S. Typhimurium virulence changes caused by exposure to different non-thermal preservation treatments using C. elegans

Caenorhabditis elegans as an In Vivo Model for the Discovery and Development of Natural Plant-Based Antimicrobial Compounds

Antimicrobial resistance (AMR) due to the prevalence of multidrug-resistant (MDR) pathogens is rapidly increasing worldwide, and the identification of new antimicrobial agents with innovative mechanisms of action is urgently required. Medicinal plants that have been utilised for centuries with minor side effects may hold great promise as sources of effective antimicrobial products. The free-living nematode Caenorhabditis elegans (C. elegans) is an excellent live infection model for the discovery and development of new antimicrobial compounds. However, while C. elegans has widely been utilised to explore the effectiveness and toxicity of synthetic antibiotics, it has not been used to a comparable extent for the analysis of natural products. By screening the PubMed database, we identified articles reporting the use of the C. elegans model for the identification of natural products endowed with antibacterial and antifungal potential, and we critically analysed their results. The studies discussed here provide important information regarding "in vivo" antimicrobial effectiveness and toxicity of natural products, as evaluated prior to testing in conventional vertebrate models, thereby supporting the relevance of C. elegans as a highly proficient model for their identification and functional assessment. However, their critical evaluation also underlines that the characterisation of active phytochemicals and of their chemical structure, and the unravelling of their mechanisms of action represent decisive challenges for future research in this area.

The efficacy and safety of high-pressure processing of food

High-pressure processing (HPP) is a non-thermal treatment in which, for microbial inactivation, foods are subjected to isostatic pressures (P) of 400-600 MPa with common holding times (t) from 1.5 to 6 min. The main factors that influence the efficacy (log10 reduction of vegetative microorganisms) of HPP when applied to foodstuffs are intrinsic (e.g. water activity and pH), extrinsic (P and t) and microorganism-related (type, taxonomic unit, strain and physiological state). It was concluded that HPP of food will not present any additional microbial or chemical food safety concerns when compared to other routinely applied treatments (e.g. pasteurisation). Pathogen reductions in milk/colostrum caused by the current HPP conditions applied by the industry are lower than those achieved by the legal requirements for thermal pasteurisation. However, HPP minimum requirements (P/t combinations) could be identified to achieve specific log10 reductions of relevant hazards based on performance criteria (PC) proposed by international standard agencies (5-8 log10 reductions). The most stringent HPP conditions used industrially (600 MPa, 6 min) would achieve the above-mentioned PC, except for Staphylococcus aureus. Alkaline phosphatase (ALP), the endogenous milk enzyme that is widely used to verify adequate thermal pasteurisation of cows' milk, is relatively pressure resistant and its use would be limited to that of an overprocessing indicator. Current data are not robust enough to support the proposal of an appropriate indicator to verify the efficacy of HPP under the current HPP conditions applied by the industry. Minimum HPP requirements to reduce Listeria monocytogenes levels by specific log10 reductions could be identified when HPP is applied to ready-to-eat (RTE) cooked meat products, but not for other types of RTE foods. These identified minimum requirements would result in the inactivation of other relevant pathogens (Salmonella and Escherichia coli) in these RTE foods to a similar or higher extent.

In vivo Assessment of Cold Atmospheric Pressure Plasma Technology on the Bioactivity of Spirulina

The present study challenges the in vivo assessment of cold atmospheric pressure plasma (CAPP) technology on the bioactive activity (antioxidant/antiaging and antimicrobial potential) of Spirulina powder, using Caenorhabditis elegans as an animal model. Surface microdischarge cold atmospheric pressure plasma (SMD-CAPP) treatment was 3.3 W discharge power for 7 min. C. elegans lifespan and egg laying were used as indicators of antioxidant/antiaging potential of Spirulina (1 mg/mL), when grown with Spirulina CP-treated [E_SCP] and untreated [E_S], compared with a control [E_0] (non-supplemented with Spirulina). According to our results, under both Spirulina supplemented media [E_SCP and E_S] and for the first 17 days, nematodes experienced an increase in lifespan but without significant differences (p > 0.05) between control and Spirulina CP-treated. Regarding the in vivo assay of the antimicrobial potential of Spirulina against Salmonella enterica serovar Typhimurium (infected worms), no significant differences (p > 0.05) were found between the three exposure scenarios (control [S_0]; Spirulina supplemented media [S_S]; CP-treated Spirulina supplemented media [S_SCP]). According to present results, CAPP-treatment do not influence negatively the lifespan of C. elegans but a reduction in the Spirulina antiaging potential was found. No in vivo modifications in antimicrobial activity seem to be linked to CAPP-processed Spirulina.

