Formation of Biofilms by Foodborne Pathogens and Development of Laboratory In Vitro Model for the Study of Campylobacter Genus Bacteria Based on These Biofilms

Assessment of biofilm formation by Campylobacter spp. isolates mimicking poultry slaughterhouse conditions

This research aimed to assess the biofilm formation ability of Campylobacter strains under temperature and oxygen stress conditions, similar to those found in the industrial environment, to explain the persistence of this pathogen on the poultry slaughter line. A collection of C. jejuni and C. coli isolates (n = 143) obtained from poultry samples (cecal content and neck skin), collected at slaughterhouse level, from diverse flocks, on different working days, was genotyped by flaA-restriction fragment length polymorphism (RFLP) typing method. A clustering analysis resulted in the assignment of 10 main clusters, from which 15 strains with different flaA-RFLP genotypes were selected for the assessment of biofilm formation ability and antimicrobial susceptibility. Biofilm assays, performed by crystal violet staining method, were conducted with the goal of mimicking some conditions present at the slaughterhouse environment, based on temperature, atmosphere, and contamination levels. Results indicated that many C. jejuni strains with similar flaA-RFLP profiles were present at the slaughterhouse on different processing days. All the strains tested (n = 15) were multidrug-resistant except for one. Biofilm formation ability was strain-dependent, and it appeared to have been affected by inoculum concentration, temperature, and tolerance to oxygen levels. At 10°C, adherence levels were significantly lower than at 42°C. Under microaerobic and aerobic atmospheres, at 42°C, 3 strains (C. jejuni 46E, C. jejuni 61C, and C. coli 65B) stood out, exhibiting significant levels of biofilm formation. C. jejuni strains 46E and 61C were inserted in clusters with evidence of persistence at the slaughterhouse for a long period of time. This study demonstrated that Campylobacter strains from broilers are capable of forming biofilms under conditions resembling the slaughterhouse environment. These results should be seen as a cue to improve the programs of hygiene implemented, particularly in those zones that can promote biofilm formation.

Biofilm viability checker: An open-source tool for automated biofilm viability analysis from confocal microscopy images

Quantifying biofilm formation on surfaces is challenging because traditional microbiological methods, such as total colony-forming units (CFUs), often rely on manual counting. These are laborious, resource intensive techniques, more susceptible to human error. Confocal laser scanning microscopy (CLSM) is a high-resolution technique that allows 3D visualisation of biofilm architecture. In combination with a live/dead stain, it can be used to quantify biofilm viability on both transparent and opaque surfaces. However, there is little consensus on the appropriate methodology to apply in confocal micrograph processing. In this study, we report the development of an image analysis approach to repeatably quantify biofilm viability and surface coverage. We also demonstrate its use for a range of bacterial species and translational applications. This protocol has been created with ease of use and accessibility in mind, to enable researchers who do not specialise in computational techniques to be confident in applying these methods to analyse biofilm micrographs. Furthermore, the simplicity of the method enables the user to adapt it for their bespoke needs. Validation experiments demonstrate the automated analysis is robust and accurate across a range of bacterial species and an improvement on traditional microbiological analysis. Furthermore, application to translational case studies show the automated method is a reliable measurement of biomass and cell viability. This approach will ensure image analysis is an accessible option for those in the microbiology and biomaterials field, improve current detection approaches and ultimately support the development of novel strategies for preventing biofilm formation by ensuring comparability across studies.

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.

