Mixtures of natural antimicrobials can reduce Campylobacter jejuni, Salmonella enterica and Clostridium perfringens infections and cellular inflammatory response in MDCK cells

Background

The classification of natural antimicrobials as potential antibiotic replacements is still hampered by the absence of clear biological mechanisms behind their mode of action. This study investigated the mechanisms underlying the anti-bacterial effect of a mixture of natural antimicrobials (maltodextrin, citric acid, sodium citrate, malic acid, citrus extract and olive extract) against Campylobacter jejuni RC039, Salmonella enterica SE 10/72 and Clostridium perfringens ATCC® 13124 invasion of Madin–Darby Canine Kidney cells (MDCK).

Results

Minimum sub-inhibitory concentrations were determined for Campylobacter jejuni (0.25%), Salmonella enterica (0.50%) and Clostridium perfringens (0.50%) required for the in vitro infection assays with MDCK cells. The antimicrobial mixture significantly reduced the virulence of all three pathogens towards MDCK cells and restored the integrity of cellular tight junctions through increased transepithelial resistance (TEER) and higher expression levels of ZO-1 (zonula occludens 1) and occludin. This study also identified the ERK (external regulated kinase) signalling pathway as a key mechanism in blocking the pro-inflammatory cytokine production (IL-1β, IL-6, IL-8, TNF-α) in infected cells. The reduction in hydrogen peroxide (H₂O₂) production and release by infected MDCK cells, in the presence of the antimicrobial mixture, was also associated with less tetrathionate formed by oxidation of thiosulphate (p < 0.0001).

Conclusion

The present study describes for the first time that mixtures of natural antimicrobials can prevent the formation of substrates used by bacterial pathogens to grow and survive in anaerobic environments (e.g. tetrathionate). Moreover, we provide further insights into pathogen invasion mechanisms through restoration of cellular structures and describe their ability to block the ERK–MAPK kinase pathway responsible for inflammatory cytokine release

The Effect Citrox BCL on Legionella pneumophila Mechanisms of Biofilm Formation, Oxidative Stress and Virulence

Legionella pneumophila is responsible for causing Legionnaires' disease and Pontiac fever, also known as legionellosis. The aim of this study was to investigate the mechanistic effect of a mixture of natural antimicrobials (Citrox BCL) in preventing L. pneumophila biofilm formation and reducing its in vitro virulence. The minimum inhibitory concentrations were detected at 0.06%, and the MBC was established at 0.125%. Based on the growth curve profile, the sub-inhibitory concentration of 0.02% was further used to study the mechanistic implications in the absence of a cytotoxic effect on A549 cells. At 24 h post-infection, Citrox BCL reduced (p = 0.005) the intracellular growth of L. pneumophila when the A549 cells or the bacteria were pre-treated with 0.02% Citrox BCL. This result was replicated when Citrox BCL was added during the 24 h infection assay leading to a reduction in intracellular growth (p = 0.003). Herein we show that at the sub-inhibitory concentration of 0.02%, Citrox CBL lowers the ROS levels in infected A549 cells and causes a 45% reduction in L. pneumophila EPS production, a reduction associated with the decline in biofilm formation. Overall, our results corroborate the low c-di-GMP production with the decrease in biofilm formation and low EPS levels. The low EPS levels seemed to be caused by the downregulation of the tatB and tatC gene expressions. Moreover, inhibition of pvcA and pvcB gene expressions, leading to lower siderophore levels, suggests that Citrox BCL reduces the ability of L. pneumophila to sequester iron and reduce biofilm formation through iron starvation.

Clinical chemistry, haematology, immune response and histological evaluation of rabbits after immunisation and challenge with rabbit haemorrhagic disease (RHD) virus

<p>Following their immunisation and infection with a VSHI-CN-6 viral strain, a group of 15 rabbits were examined in a study of Rabbit Haemorrhagic Disease (RHD). Serum samples were collected from the external ear vein at 0, 15, 30 and 60 days post-immunisation. The recorded platelet numbers were closer to the lower physiological limit, indicating a mild thrombocytopenia, with values ranging from 26.6 to 30.43×10⁴/mm³. The phagocytic index revealed significant differences (P&lt;0.001) between the mean values obtained before vaccination (day 0) and the 3 post-vaccination measurements, confirming the increase in phagocytic capacity after immunisation. Additionally, the serum lysozyme average value equalled 9.14 mg/mL post-vaccination. The analysis of variance revealed significant statistical differences (P&lt;0.05) between the average values obtained before vaccination (0) and the post-vaccination values, measured on day 14 and 30, respectively. The morphology of the samples collected from the main organs involved in immune protection, spleen and gastric and portal lymph nodes highlighted changes corresponding to the post-vaccination immunological response. The white pulp of the spleen appeared as a diffuse lymphoid tissue, presenting with primary and secondary lymphoid follicles. The ratio of white/red pulp was in favour of the white pulp and multiple lymphoid follicles were present, indicating their reactivation. In the medullary area of gastric and portal lymph nodes, narrow lymphoid cords, circumscribed by relatively large lymphatic sinuses, and well defined lymphocytolysis were observed. Moreover, the exudate and lymphoid follicles during activation were noted in the cortical area. Furthermore, the inflammatory processes were identified, morphologically manifested by the thickening of connective tissue in the lymph node capsule, dilacerations of the connective fibres and the presence of light acidophilic serous exudate with rare inflammatory cells (serous lymphoreticulitis).</p>

