no mycoplasmas were detected in acridine orange-stained (A) blood smears, whereas in SEM singleM. and transmission electron microscopy, we proved that the localization ofM. suiswas intracellular. This organism invades erythrocytes in an endocytosis-like process and is initially surrounded by two membranes, and it was also found floating freely in the cytoplasm. In conclusion, we were able to prove for the first time that a member of the hemotrophic mycoplasma group is able to invade the erythrocytes of its host. Such colonization should protect the bacterial cells from the host’s immune response and hamper antibiotic treatment. In addition, an intracellular life cycle may explain the chronic nature of hemotrophic mycoplasma infections and should serve as the foundation for novel strategies in hemotrophic mycoplasma research (e.g., treatment or prophylaxis). Mycoplasma suisis a member of the familyMycoplasmataceae. This organism belongs to a group of uncultivable highly specialized bacteria which parasitize the surface of erythrocytes of a variety of mammals (34). These species represent a distinct new cluster in the genusMycoplasmaand have been given the trivial name hemotrophic mycoplasmas (HM). Infections with HM are identified clinically by overt life-threatening hemolytic anemia or by subtle chronic anemia characterized by infertility, immune suppression, and greater susceptibility to infections (34). It is noteworthy that organisms that morphologically resemble S107 hydrochloride HM have also been detected in the blood of humans (1,8,42,50). M. suiscauses febrile acute icteroanemia in pigs (IAP), which is accompanied by high numbers ofM. suiscells in the blood, as confirmed by microscopy as well as by PCR (18,21,34). Clinical symptoms are successfully cured by treatment with tetracycline. Nevertheless, once pigs are infected withM. suis, they remain lifelong carrier animals and therefore are epidemiologically important (19). ChronicM. suisinfections result in reproductive disorders in sows, growth retardation in piglets, and increased susceptibility to respiratory and enteric infections in feeder pigs.M. S107 hydrochloride suisoccurs worldwide, and chronic S107 hydrochloride IAP, in particular, is of major economic importance (19). Contrary to the well-established clinical picture of IAP (i.e., high morbidity and low mortality), we recently observed an increased incidence of acute IAP in feeder pigs with a predominantly fatal outcome despite antibiotic therapy. And contrary to the S107 hydrochloride expected high numbers ofM. suiscells on and between the erythrocytes in acridine orange-stained blood smears (the established diagnostic feature of acute IAP), S107 hydrochloride only marginal numbers of bacterial cells were observed. This microscopic finding conflicted with the results of quantitative real-time PCR, which detected high numbers ofM. suiscells (109to 1010cells per ml of blood) in the same blood samples. The striking difference between the microscopy and PCR results raises the issue of putative intracellular localization Ccr7 of a novelM. suisisolate within the erythrocytes. To date, severalMycoplasmaspecies are known to invade cells (2,28,33,46); for example,M. penetransinvades the epithelial cells of the human urogenital tract (28), andM. genitaliuminfects human lung fibroblasts (2,33).M. gallisepticumcan invade nonphagocytic cell lines, such as HeLa cells and chicken embryo fibroblasts (49), and is the only knownMycoplasmaspecies that is able to invade erythrocytes (47). The general advantages associated with invasion of eukaryotic cells by bacterial pathogens include protection from the immune system, reduction in the efficacy of antibiotics during treatment, and nutritional benefits. The intraerythrocytic localization ofM. suismight provide the organism with a supply of iron, large amounts of which can be found inside the red blood cells (RBCs) in the form of hemin, or other trace metals (47). It is known that hemin can support the growth of invasive bacteria, such asBartonella quintana(43). Moreover, the persistence of someBartonellaspecies is directly linked to nonhemolytic erythrocyte parasitism (43). However, no influence of hemin on the growth of mycoplasmas has been demonstrated so far. It is interesting that hemotrophic mycoplasmas have a tendency to establish chronic infections that often are not apparent clinically (34). The long persistence ofM. suis(and other HM) might be linked to their ability to invade the cytoplasm of host cells. Dallo and Basemann (6) assumed that the chronic nature of mycoplasma infections (M. pneumoniae,M. penetrans,M. genitalium) can be explained by a subpopulation of mycoplasmas that enter mammalian cells, where they can persist in a latent or nongrowth maintenance form. Such biological latency would.
no mycoplasmas were detected in acridine orange-stained (A) blood smears, whereas in SEM singleM
