Skin Infections

Question 1

6. The student will be able to describe the diseases caused by Staphylococcus aureus

Answer 1

Impetigo: localized superficial, spreading, honey crusted skin lesion generally on face of children
Cellulitis: infection of skin involves subcutaneous tissue. Appears red, hot, shiny, swollen
Local abscesses (collection of puss), folliculitis, furuncle (boil), carbuncle(clusters of furuncles)

Question 2

8. The student will be able to explain the clinical significance of Staphylococcus epidermidis and Staphylococcus saprophyticus

Answer 2

Staphylococcus epidermidis: common cause of catheter / prosthetic device infections. Produces slime layer
Staphylococcus saprophyticus: part of normal vaginal microbiota, important cause of UTI

Question 3

10. The student will be able to explain the niches, common modes of infection, general features, classification (Hemolytic properties and Lancefield groups), virulence factors and diseases of Streptococcus species.

Explain virulence factors/diseases in the next card

Answer 3

Niche: skin, mucous membrane, nasal oral cavity, throat
Common modes of infection: sneezing coughing direct contact with carriers
General features: Gram positive cocci (ovoid /spherical), tend to occur chains, non-motile, catalase negative, virulent strains encapsulated.
Fastidious (demanding in nutritional requirement)
Colonies are round, translucent, grayish, smooth
Oxygen requirement, most are aerotolerant anaerobes.
Classification:
Based on Hemolytic properties (ability to lyse RBCs): alpha, beta, gamma hemolysis
Beta: completely lyse RBCs
Alpha: partially lyse
Gamma: cannot lyse
Based on serological Lancefield groups: Primarily beta hemolytic Strep.

Question 4

Virulence factors of streptococcus species

Answer 4

Virulence factors:
SPE-A, SPE-C : Responsible for scarlet fever
M protein: Needed for infection to occur, Antiphagocytic, Anti-complement binds. Determines type-specific immunity. Antibody for M protein protects that organism.
Capsule: antiphagocytic
Streptodornase: Depolymerize DNA in pus
Hyaluronidase: Breaks down hyaluronic acid in connective tissue making the tissue more permeability
Lipoteichoic acid: Facilitates adherence to epithelial cells

Question 5

Diseases of Streptococcus species

What is group A and what infections do they cause?

Answer 5

Group A: S. Pyogenes

Most common type is Pharyngitis
Cellulitis, impetigo, necrotizing fasciitis (flesh eating disease, surgery asap), erysipelas (lymph node enlargement, painful), scarlet fever (strawberry tongue, red skin rash), rheumatic fever, glomerulonephritis

Question 6

What is group B and what is it responsible for?

Answer 6

Group B is S. agalactiae
Present in vagina of females
Important cause of bovine mastitis (breast inflammation), neonatal bacteremia, pneumonia, meningitis

Question 7

What is acute glomerulonephritis

Answer 7

This disease follows pharyngitis/impetigo about a week after the infection. The antigen-antibody complex enter the glomerular activating the complement, leading to glomerular destruction

Question 8

What is Rheumatic Fever?

Answer 8

This also follows pharyngitis
The streptococcal cell wall stimulated antibody response and some of those antibodies cross-react with heart tissue causing rheumatic fever. causes myocarditis (heart inflammation)

Question 9

11. The student will be able to explain the role of Streptococcus Viridans in dental caries and subacute bacterial endocarditis

Answer 9

S. mutans (dental caries), S. mitis, S. salivarius, S. sanguinis make up this.
Usually triggered by oral surgery / trauma
Normal oro-phayngeal flora
Common cause of SBE