sreptococci - prac. microbiology
TRANSCRIPT
Streptococci
Gram-positive cocci in chains
• Gram positive cocci arranged in chains
Planes of division
Catalase –veStreptococci
Catalase +veStaphylococci
Catalase Test
• 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
Gram-positive cocci in chains
Beta hemolytic
Group A Streptococci
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 InfectionsCellulitis & 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
– Detection of group A streptococcal antigen from throat swab.
S. pyogenes
• Culture:
Blood Agar
Throat swab
Pus
CSF
Culture on
Blood
Blood culture bottle
Culture on
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 BacterialEndocarditis (SBE)
- Dental Caries
Laboratory diagnosis of SBE
Blood culture technique
Streptococcus pneumoniae
Gram positivecapsulated 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 Agar
Throat swab
Pus
CSF
Culture on
Blood
Blood culture bottle
Culture on
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 herprimary care physician with :
o severe sore throat, o fever, o headache, nausea, and abdominal
pain.
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.)
A. Specimen
Throat swabs
Specimen
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
catalase negative Gram positive cocci
in chains
1.Gram-stained smear 2. Catalase test
Identification from colonies:
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. Rheumatic Fever2. 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 testb) Bacitracin testc) Gram staind) Catalase teste) 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 pyogenesb) Viridans streptococcic) Streptococcus pneumoniaed) Staphylococcus aureuse) Enterococci
6. Blood culture is required for the diagnosis of:
a) Subacute bacterial endocarditisb) Pharyngitisc) Glomerulonephritisd) Rheumatic fevere) Scarlet fever
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