2.2 Strep and Staph

Question 1

Streptococcus and Staphylococcus are both gram (+) or (-)

Answer 1

Gram (+)

Question 2

How do we differentiate Streptococcus and Staphylococcus?

Answer 2

Catalase test

Streptococcus = Catalase (-)
Staphylococcus = Catalase (+)

Question 3

Describe the catalase test

Include the principals behind it and what the results would show

Answer 3

Catalase is an enzyme produced by organisms that live in oxygenated environments to neutralize the toxic oxygen metabolites H2O2 for protection.

Bacteria that are catalase (+) include strict aerobes and facultative anaerobes

Catalase (-) organisms lack the catalase enzyme and include anaerobes and facultative anaerobes

In the test Catalase (+) organisms will show gas bubbles representing the presence of catalase undergoing the following:
2H2O2 → 2H2O+ O2

Question 4

Compare how Staphylococcus grow vs Streptococcus

Answer 4

Staph = clusters
Strep = pairs or chains

Question 5

What is the most pathogenic species of bacteria

Answer 5

Coagulase (+) Staphylococcus. Aures; capsular polysaccharide, protein A and leukocidin

Question 6

List 4 virulence factors of Staphylococcus

Answer 6

1) capsule/slime layer: enables biofilm formation
2) adhesions: aid binding
3) Leukocidins: toxic product that allows invasion of WBCs (neutrophils)
4) Secreted factors

Question 7

How do we differentiate different species of Staphylococci?

Explain this test

Answer 7

Coagulase test:

1) extract bacteria from site of infection
2) plate on solid substance (agar) to allow growth
3) once colony formation is present, extract and add plasma
4) if Coagulase (+) then Fibrinogen → fibrin clot, if Coagulase (-) then there will be no clot formation

Question 8

What other enzyme is produced alongside coagulase (+) staphylococci?

How to these work together to aid virulence

Answer 8

Coagulase and Kinase are produced and allow bacteria to hide within the body

1) bacteria produce coagulase from within the cell
2) this causes recruitment of clotting factors
3) clot forms around bacteria protecting it
4) eventually when there is a lack of nutrition, bacteria dissolve the clot using kinases
5) bacteria can then enter blood stream and circulate body

Question 9

Is Staphylococcus harmful under normal circumstances?

If it becomes harmful list 3 conditions a Staph Infection can cause

Answer 9

Bacteria is found as part of normal microbiota in nasal cavity and skin but can become opportunistic and lead to:

Pneumonia, skin infections and endocarditis (due to biofilm formation on stents)

Question 10

Staph infection can cause osteomyelitis, what is this?

Answer 10

abscess formation on bone that can process to the bone shaft

Question 11

What is the most common site of Staphylococcus infections

List 3 routes of infection

Answer 11

Skin through:

1) Skin (pores, hair follicles)
2) Wounds (scratches, cuts, burns)
3) Insect and animal bites

Question 12

Name 4 ways the skin protects the body from pathogens entering

Answer 12

1) Keratinised
2) sebaceous glands produce antibacterial peptides
3) langerhan cells detect pathogens
4) Structure: multilayered, hardened and flattened

Question 13

Name 3 toxin mediated staphylococcal diseases

Answer 13

1) TSS
2) Staphylococcal scalded skin syndrome
3) Staphyloccocal food poisoning

Question 14

Name 3 similarities and 2 differences between Strep and Staph

Answer 14

Similarities:

             1) gram-positive,
             2) non-spore forming
             3) non-motile 
             4) cocci 

Differences:

              1) Staph is catalase-positive (strep isn't) 
             2) Staph grows in clusters while strep grows in              chains and pairs

Question 15

What determines the type of skin infection that can occur (staph)?

List 4 skin infections caused by staph

Answer 15

The depth of the infection in the skin layer

1) Folliculitis
2) Boil
3) Cellulitis
4) Cutaneous abscess

Question 16

What is folliculitis and what layer of the skin does it involve?

Answer 16

Common Staph infection: occurs in superficial hair follicles
causes recruitment of WBCs leading to red nodule formation

Question 17

What is a Boil and what layer of the skin does it involve?

What are multiple boils known as?

Answer 17

Infection to the epidermis of the skin

Multiple = carbuncle

Question 18

What is a cutaneous abscess?

What is found in the abscess?

Answer 18

a localized collection of pus in the skin and may occur on any skin surface.
Pus = dead leukocytes

Question 19

What is Cellulitis?
What commonly causes it?
Who is most at risk?
Where on the body does it most commonly occur in adults and children?

Answer 19

Bacterial infection of the skin and subcutaneous tissue

Commonly caused by strep or staph.

