Microbiology: Strep vs Staph Flashcards

Study Notes

General Characteristics of Strep and Staph

Both Strep (Streptococcus) and Staph (Staphylococcus) are classified as gram positive bacteria.

Distinguishing Strep from Staph

On gram stain, Streptococci align in chains or pairs resembling a strip of candy, while Staphylococci form clusters, akin to a group photo of hospital staff.
Streptococci divide in one plane, leading to their characteristic chain formation.

Catalase Production

Streptococci do not produce catalase, contrasting with Staphylococci which do.
Catalase converts hydrogen peroxide into water and oxygen, helping protect Staphylococci from oxidative damage.

Hemolytic Properties of Streptococci

Streptococci can be categorized based on hemolytic ability:
- Beta-hemolytic: Completely lyses red blood cells, creating a clear halo (e.g., S. pyogenes).
- Alpha-hemolytic: Partially lyses red blood cells, resulting in a greenish hue (e.g., S. pneumoniae).
- Gamma-hemolytic: No lysis of red blood cells; not typically referred to as hemolytic (e.g., E. faecalis).

Lancefield Antigens

Classification of Streptococci includes Lancefield antigens, which are identifiable C carbohydrates on cell walls, labeled A-S.
Primarily used for beta-hemolytic strains; however, reliance on this system has decreased due to the diversity of Streptococcus species.
Notable human pathogenic groups include:
- Group A, B, and D (have Lancefield antigens)
- Streptococcus pneumoniae and Viridans group Strep (lack Lancefield antigens).

Group Identifications

Group A Lancefield Strep: Streptococcus pyogenes
Group B Lancefield Strep: Streptococcus agalactiae
Group C/G Lancefield Strep: S. milleri and S. dysgalactiae; associated with strep throat.
Group D Lancefield Strep: Includes Enterococci like E. faecalis and E. faecium, as well as Non-enterococci like S. bovis, which can cause endocarditis linked to gastrointestinal issues.
Viridans Group Strep: Comprises various species like S. salivarius, S. mitis, S. sanguis, and S. mutans, known for potential alpha hemolytic or non-hemolytic properties and associations with endocarditis.

Disease Associations

Streptococcus pneumoniae: Recognized cause of bacterial pneumonia.
Group A Beta-hemolytic Strep: Also known as Strep Pyogenes, known to cause:
- Strep throat
- Scarlet fever
- Rheumatic fever
- Post-streptococcal glomerulonephritis.

Antigenic Components of Group A Strep

C-Carbohydrate: Specific to S. pyogenes, used in Lancefield classification.
M Protein: Major virulence factor inhibiting complement activation and phagocytosis. However, serves as a target for antibodies aiding in bacterial clearance.

Enzymatic Contributions to Pathogenicity

Streptolysin O: Oxygen-labile enzyme causing destruction of red and white blood cells, contributing to beta-hemolytic activity.
Following an infection, the body produces anti-streptolysin O (ASO) antibodies, which can be detected in ASO titer blood tests.

Description

Test your knowledge about Streptococcus and Staphylococcus with these flashcards. Learn the key differences in their gram stain appearance and characteristics. Perfect for microbiology students or anyone interested in bacteria classification.