streptococci

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STREPTOCOCCUSSTREPTOCOCCUS

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Strepto-cocci

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Commensals or Parasites of man & animals or Saprophytes of decaying matter

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Genus Streptococcus

Gram-Positive Cocci in Pairs or Chains

v/s

Staph – gram positive cocci in clusters (grape like)

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Gram-PositiveStreptococcus

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Gram positive cocci in clusters

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Classification

On the basis of their growth characteristics on blood agar

Alpha hemolytic Beta hemolytic Gamma hemolytic

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Example –

Streptococcus viridans (Viridans = green)

Streptococcus pneumoniae

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Example – enterococcus group

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Beta hemolytic streptococciLancefield grouping Group A to Group V without I and J Divided according to differences in Cell wall

carbohydrate antigen Out of all these, those of Group A known as

streptococcus pyogenes produce majority of human infections

Group B are known as S agalactiae

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Group A beta hemolytic streptococci / strep pyogenes These are further subdivided according to sell

surface M, T and R antigens Griffith typing

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Streptococcus Pyogenes(Group A beta hemolytic)

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Description headings

Morphology Growth characteristics Biochemical reactions Resistance Pathogenicity and virulence Epidemiology Diseases caused Laboratory diagnosis Treatment

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Morphology

Cocci in long chains

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Growth characteristics

Facultative anaerobe, grows best in presence of 10% CO2

Grows on enriched media only Beta hemolysis around colonies on blood

agar

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Biochemical reactions

Ferment sugars – produce acid , no gas Catalase negative Catalase helps to differentiate staphylococci

from streptococci

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Catalase test

Add hydrogen peroxide to culture material

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Resistance

Most are still susceptible to penicillin and erythromycin

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Pathogenicity and virulence Antigenic structure

Antigens on surface of strep cross react with body proteins Capsular hyaluronic acid – human joints – autoimmune arthritis Carbohydrate antigen – cardiac valves – rheumatic heart

disease Toxins Enzymes

Streptolysin O – ASO titre for diagnosis Streptolysin S – for hemolysis around colonies Streptokinase – lysis of clots – given iv for treatment of MI DNA ase – Anti DNAase is useful for diagnosis of S.

pyogenes skin infection Hyaluronidase – breaks down tissues – helps in spread of

strep infection

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Epidemiology

Source – human upper respiratory tract – throat, pharynx, nose

Transmission – direct contact, fomites

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Diseases caused

Pus producing (suppurative) Respiratory infections Skin and soft tissue infections Genital infections

Non suppurative Acute rheumatic fever Rheumatic heart disease Acute glomerulonephritis (kidney)

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Respiratory infections

Tonsillitis Pharyngitis

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Skin and soft tissue infections

Skin Erysipelas – involves lymphatics – older pts Impetigo – young children Pyoderma

Soft tissue Cellulitis Necrotising fascitis

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Erysipelas

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Impetigo

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Pyoderma

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Cellulitis

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Necrotising fascitisflesh eating bacteria (anaerobes)

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Non suppurative complications

After 1-3 weeks of primary infection

Due to cross reactivity

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Acute rheumatic fever

Follows streptococcal sore throat

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Acute glomerulonephritis

Cross reaction between streptococci and kidney tissues

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Rheumatic heart disease

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Suppurative infections

Examination of pus/throat swabs Microscopy, staining and culture Gram stain Blood agar

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Non suppurative infections

Demonstration of antibodies Like ASO and anti DNA ase B

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Treatment

Penicillin Erythromycin Drugs have no effect if non suppurative

complications have developed

Prophylaxis – can prevent rheumatic fever, not glomerulonephritis

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OTHER STREPTOCOCCI

BETA HEMOLYTIC - GROUP B AND GROUP D

ALPHA HEMOLYTIC (VIRIDANS GROUP)– STREPTOCOCCUS

PNEUMONIAE

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Group B Streptococcus

Streptococcus agalactiae

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Group B Streptococcus S. agalactiae

1. Infect newborns

2. Infection acquired through maternal vagina during birth

3. Presents as meningitis, pneumonia or septicemia

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Diagnostic Laboratory Tests

CAMP factor positive Hippurase positive

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CAMP (Christie, atkins, munch-peterson) Factor Test

S. aureus

(Spingomyelinase C)Group B

Streptococcus

(CAMP Factor)

Group A Streptococcus

Enhanced Zone of

Hemolysis

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Hippurase NEG

Streptococcus agalactiae not added

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Hippurase POS

Grp B Streptococci

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Viridans group


• Commonly referred to as pneumococcus

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Lancet shaped (one end broad, other pointed)

Capsulated Diplococci

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S. pneumoniae: lancet-shaped diplococcus

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S. pneumoniae

• Diplococcus

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Capsular stain

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Growth characteristics

Alpha hemolysis on blood agar On further incubation, the colonies become

flat with raised edges and central elevation resembling carrom coins

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Example –

Streptococcus viridans (Viridans = green)


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Biochemical reactions

Hiss serum water – fermentation of inulin Bile solubility

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Inulin fermentation

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Resistance

Pneumococcus is sensitive to optochin – used for typing

Resistance to penicillin – third generation cephalosporin like ceftriaxone

May be resistant to third gen ceph also

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Pathogenicity and virulence

Capsule Toxins – pneumolysin C reactive protein

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Capsule

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Pneumolysin

Membrane damaging toxin Cytotoxic activity

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C reactive protein

Abnormal immunoglobulin against C protein of S. pneumoniae appears in serum of patients

Also seen in acute phase of infections and inflammations

CRP titre is tested in acute infections

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Epidemiology

Source – respiratory tract of humans Spread – droplets Carriers – pharynx Low immunity is responsible for fulminant

infections RSV infection, pulmonary congestion, stress,

malnutrition, alcoholism Splenectomy Sickle cell disease

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Diseases caused

Middle ear – otitis media Para nasal sinuses – sinusitis Respiratory tract – pneumonia, bronchitis,

empyema Meningitis is secondary to otitis media,

penumonia, sinusitis and conjunctivitis

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Laboratory diagnosis

Sample sputum – pneumonia septicemia - blood culture Otitis media - fluid from middle ear Meningitis - CSF

Method Gram stain, microscopy culture

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Latex agglutination for pneumococcal antigen in serum of patients

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Treatment

Penicillin Amoxycillin ceftriaxone/ceftazidime Vancomycin

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Prophylaxis

Pneumococcal conjugate vaccine is available

Given to splenectomy patients, sickle cell anemia patients and susceptible individuals

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GROUP D STREPTOCOCCI

Enterococcus faecalis Enterococcus faecium

• GI tract of humans and animals

• Group D carbohydrate cell wall antigen

• Formerly Streptococcus

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Cause UTI, wound infection Endocarditis Intra abdominal abcesses

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Health & Medicine

streptococci