Campylobacter jejuni is highly susceptible to killing by chicken host defense peptide cathelicidin-2 and suppresses intestinal cathelicidin-2 expression in young broilers

Immunomodulatory properties of chicken cathelicidin-2 investigated on an ileal explant culture

As the threat posed by antimicrobial resistance grows more crucial, the development of compounds that can replace antibiotics becomes increasingly vital. Chicken cathelicidin-2 (Cath-2) belongs to the group of Host Defense Peptides (HDPs), which could provide a feasible solution for the treatment of gastrointestinal infections in poultry. It is a small peptide produced by the heterophil granulocytes of chickens as part of the innate immune response, and its immunomodulatory activity has already been demonstrated in several cell types. In this study, the effects of Cath-2 on the intestinal immune response were examined using ileal explant cultures isolated from chicken. Regarding our results, Cath-2 displayed a potent anti-inflammatory effect as it alleviated the LTA-caused elevation of interleukin (IL)-6 and IL-2 concentrations, and that of the IFN-γ/IL-10 ratio, furthermore, it increased the concentration of IL-10, alleviating the LTA-evoked decreased level of the anti-inflammatory cytokine. Moreover, when applied alone, it elevated the concentrations of IL-6, CXCLi2, and IL-2, providing evidence of its complex immunomodulatory mechanisms. In summary, Cath-2 was able to modulate the immune response of the intestinal wall not only by reducing pro-inflammatory cytokine release, but also through immune stimulation, demonstrating that it has the ability to improve innate immunity via a complex mechanism that may make it a suitable candidate for the control of intestinal infections.

Intestinal Colonization of Campylobacter jejuni and Its Hepatic Dissemination Are Associated with Local and Systemic Immune Responses in Broiler Chickens

Campylobacter jejuni is an important foodborne pathogen. Despite the lack of clinical signs associated with its colonization in poultry, it has been reported to interact with the intestinal immune system. However, little is known about the interaction between C. jejuni and the chicken immune system, especially in the context of hepatic dissemination. Therefore, to follow up on our previous study showing intestinal colonization and hepatic spread of C. jejuni, cecal tonsils and liver samples were collected from these birds to determine the mRNA levels of chemokines and cytokines. Serum samples were also collected to determine serum amyloid A (SAA) concentrations and specific IgY titers. Lack of Th17 induction was observed in the cecal tonsils of only the liver-contaminated groups. This hepatic dissemination was accompanied by innate, Th1 and Th2 immune responses in livers, as well as an increase in SAA concentrations and specific IgY levels in sera. Campylobacter appears to be able to restrain the induction of the chicken gut immunity in particular conditions, possibly enhancing its hepatic dissemination and thus eliciting systemic immune responses. Although Campylobacter is often recognized as a commensal-like bacterium in chickens, it seems to modulate the gut immune system and induce systemic immunity.

Current and future interventions for improving poultry health and poultry food safety and security: A comprehensive review

Poultry is thriving across the globe. Chicken meat is the most preferred poultry worldwide, and its popularity is increasing. However, poultry also threatens human hygiene, especially as a fomite of infectious diseases caused by the major foodborne pathogens (Campylobacter, Salmonella, and Listeria). Preventing pathogenic bacterial biofilm is crucial in the chicken industry due to increasing food safety hazards caused by recurring contamination and the rapid degradation of meat, as well as the increased resistance of bacteria to cleaning and disinfection procedures commonly used in chicken processing plants. To address this, various innovative and promising strategies to combat bacterial resistance and biofilm are emerging to improve food safety and quality and extend shelf-life. In particular, natural compounds are attractive because of their potential antimicrobial activities. Natural compounds can also boost the immune system and improve poultry health and performance. In addition to phytochemicals, bacteriophages, nanoparticles, coatings, enzymes, and probiotics represent unique and environmentally friendly strategies in the poultry processing industry to prevent foodborne pathogens from reaching the consumer. Lactoferrin, bacteriocin, antimicrobial peptides, cell-free supernatants, and biosurfactants are also of considerable interest for their prospective application as natural antimicrobials for improving the safety of raw poultry meat. This review aims to describe the feasibility of these proposed strategies and provide an overview of recent published evidences to control microorganisms in the poultry industry, considering the human health, food safety, and economic aspects of poultry production.

