Release of SpeA from Streptococcus pyogenes after exposure to penicillin : dependency on dose and inhibition by clindamycin

• The amount and time course of SpeA release from group A streptococci (GAS) was studied at different starting inoculae after exposure to different doses of penicillin, clindamycin or a combination of the 2. The release was related to the bacterial concentration and killing rate. A clinical GAS strain was exposed to benzylpenicillin, 2 and 1000 × MIC, clindamycin, 2 and 32 × MIC, or combinations of the 2. Samples for viable counts and SpeA analyses were drawn before and after the addition of antibiotics and at 3, 6 and 24 h. The SpeA release was higher at low than at high concentrations of penicillin and the combination (both, p < 0.05). The addition of clindamycin to penicillin reduced SpeA production at both concentrations (p < 0.01). Most SpeA was released before 3 h, and for penicillin and the combination, the amount correlated to the number of killed bacteria during this period (r = 0.50; p < 0.05). A positive correlation was found between the inoculum size and the SpeA concentration at time zero (r = 0.54; p < 0.05). The SpeA concentration was dependent on the initial number of bacteria, the class of antibiotic, the dose of penicillin and the killing rate.

Keyword

MEDICINE

MEDICIN

Publication and Content Type

ref (subject category)

art (subject category)