Streptococci

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Streptococci

Classification

b haemolytic streptococci

Main group of pathogenic streptococci

Group A

Virulence

Relates to surface structures and proteins released from cells during growth

• Surface structures

  • M protein shows cross-reactivity with cardiac muscle proteins and antibodies to these surface proteins may play a role in the pathogenesis of rheumatic fever.

  • M protein appears to inhibit phagocytosis

  • Other surface proteins have the ability to inhibits activation of complement via the classical pathway

• Extracellular products

• Streptolysin O

  • Cardiotoxic effect in animals

  • Inhibits chemotaxis, neutrophil mobility and phagocytosis by macrophages

• Streptokinase

  • May play a role in the pathogenesis of nephrotoxicity

  • Pyrogenic exotoxins

  • May be responsible for the development of streptococcal toxic shock syndrome

Clinical manifestations

• Uncomplicated superficial infections

  • URTI

  • Skin infections: impetigo, ecthyma, erysipelas, cellulitis

• Invasive infections

  • Septic shock

  • Puerperal sepsis

  • Pneumonia

  • Meningitis

  • Lymphangitis

  • Necrotizing fasciitis

  • Toxic shock-like syndrome

    • Skin serves as main portal of entry, followed by mucous membranes of throat

    • Early features before the development of toxic shock:

      • Fever

      • Sore throat

      • Vomiting & diarrhoea

• Autoimmune sequelae

  • Rheumatic fever

  • Acute glomerulonephritis

Treatment

• Penicillin

• Erythromycin for penicillin sensitive patients. However incidence of erythromycin resistance is increasing and in some areas is as high as 40%

• Addition of aminoglycoside to penicillin has a synergistic effect

• Penicillin should be combined with clindamycin in the treatment of life-threatening conditions such as necrotizing fasciitis and streptococcal toxic shock.

Group C and G

• Not associated with rheumatic fever

• Can cause similar infections to group A strep.

• Occasionally reported as cause of nosocomial and opportunistic infections including:

  • endocarditis

  • arthritis

  • puerperal sepsis and septic abortion

  • neonatal sepsis

  • pneumonia, pleural empyema

  • peritonitis

  • meningitis

  • cellulitis

• Malignancy, diabetes, cardiovascular disease, alcoholism are important predisposing factors to invasive infection.

Treatment

• Penicillin

• Add aminoglycoside for immunocompromised patients with serious infections such as endocarditis, meningitis or septic shock

Group B

• Colonizes the vagina in many adult women

• Transmission to infant during childbirth occurs in 50-75%. However only a small proportion develop infection.

• In recent years increasingly recognized as a cause of infection amongst adults

• At risk groups: pregnant women, patients with serious underlying disease.

Manifestations:

• Septic shock

• Cellulitis and other soft tissue infections

• Pneumonia

• Arthritis

• Meningitis

• Osteomyelitis

• Pyometritis

• Endocarditis

• UTI

Prognosis

Mortality 30-35%. Worse prognosis in those >60 yrs

Treatment

• Penicillin, ampicillin or cephalosporin

• Resistance

  • erythromycin and clindamycin in 1-18%

  • tetracycline 85-92%

  • Resistant to aminoglycosides but combination of penicillin and gentamicin has synergistic activity and accelerates killing of grp B strep in vitro.

• Duration of therapy relatively arbitrary but most recommend 10 days for bacteraemia, 2-3 weeks for meningitis and 3-4 weeks for osteomyelitis or endocarditis

Streptococcus pneumoniae

• Alpha haemolytic

• Virulence associated with the production of an antiphagocytic capsular polysaccharide. Strains that do not produce this are non-pathogenic

• Also produce hemolysin (similar to streptolysin O of group A strep.), hyaluronidase and neuraminadase. However none of these appear to play a direct role in the disease process.

Risk factors for infection

• Important pathogen at extremes of age and in those with underlying disease

• Infection most commonly associated with:

  • Antecedent viral respiratory infection

  • Chronic conditions eg COPD, DM, CCF, renal failure

  • Smoking

  • Alcoholism

  • Splenic dysfunction or splenectomy

Clinical manifestations

• Most common cause of community acquired pneumonia and otitis media

• One of the 3 major causes of bacterial meningitis

• Important cause of septic shock and sinusitis

Treatment

• Penicillin-sensitive strains: penicillin

• Intermediate penicillin resistance (MIC 0.12-1 mcg/ml):

  • high dose penicillin

  • cefotaxime/ceftriaxone for meningitis

• Highly penicillin resistant (MIC 2 mcg/ml or above): 3rd generation cephalosporin and glycopeptide

• However recent data on penicillin resistant pneumococcal infections suggest that outcome is no different, almost regardless of the beta-lactam used

Prevention

• Currently available vaccine is a mixture of 23 pneumococcal capsular polysaccharides

• Does not cover all strains

• Insufficient antibody response seen in asplenic and elderly patients and in young children (ie the at risk groups).

• Antibody levels subside with time and may not be detectable after 5 years in older patients. Therefore, patients at high risk of pneumococcal disease should be vaccinated every 3-5 years

©Charles Gomersall, October, 2009 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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