Campylobacter jejuni infection induces dynamic expression of avian host defense peptides in vitro and in vivo

Campylobacter jejuni is considered as the leading cause of worldwide foodborne bacterial gastroenteritis. Chicken is the main reservoir of C. jejuni. Avian innate immune responses to C. jejuni remain poorly defined. Chicken host defense peptides (HDPs) are the major components of avian innate immune system. This study aimed to characterize the chicken HDPs responses to C. jejuni in vitro and in vivo. In the HD11 macrophage cell line, the HDPs, including AvBD1-2, CATH1-3, AvBD7, AvBD4, and AvBD6, were relatively higher expressed in untreated cells, whereas the expressions were suppressed after C. jejuni infection. In contrast, C. jejuni infection significantly increased the expression of the lower expressed HDPs, such as AvBD3, AvBD5, AvBD8-14, and CATHB1, in untreated cells. In the chicken challenge experiment, the immune tissues of spleens and cecal tonsils were collected from C. jejuni-infected and uninfected chickens at 1, 3 and 15 day post inoculation (DPI). In spleens of C. jejuni-infected chickens, only AvBD14 expression was elevated at 1 DPI. The majority of avian HDPs were significantly up-regulated at 3 DPI and dramatically decreased to the levels of uninfected controls at 15 DPI. In chicken cecal tonsils, only AvBD9 and AvBD14 were significantly up-regulated at 1 DPI with C. jejuni infection. Collectively, C. jejuni infection induced dynamic expression of chicken HDPs in both macrophage HD11 and immune tissues of chickens. Suppression of chicken HDPs expression may be an evasion strategy of C. jejuni for persistent colonization in chicken intestine by circumventing the chicken immune system.

Selected Antimicrobial Peptides Inhibit In Vitro Growth of Campylobacter spp

Campylobacter is a major cause of acute human diarrheal illness. Broiler chickens constitute a primary reservoir for C. jejuni leading to human infection. Consequently, there is a need for developing novel intervention methods. Antimicrobial peptides (AMP) are small proteins which have evolved in most lifeforms to provide defense against microbial infections. To date, over 3000 AMP have been discovered; however, few of them have been analyzed specifically for ability to kill campylobacters. We selected and evaluated a set of 11 unique chemically synthesized AMP for ability to inhibit growth of C. jejuni. Six of the AMP we tested produced zones of inhibition on lawns of C. jejuni. These AMP included: NRC-13, RL-37, Temporin L, Cecropin–Magainin, Dermaseptin, and C12K-2β12. In addition, MIC were determined for Cecropin–Magainin, RL-37 and C12K-2β12 against 15 isolates of Campylobacter representing the three most common pathogenic strains. MIC for campylobacters were approximately 3.1 µg/mL for AMP RL-37 and C12K-2β12. MIC were slightly higher for the Cecropin–Magainin AMP in the range of 12.5 to 100 µg/mL. These AMP are attractive subjects for future study and potential in vivo delivery to poultry to reduce Campylobacter spp. populations.

The Role of Antimicrobial Peptides as Antimicrobial and Antibiofilm Agents in Tackling the Silent Pandemic of Antimicrobial Resistance

Just over a million people died globally in 2019 due to antibiotic resistance caused by ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). The World Health Organization (WHO) also lists antibiotic-resistant Campylobacter and Helicobacter as bacteria that pose the greatest threat to human health. As it is becoming increasingly difficult to discover new antibiotics, new alternatives are needed to solve the crisis of antimicrobial resistance (AMR). Bacteria commonly found in complex communities enclosed within self-produced matrices called biofilms are difficult to eradicate and develop increased stress and antimicrobial tolerance. This review summarises the role of antimicrobial peptides (AMPs) in combating the silent pandemic of AMR and their application in clinical medicine, focusing on both the advantages and disadvantages of AMPs as antibiofilm agents. It is known that many AMPs display broad-spectrum antimicrobial activities, but in a variety of organisms AMPs are not stable (short half-life) or have some toxic side effects. Hence, it is also important to develop new AMP analogues for their potential use as drug candidates. The use of one health approach along with developing novel therapies using phages and breakthroughs in novel antimicrobial peptide synthesis can help us in tackling the problem of AMR.

d-enantiomers of CATH-2 enhance the response of macrophages against Streptococcus suis serotype 2

•

D-CATH-2 has strong antimicrobial activities towards multiple S.suis strains.

•

D-CATH-2 ameliorates macrophage function.

•

DCATH-2 binds LTA.

•

DCATH-2 has prophylactic effect against S. suis infection in vivo.

