Lecture 1 Gram Positive Flashcards
Why do Gram Positive bacteria retain dye?
Thick peptidoglycan cell wall
Why do Gram Negative bacteria not retain dye?
Thinner peptidoglycan cell wall layer
What do Gram Positive Bacteria mainly comprise of?
Cocci, Bacilli or branching filaments
Where are Staphylococcus found?
All over the skin, part of human’s natural flora
How is Staphylococcus transmitted
Direct contact, fomites and medical instruments
Are Staphylococcus opportunistic?
Yes
Is Staphylococcus anaerobic or aerobic?
Anaerobic
Describe the appearance of Staphylococcus
Spherical cells, grape like
Why does Staphylococcus look like the way it is?
Due to cell division occurring successively on different planes, the daughter cells can remain attached
What two Staphs cause disease?
S.aureus and S.epidermidis
Which is more virulent, aureus or epidermidis?
Aureus
What are the 4 features of Staphylococcus?
Non-motile
Salt tolerant
Tolerant to desiccation, radiation and 60 degrees on environment surfaces.
Produces catalase
How does Protein A help S.aureus against the immune system?
Staph aureus is coated in Protein A. This binds to IgG stems and inhibits the complement cascade. By neutralising antibodies, this allows the bacteria to continue to persist and grow within the host body.
How does coagulase help S.aureus against the immune system?
Produces coagulase that converts the fibrinogen into fibrin. Can then use this fibrin to form blood clots where it can hide inside. The blood clot provides a source of protection and a source of nutrients as it can break down the clot to access it’s amino acids.
Which strain is opportunistic, aureus or epidermidis?
Both
Stats on Staph epidermidis
Relies heavily on slime
Opportunistic- attached to urinary catheters (made of plastic), intravascular catheters - form biofilms
What are the 4 enzymes that Staph Aureus can produce?
Hyaluronidase
Staphylokinase
Lipases
Beta lactamase
What does hyaluronidase do?
Breaks down the hyaluronic acid. This is important to human cells as this acid is responsible in maintaining the hydration of the skin
What does staphylokinase do?
Dissolves fibrin threads
What does lipase do?
Digests lipids, giving staph aureus the ability to grow on skin and in cutaneous oil glands (acne).
What does beta lactamase do?
Breaks down antibiotics and can stop them from working. This mutation can be passed to other staph aureus to increase antibiotic resistance
What are the 4 types of toxins produced by Staphylococcus?
Cytolytic toxins
Exfoliative toxins
TSS toxins
Enterotoxins
What do cytolytic toxins do?
Coded by genes, they disrupt the cytoplasmic membranes of cells including leukocytes
What do exfoliative toxins do?
Dissolve intercellular bridge proteins causing skin sloughing
What does the TSS toxin cause?
Toxic shock syndrome. Tampons are a common cause of this syndrome as they can both grow the staphylococcus and store the toxin
What do enterotoxins do?
Causes vomiting associated with Staphylococcal food poisoning
What status effects does Staph cause?
Systemic diseases
TSS: Fever, rash, low blood pressure and loss of skin
Bacteremia: Blood infection
Endocarditis
Pneumonia and empyema
Osteomyelitis
Name 7 other Gram Positive Bacteria
Streptococci
Bacillus
Clostridium
Listeria
Corynebacteria
Mycobacteria
Propionibacteria
