StreptococciStreptococci

Consultant Microbiologist & Head of the Bacteriology

By: Prof. A.M.Kambal By: Prof. A.M.Kambal

StreptococciStreptococci

Definition:

Gram position cocci in chains, non sporing, non motile, some capsulated, facultatively

anaerobic and fastidious in nutritional requirements.

Growth & Clonial MorphologyGrowth & Clonial Morphology

Blood agar best medium with optimum temperature of 35 - 37°C & under aerobic

conditions. Colonies after 24 hours incubation: about 0.5 –

1mm in diameter & may/may not be surrounded by haemolysis.

They are catalase negative.

Classification on Basis of:Classification on Basis of:

1. Haemolysis on Blood Agar

2. Lancefield Grouping

3. Sterotyping

1.1. Based on Haemolysis on Blood AgarBased on Haemolysis on Blood Agar

(i) β-haemolytic Streptococci (BHS) – complete haemolysis of the red cells around the

colonies, producing clear zones around them. e.g. group A, group B etc…

(ii) -haemolytic Streptococci – partial haemolysis with greenish discoloration of the areas

surrounding the colonies. e.g.Streptococcus viridans,

Streptococcus pneumoniae

(iii) Non-haemolytic Streptococci e.g. Enterococcus faecalis

2.2. Lancefield GroupingLancefield Grouping

Usually done on β-haemolytic streptococci (BHS). Based on the presence of a

carbohydrate component of cell wall the C carbohydrate. About 20 Lancefield groups

designated as A,B,C,D, (A-H) (K-U).

Detected by reacting extract of carbohydrate C antigen with specific

antisera raised against it.

3.3. M SerotypingM Serotyping

Done on only group A streptococci and based on the M protein found in

Group A Streptococci. 60 such serotypes; useful for epidemiological

studies.

Group A StreptococciGroup A Streptococci(Lancefield Grouping)(Lancefield Grouping)

((Streptococci PyogenesStreptococci Pyogenes))

Most common pathogen of the streptococci.

Causes 90% of Streptococcal diseases.

Distinguished from other BHS by the bacitracin test: All Group A are sensitive

while the rest are resistant.

It may be capsulated and the capsule is composed of hyaluronic acid.

Pathogenicity Determinants:Pathogenicity Determinants:

Extracellular Determinants:

1) Streptokinase: Convert plasminogen to plasmin which then lyses fibrin. Used to treat thrombotic states. e.g. Coronary thrombosis.

4 main DNAases: A B C D

Antibodies produced against DNAase

(anti-DNAase B) is useful for diagnosing

recent Group A Streptococcal infections

especially skin infections.

2)2) DNAase: depolymerises DNADNAase: depolymerises DNA

3)3) Erythrogenic ExotoxinErythrogenic Exotoxin

Produced only by Group A Streptococcal

lysogenised by a β-bacteriophage. It is also called

Streptococcal pyrogenic exotoxin (SPE).

4)4) Streptolysin (Haemolysin)Streptolysin (Haemolysin)

Lyses all types of cells, not only

RBC.

Two Types:

a. Streptolysin O – Oxygen Labile

b. Streptolysin S – Oxygen Stable

5) Leucocidin:

Destroys WBC and platelets.

6) Hyaluronidase:

Degrades hyaluronic acid

PathogenesisPathogenesis

Causes suppurative infections and non-

suppurative complications (or sequalae).

Capsule Hyaluronic Acid

Nonantigenic; limited role in pathogenicity

Protein M, R & T ANTIGENS

M is type antigen & adherence & antiphagocytic factors.

Polysaccharide

Rhamnose – galactosamine polymer

C-substance; Group A antigen.

Peptidoglycan

Glucosamine muramic acid w/cross-linked peptide chains

Cell wall backbone

Cytoplasmic Membrane

Protein-lipid Nutrient & enzyme transport

Structure Composition Comments

Diagram of Cell Wall

Section of

Streptococcus Pyogenes

A.A. Suppurative Suppurative (Pyogenic)(Pyogenic) Infections Infections

a) Virulence Factors(i) Principal virulence factors is the M protein.

Originated from the cytoplasmic membrane.

Associated with pili.

It is antiphagocytic.

(ii) Lipotechoic Acid (LTA)

For attachment to epithelial surfaces.

(iii) Hyaluronic Acid

An antiphagocytic capsules.

B.B. DiseasesDiseases

1) Tonsillitis/Pharyngitis: Acute suppurative infection of the tonsils & pharynx.

Prevalent in children. most common bacterial infection of throat. May spread to adjacent tissues &

cause: Peritonsillar abscess (Quinsy), sinusitis, ototis.

2) Impetigo (Pyoderma): An infection of the epidermis presenting as

pustules. Seen most often in infants and toddlers.

3) Erysipelas: A serious infection often complicating surgical

wounds.

