Localization and persistence of spiroplasmas in an experimental brain infection in suckling rats

Spiroplasma Infection among Ixodid Ticks Exhibits Species Dependence and Suggests a Vertical Pattern of Transmission

Members of the genus Spiroplasma are Gram-positive bacteria without cell walls. Some Spiroplasma species can cause disease in arthropods such as bees, whereas others provide their host with resistance to pathogens. Ticks also harbour Spiroplasma, but their role has not been elucidated yet. Here, the infection status and genetic diversity of Spiroplasma in ticks were investigated using samples collected from different geographic regions in Japan. A total of 712 ticks were tested for Spiroplasma infection by PCR targeting 16S rDNA, and Spiroplasma species were genetically characterized based on 16S rDNA, ITS, dnaA, and rpoB gene sequences. A total of 109 samples originating from eight tick species were positive for Spiroplasma infection, with infection rates ranging from 0% to 84% depending on the species. A linear mixed model indicated that tick species was the primary factor associated with Spiroplasma infection. Moreover, certain Spiroplasma alleles that are highly adapted to specific tick species may explain the high infection rates in Ixodes ovatus and Haemaphysalis kitaokai. A comparison of the alleles obtained suggests that horizontal transmission between tick species may not be a frequent event. These findings provide clues to understand the transmission cycle of Spiroplasma species in wild tick populations and their roles in host ticks.

The case for involvement of spiroplasma in the pathogenesis of transmissible spongiform encephalopathies

Spiroplasma biofilm formation explains the role of these wall-less bacteria in the pathogenesis of transmissible spongiform encephalopathies (TSEs). Spiroplasma embedded in the biofilm polysaccharide matrix are markedly resistant to physical and chemical treatment, simulating the biologic properties of the TSE agent. Microcolonies of spiroplasma embedded in biofilm bound to clay are the likely mechanism of lateral transmission of scrapie in sheep and chronic wasting disease in deer via soil ingestion. Spiroplasma in biofilm bound to the stainless steel of surgical instruments may also cause iatrogenic transmission of Creutzfeldt-Jakob disease. Sessile spiroplasma in biofilm attach to the surface by curli-like fibrils, a functional amyloid that is important for spiroplasma entering cells. Curli fibers have been shown to interact with host proteins and initiate formation of a potentially toxic amyloid that multiplies by self-assembly. In TSE, this mechanism may explain how spiroplasma trigger the formation of prion amyloid. This possibility is supported by experiments that show spiroplasma produce α-synuclein in mammalian tissue cultures. The data linking spiroplasma to neurodegenerative diseases provide a rationale for developing diagnostic tests for TSE based on the presence of spiroplasma-specific proteins or nucleic acid. Research efforts should focus on this bacterium for development of therapeutic regimens for Creutzfeldt-Jakob disease.

Spiroplasma spp. biofilm formation is instrumental for their role in the pathogenesis of plant, insect and animal diseases

Spiroplasma spp. are important phyto and insect pathogens, and candidate causal agent/s of transmissible spongiform encephalopathies (TSE) in man and animals. These filterable wall-less bacteria are widely distributed in nature with an unspecified environmental reservoir. In this study we showed by scanning electron microscopy that spiroplasma form biofilm on an assortment of hard surfaces including mica, nickel and stainless steel. Spiroplasma were stuck to the surfaces by fibrillar threads consistent with curli fibers (an amyloid protein found in bacterial biofilms). After a lengthy time in cultures (6 weeks), spiroplasma in biofilm bound to mica disks lost their spiral shapes and formed coccoid forms interconnected by long (>2 μm) branched membranous nanotubules, therein representing direct conjugate connections between the cells. The affinity of spiroplasma biofilms for mica and nickel, and the membrane communications suggest that soil could be a reservoir for these bacteria. The persistence of clay bound spiroplasma in soil could serve as the mechanism of lateral spread of TSEs by ingestion of soil by ruminants. Spiroplasma binding to stainless steel wire supports bacterial contamination of surgical instruments following surgery on dementia patients as a mechanism of iatrogenic transmission of TSEs, especially with resistance of spiroplasma in biofilms to drying or exposure to 50% glutaraldehyde. The discovery of biofilm formation by spiroplasma addresses questions regarding environmental persistence of these organisms in nature and suggests novel mechanisms of intercellular communication and transmission.

Effect of trimethoprim/sulphamethoxazole and hyperbaric oxygen on experimental Spiroplasma mirum encephalitis

This study was undertaken to determine the susceptibility of experimentally induced Spiroplasma mirum infection in the rat to trimethoprim/sulfamethoxazole (TMP/SMX) in combination with hyperbaric oxygen (HBO). One-day-old Fisher 344 rats were intracerebrally inoculated with the GT-48 strain of S. mirum and were exposed to regimens employed combined antibiotic and HBO treatments. The exclusive use of TMP/SMX produced a significant reduction in mortality (P less than 0.0001) and an absence of clinical signs of infection. HBO in combination with TMP/SMX showed similar effect on mortality and no evident clinical disease. The addition of HBO did result in a significant decrease in spiroplasma brain titres but was no more effective in preventing the spiroplasma-induced fatal microcystic encephalopathy than when the antibiotics were used alone. The exclusive use of HBO produced a catastrophic mortality rate in the spiroplasma-infected rats, which is contrary to the effect of HBO on conventional bacterial infections.

Antiserum to scrapie-associated fibril protein cross-reacts with Spiroplasma mirum fibril proteins

Protease-resistant fibril proteins purified from Spiroplasma mirum and from Creutzfeldt-Jakob disease-infected brain tissues reacted with antisera to scrapie-associated fibrils on Western immunoblot analysis. These data suggest that there are conformational similarities among spiroplasma proteins and infection-specific proteins of the transmissible spongiform encephalopathies.

Neurotropic response of Spiroplasma mirum following peripheral inoculation in the rat

Spiroplasma mirum experimentally produces a persistent brain infection in suckling rats when administered intracerebrally. In order to examine spiroplasma infection induced by a more natural route, suckling rats were inoculated both intraperitoneally and subcutaneously with strain GT-48. No mortality was recorded over a 50-day study period. Rats developed localized alopecia and showed a significant reduction in body weight. Minimal pathological alterations were observed in brain tissues, in addition to cataracts, retinal degeneration and panophthalmitis. Spiroplasmas were recovered from brain and spleen on day 2 following peripheral inoculation with highest titres in the spleen. Spleen titres significantly declined (p less than 0.022) during the 50-day study period. On day 50, brain titres exceeded those in the spleen. The attraction of spiroplasma to central nervous system tissues may be related to its nutritional dependence on sterols.

Malignant transformation of NIH-3T3 and CV-1 cells by a helical mycoplasma, Spiroplasma mirum, strain SMCA

A helical mycoplasma, Spiroplasma mirum strain SMCA, produced malignant transformation in mouse NIH 3T3 cells and monkey kidney CV-1 cells. The transformed cells exhibited morphological changes consistent with the transformed phenotype, grew in soft agar and produced tumors in athymic and BALB/c mice. Transmission electron microscopy revealed structures morphologically similar to mycoplasmas present in the cytoplasm of transformed but not untransformed 3T3 cells. The time of inoculation of S. mirum SMCA to 3T3 cells and the passage level of 3T3 cells affected transformation.