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Electron microscopy study revealed changes in the ultrastructure of bacteria of Yersinia pseudotuberculosis strains characterized by significantly reduced reproductive ability and virulence potential after long-term storage at low temperature of 4-8°C. Most bacterial cells contained dark cytosol with reduced cellular material or empty cytosol, while the cell wall was preserved. The revealed ultrastructural changes in the bacterial cells of the static culture of Y. pseudotuberculosis suggest that storage of strains under low positive temperatures could induce the transition of the majority of bacterial cell population to a dormant, non-cultivated state with a decrease in their virulence. This fact is of great scientific and applied importance in studies of causative agents of saprozoonoses, including pseudotuberculosis, which has the etiopathogenetic background of persistent infection. [ABSTRACT FROM AUTHOR]

Listeria (L.) monocytogenes is an environmental bacterium that may become an intracellular pathogen upon ingestion to cause gastroenteritis, septicaemia, abortions, and/or fatal infections of the central nervous system. We here describe a L. monocytogenes field strain (JF5171) isolated from a bovine placenta in the context of abortion, which exhibited attenuation in bovine brain-slice cultures. The whole genome of strain JF5171 was sequenced, and the invasion, replication, and intercellular spread of JF5171 were further analyzed by quantification of colony forming units and immunofluorescence studies. Phospholipase and hemolysis activity of JF5171 were also quantified along with transcription levels of actA , hly and prfA . The data obtained were compared to those of the widely used L. monocytogenes reference strain, EGD-e. JF5171 exhibited reduced replication and lower levels of phospholipase and hemolysis activity. Invasion and cell-to-cell spread was strongly decreased compared to EGD-e, and actin polymerization was absent. A frame shift deletion was identified in the JF5171 coding region of the major regulator for virulence, prfA . This resulted in a truncated C-terminus sequence (WEN* vs . WGKLN*). In addition, a point mutation resulted in a lysine to arginine substitution at amino acid position 197. Complementation with prfA from EGD-e and with (EGD-e) prfA -K197N increased the replication and spread efficiency of JF5171. In contrast, complementation with the truncated version of prfA had no effect. Taken together, these results suggest that the truncated C-terminus of prfA considerably contributes to the strongly attenuated phenotype observed in vitro . [ABSTRACT FROM AUTHOR]

Background: Since 2010, a variant Porcine epidemic diarrhea virus (PEDV), which causes an acute, highly contagious, and devastating viral enteric disease with a high mortality rate in suckling pigs, broke out in China and spread rapidly to neighboring countries, even to the North America. This virus gradually became the main subtype of PEDV worldwide. However, there were no reports of mild pathogenicity of a variant porcine epidemic diarrhea virus in China. Findings: In 2013, a PEDV-positive sample from a sow with very mild clinical sign was used to inoculate in Vero cells to isolate the virus. This PEDV field strain, designated FL2013 strain, was successfully propagated and genetically characterized. The phylogenetic trees based upon either the complete genome or S gene showed that the FL2013 strain belongs to the genogroup G2b. The S gene of FL2013 has a 7-aa deletion (FEKVHVQ) in the C-terminus comparison with the other G2 PEDV sequences. Further comparative pathology study indicated that the FL2013 strain had reduced virulence to newborn piglets. Conclusions: A novel variant PEDV strain FL2013 with reduced virulence, as determined by the pathological study, was identified from east China. This strain is closely related to the genogroup-2 PEDV strains prevalent in the U.S. and China currently, but had a short deletion at the 3'- end of the spike gene. [ABSTRACT FROM AUTHOR]

