Dr. Manal El Said

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Staphylococcus aureus
Streptococci
Dr. Manal El Said
Head of Microbiology Department

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Streptococcus pyogenes (Group A Streptococcus)
Diseases
Suppurative (pus-producing) diseases -
Pharyngitis - Cellulitis Nonsuppurative
(immunologic) diseases - Rheumatic fever -
Acute glomerulonephritis.
Characteristics

• Gram-positive cocci in chains
• ß-hemolytic
• Catalase-negative.
• Bacitracin-sensitive
• Streptococci are subdivided into group A, B,
  etc., by differences in the antigenicity of their
  cell wall carbohydrate.

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Streptococcus pyogenes (Group A Streptococcus)
Habitat and Transmission

• Habitat is the human throat skin.
• Transmission is via respiratory droplets.

Pathogenesis

• For suppurative infections
• Hyaluronidase (spreading factor)
  subcutaneous spread in cellulitis
• Erythrogenic toxin (a superantigen) rash
  of scarlet fever
• M protein impedes phagocytosis.

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Streptococcus pyogenes (Group A Streptococcus)
Pathogenesis

• For nonsuppurative (immunologic) diseases
• Rheumatic fever
• Immunologic cross-reaction between bacterial
  antigen and human heart joint tissue (antibody
  against streptococcal M protein reacts with
  myosin in cardiac muscle)
• Acute glomerulonephritis
• Immune complexes formed between streptococcal
  antigens and antibody to those antigens.
• The immune complexes are trapped by glomeruli
• Complement is activated
• Neutrophils are attracted to the site by C5a
• Proteases produced by neutrophils damage glomeruli

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Streptococcus pyogenes (Group A Streptococcus)
Laboratory Diagnosis

• For suppurative infections
• Gram-stained smear and culture.

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Streptococcus pyogenes (Group A Streptococcus)
Laboratory Diagnosis

• For suppurative infections
• Gram-stained smear and culture.
• ß-hemolytic colonies on blood agar (Hemolysis due
  to streptolysins O S).
• Bacitracin sensitive
• ELISA for group A streptococcal antigens in
  throat swabs.

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Streptococcus pyogenes (Group A Streptococcus)
Laboratory Diagnosis
If rheumatic fever is suspected Patient's
antistreptolysin O antibody titer is tested to
determine previous exposure to S. pyogenes If
acute glomerulonephritis is suspected Antibody
to streptococcal DNase B is used as evidence of a
previous skin infection by S. pyogenes.
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Streptococcus pyogenes (Group A Streptococcus)
Treatment
Penicillin G (no significant resistance).
Prevention

• Penicillin is used in rheumatic fever patients to
  prevents
• - Recurrent S. pyogenes pharyngitis
• - Damage to heart valves.

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Streptococcus agalactiae (Group B Streptococcus)
Diseases
Neonatal meningitis sepsis.
Characteristics

• Gram-positive cocci in chains.
• ß hemolytic.
• Catalase-negative.
• Bacitracin-resistant.
• They are subdivided into group A, B, etc., by
  differences in antigenicity of their cell wall
  carbohydrate

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Streptococcus agalactiae (Group B Streptococcus)
Habitat and Transmission

• Main habitat is the human vagina.
• Transmission occurs during birth.

Pathogenesis

• Pyogenic organism.
• Predisposing factors to neonatal infection
  include
• - Rupture of membranes more than 18 hours
  before delivery
• - Labor prior to 37 weeks (infant is premature)
• - Absence of maternal antibody
• - Heavy colonization of the genital tract by
  the organism.

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Streptococcus agalactiae (Group B Streptococcus)
Laboratory Diagnosis

• Gram-stained smear and culture
• ß- hemolytic (narrow zone) colonies on blood agar
  
• Resistant to bacitracin Hydrolyze hippurate

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Streptococcus agalactiae (Group B Streptococcus)
Laboratory Diagnosis

• Hippurate (hippuric acid) is benzene (6 carbon)
  ring with amino acid serine attached to one of
  carbon molecules.
• Hippuricase, enzyme, cleaves benzene ring
  serine free from each other.
• In this case, some of growth on blood agar plate
  is suspended in hippurate broth incubated for 4
  hours.
• Next, reagent ninhydrin is added.
• if purple color develops, in tube, test is
  positive (test detects amino acid serine that has
  been cleaved from hippuric acid).
• Second tube is positive for hippurate hemolysis

Hydrolyze hippurate
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Streptococcus agalactiae (Group B Streptococcus)
Laboratory Diagnosis

• CAMP testpositive.

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Streptococcus agalactiae (Group B Streptococcus)
Treatment
Penicillin G.
Prevention

• Ampicillin should be given to mothers if
• - Prolonged rupture of membranes
• - Mother has a fever
• - The neonate is premature.

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Streptococcus pneumoniae (Pneumococcus)
Diseases

• Pneumonia meningitis in adults
• Otitis media sinusitis in children.

Characteristics

• Gram-positive "lancet-shaped" cocci in pairs
  (diplococci)
• ß -hemolytic.
• Catalase-negative.
• Sensitive to bile optochin
• Prominent polysaccharide capsule.
• One of three classical encapsulated pyogenic
  bacteria (Neisseria meningitidis Haemophilus
  influenzae are the other two).