Introduction

Due to the increase of antibiotic resistant bacterial strains, there is an urgent need for development of alternatives to antibiotics. Cathelicidins can be such an alternative to antibiotics having both a direct antimicrobial capacity as well as an immunomodulatory function. Previously, the full d-enantiomer of chicken cathelicidin-2 (d-CATH-2) has shown to prophylactically protect chickens against infection 7 days post hatch when administered in ovo three days before hatch.

Objectives

To further evaluate d-CATH-2 in mammals as a candidate for an alternative to antibiotics.

In this study, the prophylactic capacity of d-CATH-2 and two truncated derivatives, d-C(1–21) and d-C(4–21), was determined in mammalian cells.

Methods

Antibacterial assays; immune cell differentiation and modulation; cytotoxicity, isothermal titration calorimetry; in vivo prophylactic capacity of peptides in an S. suis infection model.

Results

d-CATH-2 and its derivatives were shown to have a strong direct antibacterial capacity against four different S. suis serotype 2 strains (P1/7, S735, D282, and OV625) in bacterial medium and even stronger in cell culture medium. In addition, d-CATH-2 and its derivatives ameliorated the efficiency of mouse bone marrow-derived macrophages (BMDM) and skewed mouse bone marrow-derived dendritic cells (BMDC) towards cells with a more macrophage-like phenotype. The peptides directly bind lipoteichoic acid (LTA) and inhibit LTA-induced activation of macrophages. In addition, S. suis killed by the peptide was unable to further activate mouse macrophages, which indicates that S. suis was eliminated by the previously reported silent killing mechanism. Administration of d-C(1–21) at 24 h or 7 days before infection resulted in a small prophylactic protection with reduced disease severity and reduced mortality of the treated mice.

Conclusion

d-enantiomers of CATH-2 show promise as anti-infectives against pathogenic S. suis for application in mammals.

Approaches to prevent and control Campylobacter spp. colonization in broiler chickens: a review

Campylobacter, Gram-negative bacteria, is the most common cause of acute bacterial enteritis in human beings, both in developing and developed countries. It is believed that poultry, in particular broiler chickens, is the main host of human infection with Campylobacter. Handling and consumption of contaminated chicken meat are the usual modes of transmission. Prevention and reduction of Campylobacter colonization in poultry farms will cut off the road of infection transmission to humans throughout the food chain. With the incidence of antibiotic resistance and with growing concern about superbugs, the search for natural and safe alternatives will considerably increase in the coming years. In this review, we will discuss the prevalence and risk factors of Campylobacter colonization in broiler chickens and sources of infection. This review also provides extensive and recent approaches to prevent and control Campylobacter colonization in broiler chickens, including biosecurity measures, natural feed/drinking water additives with antimicrobial properties, bacteriocins, bacteriophages, antimicrobial peptides, and vaccination strategies to prevent and control the incidence of human campylobacteriosis.

Murine Models for the Investigation of Colonization Resistance and Innate Immune Responses in Campylobacter Jejuni Infections

Human infections with the food-borne pathogen Campylobacter jejuni are progressively increasing worldwide and constitute a significant socioeconomic burden to mankind. Intestinal campylobacteriosis in humans is characterized by bloody diarrhea, fever, abdominal pain, and severe malaise. Some individuals develop chronic post-infectious sequelae including neurological and autoimmune diseases such as reactive arthritis and Guillain-Barré syndrome. Studies unraveling the molecular mechanisms underlying campylobacteriosis and post-infectious sequelae have been hampered by the scarcity of appropriate experimental in vivo models. Particularly, conventional laboratory mice are protected from C. jejuni infection due to the physiological colonization resistance exerted by the murine gut microbiota composition. Additionally, as compared to humans, mice are up to 10,000 times more resistant to C. jejuni lipooligosaccharide (LOS) constituting a major pathogenicity factor responsible for the immunopathological host responses during campylobacteriosis. In this chapter, we summarize the recent progress that has been made in overcoming these fundamental obstacles in Campylobacter research in mice. Modification of the murine host-specific gut microbiota composition and sensitization of the mice to C. jejuni LOS by deletion of genes encoding interleukin-10 or a single IL-1 receptor-related molecule as well as by dietary zinc depletion have yielded reliable murine infection models resembling key features of human campylobacteriosis. These substantial improvements pave the way for a better understanding of the molecular mechanisms underlying pathogen-host interactions. The ongoing validation and standardization of these novel murine infection models will provide the basis for the development of innovative treatment and prevention strategies to combat human campylobacteriosis and collateral damages of C. jejuni infections.