4) Cellulitis: A spreading infection of the subcutaneous tissue.

5) Scarlet Fever: This is a combination of tonsillitis & a red skin rash. Toxin lysogenised by β-bacteriophage.

6) Puerperal Sepsis:

Acute infection of the female genital tract.

7) Severe Necrotising Fasciitis & Other Soft Tissues:

Severe infection usually seen in people under 50 years with no underlying disease.

B.B. Non-suppurative Complications of Non-suppurative Complications of Group A Streptococcal InfectionsGroup A Streptococcal Infections

These are antigen-antibody mediated disease and occur about 1-5 weeks

after the primary suppurative infection. Tend to follow either throat

or skin infections or both. Streptococci are not found in the

affected organ.

a)a) Acute Rheumatic Fever:Acute Rheumatic Fever:

Considered to be an autoimmune disease involving the myocardium and its valves, connective tissues and the big joints.

Group A Strep cell wall has some antigenic similarity with some of these human tissues. Follows after throat infections only. Tends to recur. Many serotypes are associated with acute rheumatic fever.

b)b) Acute Glomerulonephritis:Acute Glomerulonephritis:

Due to antigen-antibody complexes deposited

on the basal membrane of glomeruli also can

be due to similarity between group A cell

components and glomerular tissue. May

follow after either throat or skin. Tends not to

recur. Serotypes involved are few called

nephrotogenic strains.

Differences Between Glomerulonephritis &Differences Between Glomerulonephritis & Rheumatic Fever Rheumatic Fever

1. Latent period between infection and first attack.

1 – 5 weeks

(Average 18 days)

1 – 5 weeks

(Average 10 days)

2. Preceding infection

Throat only Throat or Skin

3. Pathogenesis Both Based On

Immunological Reaction (Either

Due to auto antibody Or due to

cross reactive antigen).

Similarity between

organism antigens &

tissue antigens

Similarity between

a) Organism & tissue antigens.

b) Deposition of immunocomplexes in glomeruli

Rheumatic Fever Glomerulonephritis

4. Second Attacks Common Rare if any

5. Prophylactic use of penicillin. Essential Usually NOT used.

6. Serotypes (M Types) Any of the 60

serotypes

Limited No. of serotypes e.g. type 12, 45 etc.

7. Serum whole complement & C3 Increased Decreased

Differences Between Glomerulonephritis &Differences Between Glomerulonephritis & Rheumatic Fever Rheumatic Fever (Continued)(Continued)

Rheumatic Fever Glomerulonephritis

Epidemiology of Epidemiology of StreptococcalStreptococcal Infections Infections

1. Acquisition is acquired through infected respiratory droplets.

2. Sources of Infection

a)Those with active disease or convalescent carriers in throat.

b)Asymptomatic carriers – the most common source. Up to 20% of school going children may carry Group A

streptococci in their throats.

3. Age Group: prevalent in children especially between 3 – 8 years.

Diagnosis of Suppurative InfectionsDiagnosis of Suppurative Infections

1) Specimen: Swabs: Wounds

Throat Blood

Aspirates

2) Culture – B.A. At 37°C

Aerobic; 18 – 24 Hrs, Incubation Period.

3) Bacitracin Test

4) Lancefield Grouping

TreatmentTreatment

Penicillin : Antibiotic of choice

Other Antibiotics:

Erythromycin/other macroslides

Cefuroxime & the 3rd generation

Cephalosporins

e.g. Ceftriaxone

Group B StreptococciGroup B Streptococci((Streptococci agalactiaeStreptococci agalactiae))

A member of the normal flora of the female

genital tract and rectum. Up to about 25%

pregnant women carry it.

Disease By Group B StreptococciDisease By Group B Streptococci

Important in Neonatal infection:a) Early-onset Disease:

severe disease develops within 24 – 48 hrs. after birth. Infection acquired either in-utero or

during passage through birth canal.

Associated with:(i) Premature Birth

(ii) Prolonged & early rupture of foetal membranes.(iii) High mortality rate: 60 – 70%

Disease presents as Respiratory Distress syndrome or Septicaemia or Meningitis.

b) Late-onset Disease:

Often occurs in full term neonates without any

underlying disease. Infection occurs in the 2nd week

of birth. Prognosis better than early onset: Mortality

rate about 10%. Usually present as meningitis.

TreatmentTreatment

Penicillin /Ampicillin

Sometimes may be combined with Gentamicin.

Group D StreptococciGroup D Streptococci

Has 2 main subgroups:

(i) Enterococci

(ii) Non-enterococci

Both are part of the normal intestinal flora.

1) Enterococci:can grow in the presence of 40% bile

& 6.5% sodium chloride. They are generally

resistant to Penicillin, but sensitive to Ampicillin.

