S. aureus and E. coli Co-culture Growth Under Shear

Growing monocultures of two different species of human commensal/pathogenic bacteria, Staphylococcus aureus – a non-motile grampositive coccus and Escherichia coli – a motile gram-negative rod, were characterized using a real-time in situ rheology and rheo-imaging strategy. Subjecting bacterial populations to a shear flow is a closer approximation to bacterial thriving in the host, where they experience mechanical forces such as arterial or venous pressure. For both cultures, as the cell density of the population increases, cells rearrange themselves in different aggregates, capable of strongly influencing their environment, and leading to very different physical rheological responses, where motility appears to be determinant. One of the most striking observations is the behavior of the viscosity growth curve, showing dramatic value variations, with no counterpart in traditional biological measurements, as well as the coupling between translational and rotational motion of the E. coli aggregates along the growth curve [1], while S. aureus cells tend to sediment [2], over long periods of time. In the present study, a similar approach was applied to a co-culture of these two bacteria, S. aureus and E. coli, to evaluate the effect of possible interspecies interactions on the viscosity curve of the culture, during growth, when subject to a shear flow. Surprisingly, the observed behavior of the viscosity growth curve was enhanced in comparison to each individual curve and reveals a combination of details specific of each monoculture, suggesting synergy between these two bacterial species. After the rheological analysis, the final co-culture was recovered and inoculated on different solid media that allow to distinguish the development of S. aureus or E. coli colonies. Unexpectedly, S. aureus showed the capacity to accelerate its growth rate relatively to E. coli, when the two-species community is subjected to a shear flow. This behavior may reflect the occurrence of specific growth adaptations during co-culture upon shear flow, getting one step closer to physiological conditions.info:eu-repo/semantics/publishedVersio

Adaptations to the Arctic: low-temperature development and cold tolerance in the free-living stages of a parasitic nematode from Svalbard

For nematodes with a direct life cycle, transmission is highly dependent on temperature-related development and survival of the free-living stages. Therefore, in the Arctic, where the winter lasts from October to May, nematode transmission is expected to be focused in the short summer season, yet there is strong evidence that as well as focussing egg output during winter months, the nematode parasite, Marshallagia marshalli, infects Svalbard reindeer during the Arctic winter when temperatures are persistently below freezing. To investigate the potential for development and survival of eggs and infective third-stage larvae in winter and therefore the possibility of for winter transmission, we ran a series of low-temperature laboratory experiments. These provide five key insights into the transmission and survival of the free-living stages of M. marshalli: (1) eggs hatched at temperatures as low as 2 degrees C, but not below 0 degrees C, (2) eggs were viable and developed after being exposed to sub-zero temperatures for up to 28 months, (3) infective-stage larvae survived for up to 80 days at 5 degrees C, (4) infective-stage larvae could survive rapid exposure to temperatures below -30 degrees C, and (5) desiccation resistance may be important for long-term larval survival at low temperatures. Together, these results indicate that eggs deposited during the winter are highly tolerant of prevailing environmental conditions and have the potential for rapid development with the onset of spring. It is therefore likely that the parasite remains in the egg stage in the faeces during the winter of deposition, hatch and develop into the infective larval stage in the summer, remaining viable on the tundra until the reindeer host returns to the winter feeding grounds the following winter