The Prebiotic Effect of an Organic Acid Mixture on Faecalibacterium prausnitzii Metabolism and Its Anti-Pathogenic Role against Vibrio parahaemolyticus in Shrimp

Increasing the abundance of probiotic bacteria in the gut requires either direct dietary supplementation or the inclusion of feed additives able to support the growth of beneficial commensal bacteria. In crustaceans, the increased presence of probiotic-like bacteria in the gut, including of Faecalibacterium prausnitzii (F. prausnitzii), will guarantee a positive health status and a gut environment that will ensure enhanced performance. The aim of this study was to investigate if a mixture of organic acids, AuraAqua (Aq) can stimulate the growth and the anti-pathogenic efficacy of F. prausnitzii through a combination of in vitro and ex vivo models. The results showed that 0.5% Aq was able to improve the growth rate of F. prausnitzii in vitro and in an ex vivo shrimp gut model. Moreover, we were able to demonstrate that Aq increases butyrate production and cellulose degradation in culture or in the shrimp gut model. The growth-stimulating effect of Aq also led to an improved and anti-pathogenic effect against Vibrio parahaemolyticus in a co-culture experiment with shrimp gut primary epithelial cells (SGP). In conclusion, our work demonstrates that Aq can stimulate the growth of F. prausnitzii, increase the production of short-chain fatty acid (SCFA) butyrate, improve substrate digestion, and prevent V. parahaemolyticus invasion of SGP cells.

[Dynamics of the composition of lipids in human milk during lactation]

The authors have studied the total lipids, triglycerides and cholesterol in the milk of 30 mothers over a lactation period of 4 days to 10 months. The total lipids showed diurnal oscillations with a minimal level in the morning and maximal level (P less than 0.001) at 1 p.m. and a slight decrease in the evening, without reaching the levels found in the morning. The lipid concentration in the milk decreases after 4 months of lactation. The oscillations of the lipids take place on the expense of the triglyceride content (r = 0.99). Cholesterol represented on the average 1.54% of the lipid content, showed a maximum level at a month and decreased after 6 months of lactation. The dynamics of lipid composition of the human milk suggests a physiologic significance in the development of the infant.

Heterogeneous nuclear ribonucleoprotein complexes from Xenopus laevis oocytes and somatic cells

HnRNP proteins have been implicated in most stages of cellular mRNA metabolism, including processing, nucleocytoplasmic transport, stability, and localization. Several hnRNP proteins are also known to participate in key early developmental decisions. In order to facilitate functional studies of these pre-mRNA- and mRNA-binding proteins in a vertebrate organism amenable to developmental studies and experimental manipulation, we identified and purified the major hnRNP proteins and isolated the hnRNP complex from Xenopus laevis oocytes and somatic cells. Using affinity chromatography and immunological methods, we isolated a family of >15 abundant single-stranded nucleic acid-binding proteins, which range in apparent molecular weight from approximately 20 kDa to >150 kDa, and with isoelectric points from <5 to >8. Monoclonal antibodies revealed that a subset of these proteins are major hnRNP proteins in both oocytes and somatic cells in culture, and include proteins related to human hnRNP A2/B1/B2 and hnRNP K. UV crosslinking in living cells demonstrated that these proteins bind poly(A)+ RNA in vivo. Immunopurification using a monoclonal antibodyto X. aevishnRNPA2 resulted in the isolation of RNP complexes that contain a specific subset of single-stranded nucleic acid-binding proteins. The protein composition of complexes isolated from somatic cells and from oocyte germinal vesicles was similar, suggesting that the overall properties and functions of hnRNP proteins in these two cell types are comparable. These findings, together with the novel probes generated here, will also facilitate studies of the function of vertebrate RNA-binding proteins using the well characterized X. laevis oocyte and early embryo as experimental systems.

Blends of Organic Acids Are Weaponizing the Host iNOS and Nitric Oxide to Reduce Infection of Piscirickettsia salmonis in vitro

For the last 30 years, Piscirickettsia salmonis has caused major economic losses to the aquaculture industry as the aetiological agent for the piscirickettsiosis disease. Replacing the current interventions, based on antibiotics, with natural alternatives (e.g., organic acids) represents a priority. With this study, we aimed to better understand their biological mechanism of action in an in vitro model of infection with salmon epithelial cells (CHSE-214). Our first observation revealed that at the sub-inhibitory concentration of 0.5%, the organic acid blend (Aq) protected epithelial cell integrity and significantly reduced P. salmonis invasion. The MIC was established at 1% Aq and the MBC at 2% against P. salmonis. The sub-inhibitory concentration significantly increased the expression of the antimicrobial peptides Cath2 and Hepcidin1, and stimulated the activity of the innate immune effector iNOS. The increase in iNOS activity also led to higher levels of nitric oxide (NO) being released in the extracellular space. The exposure of P. salmonis to the endogenous NO caused an increase in bacterial lipid peroxidation levels, a damaging effect which can ultimately reduce the pathogen's ability to attach or multiply intracellularly. We also demonstrate that the increased NO release by the host CHSE-214 cells is a consequence of direct exposure to Aq and is not dependent on P. salmonis infection. Additionally, the presence of Aq during P. salmonis infection of CHSE-214 cells significantly mitigated the expression of the pro-inflammatory cytokines IL-1β, IL-8, IL-12, and IFNγ. Taken together, these results indicate that, unlike antibiotics, natural antimicrobials can weaponize the iNOS pathway and secreted nitric oxide to reduce infection and inflammation in a Piscirickettsia salmonis in vitro model of infection.