Structures suggesting cell-wall-deficient forms detected in circulating erythrocytes by fluorochrome staining

Cell-wall-deficient (CWD) forms of bacteria are associated with certain cases of idiopathic septicemia. In this preliminary study of blood examined immediately after venipuncture, structures with a morphology characteristic of CWD forms were seen parasitizing the erythrocytes. These inclusions were usually circumferential, but in some cases they protruded from the red cells. The CWD forms were detected by staining with Gould's rhodamine-labeled muramidase, which reacted similarly to acridine orange but with greater specificity. A blocking test, employing unlabeled muramidase, indicated the specificity of the reaction between muramidase and the microbial substrate. Reaction of the forms with muramidase indicates their bacterial, rather than mycoplasmal, nature. Thus in vivo CWD forms have a detectable component of muramic acid, at least in certain cases. Sixty-eight individuals with a diagnosis of fever of unknown origin were tested, with 51 nondebilitated individuals serving as controls. More intraerythrocytic forms reacting with muramidase were found in the patients than in the controls. Nearly 40% of the cases had a relatively high incidence of erythrocyte parasitism. In some instances when freshly drawn blood was examined, the structures, which appear to be microbial, extended in rhizoid filaments from the erythrocytes.