Alteration of neutrophil function in BCG-treated and non-treated swine after exposure to Salmonella typhimurium

Innate Immunomodulation in Food Animals: Evidence for Trained Immunity?

Antimicrobial resistance (AMR) is a significant problem in health care, animal health, and food safety. To limit AMR, there is a need for alternatives to antibiotics to enhance disease resistance and support judicious antibiotic usage in animals and humans. Immunomodulation is a promising strategy to enhance disease resistance without antibiotics in food animals. One rapidly evolving field of immunomodulation is innate memory in which innate immune cells undergo epigenetic changes of chromatin remodeling and metabolic reprogramming upon a priming event that results in either enhanced or suppressed responsiveness to secondary stimuli (training or tolerance, respectively). Exposure to live agents such as bacille Calmette-Guerin (BCG) or microbe-derived products such as LPS or yeast cell wall ß-glucans can reprogram or "train" the innate immune system. Over the last decade, significant advancements increased our understanding of innate training in humans and rodent models, and strategies are being developed to specifically target or regulate innate memory. In veterinary species, the concept of enhancing the innate immune system is not new; however, there are few available studies which have purposefully investigated innate training as it has been defined in human literature. The development of targeted approaches to engage innate training in food animals, with the practical goal of enhancing the capacity to limit disease without the use of antibiotics, is an area which deserves attention. In this review, we provide an overview of innate immunomodulation and memory, and the mechanisms which regulate this long-term functional reprogramming in other animals (e.g., humans, rodents). We focus on studies describing innate training, or similar phenomenon (often referred to as heterologous or non-specific protection), in cattle, sheep, goats, swine, poultry, and fish species; and discuss the potential benefits and shortcomings of engaging innate training for enhancing disease resistance.

Tunicamycin Mediated Inhibition of Wall Teichoic Acid Affects Staphylococcus aureus and Listeria monocytogenes Cell Morphology, Biofilm Formation and Virulence

The emergence of bacterial resistance to therapeutic antibiotics limits options for treatment of common microbial diseases. Subinhibitory antibiotics dosing, often aid in the emergence of resistance, but its impact on pathogen’s physiology and pathogenesis is not well understood. Here we investigated the effect of tunicamycin, a cell wall teichoic acid (WTA) biosynthesis inhibiting antibiotic at the subinhibitory dosage on Staphylococcus aureus and Listeria monocytogenes physiology, antibiotic cross-resistance, biofilm-formation, and virulence. Minimum inhibitory concentration (MIC) of tunicamycin to S. aureus and L. monocytogenes was 20–40 μg/ml and 2.5–5 μg/ml, respectively, and the subinhibitory concentration was 2.5–5 μg/ml and 0.31–0.62 μg/ml, respectively. Tunicamycin pre-exposure reduced cellular WTA levels by 18–20% and affected bacterial cell wall ultrastructure, cell membrane permeability, morphology, laser-induced colony scatter signature, and bacterial ability to form biofilms. It also induced a moderate level of cross-resistance to tetracycline, ampicillin, erythromycin, and meropenem for S. aureus, and ampicillin, erythromycin, vancomycin, and meropenem for L. monocytogenes. Pre-treatment of bacterial cells with subinhibitory concentrations of tunicamycin also significantly reduced bacterial adhesion to and invasion into an enterocyte-like Caco-2 cell line, which is supported by reduced expression of key virulence factors, Internalin B (InlB) and Listeria adhesion protein (LAP) in L. monocytogenes, and a S. aureus surface protein A (SasA) in S. aureus. Tunicamycin-treated bacteria or the bacterial WTA preparation suppressed NF-κB and inflammatory cytokine production (TNFα, and IL-6) from murine macrophage cell line (RAW 264.7) indicating the reduced WTA level possibly attenuates an inflammatory response. These results suggest that at the subinhibitory dosage, tunicamycin-mediated inhibition of WTA biosynthesis interferes with cell wall structure, pathogens infectivity and inflammatory response, and ability to form biofilms but promotes the development of antibiotic cross-resistance.