Most at-risk people include those with a weak immune system and those who handle fish/meat/poultry or soil without gloves.

In adults: legs, face and arms
Children: face, anus

Question 20

List 4 virulence factors of group A Streptococci

Answer 20

1) hyaluronic acid capsule inhibits phagocytosis
2) M protein and lipoteichoic acid for attachment
3) Extracellular products eg. pyrogenic toxin (causing the rash in scarlet fever), streptokinase, streptodornase, streptolysin

Question 21

What are the 3 (major) classes of strep and what differentiates them?

What is their subsequent classification

Answer 21

Differentiated based on their appearance in sheep agar plate:

1) alpha; surrounded by green -> incomplete hemolysis
2) beta; surrounded by clear -> complete hemolysis
3) gama; red -> non-hemolytic

Subsequent classification is the Lansfield characteristic: study of glycoproteins on the surface

Question 22

Name 3 most common acute diseases caused by Strep

Answer 22

1) Pharyngitis
2) Scarlet fever
3) Skin infections

Question 23

What is Necrotizing fasciitis? What bacteria causes this?

How is the prognosis and what does treatment involve?

Answer 23

Trauma inoculates bacteria in fascia of muscles, highly toxic infection. Leads to Rapid necrosis along fascial planes

Most commonly cause Streptococcus pyogenes releasing exotoxin B (can be caused by MRSA)

Since the bacteria rapidly spreads up the fascial planes (not muscles) prognosis is poor without early and aggressive treatment.

Treatment includes antibiotics, surgery and amputation

Question 24

Name 4 main upper resp tract defence mechanisms

Answer 24

1) mucociliary escalator
2) mechanical barriers: glottis and nasal turbinates
3) Reflexes: cough, sneeze
4) Maintenance of oropharyngeal flora (Saliva, local immunoglobulins, etc)

Question 25

What is sinusitis? What bacteria is the most common cause?

Answer 25

Bacteria initiates an immune response causing a buildup of fluid in the maxillary sinuses - causing pressure and pain accompanied by malaise

30% cause by Streptococcus pneumoniae

Question 26

What is Otitis Media?
Give 2 bacteria that can cause it?
What is the main sign/symptom?
How can Pharyngitis cause Otitis?

Answer 26

General term for infection or inflammation of the ear

Can be cause by Streptococcus pneuomoniae or Staphylococcus aureus

Causes severe pain in ear

Pharyngitis can cause otitis due to a connection between the ear and pharynx. Bacteria can move into the eustachian tube causing bulging of the tympanic membrane (and possible rupture)

Question 27

What is a classic Pharyngitis infection?
What pathogen commonly causes this?
How does the pathogen cause symptoms?
What can this commonly progress too?

Answer 27

A classic infection is strep throat caused by Streptococcus pyogenes

Contains M proteins which inhibits phagocytosis and produces pyrogenic toxins which cause the symptoms seen with pharyngitis

Strep throat can progress to scarlet fever

Question 28

What can Group A streptococci commonly cause in the mouth?

Answer 28

Group A streptococci can cause abscesses on the tonsils.

Question 29

List 3 systemic complications of a group A strep infection

Answer 29

Glomerulonephritis
Scarlet fever
Toxic shock syndrome

Question 30

What is characteristically seen in strep throat and why?

Answer 30

white substance in the back of the throat -> caused by toxins produced leading too neutrophils and dead tissues being eroded away by toxins (white colour)

Question 31

Why can a Group A strep infection cause Glomerulonephritis?

Answer 31

Inflammation of the kidneys

During infection the body produces a large amount of antibodies. As the kidneys filter blood, too many antibodies can cause blockage to the glomerulus leading to inflammation

Question 32

What is Scarlet fever?
Who does it commonly affect?
List the common signs and symptoms?
How do you treat it?

Answer 32

Highly contagious infection commonly caused by Group A streptococci

Usually seen in children under age of 18 years

Symptoms usually begin with appearance of a rash which progress to tiny bumps on the chest and abdomen which can spread over the entire body (appears redder in armpits and groin)

Symptoms can also include:
• Very sore throat with yellow or white papules
• Fever 
• Lymphadenopathy in neck
• Headache, body aches, and nausea

A variety of antibiotic therapies is required

Question 33

If a Group A strep infection enters the blood stream where does it commonly spread in the body and what can this lead too?

Specifically what can occur in the heart?

Answer 33

If it spreads to joints, heart, skin and nervous system it can lead to Rheumatic fever

If infection has spread to the heart -> even once cleared the body continues to illicit an immune response which attacks valves of the heart leading to Rheumatic heart disease