Characterization of Ligand-Receptor Interactions: Chemotaxis, Biofilm, Cell Culture Assays, and Animal Model Methodologies

Molecular structures mediating adhesion of Campylobacter jejuni to abiotic and biotic surfaces

Microaerophilic, Gram-negative Campylobacter jejuni is the causative agent of campylobacteriosis, the most common bacterial gastrointestinal infection worldwide. Adhesion is the crucial first step in both infection or interaction with the host and biofilm formation, and is a critical factor for bacterial persistence. Here we describe the proteins and other surface structures that promote adhesion to various surfaces, including abiotic surfaces, microorganisms, and animal and human hosts. In addition, we provide insight into the distribution of adhesion proteins among strains from different ecological niches and highlight unexplored proteins involved in C. jejuni adhesion. Protein-protein, protein-glycan, and glycan-glycan interactions are involved in C. jejuni adhesion, with different factors contributing to adhesion to varying degrees under different circumstances. As adhesion is essential for survival and persistence, it represents an interesting target for C. jejuni control. Knowledge of the adhesion process is incomplete, as different molecular and functional aspects have been studied for different structures involved in adhesion. Therefore, it is important to strive for an integration of different approaches to obtain a clearer picture of the adhesion process on different surfaces and to consider the involvement of proteins, glycoconjugates, and polysaccharides and their cooperation.

Atomic Force Microscopy (AFM) As a Surface Mapping Tool in Microorganisms Resistant Toward Antimicrobials: A Mini-Review

The worldwide emergence of antimicrobial resistance (AMR) in pathogenic microorganisms, including bacteria and viruses due to a plethora of reasons, such as genetic mutation and indiscriminate use of antimicrobials, is a major challenge faced by the healthcare sector today. One of the issues at hand is to effectively screen and isolate resistant strains from sensitive ones. Utilizing the distinct nanomechanical properties (e.g., elasticity, intracellular turgor pressure, and Young’s modulus) of microbes can be an intriguing way to achieve this; while atomic force microscopy (AFM), with or without modification of the tips, presents an effective way to investigate such biophysical properties of microbial surfaces or an entire microbial cell. Additionally, advanced AFM instruments, apart from being compatible with aqueous environments—as often is the case for biological samples—can measure the adhesive forces acting between AFM tips/cantilevers (conjugated to bacterium/virion, substrates, and molecules) and target cells/surfaces to develop informative force-distance curves. Moreover, such force spectroscopies provide an idea of the nature of intercellular interactions (e.g., receptor-ligand) or propensity of microbes to aggregate into densely packed layers, that is, the formation of biofilms—a property of resistant strains (e.g., Staphylococcus aureus, Pseudomonas aeruginosa). This mini-review will revisit the use of single-cell force spectroscopy (SCFS) and single-molecule force spectroscopy (SMFS) that are emerging as powerful additions to the arsenal of researchers in the struggle against resistant microbes, identify their strengths and weakness and, finally, prioritize some future directions for research.

Peculiarities of Biofilms Formation by Campylobacter Bacteria in Mixed Populations with Other Microbial Contaminants of Food Products

Peculiarities of biofilms formation by Campylobacter bacteria in mixed populations with other microbial contaminants was studied by real-time impedance spectroscopy on an automated xCelligence real time cell analyzer (RTCA). This method is based on measuring the medium resistance in special plates (E-plates) with interdigitated microelectrodes. Coculturing of campylobacter with coliform bacteria is accompanied by film formation; the intensity of this process varies depending on the type of the test cultures and the nature of their interaction in mixed populations. Film formation by C. jejuni during co-culturing with enterobacteria is maximum during the first hours and depends on the presence of stress factors in the environment. The biomatrix film was synthesized by 3 times more intensively in the presence of oxygen than in microaerobic conditions, and also by 1.7-4.3 times more active in the mixed culture with Enterobacter cloacae, E. coli, and K. pneumoniae. During co-culturing of campylobacter with salmonella, no enhanced film formation by the tested strains was observed. Unlike members of the genus Enterobacter intensively producing exopolysaccharides, pathogenic member of Enterobacteriaceae, salmonella, demonstrated weak capacity to form film matrix. The study of film formation by Campylobacter allows more accurate assessment of the effectiveness of sanitary bactericidal treatment of food industry facilities, predict the appearance of biofilms and the intensity of their formation depending son the nature of the antimicrobial effect and the used means.

A peculiar case of Campylobacter jejuni attenuated aspartate chemosensory mutant, able to cause pathology and inflammation in avian and murine model animals

An attenuated Campylobacter jejuni aspartate chemoreceptor ccaA mutant caused gross pathological changes despite reduced colonisation ability in animal models. In chickens, the pathological changes included connective tissue and thickening of the mesenteric fat, as well as the disintegration of the villus tips in the large intestine, whereas in mice, hepatomegaly occurred between 48–72 hours post infection and persisted for the six days of the time course. In addition, there was a significant change in the levels of IL-12p70 in mice infected with the C. jejuni ccaA mutant. CcaA isogenic mutant was hyper-invasive in cell culture and microscopic examination revealed that it had a “run” bias in its “run-and-tumble” chemotactic behaviour. The mutant cells also exhibited lower level of binding to fucosylated and higher binding to sialylated glycan structures in glycan array analysis. This study highlights the importance of investigating phenotypic changes in C. jejuni, as we have shown that specific mutants can cause pathological changes in the host, despite reduction in colonisation potential.