Culturability, injury and morphological dynamics of thermophilic Campylobacter spp. within a laboratory-based aquatic model system.

AIMS: To study the survival processes of thermophilic Campylobacter spp. within a modelled aquatic system and particularly the involvement and survival potential of viable but non-culturable forms. METHODS AND RESULTS: The survival and morphological characteristics of populations of thermophilic Campylobacter species exposed to simulated aquatic conditions were examined using a combination of cultural and microscopic techniques. Populations underwent progressive decay when exposed to simulated aquatic conditions. The rates of population decay were observed to be significantly greater at the higher temperature (20 degrees C) with a rapid transition of the dominant sub-populations from non-stressed to dead cells occurred within 3 days. At 10 degrees C the rate of culturability loss was much reduced with substantial development (approx. 80% of total population) of viable but non-culturable (VBNC) populations by all species within 3 days, declining to represent approximately 5-25% of the total population at day 60. Significant differences (P < 0.001) were identified between decay rates as a consequence of different species, sub-populations and temperature but not between sub-populations of different species. Morphological variants including spiral, elongated spirals and rods, short rods and coccoid forms were identified. The endpoints of morphological transition were temperature-independent and isolate-specific yet the rate of morphological transition was directly related to temperature and approximately equivalent between species. CONCLUSION: The VBNC state is a transitory stage in the degeneration of Campylobacter population within the aquatic environments simulated during this study. SIGNIFICANCE AND IMPACT OF THE STUDY: VBNC cells form the most persistent, viable, potentially pathogenic sub-population of Campylobacter populations exposed to aquatic stress conditions

Putative mechanisms and biological role of coccoid form formation in Campylobacter jejuni.

In certain conditions Campylobacter jejuni cells are capable of changing their cell shape from a typically spiral to a coccoid form (CF). By similarity to other bacteria, the latter was initially considered to be a viable but non-culturable form capable of survival in unfavourable conditions. However, subsequent studies with C. jejuni and closely related bacteria Helicobacter pylori suggested that CF represents a non-viable, degenerative form. Until now, the issue on whether the CF of C. jejuni is viable and infective is highly controversial. Despite some preliminary experiments on characterization of CF cells, neither biochemical mechanisms nor genetic determinants involved in C. jejuni cell shape changes have been characterized. In this review, we highlight known molecular mechanisms and genes involved in CF formation in other bacteria. Since orthologous genes are also present in C. jejuni, we suggest that CF formation in these bacteria is also a regulated and genetically determined process. A possible significance of CF in the lifestyle of this important bacterial pathogen is discussed

Observation of the Gamma-Ray Binary HESS J0632+057 with the H.E.S.S., MAGIC, and VERITAS Telescopes

The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the Hα emission line. A significant detection of the modulation of the very high-energy gamma-ray fluxes with a period of 316.7 ± 4.4 days is reported, consistent with the period of 317.3 ± 0.7 days obtained with a refined analysis of X-ray data. The analysis of data from four orbital cycles with dense observational coverage reveals short-timescale variability, with flux-decay timescales of less than 20 days at very high energies. Flux variations observed over a timescale of several years indicate orbit-to-orbit variability. The analysis confirms the previously reported correlation of X-ray and gamma-ray emission from the system at very high significance, but cannot find any correlation of optical Hα parameters with fluxes at X-ray or gamma-ray energies in simultaneous observations. The key finding is that the emission of HESS J0632 + 057 in the X-ray and gamma-ray energy bands is highly variable on different timescales. The ratio of gamma-ray to X-ray flux shows the equality or even dominance of the gamma-ray energy range. This wealth of new data is interpreted taking into account the insufficient knowledge of the ephemeris of the system, and discussed in the context of results reported on other gamma-ray binary systems