Avian host defense cathelicidins: structure, expression, biological functions, and potential therapeutic applications

Host defense peptides (HDP) are multifunctional effectors of the innate immune system, which has antimicrobial and pleiotropic immunomodulatory functions. Although there is a very sophisticated superposition of adaptive immune systems in vertebrates, this system is still essential. As an important family of HDP, cathelicidins are also known for their broad-spectrum antibacterial activity against bacteria, fungi, and enveloped viruses. It has been found in humans and other species, including cattle, pigs, sheep, goats, chickens, rabbits, and some kind of fish. Among them, cathelicidins in birds were described for the first time in 2005. This review focuses on the structure, biological activities, expression, and regulation of avian cathelicidin, especially main effects of host defense cathelicidin on potential therapeutic applications. According to the results obtained both in vitro and in vivo, good perspectives have been opened for cathelicidin. Nevertheless, further studies are needed to better characterize the mechanisms of action underlying the beneficial effects of cathelicidin as novel therapeutic alternatives to antibiotics.

Novel Clinical Campylobacter jejuni Infection Models Based on Sensitization of Mice to Lipooligosaccharide, a Major Bacterial Factor Triggering Innate Immune Responses in Human Campylobacteriosis

Human Campylobacter jejuni infections inducing campylobacteriosis including post-infectious sequelae such as Guillain-Barré syndrome and reactive arthritis are rising worldwide and progress into a global burden of high socioeconomic impact. Intestinal immunopathology underlying campylobacteriosis is a classical response of the innate immune system characterized by the accumulation of neutrophils and macrophages which cause tissue destruction, barrier defects and malabsorption leading to bloody diarrhea. Clinical studies revealed that enteritis and post-infectious morbidities of human C. jejuni infections are strongly dependent on the structure of pathogenic lipooligosaccharides (LOS) triggering the innate immune system via Toll-like-receptor (TLR)-4 signaling. Compared to humans, mice display an approximately 10,000 times weaker TLR-4 response and a pronounced colonization resistance (CR) against C. jejuni maintained by the murine gut microbiota. In consequence, investigations of campylobacteriosis have been hampered by the lack of experimental animal models. We here summarize recent progress made in the development of murine C. jejuni infection models that are based on the abolishment of CR by modulating the murine gut microbiota and by sensitization of mice to LOS. These advances support the major role of LOS driven innate immunity in pathogenesis of campylobacteriosis including post-infectious autoimmune diseases and promote the preclinical evaluation of novel pharmaceutical strategies for prophylaxis and treatment.

Effects of Probiotics Lactobacillus reuteri and Clostridium butyricum on the Expression of Toll-like Receptors, Pro- and Anti-inflammatory Cytokines, and Antimicrobial Peptides in Broiler Chick Intestine

The aim of this study was to determine the effects of live probiotics Lactobacillus reuteri (LR) and Clostridium butyricum (CB) on the expression of genes of innate immune system in broiler chick ileum and cecum. Chicks were administered 500 µl water with or without LR or CB, daily from day 1 to 6 after hatching. The ileum and cecum were collected on day 7 for analysis of gene expression of Toll-like receptors (TLRs), pro- and anti-inflammatory cytokines, and antimicrobial peptides (AMPs) using real-time PCR. The expression of TLR2-1 was upregulated by CB in the ileum and that of TLR5 was upregulated by both LR and CB. Expression of IL-1β and TGFβ2 in the ileum and of TGFβ3 and TGFβ4 in the cecum was upregulated by both LR and CB. The gene expressions of avian β-defensin (AvBD) 1 and cathelicidin (CATH) 3 were upregulated by CB and that of AvBD4 was upregulated by LR in the cecum. However, the expression of CATH2 in the ileum was downregulated by LR. These results suggest that probiotic LR and CB treatments affect a part of the innate defense system in the ileum and cecum by modulating the expression of innate immune molecules including TLRs, pro- and anti-inflammatory cytokines, and AMPs.

