Some strains of Group B streptococcus (Streptococcus agalactiae) may be tolerant to penicillins. This may have a number of implications for the patient.
A tolerant strain may be associated with persistent or recurrent infections that cannot be explained by re-exposure, noncompliance or other mechanism.
Tolerance may be defined in several ways.
(1) minimum bacteriocidal concentration much higher than the minimum inhibitory concentration (MBC to MIC ratio >= 32)
(2) kinetic killing curve demonstrating a higher than normal concentration of culture forming units following exposure to a penicillin
Proposed mechanisms for tolerance:
(1) selection for strains with impaired self-destruction mechanism
(2) variation in antibiotic susceptibility related to environmental factors such as pH
A tolerant strain of Group B Streptococci often responds promptly to combined penicillin and aminoglycoside therapy.
To read more or access our algorithms and calculators, please log in or register.
