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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
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
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.
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