Streptococcus

Streptococci

By : Assist .Prof. Eman Abdul-Aziz

The Streptococcus

Streptococci:General properties:Characteristics:Catalase negative.Gram positive spherical or oval cocci in pairs and chains.0.7 – 0.9 µm in diameter.Chain formation is best seen in liquid cultures or pus.

Gram stain of Streptococcus species

Culture Grow well on blood agar, enrichment media with glucose and serum

Haemolytic reactions on blood agar α – haemolysis: narrow zone of partial haemolysis and green discoloration around the colony. e.g., Viridans streptococci.β – haemolysis: wide, clear, translucent zone of complete haemolysis around the colony. e.g., Streptococcus pyogenesNo haemolysis (γ- haemolysis) e.g., Str.feacalis

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Hemolysis alpha

beta

gamma

Serology:Serogrouping termed Lancefield grouping is useful in the identification of the more virulent Β – haemolytic species.The carbohydrate antigens found on the cell walls of the organisms are related to their virulence.20 Lancefield groups are recognized (A – H and K – V) but not all are important as human pathogens.

Cell surface structure of S pyogenes and extracellular substances

Lancefield groups one or more species per group surface antigens: M, T, R
groupable streptococci A, B and D most important C, G, F Rare
Non-groupable S. pneumoniae pneumonia viridans streptococci e.g. S. mutans dental caries


Group A include the important human pathogens Str. pyogenes Group B contains one species Str. agalactiae (an inhabitant of the female genital tract). It causes infection in neonates. Group C (cause diseases in animals).St equisimitis Group D include enterococci( Str. faecalis )


Streptococcus pyogenes (Group A): Habitat and transmission: # Human upper respiratory tract & skin(normal habitat) #It may survive in dust; spread is by airborne droplets and contact.


Characteristics:.Nasopharynx(commensal in healthy adults) but more commonly in childrenGrow well on blood agar (β – haemolysis).Some strains produce mucoid colonies (having a hyaluronic acid capsule (resistance to phagocytosis).


Exotoxins and Enzymes: #Streptokinase or fibrinolysin: a proteolytic enzyme which lyses fibrin. #Hyaluronidase (spreading factor) attacks the material that binds the connective tissue, causing increasing permeability. #DNases (Streptodornases): destroy cellular DNA. #(Streptolysins, Leucocidins):lysis of blood due to streptolysin S&O #Erythrogenic toxin :responsible for the erythematous rash in scarlet fever;the rash is due to a delayed hypersensitivity reaction that is enhancing by toxin,this toxin may be involved in causing a toxin shock syndrome as that by Staph aureus. Note:not all these products are produced by every strain

Culture and Identification:β – haemolytic colonies on blood agar (lysis of blood due to streptolysins O and S).Sensitive to bacitracin.If rheumatic fever is suspected, then testing the patients antistreptolysin O (ASO) antibody titre will demonstrate previous exposure to Str. pyogenes

Pathogenicity:1-Tonsilitis and pharyngitis.2-Peritonsillar abscess (now rare). 3-Scarlet fever.4-Mastoiditis and sinusitis.5-Otitis media (middle – ear infection).5-Wound infections leading to cellulitis and lymphangitis. 6-Impetigo ( a skin infection)

Scarlet fever

Impetigo


Complications: after infection some patients develop complications such as rheumatic fever, glomerulonephritis and erythema nodosum which may have long – lasting effects.

7-In cellulitis, hyaluronidase (spreading factor) mediates the subcutaneous spread of infection.8-Erythrogenic toxin causes the rash of scarlet fever.Post – Streptococcal infection, manifesting as rheumatic fever, is caused by immunological cross – reaction between bacterial antigen and human heart tissue and acute glomerulonephritis is caused by immune complexes bound to glomeruli.

Treatment: Penicillin is the drug of choice Erythromycin(patient hypersensitive to penicillin) No vaccine is available


Streptococcus agalactia (Group B): This species cause neonatal meningitis and sepsis in human. Habitat and transmission: # Found in human vagina. # Babies acquire infection from colonized mother (during delivery or during nursing).



