streptococci

STREPTOCOCCUSSTREPTOCOCCUS

Strepto-cocci

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

Genus Streptococcus

Gram-Positive Cocci in Pairs or Chains

Staph – gram positive cocci in clusters (grape like)

Gram-PositiveStreptococcus

Gram positive cocci in clusters

Classification

On the basis of their growth characteristics on blood agar

Alpha hemolytic Beta hemolytic Gamma hemolytic

Example –

Streptococcus viridans (Viridans = green)

Streptococcus pneumoniae

Example – enterococcus group

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

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

surface M, T and R antigens Griffith typing

Streptococcus Pyogenes(Group A beta hemolytic)

Description headings

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

Morphology

Cocci in long chains

Growth characteristics

Facultative anaerobe, grows best in presence of 10% CO2

Grows on enriched media only Beta hemolysis around colonies on blood

Biochemical reactions

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

from streptococci

Catalase test

Add hydrogen peroxide to culture material

Resistance

Most are still susceptible to penicillin and erythromycin

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

Epidemiology

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

Transmission – direct contact, fomites

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)

Respiratory infections

Tonsillitis Pharyngitis

34 tonsillitis

35 pharyngitis

Skin and soft tissue infections

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

Soft tissue Cellulitis Necrotising fascitis

Erysipelas

Impetigo

Pyoderma

Cellulitis

Necrotising fascitisflesh eating bacteria (anaerobes)

Non suppurative complications

After 1-3 weeks of primary infection

Due to cross reactivity

Acute rheumatic fever

Follows streptococcal sore throat

Acute glomerulonephritis

Cross reaction between streptococci and kidney tissues

Rheumatic heart disease

Suppurative infections

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

Non suppurative infections

Demonstration of antibodies Like ASO and anti DNA ase B

Treatment

Penicillin Erythromycin Drugs have no effect if non suppurative

complications have developed

Prophylaxis – can prevent rheumatic fever, not glomerulonephritis

OTHER STREPTOCOCCI

BETA HEMOLYTIC - GROUP B AND GROUP D

ALPHA HEMOLYTIC (VIRIDANS GROUP)– STREPTOCOCCUS

PNEUMONIAE

Group B Streptococcus

Streptococcus agalactiae

Group B Streptococcus S. agalactiae

1. Infect newborns

2. Infection acquired through maternal vagina during birth

3. Presents as meningitis, pneumonia or septicemia

Diagnostic Laboratory Tests

CAMP factor positive Hippurase positive

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

S. aureus

(Spingomyelinase C)Group B

Streptococcus

(CAMP Factor)

Group A Streptococcus

Enhanced Zone of

Hemolysis

Hippurase NEG

Streptococcus agalactiae not added

Hippurase POS

Grp B Streptococci

Viridans group

• Commonly referred to as pneumococcus

Lancet shaped (one end broad, other pointed)

Capsulated Diplococci

S. pneumoniae: lancet-shaped diplococcus

S. pneumoniae

• Diplococcus

Capsular stain

Growth characteristics

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

flat with raised edges and central elevation resembling carrom coins

Example –

Streptococcus viridans (Viridans = green)

Biochemical reactions

Hiss serum water – fermentation of inulin Bile solubility

Inulin fermentation

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

Pathogenicity and virulence

Capsule Toxins – pneumolysin C reactive protein

Capsule

Pneumolysin

Membrane damaging toxin Cytotoxic activity

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

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

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

Laboratory diagnosis

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

Method Gram stain, microscopy culture

Latex agglutination for pneumococcal antigen in serum of patients

Treatment

Penicillin Amoxycillin ceftriaxone/ceftazidime Vancomycin

Prophylaxis

Pneumococcal conjugate vaccine is available

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

GROUP D STREPTOCOCCI

Enterococcus faecalis Enterococcus faecium

• GI tract of humans and animals

• Group D carbohydrate cell wall antigen

• Formerly Streptococcus

Cause UTI, wound infection Endocarditis Intra abdominal abcesses

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Streptococci With Pics(2)

-Hemolytic Streptococci

Aerobic Gram- Positive Cocci Negative Streptococci See Streptococci identification chart Positive Staphylococci See Staphylococci Identification chart

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Group A Streptococci