacteroides Fusobacterium Streptococci Actinomyces
What are some of the Normal Flora of the Mouth?
Streptococci mitis
Other streptococci
Trichomonas tenax
Candida sp.
What are some of the Normal Flora of the Throat?
Streptococcus viridans Streptococcus pyogenes Streptococcus pneumoniae Neisseria spp. Staphylococcus epidermidis Haemophilus influenzae
Define: Species
A collection of strains that share many stable properties and differ from other groups of strains.
What three properties are used to identify bacteria at the species level?
Morphology - gram stain & colony appearance
Physiology - environmental conditions under which it grows
Metabolic Activity - substances used and by-products produced
What is an anaerobe?
A bacteria that requires oxygen for survival
What is an anaerobe?
A bacteria that can grow in the absence of oxygen
What is a facultative anaerobe?
A organism that can grow in the presence or absence of oxygen. Most medically relevant organisms are facultative anaerobes.
What class of organisms grow at human body temperatures?
Mesophiles
Describe beta haemolysis and give examples.
Complete lysis of RBCs by steptolysin.
Streptococcus pyogenes, strep. agalactiae. Group C & G strep.
Descrive alpha haemolysis and give examples.
Hydrogen peroxide is produced by the bacterium oxidising haemoglobin to the green methaemoglobin.
Streptococcus viridans group, strep. pneumoniae.
Describe gamma haemolysis and provide examples.
No haemolysis.
Some enterococcus species, streptococcus bovid. Some streptococcus viridans group.
Where in the body are streptococcal species usually found?
Nose Teeth Mouth Throat Urethra and Vagina Skin
What are the five types of virulence factors?
Adhesin Invasin Impedin Aggressin Modulin
What is an Adhesin?
Coordinates the binding of the organisms to a host tissue
What is an Invasin?
Enables the organism to invade a host cell
What is an Impedin?
Allows the organism to avoid one or more of the hosts immune responses
What is an Aggressin?
Causes direct damage to the host
What is a Modulin?
Induces damage in the host indirectly. E.g. molecules produced by the bacteria that promote cytokine release and subsequent damage
What are some examples of S. pyogenes Adhesins?
M Protein
Lipoteichoic Acid
What are some examples of S. pyogenes Impedins?
M Protein (prevents complement activation)
Hyaluronic Acid (similar to that in human connective tissue)
C5a peptidase
Mac (prevents complement activation)
Capsule
What are some examples of S. pyogenes Aggressins?
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
How is the serotype of S. pyogenes determined?
The amino acid sequence of the hyper variable region in the N-terminal domain of the M-Protein.
What are the steps in Phagocytosis?
Binding of pathogen to the phagocyte
Pathogen is internalised in the phagosome
Phagosome fused with lysosome, which contain antimicrobial factors
Microbial death
Describe the Direct and Indirect methods of pathogen binding in phagocytosis
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.
What are some examples of bacterial PAMPs?
Lipoteichoic Acid
Peptidoglycan
What are some infections associated with S. pyogenes?
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
What are some of the basic features of S. pyogenes?
Gram + Cocci Chains Can be Capsulated Group A Strep. Mesophiles Commensal Facultative Anaerobe Grow at slightly acidic pH Extracellular pathogen
