Survival of Streptococcus pyogenes under stress and starvation

The ability of Streptococcus pyogenes to enter a quiescent stale, similar t o the stationary phase of lab cultures, is believed to be an important fact or in its ability to persist within the host and to subsequently cause dise ase. Using a model broth system, we determined that after entering the stat ionary phase, there was a 99.99% reduction in cell viability over a 4-day p eriod, following which the cells appeared to enter a resistant starvation s tale where cell numbers remained constant over the subsequent 3-4 weeks. Th is starvation response was induced by carbon or phosphorous limitation, but not by nitrogen limitation in the form of amino acids where cells became n on-culturable after 4 days, Amino acid utilization in the absence of a carb on source may be an essential factor for the long-term survival of this bac terium in the stationary phase. Early stationary phase cells showed a great er resistance to oxidative and pH stress compared to 24-h-starved cultures. There was evidence for the formation of a viable but non-culturable stale as indicated by a comparison of the numbers of cells with a functional memb rane potential (rhodamine 123) against culturable cells on either Todd Hewi tt broth agar or sheep blood agar. Long-term survival of S. pyogenes was de pendent on both cell wall and protein synthesis, suggesting that starving c ultures are a dynamic cell population. (C) 1999 Federation of European Micr obiological Societies. Published by Elsevier Science B.V. All rights reserv ed.