Expression of nutrient transporters and host defense peptides in Campylobacter challenged broilers

Campylobacter is a bacterium that colonizes the lower gastrointestinal tract of poultry and may influence the intestinal environment to promote its survival. The objective of this study was to characterize the effects of Campylobacter challenge on the mRNA abundance of nutrient transporters and host defense peptides (HDP), such as the avian β-defensins (AvBD) and liver expressed antimicrobial peptide 2 (LEAP2). On the day of hatch, broiler chicks were challenged with one of three (106, 107, 108 colony-forming units, cfu) levels of Campylobacter jejuni. Quantitative PCR analysis revealed that there were dose-, tissue-, and age-specific changes in gene expression for both nutrient transporters and HDP. Expression of zinc transporter 1 (ZnT1) mRNA increased on d 7 in the duodenum, ileum, and cecum of birds challenged with 106 cfu of C. jejuni. At d 14, there was upregulation of the amino acid transporter bo,+AT mRNA in the duodenum, jejunum, and ileum of birds challenged with 106 cfu of C. jejuni. Other transporters such as EAAT3, GLUT2, SGLT1, and ZnT1 showed upregulation of mRNA in the ileum of the 106 cfu challenged group. There was a delayed response of the HDP to the C. jejuni challenge, with only a few HDP changed at d 7 but all HDP changed at d 14. At d 7, there was upregulation of AvBD10 mRNA in the duodenum of the 106 cfu challenged group but downregulation of AvBD10 in the ileum and AvBD12 and LEAP2 in the cecum of the 108 cfu challenged group. At d 14, there was upregulation of AvBD1, AvBD6, AvBD8, AvBD10, AvBD11, AvBD12, and AvBD13 mRNA in the ileum and cecum of the 106 cfu challenged group but not the 107 and 108 cfu challenged groups compared to control. These results indicated that at a low dose (106 cfu) of C. jejuni, intestinal cells increased nutrient transporter and AvBD mRNA abundance to try to counter the infection, but that at higher doses the cellular response was suppressed.

The potential for immunoglobulins and host defense peptides (HDPs) to reduce the use of antibiotics in animal production

Innate defense mechanisms are aimed at quickly containing and removing infectious microorganisms and involve local stromal and immune cell activation, neutrophil recruitment and activation and the induction of host defense peptides (defensins and cathelicidins), acute phase proteins and complement activation. As an alternative to antibiotics, innate immune mechanisms are highly relevant as they offer rapid general ways to, at least partially, protect against infections and enable the build-up of a sufficient adaptive immune response. This review describes two classes of promising alternatives to antibiotics based on components of the innate host defense. First we describe immunoglobulins applied to mimic the way in which they work in the newborn as locally acting broadly active defense molecules enforcing innate immunity barriers. Secondly, the potential of host defense peptides with different modes of action, used directly, induced in situ or used as vaccine adjuvants is described.

Expression of host defense peptides in the intestine of Eimeria-challenged chickens

Avian coccidiosis is caused by the intracellular protozoan Eimeria, which produces intestinal lesions leading to weight gain depression. Current control methods include vaccination and anticoccidial drugs. An alternative approach involves modulating the immune system. The objective of this study was to profile the expression of host defense peptides such as avian beta-defensins (AvBDs) and liver expressed antimicrobial peptide 2 (LEAP2), which are part of the innate immune system. The mRNA expression of AvBD family members 1, 6, 8, 10, 11, 12, and 13 and LEAP2 was examined in chickens challenged with either E. acervulina, E. maxima, or E. tenella. The duodenum, jejunum, ileum, and ceca were collected 7 d post challenge. In study 1, E. acervulina challenge resulted in down-regulation of AvBD1, AvBD6, AvBD10, AvBD11, AvBD12, and AvBD13 in the duodenum. E. maxima challenge caused down-regulation of AvBD6, AvBD10, and AvBD11 in the duodenum, down-regulation of AvBD10 in the jejunum, but up-regulation of AvBD8 and AvBD13 in the ceca. E. tenella challenge showed no change in AvBD expression in any tissue. In study 2, which involved challenge with only E. maxima, there was down-regulation of AvBD1 in the ileum, AvBD11 in the jejunum and ileum, and LEAP2 in all 3 segments of the small intestine. The expression of LEAP2 was further examined by in situ hybridization in the jejunum of chickens from study 2. LEAP2 mRNA was expressed similarly in the enterocytes lining the villi, but not in the crypts of control and Eimeria challenged chickens. The lengths of the villi in the Eimeria challenged chickens were less than those in the control chickens, which may in part account for the observed down-regulation of LEAP2 mRNA quantified by PCR. Overall, the AvBD response to Eimeria challenge was not consistent; whereas LEAP2 was consistently down-regulated, which suggests that LEAP2 plays an important role in modulating an Eimeria infection.

