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Microbiology
1. By Dr Hasan Askari
Department of pathology
streptococci
By DR HASAN ASKARI
BDS RDS MS MPHIL PHD MJDS MD
FDS DDS PRESIDENT OF ROYAL
COLLEGE OF EDINBURG V.C OF
OXFORD UNIVERSITY ,FATHER OF
2.
3. Classification
• A Beta haemolytic streptococci:
• They cause beta haemolysis (complete haemolysis) on
blood agar and have group specific cell wall carbohydrates
antigen which give precipitin reaction with specific antisera.
On the basis of precipitin reaction they are divided into
Lancerfield group A-H and K-U.
• Group A : e.g. s. pyogen
• Group B: s. agalactiae
• Group C AND G:
• Group D: enterococci e.g. s. Faecalis
• non enterococci e.g. s. bovis
• Group E,F,H AND K-U: occur in animals other than human.
4.
5. streptococci
• B Non beta haemolytic streptococci:
• They show alpha haemolysis (incomplete haemolysis ) or
no haemolysis.
• 1 streptococcus pneumonia (pnemoniae)
• 2 streptococcus viridians :
• They are alpha haemolytic e.g.
• S. Salivarius(group k)
• S. Sanguis (group H)
• S. Mutans
• S. Mitis
• 3 group N streptococci: also called lactic streptococci and
are non haemolytic.
8. streptococci
• Morphology:
• Shape: spherical
• Arrangement : arrange in chains or pairs
• Division: cocci divide in a plane perpendicular
to long axis of chain.
• Capsule : some strain are capsulated
• Mobility: non mobile
• Spore: non spore forming
10. streptococci
• Culture
• Nutrient agar, blood agar,maconkeys only for (s. Faecalis)
• Colonies:
• Discoid colonies (1-2mm in diameter)
• 1 on nutrient agar small translucent dew drop like colonies.
• 2 on blood agar 2 type of haemolysis are seen;
• a beta complete haemolysis a clear zone of haemolysis is formed around
colonies due to rupture of RBCs with release of haemoglobin.
• b alpha incomplete haemolysis a zone of greenish brown discoloration is
formed around colonies that contain unlysed RBCs and a green,
unidentified. Reduced product of haemoglobin.
11. streptococci
• 3 on MacConkeys medium s. Faecalis produce
small pink colonies.
• 4 group A streptococci produce 2 types of
colonies:
• A matt or mucoid colonies consist of
streptococci that produce much M protein.
Virulent.
• B glossy colonies consist of streptococci that
produce little M protein non virulent.
12.
13. streptococci
• Growth characistics
• Oxygen requirements: most streptococci are
aerobic and facultative anaerobes.
• Peptostreptococci are obligate anaerobes
• Energy source is ferment sugar
• Temperature streptococci grow at 37degree c
• Group d enterococci grow between 15-45 degree
c.
• 10% co2 promotes growth.
14. streptococci
• Antigen
• 1 group specific carbohydrate antigen
• Present in cell wall
• Function:
• Given precipitin reaction with specific antisera
and forms basis for lancefield group A-H and K-u.
• Serologic specificity of this antigen is determined
by an amino sugar.
15.
16. streptococci
• 2 M protein
• Present in cell wall of organisms producing matt
or mucoid colonies.
• Function:
• Associated with virulence of group A strptococci.
• Gives agglutination or precipitation reaction with
M protein type specific antisera .
• Interfere in phagocytosis.
• Causes production of antibodies that acts as
opsonion and protect against reinfection .
18. streptococci
• Enzymes
• 1 streptokinase fibrinolysin
• Transforms plasmogen into plasmin that digest
fibrin and is partially responsible for rapid spread
of streptococcal infection by preventing
formation of fibrin barrier around the infected
site
• Clinical use
• Give iv pulmonary emboli, venous thromboses.
19. streptococci
• 2 sreptodornase steptococcal Dnasa
• Deploymerises DNA thus help to liquefy exudates and
facilitate removal of pus and necrotic tissue.
• 3 hyaluronidase spreading factor
• Splits hyaluronic acid in ground substance of connective
tissue thus hail in spreading of infecting microorganism.
• 4 diphosphopyridine nucleotidase kills leukocytes
20. streptococci
• Toxin
• 1 Hemolysins:
• Beta haemolytic group a streptococci produce two haemolysin (streptomycin)
• A streptolysin O:
• 1 causes haemolysis only in anaerobic condition b/c it is o2 labile.
• 2 it binds to sterol in host leukocyte membrane where it forms toxin oligomers
resulting in large transmembrane pores . This causes release of lysosomal enzymes
that results in degranulation and death of leukocytes as well as destruction of
adjacent tissues.
• 3 suppresses chemotaxis and leukocyte mobility.
• 4 it is antigenic and causes production of antistreptolysin o antibodies.
• B streptococci S:
• 1 Being o2 stable it is responsible for haemolytic zone around streptococcal
colonies on blood agar plate.
• 2 it is not antigenic
• 3 inhibits chemotaxis and phagocytosis.
22. streptococci
• 2 erythrogenic toxin:
• A produced only by lysogenic streptococci.
• B possessses two functional parts:
• 1 heat labile part , induces fever and
suppresses immune system.