Impact of the Resistance Responses to Stress Conditions Encountered in Food and Food Processing Environments on the Virulence and Growth Fitness of Non-Typhoidal Salmonellae

The success of Salmonella as a foodborne pathogen can probably be attributed to two major features: its remarkable genetic diversity and its extraordinary ability to adapt. Salmonella cells can survive in harsh environments, successfully compete for nutrients, and cause disease once inside the host. Furthermore, they are capable of rapidly reprogramming their metabolism, evolving in a short time from a stress-resistance mode to a growth or virulent mode, or even to express stress resistance and virulence factors at the same time if needed, thanks to a complex and fine-tuned regulatory network. It is nevertheless generally acknowledged that the development of stress resistance usually has a fitness cost for bacterial cells and that induction of stress resistance responses to certain agents can trigger changes in Salmonella virulence. In this review, we summarize and discuss current knowledge concerning the effects that the development of resistance responses to stress conditions encountered in food and food processing environments (including acid, osmotic and oxidative stress, starvation, modified atmospheres, detergents and disinfectants, chilling, heat, and non-thermal technologies) exerts on different aspects of the physiology of non-typhoidal Salmonellae, with special emphasis on virulence and growth fitness.

Caenorhabditis elegans as an in vivo model to assess fucoidan bioactivity preventing Helicobacter pylori infection

Currently, Helicobacter pylori is the unique biological carcinogenic agent. The search for antimicrobial alternatives to antibiotics against this pathogen has been categorized as a priority due to the drastic failure associated with current applied antibiotic therapy. The present study assessed the bioactive antimicrobial capability of fucoidan ("Generally Recognized as Safe" approval - European Commission December 2017) from different species of Phaeophyceae algae (Fucus vesiculosus, Undaria pinnatifida, Macrocystis pyrifera) against H. pylori. All the studied fucoidans showed bacteriostatic and bactericidal effects at the studied concentrations [5-100] μg ml-1 and exposure times [0-7 days]. The most effective anti-H. pylori fucoidan was validated in Caenorhabditis elegans as an in vivo model. C. elegans feed was supplemented with Undaria pinnatifida [0-100] μg ml-1 fucoidan, resulting in a significant improvement in lifespan, lowered H. pylori concentration in the digestive tract, and increased egg-laying pattern. New research lines proposing this compound as an active agent in nutraceutical and preventive novel therapies should be opened.

Occurrence of Salmonella typhimurium resistance under sublethal/repeated exposure to cauliflower infusion and infection effects on Caernohabditis elegans host test organism

Resistant bacteria to antimicrobials are increasingly emerging in medical, food industry and livestock environments. The present research work assesses the capability of Salmonella enterica var Typhimurium to become adapted under the exposure to a natural cauliflower antimicrobial by-product infusion in consecutive repeated exposure cycles. Caenorhabditis elegans was proposed as in vivo host-test organism to compare possible changes in the virulent pattern of the different rounds treated S. enterica var Typhimurium and untreated bacterial cells. According to the obtained results, S. enterica var Typhimurium was able to generate resistance against a repeated exposure to cauliflower by-product infusion 5% (w/v), increasing the resistance with the number of exposed repetitions. Meanwhile, at the first exposure, cauliflower by-product infusion was effective in reducing S. enterica var Typhimurium (≈1 log₁₀ cycle), and S. enterica var Typhimurium became resistant to this natural antimicrobial after the second and third treatment-round and was able to grow (≈1 log₁₀ cycle). In spite of the increased resistance observed for repeatedly treated bacteria, the present study reveals no changes on C. elegans infection effects between resistant and untreated S. enterica var Typhimurium, according to phenotypic parameters evaluation (lifespan duration and egg-laying).

Replacement, Refinement, and Reduction in Animal Studies With Biohazardous Agents

Animal models are critical to the advancement of our knowledge of infectious disease pathogenesis, diagnostics, therapeutics, and prevention strategies. The use of animal models requires thoughtful consideration for their well-being, as infections can significantly impact the general health of an animal and impair their welfare. Application of the 3Rs—replacement, refinement, and reduction—to animal models using biohazardous agents can improve the scientific merit and animal welfare. Replacement of animal models can use in vitro techniques such as cell culture systems, mathematical models, and engineered tissues or invertebrate animal hosts such as amoeba, worms, fruit flies, and cockroaches. Refinements can use a variety of techniques to more closely monitor the course of disease. These include the use of biomarkers, body temperature, behavioral observations, and clinical scoring systems. Reduction is possible using advanced technologies such as in vivo telemetry and imaging, allowing longitudinal assessment of animals during the course of disease. While there is no single method to universally replace, refine, or reduce animal models, the alternatives and techniques discussed are broadly applicable and they should be considered when infectious disease animal models are developed.