Comparative expression of host defense peptides in turkey poults

Host defense peptides (HDPs) are a large group of small, positively charged peptides that play an important role in innate immunity, particularly at early ages when other components of the immune system have not fully developed. There are 3 classes of avian HDPs: avian beta defensins (AvBDs), cathelicidins (Cath), and liver-expressed antimicrobial peptide 2 (LEAP-2). The objective was to compare expression of HDP mRNAs in male turkey poults at day of hatch (d 0), d 7, d 14, d 21 and d 28 from the thymus, spleen, bursa, duodenum, jejunum, and ileum. The expression of AvBD1, AvBD2, AvBD8, AvBD9, AvBD10, AvBD13, Cath2, Cath3, and LEAP-2 mRNA was measured using qPCR (n = 6 birds/tissue/age). Data were analyzed by one-way ANOVA and Tukey's test, and significance considered at P < 0.05. AvBDs and Caths exhibited greater expression in immune organs (thymus, spleen, and bursa) than intestinal tissues. In the thymus, expression of all AvBDs examined, except AvBD8, showed an increase from d 0 to d 21. In the spleen, AvBD1 and AvBD2 exhibited reduced expression from d 0 to d 7 and low expression thereafter. In the intestine, AVBD1, AVBD8, and AvBD13 increased expression from d 0 to d 28 in the duodenum, while AvBD10 showed the greatest expression at d 0 that declined to d 7 and stayed low thereafter in the duodenum, jejunum, and ileum. Cath2 and Cath3 demonstrated the highest expression in the spleen, which was greatest at d 0 then declined to d 7 through d 28. Conversely, LEAP-2 showed greater expression in the intestinal tissues than in the immune organs. LEAP-2 expression was upregulated from d 0 to d 7 and then remained elevated from d 7 through d 14 in the duodenum. In the jejunum, LEAP-2 increased from d 0 to d 21 and d 28. Understanding the differential expression of HDPs could reveal the innate immune status of turkey poults, and may subsequently allow improvement of their health through appropriate mitigation strategies.

Imaging the Antistaphylococcal Activity of CATH-2: Mechanism of Attack and Regulation of Inflammatory Response

Chicken cathelicidin-2 (CATH-2) is a broad-spectrum antimicrobial host defense peptide (HDP) that may serve as a paradigm for the development of new antimicrobial agents. While previous studies have elucidated the mechanism by which CATH-2 kills Escherichia coli, its mode of action against Gram-positive bacteria remains to be determined. In this study, we explored the underlying antibacterial mechanism of CATH-2 against a methicillin-resistant strain of Staphylococcus aureus and the effect of CATH-2-mediated S. aureus killing on immune activation. Visualization of the antimicrobial activity of CATH-2 against S. aureus with live-imaging confocal microscopy demonstrated that CATH-2 directly binds the bacteria, which is followed by membrane permeabilization and cell shrinkage. Transmission electron microscopy (TEM) studies further showed that CATH-2 initiated pronounced morphological changes of the membrane (mesosome formation) and ribosomal structures (clustering) in a dose-dependent manner. Immunolabeling of these sections demonstrated that CATH-2 binds and passes the bacterial membrane at subminimal bactericidal concentrations (sub-MBCs). Furthermore, competition assays and isothermal titration calorimetry (ITC) analysis provided evidence that CATH-2 directly interacts with lipoteichoic acid and cardiolipin. Finally, stimulation of macrophages with S. aureus and CATH-2 showed that CATH-2 not only kills S. aureus but also has the potential to limit S. aureus-induced inflammation at or above the MBC. Taken together, it is concluded that at sub-MBCs, CATH-2 perturbs the bacterial membrane and subsequently enters the cell and binds intracellular S. aureus components, while at or above the MBC, CATH-2 causes disruption of membrane integrity and inhibits S. aureus-induced macrophage activation. IMPORTANCE Due to the high use of antibiotics in both human and veterinary settings, many bacteria have become resistant to those antibiotics that we so heavily rely on. Methicillin-resistant S. aureus (MRSA) is one of these difficult-to-treat resistant pathogens for which novel antimicrobial therapies will be required in the near future. One novel approach could be the utilization of naturally occurring antimicrobial peptides, such as chicken CATH-2, which have been show to act against a wide variety of bacteria. However, before these peptides can be used clinically, more knowledge of their functions and mechanisms of action is required. In this study, we used live imaging and electron microscopy to visualize in detail how CATH-2 kills S. aureus, and we investigated how CATH-2 affects immune activation by S. aureus. Together, these results give a better understanding of how CATH-2 kills S. aureus and what the potential immunological consequences of this killing can be.