• 2 heat stable part ,enhances pyrogenicity and
produces rash in scarlet fever as a result of
hypersensitivity reaction to this part.
23.
24.
25. streptococci
• Habitat and transmission
• Habitat
• S pyogene human skin,oropharynx
• S agalactiae normal flora of female genital tract.
• Group C and G pharynx
• Enterococci lower intestinal tract
• Viridans normal flora of u.respiratory tract
• TRANSIMISSION
• Via respiratory droplets
26.
27. streptococci
• Pathogenesis and clinical findings
• A Diseases due to invasion by beta haemolytic group A streptococci.
• 1Erysipeles
• Caused by invasion of skin.
• Clinical finding
• massive brawny edema with a rapidly advancing margin of
infection.
• 2 puerperal fever septicaemia
• Caused by invasion of uterus after delivery
• 3 sepsis (surgical scarlet fever)
• Caused by invasion of traumatic or surgical wound by streptococci.
28. streptococci
• B disease due to local infection with beta haemolytic group a streptococci
• 1 streptococcal sore throat
• Caused by attachment of group A streptococci to pharyngeal epithelium by means
of lipoteichoic acid covering surface pili.
• Clinical finding in kids
• Sub acute nasopharngitis with thin serous discharge
• Little fever
• Enlarged cervical lymph nodes.
• Clinical finding in adults
• Acute and intense nasophayngitis
• Tonsillitis
• Intense redness and edema of mucos membrane
• Purulent discharge
• High fever
• Enlarged and tender cervical lymph nodes
29. streptococci
• Stretococcal sore throat;
• 1 scarlet fever rash due to production of erythrogenic
toxin.
• Quinsy peritonsillar abscess
• Ludwigs angina characterized by blockage of air
passages by massive swelling of floor of mouth.
• Pneumonia occurs by viral infection e.g. influenza or
measles
• Streptococcal pyoderma (impetigo) local infection of
superficial layer of skin.
•
30. streptococci
• Infective endocarditis
• Acute endocarditis
• In bacteraemia beta haemolytic streptococci settle on normal or previously
injured heart valves.
• Clinical finding
• Acute endocarditis destruction of heart valves, cardiac failure.
• Sub acute endocarditis
• It involve abnormal valves (congenital deformitis,rheumatic or atherosclerotic
lesion).thrombi are formed on injured endothelium of valve leaflets.
• Causative organisms
• A viridin streptococci reach bloodstream after dental extraction.
• Gram negative rods of intestinal flora
• Enterococci of gut or urinary tract.
• Clinical finding
• Fever, anaemia, weakness, heart murmur,emboli,enlarged spleen, renal lesion.
31.
32. streptococci
• Post streptococcal disease
• Occur 1-4 week following an acute group A
streptococcal infection
• 1 acute glomerulonephritis
• It develop 3 week after skin infection with group A
streptococci (types 12, 4 , 2 and 49)it is initiated by
immune complexes formed by streptococcal antigen
and antibodies directed against it. These immune
glomerular basement mem.which is damaged by
inflammatory reaction.
• Clinical finding
• Hematuria, proteinuria,edema
33. streptococci
• Rheumatic fever
• It develop 1-4 weeks after sore throat with
group A streptococci. It is due to cross
reaction b/w human heart antigen and
antibodies directed against streptococcal M
antigens. As a result , heart valve are
damaged.
34. streptococci
• Clinical finding
• Heart: aschoff bodies are deposited in
myocardium wart like vegetation on heart valves,
fish mouth or buttonhole stenotic deformity of
valves,MacCallums plaques on arterial walls.
• Joint : migratory non suppurative arthritis.
• Skin: subcutaneous nodules, erythema
marginatum.
• Other fever and malaise.
35.
36. streptococci
• Other infection
• Group B (s agalactiae)
• In women bacteraemia and meningitis occur in diabetics
and in patient on immunosuppressive drugs
• In children born to infected mother bacteremia,pneumonia
,meningitis and sepsis.
• Group c and g sinusitis, bacteremia and endocarditis.
• Group d: enterococci: UTI endocarditis meningitis
• non enterococci: UTI endocarditis
• Streptococcus viridan: subacute endocarditis
• Streptococcus mutan : dental caries
• Group N streptococci: coagulation souring of milk
37. streptococci
• Diagnostic laboratory tests;
• Specimen throat, pus, blood, urine, CSF
• Microscopy gram +ve cocci
• Culture nutrient agar, blood agar.macConkeys medium
• Schultz charlton reaction this is used to detect erythrogenic toxin.
• Serologic test
• Group A streptococcal antigen from throat swab can be detected by
commercial kits that use enzymes linked immunosorbent assay
ELISA or agglutination.
• Bacitracin sensitivity test commercially available discs containing a
calibrate amount of bacitracin will inhibit the growth of group A
streptococci but not other group of streptococci b/c group A
streptococci is more sensitive to antibiotic bacitracin.
38. streptococci
• Prevention
• No specific vaccine
• Rhemumatic fever can be prevented by
treating group A streptococcal pharyngitis
with pencillin.
39. streptococci
• Immunity
• Type specific immunity to reinfection with
streptococci develops. It is due to anti M type
specific antibodies.
• Treatment
• Penicillin G
• Erythromycin
• amminoglcosides