2 Main Human Pathogens:2 Main Human Pathogens:

Enterococcus faecalis

Enterococcus faecium

2) Non-enterococci: Cannot grow in the presence of 6.5% sodium chloride.

Sensitive to penicillin.

Main human pathogen is Streptococcus bovis.

Group D Strep can cause urinary tract infections,

endocarditis, and wound infections.

-Haemolytic Streptococci-Haemolytic Streptococci

2 Main Members:a. Viridans streptococci and

b. Streptococcus pneumoniae (Pneumococcus)

Viridans streptococci consists of many members e.g.:

S. sanguis

S. mutans

S. salivarius

Viridans strep. Strep. pneumoniae

Resistant to optochin

Not lysed by bile salts

Opportunistic pathogen

Sensitive to optochin

Lysed by bile salts

(i.e. Bile soluble)

Primary pathogen

Viridans streptococciViridans streptococci

Members are predominant normal flora of the

oropharyn. They are generally opportunistic

pathogens.

2 Main Diseases:2 Main Diseases:

1. Dental plaques and caries.

2. Sub-acute bacterial endocarditis.

1)1) Dental PlaquesDental Plaques

This is the more common disease associated with this group. Dental plaque consists of oral bacteria + bacteria products and

salivary components. S. mutans is the most pathogenic for dental plaque. It produces enzymes that break down dietary sugars to

polysaccharides called glycans e.g. Glucans and fructans which maintain the integrity of the plaque and get it firmly fixed to the

enamel surface. Prevention:

Avoidance of sweets Good oral hygiene – frequent Tooth brushing & deflossing

2)2) Subcute Bacterial Endocarditis Subcute Bacterial Endocarditis (SBE)(SBE)

Serious infection of cardiac valves by

Viridans streptococci.

Predisposing FactorsPredisposing Factors

1. Valve must be abnormal: damage by

a. Rheumatic Fever

b. Congenital Cardiac valve

Abnormality

c. Atheroesclertic valve

d. Prolapsed valve

e. Syphilic valve

2. Dental Extraction: leading to transient bacteraemia.

Pathogenesis:Pathogenesis:

Transient bacteraemia following dental extraction/ or any

other manipulation. Circulating Viridans streptococci are

deposited on damaged cardiac valve to cause lesions called

vegetations components are:

Thrombi

Bacteria

Fibrin

WBC

Further destruction of valves, leading to cardiac

murmurs and eventually cardiac failure.

SBE: One of the causes of pyrexia of unknown origin (P.U.O).

Diagnosis: Blood Culture

Treatment:

Combination of Penicillin & Streptomycin or

Gentamycin.

NB:

Other organisms may be involved as well e.g. Enterococci, S. bovis, S. aureus.

Streptococcus pneumoniaeStreptococcus pneumoniae

Gram positive diplococci with cells arranged end to end. Some

may be capsulated. Capsulated strains usually are primary

pathogens; non capsulated strains to be opportunistic.

Culture: growth is enhanced by 5-10% extra CO2.Colonies

tend to collapse at the centre after 24 hours incubation.

Capsulated strains produce smooth (S) and mucoid colonies whist

noncapsulated produce dry and rough (R) colonies.

Antigenic Structure:Antigenic Structure:

>> 80 serotypes known based on variations in

capsular structure.

PathogenesisPathogenesis

Severe invasive and suppurative infections acquired by inhalation of respiratory droplets infected by capsulated strains. Organisms acquired by exogenous route.

1. Acute pneumonia-commonest infection and involves the alveoli: and often followed by invasion of the blood stream leading to.

2. Septicaemia3. Meningitis4. Arthritis

Infection may also be localised to the ears (otitis media), sinusitis or conjunctivities.

Secondary Infections:Secondary Infections:

Organisms tend to be non-capsulated and cause opportunistic infection when the host’s natural defense mechanisms of the respiratory tract are

impaired.

Infections are endogenous.

Infections generally confined to the lungs only.

Factors Increasing Risk To Factors Increasing Risk To Pneumococcal InfectionPneumococcal Infection

Hyposplenism

Liver Disease

Hypogamma Globinaemia

Alcoholism

Cigarette Smoking

Malnutrition

Splenectomy

Asplenia

Sickle Cell Disease

Diagnosis:Diagnosis:

Culture of Sputum

CSF

Blood

Swab / Aspirate

Optochin Test

Capsular Swelling Test (Quellung Reaction)

BA

Treatment:Treatment:

Penicillin; but an increasing number of strains

becoming resistant. In such situations.

3rd generation Cephalosporines e.g. Ceftriaxone

with either Vancomycin or Rifampicin.

Vaccination:Vaccination:

Based on polysaccharide capsule given to

those at risk of serious infection. Vaccine is

multivalent containing the serotypes frequently

associated with invasive disease.

Recommended for sickle cell disease patients

and splenectomised patients.