Localization and developmental expression of two chicken host defense peptides: cathelicidin-2 and avian β-defensin 9

In the first weeks of life young chickens are highly susceptible to infectious diseases due to immaturity of the immune system. Little is known about the expression of host defense peptides (HDPs) during this period. In this study we examined the expression pattern of two chicken HDPs, the cathelicidin CATH-2 and the β-defensin AvBD9 by immunohistochemistry in a set of organs from embryonic day 12 until four weeks posthatch. AvBD9 was predominantly found in enteroendocrine cells throughout the intestine, the first report of in vivo HDP expression in this cell type, and showed stable expression levels during development. CATH-2 was exclusively found in heterophils which decreased after hatch in most of the examined organs including spleen, bursa and small intestine. In the lung CATH-2 expression was biphasic and peaked at the first day posthatch. In short, CATH-2 and AvBD9 appear to be expressed in cell types strategically located to respond to infectious stimuli, suggesting these peptides play a role in embryonic and early posthatch defense.

Changes in expression of an antimicrobial peptide, digestive enzymes, and nutrient transporters in the intestine of E. praecox-infected chickens

Coccidiosis is a major intestinal disease of poultry, caused by several species of the protozoan Eimeria. The objective of this study was to examine changes in expression of digestive enzymes, nutrient transporters, and an antimicrobial peptide following an Eimeria praecox challenge of chickens at days 3 and 6 post-infection. Gene expression was determined by real-time PCR and analyzed by one-way ANOVA. In the duodenum, the primary site of E. praecox infection, a number of genes were downregulated at both d3 and d6 post-infection. These genes included liver expressed antimicrobial peptide 2 (LEAP2), the cationic (CAT1), anionic (EAAT3), and L-type (LAT1) amino acid transporters, the peptide transporter PepT1 and the zinc transporter ZnT1. Other transporters were downregulated either at d3 or d6. At both d3 and d6, there was downregulation of B(o)AT and CAT1 in the jejunum and downregulation of LEAP2 and LAT1 in the ileum. LEAP2, EAAT3, and ZnT1 have been found to be downregulated following challenge with other Eimeria species, suggesting a common cellular response to Eimeria.

Characterization of bacterial antimicrobial peptides active against Campylobacter jejuni

Campylobacter jejuni is one of the major causes of food poisoning, often resulting from the consumption of improperly cooked poultry products. The emergence of C. jejuni strains resistant to conventional antibiotics necessitates the evaluation of other possible treatments or preventative measures to minimize the impact and prevalence of infections. Antimicrobial peptides produced by bacteria have begun to emerge as a potential means of decreasing the levels of C. jejuni in poultry, thereby limiting Campylobacter contamination in associated food products. A number of bacteriocins produced by Gram-positive bacteria have unexpectedly been described as having antimicrobial activity against the Gram-negative C. jejuni. Additionally, some nonribosomal lipopeptides produced by Bacillus and Paenibacillus spp. show efficacy against this pathogen. This review will describe the bacterial antimicrobial peptides reported to be active against C. jejuni, with an emphasis on the characterization of their primary structures. However, for many of these peptides, little is known about their amino acid sequences and structures. Furthermore, there are unusual inconsistencies associated with the reported amino acid sequences for several of the more well-studied bacteriocins. Clarifying the chemical nature of these promising antimicrobial peptides is necessary before their potential utility for livestock protection from C. jejuni can be fully explored. Once these peptides are better characterized, they may prove to be strong candidates for minimizing the impact of Campylobacter on human health.

Expression of digestive enzymes and nutrient transporters in Eimeria-challenged broilers

Avian coccidiosis is a disease caused by the intestinal protozoa Eimeria. The site of invasion and lesions in the intestine is species-specific, for example E. acervulina affects the duodenum, E. maxima the jejunum, and E. tenella the ceca. Lesions in the intestinal mucosa cause reduced feed efficiency and body weight gain. The growth reduction may be due to changes in expression of digestive enzymes and nutrient transporters in the intestine. The objective of this study was to compare the expression of digestive enzymes, nutrient transporters and an antimicrobial peptide in broilers challenged with either E. acervulina, E. maxima or E. tenella. The genes examined included digestive enzymes (APN and SI), peptide and amino acid transporters (PepT1, ASCT1, b(0,+)AT/rBAT, B(0)AT, CAT1, CAT2, EAAT3, LAT1, y(+)LAT1 and y(+)LAT2), sugar transporters (GLUT1, GLUT2, GLUT5 and SGLT1), zinc transporter (ZnT1) and an antimicrobial peptide (LEAP2). Duodenum, jejunum, ileum and ceca were collected 7 days post challenge. E. acervulina challenge resulted in downregulation of various nutrient transporters or LEAP2 in the duodenum and ceca, but not the jejunum or ileum. E. maxima challenge produced both downregulation and upregulation of nutrient transporters and LEAP2 in all three segments of the small intestine and ceca. E. tenella challenge resulted in the downregulation and upregulation of nutrient transporters and LEAP2 in the jejunum, ileum and ceca, but not the duodenum. At the respective target tissue, E. acervulina, E. maxima and E. tenella infection caused common downregulation of APN, b(0,+)AT, rBAT, EAAT3, SI, GLUT2, GLUT5, ZnT1 and LEAP2. The downregulation of nutrient transporters would result in a decrease in the efficiency of protein and polysaccharide digestion and uptake, which may partially explain the weight loss. The downregulation of nutrient transporters may also be a cellular response to reduced expression of the host defense protein LEAP2, which would diminish intracellular pools of nutrients and inhibit pathogen replication.