Vaccination as a control strategy against Salmonella infection in pigs: A systematic review and meta-analysis of the literature

Consumption or handling of improperly processed or cooked pork is considered one of the top sources for foodborne salmonellosis, a common cause of intestinal disease worldwide. Asymptomatic carrier pigs may contaminate pork at slaughtering; therefore, pre-harvest reduction of Salmonella load can contribute to reduce public health risk. Multiple studies have evaluated the impact of vaccination on controlling Salmonella in swine farms, but results are highly variable due to the heterogeneity in vaccines and vaccination protocols. Here, we report the results of an inclusive systematic review and a meta-analysis of the peer-reviewed scientific literature to provide updated knowledge on the potential effectiveness of Salmonella vaccination. A total of 126 articles describing the use of Salmonella vaccines in swine were identified, of which 44 fulfilled the inclusion criteria. Most of the studies (36/44) used live vaccines, and S. Typhimurium and S. Choleraesuis were the predominant serotypes evaluated. Vaccine efficacy was most often measured through bacteriological isolation, and pooled estimates of vaccine efficacy were obtained as the difference in the percentage of positive animals when available. Attenuated and inactivated vaccines had similar efficacy [Risk Difference=-26.8% (-33.8, -19.71) and -29.5% (-44.4, -14.5), respectively]. No serotype effect was observed on the efficacy recorded for attenuated vaccines; however, a higher efficacy of inactivated vaccines against S. Choleraesuis was observed, though in a reduced sample. Results from the meta-analysis here demonstrate the impact that vaccination may have on the control of Salmonella in swine farms and could help in the design of programs to minimize the risk of transmission of certain serotypes through the food chain.

The effects of danofloxacin and tilmicosin on neutrophil function and lung consolidation in beef heifer calves with induced Pasteurella (Mannheimia) haemolytica pneumonia

Pneumonia caused by Pasteurella (Mannheimia) haemolytica was induced in weaned beef heifer calves, approximately 6 months of age. Calves were treated at 20 h after challenge with therapeutic doses of danofloxacin or tilmicosin. Peripheral blood neutrophils were collected at 3, 24 and 48 h after treatment. The ex vivo effects on neutrophil function, neutrophil apoptosis, and hematological parameters were examined, as was the effect on percentage lung consolidation. Neutrophil function assays included random migration under agarose, cytochrome C reduction, iodination, Staphylococcus aureus ingestion, chemotaxis, and antibody-dependent and antibody-independent cell-mediated cytotoxicity. Apoptosis was determined using a cell death detection kit. Killing was performed at 72 h after treatment. Statistical comparisons were made among the three groups of challenged-treated animals: saline, danofloxacin, and tilmicosin. Comparisons were also made between nonchallenged nontreated animals (NCH) and challenged saline-treated animals. There were no significant differences for any of the neutrophil function assays or neutrophil apoptosis among the challenged-treated groups. This suggests that danofloxacin and tilmicosin have no clinically significant effects on neutrophil function or apoptosis. There were also no significant differences in percentage lung consolidation among the challenged-treated groups. Significant differences were found between the NCH calves and the challenged saline-treated calves in several neutrophil assays, which were attributed to effects of P. haemolytica infection.

Interaction between Salmonella typhimurium and phagocytic cells in pigs. Phagocytosis, oxidative burst and killing in polymorphonuclear leukocytes and monocytes

