Examples: Staphylococcus epidermidis, Corynebacteria species
When to consider a "contaminant" as a pathogenic organism:
(1) The patient is immunocompromised or has impaired host defenses.
(2) The culture is taken from a normally sterile site (CSF, blood, etc) with careful attention to proper collection technique.
(3) The same isolate is isolated on multiple cultures.
(4) The organism is present in pure culture.
(5) The organism is present in high numbers on Gram stain and culture.
(6) The Gram stain shows a host response to the organism (inflammatory cells with ingested bacteria, etc).
When to be particularly careful about interpreting the results:
(1) The culture or Gram stain shows multiple bacterial types.
(2) There is doubt about how well the specimen was collected.
(3) There is no sign of infection or host response to the bacteria.
