Download - Sreptococci - Prac. Microbiology
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Streptococci
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Gram-positive cocci in chains
• Gram positive cocci arranged in chains
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Planes of division
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Catalase –veStreptococci
Catalase +veStaphylococci
Catalase Test
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• Growth requires enriched media containing blood or serum.
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Haemolysis on sheep blood agar can be used for
distinguishing between streptococci
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Group Antigens
• Cell wall Carbohydrate antigens
• Lancefield group antigens A – W (except I & J)
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Streptococcus pyogenes
Gram-positive cocci in chains
Beta hemolytic
Group A Streptococci
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Virulence Factors
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Pharyngitis
• Sore Throat
• Tonsillitis
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Scarlet Fever
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Skin & Soft Tissue Infections
• Impetigo– Lesions on
extremities– Commonly on face– Pustular and crusty
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Skin & Soft Tissue InfectionsCellulitis & Erysipelas
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Invasive streptococcal infections
• Puerperal fever• Acute endocarditis• Necrotizing fasciitis• Toxic shock syndrome
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Necrotizing Fasciitis
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Laboratory Diagnosis
• Specimen:– Throat swab– Pus– CSF– Blood
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• Direct detection
– Gram-stained smear
– Detection of group A streptococcal antigen from throat swab.
S. pyogenes
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• Culture:
Blood Agar
Throat swab
Pus
CSF
Culture on
Blood
Blood culture bottle
Culture on
subculture
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• Identification :A. Colony morphology
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B. Gram-stained smear
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C. Catalase test negative
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D. Bacitracin sensitivity test
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E. Agglutination by group A antibody .
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Viridans streptococci
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Diseases:
- Subacute BacterialEndocarditis (SBE)
- Dental Caries
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Laboratory diagnosis of SBE
Blood culture technique
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Streptococcus pneumoniae
Gram positivecapsulated diplococci.
Alpha haemolytic .
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Quellung test :
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Pneumococcal diseases
Three major diseases:
• Pneumonia
• Meningitis
• Otitis media
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Laboratory diagnosis
A-Specimens:– Sputum – CSF – Ear discharge – Blood
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B- Direct detection :
1- Gram-stained smear 2- Quellung test 3- Detection of capsular polysaccharide antigen
in CSF by slide agglutination test
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• Culture:
Blood Agar
Throat swab
Pus
CSF
Culture on
Blood
Blood culture bottle
Culture on
subculture
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Identification :
1-Colony morphology
2-Gram-stained smear
3-Differentiation from viridans streptococci
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A. Growth inhibition by optochin
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B. Solubility of colonies in bile
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C. Capsular polysaccharide antigen detection
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D. Quellung reaction
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E. DNA probe specific to S. pneumoniae
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F. Virulence to mice
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Populations at risk of being infected with S. pneumoniae
• Asplenic individuals
• infants
• Immunosuppressed individuals
• Alcoholics
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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
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Enterococcus• Gram +ve cocci • singly / in pairs /short chains
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Enterococcus
• Catalase negative• Hydrolyze esculin in presence of bile salts• Lancefield group D
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Enterococcus Infections
• UTI• Intra-abdominal & pelvic wound infections• Bacteraemia• Endocarditis• Abscesses, meningitis, peritonitis, osteomyelitis &
wound infection
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Case 1
A 10-year-old girl presents to herprimary care physician with :
o severe sore throat, o fever, o headache, nausea, and abdominal
pain.
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Examination shows:The back of her throat is covered with a purulent exudate with white pus-filled nodules.
How can you reach a diagnosis?
Case (cont.)
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A. Specimen
Throat swabs
Specimen
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Direct detection:
- Gram-stained smear
Gram-positive cocci arranged in chains
amongst pus cells
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B. Direct detection- Detection of group A streptococcal
antigen from throat swab.
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Culture:
On blood agar: β- hemolysis
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catalase negative Gram positive cocci
in chains
1.Gram-stained smear 2. Catalase test
Identification from colonies:
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3.Bacitracin sensitivity test
Bacitracin sensitive
Group A (S. pyogenes)
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What treatment would you offer her?
• Penicillin, or erythromycin if allergic to penicillin.
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This patient may present afterwards with one of Post - Streptococcal sequelae.
What are they? And what is the underlying mechanism?
1. Rheumatic Fever2. Post-Streptococcal glomerulonephritis
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Rheumatic Fever
Immune response against Strept. antigens similar to heart antigens.
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Post-streptococcal glomerulonephritis
Deposition of Ag-Ab complexes, activation of complement.
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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 .
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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
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Review Questions
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1. The simplest test to differentiate staphylococci from streptococci is the:
a) Coagulase testb) Bacitracin testc) Gram staind) Catalase teste) Optochin test
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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
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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
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4. Streptococcus pyogenes can not be isolated in case of:
a) Pharyngitis.b) Puerperal fever.c) Acute endocarditis.d) Rheumatic fever.e) Necrotizing fasciitis.
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5. The inhibition of growth of alpha-hemolytic colonies by optochin indicates:
a) Streptococcus pyogenesb) Viridans streptococcic) Streptococcus pneumoniaed) Staphylococcus aureuse) Enterococci
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6. Blood culture is required for the diagnosis of:
a) Subacute bacterial endocarditisb) Pharyngitisc) Glomerulonephritisd) Rheumatic fevere) Scarlet fever
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