Characteristics:Gram positive cocci in chainCulture and Identification:Culture on blood agar (β – haemolytic colonies large than Str. pyogenes).Lancefield group is determined by antiserum against cell wall polysaccharide.

Pathogenicity: No toxin or virulence factors have been identified. Cause neonatal meningitis and septicemia. Also associated with septic abortion and gynaecological sepsis.


Treatment and Prevention: Penicillin is the drug of choice Erythromycin (patient hypersensitive to penicillin)


Oral Streptococci:Live principally in the oropharynx, are a mixed group of m.o. with variable characteristics. They typically show α – haemolysis on blood agar but some strains are non – haemolytic and others β – haemolysis.

Some of recognized species Streptococci

Species
Group
Str. mutans, serotypes c, e, f
Mutans group
Str. sobrinus, serotypes d, g
Str. cricetus, serotypes a
Str. rattus, serotypes b, and others
Str. salivarius
Salivarius group
Str. vestibularis
Str. constellatus
Anginosus group
Str. intermedius
Str. anginosus
Str. Sangius & Str. oralis
Mitis group

Viridans streptococci

diverse species oral dental caries hemolytic and negative for other tests non-groupable.includes S. mutansendocarditis tooth extraction

Habitat and transmission:Half of the isolates from the tongue and saliva and quarter of the oral flora from supragingival and gingival plaque.Transmitted from mother Streptococci make up a large proportion of oral flora (approximately ј)to child.Infective endocarditis caused by these m.o. is generally a result of their entry into the blood stream during intraoral surgical procedures (e.g., tooth extraction) and sometimes even during tooth – brushing.

Culture and Identification:Gram positive cocci in chains, α – haemolytic catalase negative, growth not inhibited by bile or optochin

Treatment and Prevention: In patients at risk of infective endocarditis (those with damaged or prosthetic heart valves) prophylactic antibiotics cover should always be given before dental procedures.


Pathogenicity: Mutans group are the major agents of dental caries but in the absence of predisposing factors such as sucrose, they cannot cause caries. They have characteristic ability to produce voluminous amount of sticky extracellular polysaccharides in the presence of dietary C.H.O., these help binding of m.o. to enamel and to each other. They are also important agents of infective endocarditis (60% of cases are due to this m.o.) Bacteria released during dental procedures settle on damaged heart valves ,causing infective endocarditis.


Str. mutans The name mutans results from its frequent transition from coccal phase to coccobacillary phase. .


Str. pneumonia (pneumococcus) Habitat and Transmission: A normal commensal in the human U.R.T. Transmission by respiratory droplets.

Strep pneumoniae with mucoid colonies due to capsule

Characteristics:Gram positive (Lancet shaped) cocci in pairs or short chains.Often capsulate.α – haemolytic on blood agar.Catalase negative.Fucultative anaerobe .

Culture and Identification:From α – haemolytic colonies.Sensitive to optochin.Soluble in bile.Observation for the capsular swelling with type – specific antiserum (Quellung reaction).The latex agglutination test for capsular antigen in spinal fluid can be diagnostic.

Optochin disk (taxo P) test

Quellung reaction


Pathogenicity:No exotoxin are known.Polysaccharide – capsule retard phagocytosis.Vaccination with antipolysaccharides vaccine helps provide type specific immunity.Viral respiratory infection predisposes to pneumococcal pneumonia by damaging the mucociliary lining of U.R.T. (the mucociliary escalator).Cause: Labor pneumonia, chronic bronchitis, otitis media, sinusitis, conjunctivitis, meningitis and septicemia.

Treatment: Penicillin or erythromycin is very effective

Gram – Positive Anaerobic Cocci (GPAC)All belonged to the genus Peptostreptococcus.They comprise 3 genera: Peptostreptococcus Micromonas Finegoldia

The representative species are: 1. Peptostreptococcus anaerobius 2. Finegoldia magnus 3. Micromonas micros These GPAC can often be isolated from dental plaque and the female genital tract, they are also found in carious dentin, subgingival plaque, dentoalveolar abscesses and in advanced periodontal disease. Their pathogenic role is still unclear.