Clinically Important Gram-positive Bacteria 2

Name so basic features about genus streptococci

Gram positive cocci

May be chains or in pairs

Optimal growth on media supplemented with blood

Most are facultative anaerobes

Catalase negative

Why is the presence of catalase measured in a bacteria

To differentiate between staphylococci and streptococci

How is the presence of the catalase determined

By the ability of the bacteria to induce the reaction of reduction of hydrogen peroxide into water and oxygen. Results in the production of bubbles

List the different classification systems for streptococci

Haemolysis

Lancefield Classification

Molecular classification

In haemolysis classification, name and explain the list of categories

alpha haemolytic- Reduce Hb and cause a greenish discoloration of the blood agar

beta haemolytic- Lyse blood cells and cause complete clearing of blood agar in the vicinity of their growth

gamma haemolytic- no change in the blood agar

What is the Lancefield Classification

Serological system of grouping streptococci, based on specific antigens present in their cell walls

Basis of test- antibody/ antigen reaction

Positive if agglutination is detected

Name some Clinically Important Streptococci

Strep. pyogenes

Strep. agalactiae

Strep. pneumoniae

Enterococci

Name some of the diseases caused by Strep. pyogenes

Pharyngitis

Scarlet Fever

Pneumonia

How is Strep. pyogenes spread and what are some of the symptoms

Person- to person spread by droplets of saliva or nasal secretions

Symptoms: Redness, edema enlarged tonsils

What is Anti- Streptolysin O Titre

Serological teset ot confirm Group ! streptococcal infection or recent infection

The higher the antibody titre the more recent the infection

How does Scarlet Fever occur and what are the complications

Occurs when the group A streptococcal strain is lysogenised by a bacteriophage that stimulates production of pyrogenic toxin

Pharyngitis + rash

Complications: otis media, acute mastoiditis

What are some of the post- streptococcal auto-immune complications

Rheumatic Fever- Fever, joint pains

Glomeruonephritis- puffy face, swollen extremities

Name some of the Group A skin infections

Impetigo

cellulitis

Erysipelas

Necrotising fascilitis

Name and explain some of the alpha-haemolytic streptococci

Viridians Streptocci

Streptococcus pneumoniae

Name some of the diseases that Viridians Streptococci cause

Infective endocarditis

Brain and liver abscesses

What are some of the diseases that enterococci cause

Endocarditis

Bloodstream infection