Fastidious microorganisms
Fastidious microorganisms are rarely implicated in BSI in
clinical practice, but when they are isolated from blood
cultures they often represent serious infection. In some cases,
the observation of signal-positive Gram stain-negative blood
culture results provides a clue that a fastidious microorganism
might be implicated as the BSI aetiological agent. In those
cases, collaboration between the laboratory and clinician is
essential to ensure that appropriate steps are taken to increase
the odds of isolation of such organisms. Some organisms may
be small or of unusual morphology, and not readily recognized
by the technologist. In other cases, the organism may not stain
well with standard Gram stain protocols (e.g. Mycoplasma and
Campylobacter). In those cases, alternative staining techniques
may be employed, including the use of acridine orange (to stain
bacterial nucleic acids) or the use of carbol fuschin as an
alternative to safranin as a counterstain in the Gram stain