Growth and Persistence of Campylobacter jejuni in Foodstuffs

Campylobacter genus bacteria causing campylobacteriasis are difficult to culture. This fact necessitates creation of special approaches to studies of the behavior of these pathogens during the manufacture and storage of foodstuffs. The regularities of Campylobacter jejuni transition into an uncultivable state are studied under conditions simulating the process of immersion cooling of fresh poultry products. The proportion of viable colony-forming (CFU) cells to the total count of planktonic and uncultivable cells in the population was calculated by the level of genomic DNA in the samples evaluated by quantitative real-time PCR with intercalating dyes. PCR was carried out with primers detecting the cytolethal toxin subunit B gene cdtB and invasion gene ciaB in C. jejuni strains. The count of detected cells was 5-10-fold higher than the count of CFU; the cultural method failed to detect the agent in 40% analyzed samples of superficially infected products, while the level of uncultivable cells detected by PCR was significantly higher. The relationship between culturing conditions and formation of C. jejuni biofilms was studied. The most intensive formation of film exomatrix was observed under unfavorable conditions for this microorganism at 25oC. In microaerophilic gaseous medium, weak formation of films and intensive growth of C. jejuni populations were observed. Culturing at higher temperatures (37-42oC) was in fact inessential for the film formation process.

Studying the Phenotypic and Genotypic Expression of Antibiotic Resistance in Campylobacter jejuni under Stress Conditions

Specific features for the development of resistance in Campylobacter jejuni strains were studied after treatment with antibiotics of 6 pharmacological groups. Populations of 18 native strains of C. jejuni (isolated from raw poultry products) and their subcultures (obtained after 2-3-fold stress exposures to antimicrobial agents in subinhibitory doses) were examined to evaluate the expression of phenotypic antibiotic resistance. Genotypic properties of strains were studied by the PCR with primers that detect the presence of genes for resistance to aminoglycosides (aphA-1, aphA-3, and aphA-7), tetracyclines (tetO), and quinolones (GZgyrA). The majority of test strains of C. jejuni exhibited a high resistance to nalidixic acid, ciprofloxacin, and tetracycline, which reached the maximum value after numerous passages. The expression of antibiotic resistance was greatest in the presence of nalidixic acid and tetracycline. Ciprofloxacin resistance of 33% strains, which were initially resistant to this antibiotic, was increased after 2-3-fold treatment. We revealed a high degree of correspondence between phenotypic and genotypic profiles of antibiotic resistance in food isolates of Campylobacter. One, two, or more genes of aphA were identified in 85% strains phenotypically resistant to aminoglycosides. The tetO gene was found nearly in all strains resistant to tetracycline. Studying the biofilm matrix in C. jejuni after culturing with antibiotics in subinhibitory doses showed that quinolones (particularly nalidixic acid) and tetracyclines potentiate the formation of biofilms and increase the tolerance of Campylobacter to stress exposures. The intensity of biofilm growth was shown to depend little on the effect of macrolides and aminoglycosides. Therefore, the presence of these agents in residual concentrations is associated with a lower risk for the development of antibiotic resistance in C. jejuni populations.

In Vitro Culturing and Storage of Campylobacter Genus Bacteria

Experimental model for in vitro evaluation of Campylobacter genus bacteria growth kinetics, inhibition, or inactivation is proposed. The model allows quantitative evaluation of the sensitivity to various types of stress exposure and promotes detection of the regularities of their transformation into uncultivable forms. The model implies the use of 96-well plates for parallel culturing of several subpopulations of the test strain in media with various parameters. The proposed algorithm includes evaluation of the proportion of viable CFU to total level of planktonic and uncultivable cells in the population, which is estimated by the content of genomic DNA in the samples by quantitative PCR (or real-time PCR) with ciaB, cdtB, or 16S rRNA primers. The presence of biofilm matrix is detected by the intensity of staining of polystyrene plates. This model can be used for evaluation of the most significant types of exposure, including low-dose antibacterial treatment, promoting the formation of stable microorganism variants. The model has been used to study the effects of culturing conditions on the characteristics of C. jejuni populations. The most characteristic feature of C. jejuni is reduction of the count of viable cells up to complete disappearance of cultivable forms under favorable conditions of growth. The level of viable cells in the populations decreased 10-fold and more, on average, after 48-h incubation. Not all strains exhibit this property, some strains retain their viability, which is detected by the culturing method, and contributes to biofilm formation.