Interactions between Salmonella typhimurium and peripheral blood leucocytes from healthy, Salmonella-free pigs were investigated in vitro. Both granulocytes and monocytes phagocytized FITC-labelled heat-killed Salmonella bacteria as shown by flow cytometry. Phagocytosis in whole blood and isolated leucocytes was measured as acquired fluorescence in the leukocytes and was both time and dose related. Living, serum-opsonized Salmonella bacteria induced a dose-dependent oxidative burst in PMNs and monocytes as measured by luminol-enhanced chemiluminescence (LC). When opsonized in normal serum the Salmonella bacteria, in the range of 2-5 x 10(7) cfu, induced a LC response in monocytes comparable to the level of responses induced by phorbol myristate acetate (PMA) and opsonized zymosan, and the Salmonella-induced response was only marginally reduced by superoxide dismutase (SOD). Intracellular killing of Salmonella by monocytes was assessed from plate colony counts of lysed monocytes and showed that Salmonella typhimurium was able to survive and proliferate in adherent monocytes in vitro despite a reduction in intracellular cfu during the first hour's incubation in cells from some pigs. Experiments with the exhaustion of oxidative burst in non-adherent monocytes were performed by prestimulation with PMA, heat-killed Salmonella or buffer. Prestimulation with PMA led to a strong reduction in oxidative burst induced by living opsonized Salmonella bacteria, whereas prestimulation with heat-killed bacteria gave rise to an enhanced response. In these experiments intracellular killing of the added living Salmonella gave variable results, in that monocytes from two out of three pigs showed no essential change in intracellular bactericidal activity, but with cells from one pig a less pronounced bactericidal activity was found after prestimulation with PMA.

The determination of the cellular volume of avian, porcine and bovine phagocytes and bovine mammary epithelial cells and its relationship to uptake of tilmicosin

In order to compare the intracellular concentration of antimicrobial agents in phagocytic and nonphagocytic cells, the knowledge of their cell volume is essential. For the first time, the determination of the avian, porcine, and bovine polymorphonuclear neutrophils (PMN), monocyte-derived macrophages, macrophages, and bovine mammary epithelial cell volume was performed using [3H]-water and [14C]-carboxyinulin. The comparison of all the cells showed that the PMN have a size range between 3.58 and 4.04 microL per mg of protein, and are smaller than the monocyte-derived macrophages and mammary epithelial cells (4.32-5.01 microL per mg of protein). The macrophages show the largest size (5.84-6.57 microL per mg of protein). The cellular uptake of tilmicosin in these cells was then determined. The examination of the intracellular/extracellular concentration ratios (Ci/Ce) after 4 h of incubation with 10 mg/mL of [14C]-labelled tilmicosin revealed that tilmicosin was well accumulated and showed a ratio of 137, 169 and 193 in avian PMN, porcine PMN, and bovine alveolar macrophages, respectively. The cellular uptake data also demonstrated that tilmicosin accumulated in nonphagocytic bovine mammary epithelial cells. The importance of the use of the appropriate species and cell type specific cell volume values for calculations was exemplified by calculating the Ci/Ce of tilmicosin using cell volume data found in the literature for human and mouse cells. The subsequent comparison of these data with the Ci/Ce calculated with the actual cell volume appropriate for the species tested revealed an under evaluation of 3-13% in monocyte-macrophages, an over evaluation of 7-18%, 16-31% and 69% in PMN, macrophages, and epithelial cells, respectively. This study highlights the importance of the proper cell volume in order to determine the Ci/Ce. Moreover, the cell volumes determined here for avian, porcine and bovine cells should facilitate further in vitro and in vivo cellular studies by veterinary researchers.

Intracellular accumulation, subcellular distribution and efflux of tilmicosin in swine phagocytes

Tilmicosin is a semi-synthetic macrolide antibiotic, currently approved for veterinary use in cattle and swine respiratory disease. As the concentrations of tilmicosin are generally low in swine lung tissue, the interaction of tilmicosin with three types of swine phagocytes (monocyte-macrophages, alveolar macrophages, and neutrophils) was evaluated to provide an understanding of clinical efficacy. After incubation with radiolabelled tilmicosin, uptake was determined and expressed as the ratio of the intracellular (Ci) to the extracellular (Ce) drug concentration (Ci/Ce). Tilmicosin was avidly accumulated by the swine phagocytes (Ci/Ce 48-69 at 4 h incubation) with 51 to 85% localized in the lysosomes. Uptake was dependent on cell viability, temperature and pH, but was not influenced by the metabolic inhibitors, sodium cyanide or potassium fluoride. However, lipopolysaccharide (LPS) exposure increased tilmicosin uptake by the swine phagocytes. In neutrophils, upon removal of extracellular tilmicosin, 60% of the intracellular tilmicosin was effluxed within the first 30 min, but after 4 h of incubation in drug-free medium, 25% remained cell-associated. In contrast, after 4 h of incubation in drug-free medium, 60% and 45% of tilmicosin remained cell-associated, within alveolar macrophages and monocyte-derived macrophages, respectively. Tilmicosin uptake was observed to increase lysosomal enzyme (acid phosphatase, lysozyme and beta-glucuronidase) production. Finally, neutrophils were shown to transport and efflux bioactive tilmicosin in a test system measuring both neutrophil chemotaxis under agarose and a bioassay measuring inhibition of bacterial growth in the presence of antibiotic in agar. These in vitro interactions of tilmicosin with swine phagocytes suggest an integral role in effecting clinical efficacy.