Avian antimicrobial host defense peptides: from biology to therapeutic applications

Host defense peptides (HDPs) are an important first line of defense with antimicrobial and immunomoduatory properties. Because they act on the microbial membranes or host immune cells, HDPs pose a low risk of triggering microbial resistance and therefore, are being actively investigated as a novel class of antimicrobials and vaccine adjuvants. Cathelicidins and β-defensins are two major families of HDPs in avian species. More than a dozen HDPs exist in birds, with the genes in each HDP family clustered in a single chromosomal segment, apparently as a result of gene duplication and diversification. In contrast to their mammalian counterparts that adopt various spatial conformations, mature avian cathelicidins are mostly α-helical. Avian β-defensins, on the other hand, adopt triple-stranded β-sheet structures similar to their mammalian relatives. Besides classical β-defensins, a group of avian-specific β-defensin-related peptides, namely ovodefensins, exist with a different six-cysteine motif. Like their mammalian counterparts, avian cathelicidins and defensins are derived from either myeloid or epithelial origin expressed in a majority of tissues with broad-spectrum antibacterial and immune regulatory activities. Structure-function relationship studies with several avian HDPs have led to identification of the peptide analogs with potential for use as antimicrobials and vaccine adjuvants. Dietary modulation of endogenous HDP synthesis has also emerged as a promising alternative approach to disease control and prevention in chickens.

Avian host defense peptides

Host defense peptides (HDPs) are important effector molecules of the innate immune system of vertebrates. These antimicrobial peptides are also present in invertebrates, plants and fungi. HDPs display broad-spectrum antimicrobial activities and fulfill an important role in the first line of defense of many organisms. It is becoming increasingly clear that in the animal kingdom the functions of HDPs are not confined to direct antimicrobial actions. Research in mammals has indicated that HDPs have many immunomodulatory functions and are also involved in other physiological processes ranging from development to wound healing. During the past five years our knowledge about avian HDPs has increased considerably. This review addresses our current knowledge on the evolution, regulation and biological functions of HDPs of birds.

Alternatives to antibiotics: a symposium on the challenges and solutions for animal production

Antibiotics are one of the most important medical discoveries of the 20th century and will remain an essential tool for treating animal and human diseases in the 21st century. However, antibiotic resistance among bacterial pathogens and concerns over their extensive use in food animals has garnered global interest in limiting antibiotic use in animal agriculture. Yet, limiting the availability of medical interventions to prevent and control animal diseases on the farm will directly impact global food security and safety as well as animal and human health. Insufficient attention has been given to the scientific breakthroughs and novel technologies that provide alternatives to antibiotics. The objectives of the symposium 'Alternatives to Antibiotics' were to highlight promising research results and novel technologies that could potentially lead to alternatives to conventional antibiotics, and assess challenges associated with their commercialization, and provide actionable strategies to support development of alternative antimicrobials. The symposium focused on the latest scientific breakthroughs and technologies that could provide new options and alternative strategies for preventing and treating diseases of animals. Some of these new technologies have direct applications as medical interventions for human health, but the focus of the symposium was animal production, animal health and food safety during food-animal production. Five subject areas were explored in detail through scientific presentations and expert panel discussions, including: (1) alternatives to antibiotics, lessons from nature; (2) immune modulation approaches to enhance disease resistance and to treat animal diseases; (3) gut microbiome and immune development, health and diseases; (4) alternatives to antibiotics for animal production; and (5) regulatory pathways to enable the licensure of alternatives to antibiotics.