Features of a vancomycin-tolerant Gram positive bacterium causing infection in a cancer patient:
(1) The minimum inhibitory concentration (MIC) of the organism to vancomycin is in the susceptible range.
(2) The organism is associated with an infection that does not respond as expected to vancomycin.
(3) The minimum bactericidal concentration (MBC) is >= 32 times the MIC.
(4) The infection responds quickly after there is a change in the antibiotic regimen (addition of gentamicin, gentamicin + rifampin, or other antibiotics).
Gram-positive bacteria that may display vancomycin tolerance include:
(1) Staphylococcus aureus
(2) Group G Streptococcus
(3) Staphylococcus epidermidis
(4) Streptococcal mitis
(5) Streptococcus sanguis
(6) Streptococcus pneumoniae
Tolerance is not antibiotic resistance per se but it may be a first step in the progression of a pathway to vancomycin resistance.
