Atypical behaviour and survival of Streptococcus pyogenes L forms during intraperitoneal infection in rats

Groups of rats were injected intraperitoneally with cell wall-deficient (L) forms of Streptococcus pyogenes, with their parental (S) forms, as well as with a combined inoculum of both forms (S+L). Peritoneal exudate samples w ere harvested on days 1, 3, 7, 15 and 30 after challenge and were investiga ted by microbiological, electron microscopic, cytometric and biochemical me thods. Parental S forms were isolated from peritoneal exudate samples up to day 15 post infection, while L form cultures were isolated until the end o f the examined interval. Electron microscopic examination revealed continuo us adhesion of L forms on the macrophage surface as well as intracellular p ersistence inside them. It was demonstrated that the intraperitoneal inflam matory response to L form infection was higher than to the other infections and the monocyte-macrophage populations were predominant. The established atypical behaviour and long survival of S. pyogenes L forms in the rat's pe ritoneum could explain some of the mechanisms of the pathogens' persistence as well as the reasons for chronic streptococcal infections. (C) 2000 Fede ration of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.