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BII > Thomas Proft > Flashcards

Thomas Proft Flashcards

1
Q

What are some skin infections that can be caused by streptococcus pyogenes?

A

Cellulitis
Erysepelas
Impetigo

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2
Q

What is the immune response to bacterial infection of the skin?

A

Bacteria enters wound cause tissue damage (toxins and enzymes) -> platelets release blood clotting factors to contain the bacteria and prevent it from getting deeper -> Sentinel neutrophils and macrophages phagocytose bacteria -> macrophages release IL-8 and IL-6 that recruit leukocytes and induce chemotaxis -> Activate tissue repair

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3
Q

How are bacteria recognised by the innate immune cells?

A

PAMP are recognised by pattern recognition receptors, such as TLRs (TLR-4 and LPS). LPS is conserved on gram -ve bacteria.

This stimulation induces the activation of the innate cells and they secrete IL-1b, TNF-alpha and IL-8

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4
Q

How do leukocytes migrate through the endothelial cell wall?

A

E-selectin is upregulated on the endothelial cells

Selectin mediated adhesion to the leukocyte (E-selectin). This causes the leukocytes toroll and slow down. Then the integrins bind to integrins (LFA-1 to ICAM-1). Then they squeeze between the endothelial cells to enter the tissues. Then chemotaxis. (!L-8 and C5a)

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5
Q

What does C3b do?

A

Opsonisation

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6
Q

What does C5a do?

A

Chemotaxis

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7
Q

What are the defining features of streptococcus pyogenes?

A

Gram positive cocci.

Group A strep - agglutination by antibody

Catalase negative (no gas production when mixed with H2O2, some bacteria convert H2O2 into water and O2)

Beta haemolytic - can lyse blood cells

Bacitracin susceptibility

Transmission by human contact - touching, coughing

High infection rates in overcrowded houses.

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8
Q

What are the virulence factors of streptococcus pyogenes?

A

MSCRAMMS - microbial surface components recognizing adhesive matrix molecules. These bind to extracellular matrix proteins of host cells, such as collagen, fibronectin binding proteins

Hyaluronic acid capsule (prevents opsonisation and phagocytosis.

M protein - binds factor H, which prevents opsonisation with C3b

Secretion of toxins: streptolysins (lyse immune cells), C5a peptidase (destroys C5a), DNAses (degrades NETS).
SpyCEP - destroys IL-8

Proteases
Lipases
Hyaluronidase
Streptokinase - converts plasminogen to plasmin (anticoagulation)

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9
Q

What are the factors that allow streptococcus pyogenes to spread deeper into tissues?

A

Proteases
Lipases
Hyaluronidase
Streptokinase - converts plasminogen to plasmin (anticoagulation)

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10
Q

What does the catalase test check?

A

To see if the bacteria can convert H2O2 into water and O2.

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11
Q

What bacteria are alpha haemolytic bacteria?

A

Viridins bacteria.

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12
Q

What is the treatment for cellulitis?

A

If caused by S pyogenes then penicillin or a derrivative such as amoxycillin.

If S. Aureus then flucloxacillin (except for MRSA)

Give pain killer, rest elevation

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13
Q

How does penacillin work?

A

It binds to transpeptidase that links the peptidoglycans in the bacteria cell wall. Causes weak cell walls -> lysed.

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14
Q

What are two types of beta-lactam antibiotics?

A

Penicillins and cephalosporins

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15
Q

What are the different penicillins?

A

Benzylpenicillin is an IM injection

Amoxycillin is an oral form

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16
Q

How does osteomyelitis develop?

A

Bacteria get into the bone. This can occur from scratching (chickenpox) of the skin leading to infection that then gets into the bone.

Could also get to the bone from trauma (joint replacement, root canal), from Haematogenous route (bacteremia)

Once in the bone leukocytes can attak the bacteria causing inflammation. Bacteria may invade the bone cells to evade the immune system and drugs causing a chronic infection.

The bacteria can spread to the joint (septic arthritis)

17
Q

Who are at risk of osteomyelitis?

A 
Diabetics with foot ulcers
Patients following trauma, bone surgery
Intravenous drug users
Root canal treatment
Patients with skin and soft tissue infections.
18
Q

What bacteria is the most common cause of osteomyelitis?

A

S Aureus. (80% of cases in those >4 yo)

S Pyogenes

19
Q

What bones are infected in osteomyelitis?

A

Adults: Vertebral and hip replacement, foot, long bone,

Children: long bones mainly - tibia and femur

20
Q

How can you diagnose osteomyelitis?

A

Symptoms of pain/weakness of specific bones, redness, fever.
Blood sample with high WBCs

Need an MRI to confirm the diagnosis

21
Q

How does gram staining work?

A

Fix the slides -> cyrstal violet -> iodine (crystilises the dye trapping it in peptidoglycan) -> decolourisation -> counter stain with safranin.

Crystal violet gets trapped in the peptidoglycan in the gram positive bacteria

22
Q

How do you identify stapylococcus aureus?

A 
Gram positive
Catalase positive (h2O2 -> H20 and O2)

Coagulase positive - converts fibrinogen in plasma into fibrin - coagulation

23
Q

What is a coagulase negative bacteria?

A

Staphylococcus epidermitis

24
Q

What are the virulence factors for S Aureus?

A

Adhesion molecules - MSCRAMS (microbial surface components recognizing adhesion matrix molecules. Binds to cells extra cellular matrix - collagen, fibronectin, laminin.

Spreading factors - staphylokinase causes fibrinolysis
Lipases - hydrolises lipids
DNAses - NET degredation
Cytolisins - destroys epithelial cells

Avoids immune cells:
Cytolysins to degrade WBCs

Capsule - prevents opsonisation and phagocytosis

Biofilm formation

Protein A: binds to the Fc region of antibodies

Cell bound coagulase (clumping factor) - fibrin deposition prevents phagocytosis and opsonisation

25
Q

What are super antigens?

A

Produced by S aureus and S pyogenes

Proteins that induce a stong T cell imune response - IL-1b, TNF-alpha, IFN-y.

Causes systemic inflammation with tissue destruction, vascular leakage, toxic shock

26
Q

What is used to treat MSRA?

A

Vanocomycin

27
Q

How do you treat osteomyelitis?

A

Prolonged antibiotic treatment (weeks to months).

Determine the organism

28
Q

How do some bacteria resist against penicillins?

A

They have beta lactamases enzymes (plasmid encoded enzyme) that degrades the beta lactam ring of penicillin.

There are now beta lactam resistant penicillins

29
Q

What group of bacteria can penicillin target?

A

Gram positive bacteria.

Extended spectrum penicillins have been developed that can target gram negatives too, amoxycillin

30
Q

What are some beta lactam resistant penicillins?

A

Methicillin (prototype), flucloxacillin

Augmentin = amoxycillin + clavulanic acid

31
Q

How does MRSA occur?

A

They have acquired a new transpeptidase enzyme. No binding for any penicillins.

32
Q

What resistance to penicillin does normal S aureus have?

A

Beta lactamase that degrades penicillins beta lactam ring.

33
Q

What are some other disease caused by S aureus?

A 
Impetigo
Folliculitis
Furuncle
Carbuncle
Cellulitis
Necrotizing fascitis
Septic arthritis
Acute infectious endocarditis
Bacterial pneumonia
Toxic shock - menstrual toxic shock from tampons

BII (14 decks)

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