Sreptococci - Prac. Microbiology

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Information about Sreptococci - Prac. Microbiology

Published on March 4, 2014

Author: cud2018



Gram-positive cocci in chains • Gram positive cocci arranged in chains

Planes of division

Catalase Test Catalase +ve Catalase –ve Staphylococci Streptococci

• Growth requires enriched media containing blood or serum.

Haemolysis on sheep blood agar can be used for distinguishing between streptococci

Group Antigens • Cell wall Carbohydrate antigens • Lancefield group antigens A – W (except I & J)

Streptococcus pyogenes Group A Streptococci Gram-positive cocci in chains Beta hemolytic

Virulence Factors

Pharyngitis • Sore Throat • Tonsillitis

Scarlet Fever

Skin & Soft Tissue Infections • Impetigo – Lesions on extremities – Commonly on face – Pustular and crusty

Skin & Soft Tissue Infections Cellulitis & Erysipelas

Invasive streptococcal infections • • • • Puerperal fever Acute endocarditis Necrotizing fasciitis Toxic shock syndrome

Necrotizing Fasciitis

Laboratory Diagnosis • Specimen: – Throat swab – Pus – CSF – Blood

• Direct detection – Gram-stained smear S. pyogenes – Detection of group A streptococcal antigen from throat swab.

• Culture: Blood Throat swab Pus CSF Culture on Blood culture bottle Culture on Blood Agar subculture

• Identification : A. Colony morphology

B. Gram-stained smear

C. Catalase test negative

D. Bacitracin sensitivity test

E. Agglutination by group A antibody .

Viridans streptococci

Diseases: - Subacute Bacterial Endocarditis (SBE) - Dental Caries

Laboratory diagnosis of SBE Blood culture technique

Streptococcus pneumoniae Gram positive capsulated diplococci. Alpha haemolytic .

Quellung test :

Pneumococcal diseases Three major diseases: • Pneumonia • Meningitis • Otitis media

Laboratory diagnosis A-Specimens: – Sputum – CSF – Ear discharge – Blood

B- Direct detection : 1- Gram-stained smear 2- Quellung test 3- Detection of capsular polysaccharide antigen in CSF by slide agglutination test

• Culture: Blood Throat swab Pus CSF Culture on Blood culture bottle Culture on Blood Agar subculture

Identification : 1-Colony morphology 2-Gram-stained smear 3-Differentiation from viridans streptococci

A. Growth inhibition by optochin

B. Solubility of colonies in bile

C. Capsular polysaccharide antigen detection

D. Quellung reaction

E. DNA probe specific to S. pneumoniae

F. Virulence to mice

Populations at risk of being infected with S. pneumoniae • Asplenic individuals • infants • Immunosuppressed individuals • Alcoholics

So, how to protect them? • A vaccine is available. – Capsular polysaccharide vaccine – Antigens from 23 serotypes. • Under age of TWO years: – Pneumococcal conjugate vaccine – Capsular polysaccharide + protein carrier

Enterococcus • • Gram +ve cocci singly / in pairs /short chains

Enterococcus • • • Catalase negative Hydrolyze esculin in presence of bile salts Lancefield group D

Enterococcus Infections • • • • • UTI Intra-abdominal & pelvic wound infections Bacteraemia Endocarditis Abscesses, meningitis, peritonitis, osteomyelitis & wound infection

Case 1 A 10-year-old girl presents to her primary care physician with : o severe sore throat, o fever, o headache, nausea, and abdominal pain.

Case (cont.) Examination shows: The back of her throat is covered with a purulent exudate with white pus-filled nodules. How can you reach a diagnosis?

A. Specimen Specimen Throat swabs

Direct detection: - Gram-stained smear Gram-positive cocci arranged in chains amongst pus cells

B. Direct detection - Detection of group A streptococcal antigen from throat swab.

Culture: On blood agar: β- hemolysis

Identification from colonies: 1.Gram-stained smear Gram positive cocci in chains 2. Catalase test catalase negative

3.Bacitracin sensitivity test Bacitracin sensitive Group A (S. pyogenes)

What treatment would you offer her? • Penicillin, or erythromycin if allergic to penicillin.

This patient may present afterwards with one of Post - Streptococcal sequelae. What are they? And what is the underlying mechanism? 1. 2. Rheumatic Fever Post-Streptococcal glomerulonephritis

Rheumatic Fever Immune response against Strept. antigens similar to heart antigens.

Post-streptococcal glomerulonephritis Deposition of Ag-Ab complexes, activation of complement.

Diagnosis of ARF No single test is pathognomonic . Diagnosis is based on modified Jones criteria: a) Evidence of recent S .pyogenes infection b) Two of the five major criteria ,or one major and two minor criteria .

The evidence of recent streptococcal infection a-History of acute tonsillitis . b-Elevation of ASO titre above 200 units . N.B. In case of AGN: Anti-DNAse

Review Questions

1. The simplest test to differentiate staphylococci from streptococci is the: a) Coagulase test b) Bacitracin test c) Gram stain d) Catalase test e) Optochin test

2. Group A streptococcus growing on a blood agar plate, shows which of the following: a) Alpha hemolysis, a clear zone surrounding the colonies b) Alpha hemolysis, a green zone surrounding the colonies c) Beta-hemolysis, a clear zone surrounding the colonies d) Beta-hemolysis, a green zone surrounding the colonies e) No haemolysis

3.Susceptibility to bacitracin is used to differentiate: a) Streptococcus pneumoniae from Staphylococcus aureus. b) Streptococcus pyogenes from Streptococcus pneumoniae. c) Streptococcus pneumoniae from viridans streptococci. d) Streptococcus pyogenes from non group A beta haemolytic streptococci. e) Streptococcus pyogenes from Staphylococc aureus

4. Streptococcus pyogenes can not be isolated in case of: a) Pharyngitis. b) Puerperal fever. c) Acute endocarditis. d) Rheumatic fever. e) Necrotizing fasciitis.

5. The inhibition of growth of alpha-hemolytic colonies by optochin indicates: a) Streptococcus pyogenes b) Viridans streptococci c) Streptococcus pneumoniae d) Staphylococcus aureus e) Enterococci

6. Blood culture is required for the diagnosis of: a) Subacute bacterial endocarditis b) Pharyngitis c) Glomerulonephritis d) Rheumatic fever e) Scarlet fever


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