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Streptococcus pneumoniae (Pneumococcus)
Habitat and Transmission

• Habitat is the human upper respiratory tract.
• Transmission is via respiratory droplets.

Pathogenesis

• Induces inflammatory response.
• Polysaccharide capsule retards phagocytosis.
• Antipolysaccharide antibody opsonizes the
  organism and provides type-specific immunity.

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Streptococcus pneumoniae (Pneumococcus)
Pathogenesis

• IgA protease degrades secretory IgA on
  respiratory mucosa, allowing colonization.
• Viral respiratory infection predisposes to
  pneumococcal pneumonia by damaging mucociliary
  elevator
• Splenectomy predisposes to sepsis.
• Skull fracture with spinal fluid leakage from
  nose predisposes to meningitis.

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Streptococcus pneumoniae (Pneumococcus)
Laboratory Diagnosis

• Gram-stained smear culture.
• a  -hemolytic colonies on blood agar.

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Streptococcus pneumoniae (Pneumococcus)
Laboratory Diagnosis

• Growth inhibited by bile optochin.
• Latex agglutination test for capsular antigen in
  spinal fluid can be diagnostic.

Mucoid strain on blood agar showing alpha
hemolysis (green zone surrounding colonies). zone
of inhibition around filter paper disc
impregnated with optochin.
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Streptococcus pneumoniae (Pneumococcus)
Laboratory Diagnosis

• Quellung reaction swelling of capsule with
  type-specific antiserum.

In 'quellung' reaction, bacterial cells are
resuspended in antiserum that carries antibodies
raised against capsule. This causes capsule to
swell this can be easily visualised by
suspension in India Ink. Ink particles cannot
penetrate the capsule, which this appears as halo
around bacterial cells.
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Streptococcus pneumoniae (Pneumococcus)
Treatment

• Penicillin G.
• Low-level high-level resistance is caused by
  alterations in penicillin-binding proteins.
• No ß -lactamase is made.

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Streptococcus pneumoniae (Pneumococcus)
Prevention

• Two vaccines are available
• -Vaccine used in adults contains capsular
  polysaccharide of the 23 serotypes that cause
  bacteremia most frequently.
• - Vaccine used in children under the age of 2
  years, contains capsular polysaccharide of 7
  serotypes coupled to carrier protein (diphtheria
  toxoid).
• Oral penicillin is used in immunocompromised
  children.

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Viridans Group Streptococci (e.g., S. sanguis,
S. mutans)
Diseases

• Endocarditis.
• Brain abscess (in mixed infections with mouth
  anaerobes).
• S. mutans implicated in dental caries.

Characteristics

• Gram-positive cocci in chains.
• a-hemolytic.
• Catalase-negative.
• Resistant to bile optochin

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Viridans Group Streptococci (e.g., S. sanguis,
S. mutans)
Habitat and Transmission

• Habitat is human oropharynx.
• Organism enters bloodstream during dental
  procedures.

Pathogenesis

• Bacteremia from dental procedures spreads
  organism to damaged heart valves.
• Organism is protected from host defenses within
  vegetations.
• Glycocalyx composed of polysaccharide enhances
  adhesion to heart valves.

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Viridans Group Streptococci (e.g., S. sanguis,
S. mutans)
Laboratory Diagnosis

• Gram-stained smear and culture.
• a -hemolytic colonies on blood agar.

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Viridans Group Streptococci (e.g., S. sanguis,
S. mutans)
Laboratory Diagnosis

• Growth not inhibited by bile or optochin,
• Viridans streptococci are classified into
  species by using various biochemical tests.

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Viridans Group Streptococci (e.g., S. sanguis,
S. mutans)
Treatment
Penicillin G with or without an aminoglycoside.
Prevention
Penicillin to prevent endocarditis in patients
with damaged or prosthetic heart valves who
undergo dental procedures
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Enterococcus faecalis
Diseases

• Urinary tract biliary tract infections
• Endocarditis rare but life-threatening.

Characteristics

• Gram-positive cocci in chains.
• Catalase-negative.

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Enterococcus faecalis
Habitat and Transmission

• Habitat is human colon urethra female genital
  tract can be colonized.
• May enter bloodstream during gastrointestinal
  (GI) or genitourinary tract procedures.
• May infect other sites, e.g., endocarditis.

Pathogenesis
No exotoxins or virulence factors identified.
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Enterococcus faecalis
Laboratory Diagnosis

• Gram-stained smear and culture.
• a-, ß -, or nonhemolytic colonies on blood agar.
• Grows in 6.5 NaCl
• Hydrolyzes esculin in the presence of 40 bile.

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Enterococcus faecalis
Treatment

• Penicillin or vancomycin plus an aminoglycoside
  such as gentamicin is bactericidal.
• Organism is resistant to either drug given
  individually, but given together they have a
  synergistic effect.
• Aminoglycoside alone is ineffective because it
  cannot penetrate.
• Penicillin or vancomycin weakens the cell wall,
  allowing the aminoglycoside to penetrate.
• Vancomycin-resistant enterococci (VRE) are
  important causes of nosocomial (hospital-acquired)
  infections. Linezolid can be used to treat VRE.

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Enterococcus faecalis
Prevention

• Penicillin gentamicin should be given to
  patients with damaged heart valves prior to
  intestinal or urinary tract procedures
• No vaccine is available.