Term
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Definition
• Gram-positive cocci, arranged in pairs or chains, that are aerotolerant anaerobes
• Often categorized based on the Lancefield classification
– Divides the streptococci into serotype groups based on the bacteria’s C antigens
– Lancefield groups A and B include the significant streptococcal pathogens of humans |
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Term
| Group A Streptococcus: Streptococcus pyogenes |
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Definition
• S. pyogenes forms white colonies surrounded by zone of beta-hemolysis on blood agar plates
• Pathogenic strains often form a capsule
• Group A streptococci generally only cause disease in the following situations
– Normal microbiota are depleted
– Large inoculum enable the streptococci to establish themselves before antibodies are formed against them
– Specific immunity is impaired |
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Term
S. pyogenes S. pneumoniae
Pathogenicity |
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Definition
• Structural components
– Protein M, which interferes with opsonization and lysis of the bacteria and a hyaluronic acid capsule, which acts to camouflage the bacteria
• Enzymes
– Streptokinases, deoxynucleases, and C5a peptidase all facilitate the spread of streptococci through tissues
• Pyrogenic toxins that stimulate macrophages and helper T cells to release cytokines
• Streptolysins lyse red blood cells, white blood cells, and platelets |
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Term
| Group A Streptococcal Diseases |
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Definition
• Pharyngitis (“strep throat”)-inflammation of the pharynx
• Scarlet fever-rash that begins on the chest and spreads across the body
• Pyoderma-confined, pus-producing lesion that usually occurs on the face, arms, or legs
• Streptococcal toxic shock syndrome-bacteremia and severe multisystem infections |
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Term
| Streptococcal Pharyngitis |
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Definition
Typical scarlet
fever rash caused
by erythrogenic
toxin produced
by S. pyogenes.
This toxin is also
involved in the
pathogenesis of
puerperal sepsis,
an infection of the
Uterus
(30% mortality |
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Term
Erysipelas (S. pyogenes)
Group A Streptococcal Diseases |
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Definition
• Necrotizing fasciitis-toxin production destroys tissues and eventually muscle and fat tissue
• Rheumatic fever-inflammation that leads to damage of heart valves muscle
• Glomerulonephritits-inflammation of the glomeruli and nephrons which obstruct blood flow through the kidneys |
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Term
| Post-Streptococcal Diseases: |
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Definition
• Acute Glomerulonephritis (AGN)
– Kidney damage may be caused by cross-reacting antibodies (Type II) or deposition of immune complexes (Type III), or toxins like SLO & SLS. Can be self-limiting or fatal.
• Rheumatic Fever (RF)
– Symptoms include carditis, abnormal EKG, painful arthritis, fever, etc. Severe carditis can result in permanent damage to heart valves. Responsible for 15,000 deaths/year in U.S. |
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Term
| Diagnosis, Treatment, and Prevention of Group A |
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Definition
• Diagnosis
– Agglutination and ELISA test utilizing antibodies directed against the bacteria’s distinctive cell wall polysaccharide
– Incubation of the bacteria with bacitracin which inhibits its growth
• Treatment
– Penicillin G, sometimes in combination with an aminoglycoside |
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Term
| Transmission and Epidemiology of Group A |
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Definition
• Children (1-15 years) have higher carrier and disease rates. Those with active disease are a large source of infection.
• Transmitted by respiratory droplets and both direct and indirect contact.
• Diagnosis by culture and rapid tests. Hemolysis, bacitracin sensitivity, gram morphology, and catalase tests are useful.
• Treatment is Penicillin G.
• Prevention & Control by isolation and early and complete treatment. |
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Term
| Group B Streptococcus: Streptococcus agalactiae |
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Definition
• Gram-positive cocci that divide to form chains
• Distinguished from group A streptococcus by its buttery colonies and smaller zone of beta-hemolysis on blood agar plates and its resistance to bacitracin
• Normally colonizes the lower gastrointestinal, genital, and urinary tracts |
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Term
| Pathogenicity and Diseases of S. agalactaie |
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Definition
• Pathogenicity
– Often infects newborns who have not yet formed type-specific antibodies and whose mothers are uninfected (and so do not provide passive immunity)
– Produces various enzymes whose roles in causing disease is not yet understood
• Diseases
– Most often associated with neonatal bacteremia, meningitis, and pneumonia
– Immunocompromised older patients are at risk from group B streptococcal infections |
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Term
| Diagnosis, Treatment, and Prevention of S. agalactie |
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Definition
• Prevention
– Prophylactic administration of penicillin at birth to children whose mothers’ urinary tracts are colonized with group B streptococci
– Immunization of women against group B streptococci to prevent infection of future children |
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Term
| Alpha-Hemolytic Streptococci: The Viridans Group |
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Definition
• Lack group-specific carbohydrates and cannot be grouped by the Lancefield system
• Many produce a green discoloration when grown on blood media (-hemol.)
• Normally inhabit the mouth, pharynx, GI tract, genital tract, and urinary tract
• One of the causes of dental caries (dental plaque production)
• If they enter the blood, can cause meningitis and endocarditis |
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Term
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Definition
• Gram-positive cocci that most commonly forms pairs but may also form chains
• Forms unpigmented, alpha-hemolytic colonies when grown on blood agar (anaerobic incubation produces beta-hemolytic colonies)
• Normally colonizes the mouth and pharynx but can cause disease if they travel to the lungs
• Disease is highest in children and the elderly |
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Term
| Streptococcus pneumoniae (Pneumococcus) |
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Definition
• One of the most significant human pathogens.
– Leading cause of human death before antibiotics; still in the top ten.
– Causes 60-70% of all bacterial pneumonias.
– Causes the majority of otitis media cases in young children, some of which progress to meningitis.
• Pathogenesis tied to large polysaccharide capsule. 84 different capsular types have been identified using a serological test called the Quellung test |
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Term
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Definition
• Pneumococcal pneumonia-bacteria multiply in the alveoli causing damage to the alveolar lining and an inflammatory response
• Sinusitis and otitis media-bacteria invade the sinuses or middle ear, often following a viral infection
• Bacteremia and endocarditis-bacteria in the bloodstream or in the lining of the heart
• Pneumococcal meningitis-bacteria that have spread to the meninges |
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Term
| Diagnosis, Treatment, and Prevention |
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Definition
• Diagnosis
– Gram stain of sputum smears
– Quellung reaction: anti-capsular antibodies cause the capsule to swell, confirming the presence of bacteria, CAMP test
• Treatment
– Penicillin
• Prevention
– Vaccine made from purified capsular material
• Provides long lasting immunity in normal adults but is not as effective in children, the elderly, or AIDS patients |
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Term
CAMP Test for Group B Strep
Enterrococcus |
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Definition
• Previously classified as group D streptococci but differed enough to be reclassified as a separate genus
• Form short chains and pairs and lack a capsule
• Found in the human colon but are rarely pathogenic at this site
• Can cause disease if they are introduced into other parts of the body, such as the urinary tract or bloodstream |
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Term
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Definition
• Important cause of nosocomial infections
• Treatment is difficult because enterococci are often resistant to antimicrobials
• Prevention is difficult, especially in a health care setting, where patients’ often have weakened immune systems |
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