Sterilisation of parasites prevents host reproduction, thereby diverting host resources to their own benefit. Previous theory predicts that parasites should evolve maximum virulence, yet hosts are often incompletely sterilised. Whereas prior attempts to resolve this paradox have sought evolutionary explanations, we present theory and experiments showing that incomplete sterilisation can arise from ecologically driven fluctuations in parasite load. The African ant-plant Acacia drepanolobium reproduced more when occupied by small colonies of the sterilising symbiont Crematogaster nigriceps. In nature, small colonies result from interference competition between ant colonies; these territorial conflicts thus provide intermittent windows of opportunity for host reproduction. Our mean-field model shows that numerical insufficiency of parasites can produce partial sterilisation of host populations, creating the appearance of reduced virulence even if ants have evolved to sterilise completely. This general framework helps explain both the apparent ubiquity of partial sterilisation parasitism and the ability of these symbiotic associations to persist. [ABSTRACT FROM AUTHOR]

A novel approach for the autonomous virulence adaptation (AVA) of competing populations in a coevolutionary optimization framework is presented. Previous work has demonstrated that setting an appropriate virulence, v, of populations accelerates coevolutionary optimization by avoiding detrimental periods of disengagement. However, since the likelihood of disengagement varies both between systems and over time, choosing the ideal value of v is problematic. The AVA technique presented here uses a machine learning approach to continuously tune v as system engagement varies. In a simple, abstract domain, AVA is shown to successfully adapt to the most productive values of v. Further experiments, in more complex domains of sorting networks and maze navigation, demonstrate AVA's efficiency over reduced virulence and the layered Pareto coevolutionary archive. [ABSTRACT FROM AUTHOR]

MDR Pseudomonas aeruginosa strains are isolated from clinical specimens with increasing frequency. It seems that acquiring genes which determine antibiotic resistance usually comes at a biological cost of impaired bacterial physiology. There is no information on investigations comparing phenotypic differences in MDR and MDS P. aeruginosa strains in literature. The study included 150 clinical P. aeruginosa isolates (75 classified as MDS and 75 as MDR). PFGE analysis revealed five pairs of identical isolates in the group of MDR strains and the results obtained for these strains were not included in the statistical analyses. MDR strains adhered to polystyrene to a lesser extent than MDS strains. The growth rate in the liquid medium was significantly lower for MDR strains. Detectable amounts of alginate were present in the culture supernatants of seven MDS and six MDR strains. The MDR P. aeruginosa strains which were investigated produced significantly lower amounts of extracellular material binding Congo Red, lower lipolytic, elastase, LasA protease, phospholipase C activity and pyocyanin quantity in culture supernatants when compared with MDS strains. No significant differences were observed between MDR and MDS strains in proteolytic activity. In conclusion, the MDR P. aeruginosa strains have impaired virulence when compared to MDS strains. [ABSTRACT FROM AUTHOR]

Competition is an important evolutionary force behind population regulation and community structures. The degree of competition symmetry (competition hierarchies) between species determines coexistence, exclusion, or niche differentiation. Intraspecific competition, however, is an important component in dictating levels of symmetry/asymmetry between species and should be accounted for when attempting to understand interspecific evolutionary or ecological outcomes. Some social parasites compete for access to a common host and, thus, adhere to both parasite-host and predator-prey coevolutionary and ecological dynamics. Here I examine tripartite evolutionary dynamics with respect to intraspecific competition of two sympatric slave-making social parasites in the family of ants that conduct "brood raids" on a shared host species and use the captured brood as a functional work force. Slave-makers were challenged with either a conspecific or heterospecific parasite and the impact on hosts and parasites was evaluated. Within-species raiding occurred frequently in the "prudent" slave-maker but was almost nonexistent in the "virulent" slave-maker. Although intraspecific raiding led to larger single prudent slave-maker colonies, the preservation of two independent virulent slave-maker colonies had an early and a more devastating effect on the host. However, in response to synchronized raiding phenologies the prudent slave-maker emerged as the better direct competitor against the virulent slave-maker. Sex ratios were male biased in the virulent slave-maker colonies but numerically equal (hence female biased) in prudent slave-maker colonies. Combined, these results suggest that interspecific parasite interactions have produced ecological shifts in both slave-makers and attenuated the coevolutionary arms race between the prudent slave-maker and the shared host in sympatric populations. [ABSTRACT FROM AUTHOR]