Interaction of alveolar macrophages with Staphylococcus aureus and induction of microbial L-forms during infection in rats

In vivo cell interactions between Staphylococcus lis aureus and rat alveola r macrophages were investigated after intranasal inoculation during a 30-da ys period of examination. Some dynamic characteristics of microorganisms in the macrophages were examined by electron microscopy and acid phosphatase cytochemistry. it was found that at earlier infection intervals (days 3 and 7) the ingested cocci were sequestered in phagosomes and phagolysosomes an d later many of the microbial cells were digested. An interesting finding w as the intracellular appearance of cell wall-defective forms ii-forms) of i i. aureus at later intervals (days 14 and 30 after challenge). Infection ki netics were evaluated by isolation and enumeration of colony-forming units of S. aureus from bronchoalveolar fluid and by assessment of blood and bron choalveolar total and differential leukocyte counts. The results indicate t hat induction and survival of S. aureus L-forms may occur spontaneously in vivo. This phenomenon could explain some of the mechanisms, provoking the l atent and relapsing lung infections.