Segmented filamentous bacteria-based treatment to elicit protection against Enterobacteriaceae in Layer chickens

Introduction

Gut microbes like segmented filamentous bacteria (SFB) play a key role in gut maturation during early life, as demonstrated in humans and mice. Our previous study demonstrated oral inoculation of ileum-spores containing SFB to chickens after hatch increases early SFB gut colonization, which increases immune maturation and resistance to bacteria, like Salmonella, as tested in vitro; however, more studies are needed for treatment optimization and in vivo testing. The objectives of this study were to (1) test a treatment that includes both spores and filamentous SFB, (2) validate antimicrobial ability of the treatment in layer hens in vivo, and (3) elucidate its molecular mechanism.

Methods

One-day-old specific pathogen-free layers (n = 12 per group) were orally treated with either PBS (CON) or SFB-based treatment (SFB). At 4 days post-inoculation (DPI), both CON and SFB groups were orally challenged with Salmonella Typhimurium. Total Enterobacteriaceae and Salmonella were examined by plating and enumeration in feces at 7,10 and 14 dpi; and in the ileum, cecum, and spleen at 16 dpi in euthanized birds. The presence and levels of SFB were determined from ilea scrapings via microscopy and qPCR, respectively. Relative gene expression of host-derived antimicrobial peptides and cytokines in the distal ileum was determined by RT-qPCR.

Results

At 10 and 14 dpi, a significant decrease in total Enterobacteriaceae was observed in the feces of the SFB group. At necropsy, the level of SFB was significantly higher in the SFB group than in the CON group, while a significant decrease in total Enterobacteriaceae and Salmonella was observed in the ceca of the SFB group. RT-qPCR revealed increased expression of β-defensin 14, and cytokines IL-10 and IFNγ.

Discussion

The introduction of SFB at hatch as a prophylactic treatment may benefit commercial partners as well as consumers by reducing the incidence of Enterobacteriaceae in food animals. Reduction of these bacteria in animals would, in turn, increase animal health, productivity, and safety for consumers. Studies to optimize the treatment for poultry industry applications are ongoing in our lab.

Models for Gut-Mediated Horizontal Gene Transfer by Bacterial Plasmid Conjugation

The emergence of new antimicrobial resistant and virulent bacterial strains may pose a threat to human and animal health. Bacterial plasmid conjugation is a significant contributor to rapid microbial evolutions that results in the emergence and spread of antimicrobial resistance (AR). The gut of animals is believed to be a potent reservoir for the spread of AR and virulence genes through the horizontal exchange of mobile genetic elements such as plasmids. The study of the plasmid transfer process in the complex gut environment is limited due to the confounding factors that affect colonization, persistence, and plasmid conjugation. Furthermore, study of plasmid transfer in the gut of humans is limited to observational studies, leading to the need to identify alternate models that provide insight into the factors regulating conjugation in the gut. This review discusses key studies on the current models for in silico, in vitro, and in vivo modeling of bacterial conjugation, and their ability to reflect the gut of animals. We particularly emphasize the use of computational and in vitro models that may approximate aspects of the gut, as well as animal models that represent in vivo conditions to a greater extent. Directions on future research studies in the field are provided.

High voltage atmospheric cold plasma treatment inactivates Aspergillus flavus spores and deoxynivalenol toxin

Fungal contamination is a concern for the food industry. Fungal spores resist food sterilization treatments and produce mycotoxins that are toxic for animals and humans. Technologies that deactivate spores and toxins without impacting food quality are desirable. This study demonstrates the efficiency of a high voltage atmospheric cold plasma (HVACP) technology using air to generate reactive oxygen (ROS) and nitrogen (RNS) species for the degradation of Aspergillus flavus cultures and the deoxynivalenol (DON) mycotoxin. Optical emission and absorption spectroscopy demonstrate ionization of hydroxyl groups, atomic oxygen and nitrogen, and confirm production of ROS and RNS, e.g. O₃, NO₂, NO₃, N₂O₄, and N₂O₅. Fungal cultures show a depletion in pigmentation and an ~50% spore inactivation after 1-min treatments. Treated spores show surface ablation and membrane degradation by scanning electron microscopy. Twenty-minute direct HVACP treatments of 100 μg of DON in one mL aqueous suspensions resulted in a greater than 99% reduction in DON structure and rescued over 80% of Caco-2 cell viability; however, the same treatment on 100 μg of powdered DON toxin only showed a 33% reduction in DON and only rescued 15% of cell viability. In summary, HVACP air treatment can inactivate both fungal spores and toxins in minutes.

Mouse Genetic Background Affects Transfer of an Antibiotic Resistance Plasmid in the Gastrointestinal Tract

Dissemination of antibiotic resistance (AR) genes, often on plasmids, leads to antibiotic-resistant bacterial infections, which is a major problem for animal and public health. Bacterial conjugation is the primary route of AR gene transfer in the mammalian gastrointestinal tract. Significant gaps in knowledge about which gastrointestinal communities and host factors promote plasmid transfer remain. Here, we used Salmonella enterica serovar Kentucky strain CVM29188 carrying plasmid pCVM29188_146 (harboring streptomycin and tetracycline resistance genes) to assess plasmid transfer to Escherichia coli under in vitro conditions and in various mouse strains with a conventional or defined microbiota. As an initial test, the transfer of pCVM29188_146 to the E. coli strains was confirmed in vitro Colonization resistance and, therefore, a lack of plasmid transfer were found in wild-type mice harboring a conventional microbiota. Thus, mice harboring the altered Schaedler flora (ASF), or ASF mice, were used to probe for host factors in the context of a defined microbiota. To assess the influence of inflammation on plasmid transfer, we compared interleukin-10 gene-deficient 129S6/SvEv ASF mice (proinflammatory environment) to wild-type 129S6/SvEv ASF mice and found no difference in transconjugant yields. In contrast, the mouse strain influenced plasmid transfer, as C3H/HeN ASF mice had significantly lower levels of transconjugants than 129S6/SvEv ASF mice. Although gastrointestinal members were identical between the ASF mouse strains, a few differences from C3H/HeN ASF mice were detected, with C3H/HeN ASF mice having significantly lower abundances of ASF members 356 (Clostridium sp.), 492 (Eubacterium plexicaudatum), and 502 (Clostridium sp.) than 129S6/SvEv ASF mice. Overall, we demonstrate that microbiota complexity and mouse genetic background influence in vivo plasmid transfer.IMPORTANCE Antibiotic resistance is a threat to public health. Many clinically relevant antibiotic resistance genes are carried on plasmids that can be transferred to other bacterial members in the gastrointestinal tract. The current study used a murine model to study the transfer of a large antibiotic resistance plasmid from a foodborne Salmonella strain to a gut commensal E. coli strain in the gastrointestinal tract. We found that different mouse genetic backgrounds and a different diversity of microbial communities influenced the level of Escherichia coli that acquired the plasmid in the gastrointestinal tract. This study suggests that the complexity of the microbial community and host genetics influence plasmid transfer from donor to recipient bacteria.