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Coag. -ve staph.

Up Coag. -ve staph. Listeria Staphylococcus aureus Streptococci


Coagulase negative staphylococci

Important species:

  • S. epidermidis
  • S. saprophyticus

All humans are colonized with S. epidermidis. However it is increasingly being recognized as a cause of nosocomial infection.

Pathogenicity

  • Coagulase negative staphylococci become potentially pathogenic as soon as the natural balance between micro-organisms and the immune system is disturbed: immunocompromised patients are particular susceptible to intravascular catheter related infection.
  • Pathogenicity is increased by the ability to adhere to biomedical devices

Clinical manifestations of infection

Catheter-related infections

S. epidermidis is the most frequently isolated CNSS in catheter-related infections

CSF shunt infections

  • S. epidermidis and S. aureus are the most frequently encountered isolates in shunt infections
  • Usually occur within 2 weeks of implantation or manipulation
  • Non-specific clinical features

CAPD peritonitis

  • S. epidermidis by far the most commonly isolated organism
  • ~ 40% of patients having CAPD develop peritonitis within the first year
  • Criteria for diagnosis. Combination of:
    • Abdominal pain
    • Cloudy fluid containing >100 WBC/ml (predominance of polymorphs)
    • Positive dialysate culture

Endocarditis

  • Infection of native valves is uncommon (~5% of all cases of infective endocarditis)
  • With S. aureus accounts for the majority of cases of nosocomial infective endocarditis.
  • Causes ~40% of cases of prosthetic valve endocarditis.
    • Usually associated with valve dysfunction
    • Site of infection is most frequently the valve sewing ring. Results in complications such as dehiscence, arrhythmias, obstruction of the valve orifice. This site is relatively protected from antibiotics.
    • Indolent clinical picture with absence of classical features of endocarditis (peripheral emboli, multiple positive blood cultures).
    • Most patients become infected at the time of cardiac surgery. Incubation time:2-13 months.

Infections in the immunocompromised

  • Particularly affects neonatal ICU patients and oncology patients
  • Usually associated with use of foreign devices, especially central venous catheters.

Urinary tract infection

S. saprophyticus can cause UTI. Almost invariably occurs in women aged 16-25 who are not sexually active.

 

©Charles Gomersall, April, 2014 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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