Mycoplasmas are no exception to extracellular vesicles release: Revisiting old concepts

Release of extracellular vesicles (EV) by Gram-negative and positive bacteria is being frequently reported. EV are nano-sized, membrane-derived, non-self-replicating, spherical structures shed into the extracellular environment that could play a role in bacteria-host interactions. Evidence of EV production in bacteria belonging to the class Mollicutes, which are wall-less, is mainly restricted to the genus Acholeplasma and is scanty for the Mycoplasma genus that comprises major human and animal pathogens. Here EV release by six Mycoplasma (sub)species of clinical importance was investigated. EV were obtained under nutritional stress conditions, purified by ultracentrifugation and observed by electron microscopy. The membrane proteins of EV from three different species were further identified by mass spectrometry as a preliminary approach to determining their potential role in host-pathogen interactions. EV were shown to be released by all six (sub)species although their quantities and sizes (30-220 nm) were very variable. EV purification was complicated by the minute size of viable mycoplasmal cells. The proteins of EV-membranes from three (sub)species included major components of host-pathogen interactions, suggesting that EV could contribute to make the host-pathogen interplay more complex. The process behind EV release has yet to be deciphered, although several observations demonstrated their active release from the plasma membrane of living cells. This work shed new light on old concepts of "elementary bodies" and "not-cell bound antigens".

Free exopolysaccharide from Mycoplasma mycoides subsp. mycoides possesses anti-inflammatory properties

In this study we explored the immunomodulatory properties of highly purified free galactan, the soluble exopolysaccharide secreted by Mycoplasma mycoides subsp. mycoides (Mmm). Galactan was shown to bind to TLR2 but not TLR4 using HEK293 reporter cells and to induce the production of the anti-inflammatory cytokine IL-10 in bovine macrophages, whereas low IL-12p40 and no TNF-α, both pro-inflammatory cytokines, were induced in these cells. In addition, pre-treatment of macrophages with galactan substantially reduced lipopolysaccharide (LPS)-induced production of pro-inflammatory cytokines TNF- and IL-12p40 while increasing LPS-induced secretion of immunosuppressive IL-10. Also, galactan did not activate naïve lymphocytes and induced only low production of the Th1 cytokine IFN-γ in Mmm-experienced lymphocytes. Finally, galactan triggered weak recall proliferation of CD4+ T lymphocytes from contagious bovine pleuropneumonia-infected animals despite having a positive effect on the expression of co-stimulatory molecules on macrophages. All together, these results suggest that galactan possesses anti-inflammatory properties and potentially provides Mmm with a mechanism to evade host innate and adaptive cell-mediated immune responses.

Contagious bovine pleuropneumonia vaccines and control strategies: recent data

Contagious bovine pleuropneumonia is one of the most threatening transboundary cattle disease in Africa. However, with the exception of Botswana, very few African countries were able to implement eradication strategies for this disease, after it had recently re-infected a number of countries. Previous experimental studies have shown that emergency vaccination campaigns, based on a single injection, were not inducing a sufficient protection level to prevent further spread of the disease. In addition, post-vaccinal reactions were sometimes reported in the field when using vaccine strain T1/44, leading cattle owners to refuse the vaccination. On the contrary, antibiotics are used quite often in the field but there are insufficient data to assess their efficacy properly. Therefore experimental studies were implemented: (i) to check if higher dosages of the vaccine would be able to induce higher protection rates and (ii) to elucidate the origin of the post-vaccinal reactions observed with T1/44 and (iii) to gain preliminary results on the efficacy of long-acting tetracycline. The first experiment included the use of three doses of vaccine strains T1/44 and T1sr: 10(7), 10(8) and 10(9) mycoplasmas per dose. T1/44 seemed to induce a higher protection (70%) than T1sr (60%). However, there was no observable dose effect for these vaccine strains. The second experiment was performed by injecting various MmmSC strains subcutaneously into susceptible cattle. One of these strains was an isolate obtained from a "Willems" reaction following a vaccination with T1/44. This isolate, called T1B, induced typical invading oedema at the injection site in a similar way to the pathogenic strain, whereas the original T1/44 vaccine strain did not. These findings indicate that the strain has reverted to virulence. Finally the antibiotic trials showed that long-acting tetracycline was able to reduce the losses due to the disease but could not prevent the persistence of viable MmmSC in treated animals. The consequences of these findings are discussed. They reinforce the need for additional research on new vaccines able to elicit longer lasting protection. However, once continuing additional field research is obtained, it should allow better defined strategies to be put in place. Meanwhile, immediate action should be taken to prevent the further spread of CBPP in the Southern part of Africa.