Neutralization of G-CSF inhibits ILK-induced heterophil influx: granulocyte-colony stimulating factor mediates the Salmonella enteritidis-immune lymphokine potentiation of the acute avian inflammatory response

Hematopoietic colony stimulating factors (CSF) regulate the growth and development of phagocytic cell progenitors and also augment functional activation of phagocytes. Granulocyte-CSF (G-CSF) is the CSF that acts specifically upon granulocyte progenitor cells and mature granulocytes. We have shown that lymphokines (ILK) from T cells of birds immunized against Salmonella enteritidis (SE) induce a granulocytic (PMN) inflammatory response in chicks challenged with SE. This inflammatory response was characterized by: (a) a dramatic emigration of granulocytic cells from the bone marrow into the peripheral blood, (b) an enhancement of the biological functions of the circulating PMNs, and (c) a directed influx of these activated PMNs to the site of bacterial invasion. In the current study, we determined the presence of G-CSF in ILK by Western blot analysis using a goat polyclonal antihuman G-CSF antibody (Ab). Using this Ab, we then evaluated the role of G-CSF in the ILK-induced protective inflammatory response in chickens against SE. Pretreatment of ILK with the Ab totally abolished the colony-stimulating activity of the ILK. Furthermore, Ab treatment of ILK resulted in: (a) an elimination of the ILK-induced peripheral blood heterophilia with a dramatic inhibition of ILK-mediated protection against SE organ invasion and (b) an elimination of accumulation of inflammatory PMNs in the peritoneum with subsequent decrease in the survival rate of chicks challenged i.p. with SE. Taken together these studies demonstrate for the first time the contribution of G-CSF to avian PMN activation and the immunoprophylaxis of SE infection by ILK in neonatal chickens.

Effect of recombinant human cytokines on porcine neutrophil function

The activity of four recombinant human cytokines on porcine neutrophils was evaluated. Porcine neutrophils were treated with varying doses of recombinant human tumour necrosis factor-alpha (rHu-TNF), interferon-gamma (rHu-IFN), interleukin-8 (rHu-lL-8), or granulocyte-macrophage colony-stimulating factor (rHu-GM-CSF). The function of treated neutrophils was compared with that of non-treated controls in the following assays: antibody-independent neutrophil cytotoxicity (AINC), antibody-dependent cell-mediated cytotoxicity (ADCC), iodination, Staphylococcus aureus ingestion, cytochrome C reduction, random migration, and chemotaxis. Treatment with rHu-TNF produced significant (P < 0.05) depression of neutrophil random migration (2.5, 25, and 250 ng ml-1 rHu-TNF) and iodination (250 ng ml-1) and a near significant (P = 0.08) depression in ADCC (250 ng ml-1). Treatment with 25,000 U ml-1 of rHu-IFN caused a significant increase in AINC. At lower doses of rHu-IFN, there was a trend (0.05 < P < or = 0.08) toward depression of AINC (250 U ml-1) and ADCC (25 U ml-1) and enhancement of iodination (250 U ml-1). Treatment with 50 ng ml-1 of rHu-IL-8 caused a near significant increase (P = 0.06) in AINC. There were no significant differences noted when porcine neutrophils were treated with rHu-GM-CSF (2.5-2500 U ml-1). No synergism was noted between rHu-TNF and rHu-IFN.

Evaluation of the influence of potential toxins on neutrophil function

Neutrophils undergo a complex series of events when functioning to control bacterial, viral, and fungal infections. Any factor that interferes with neutrophil production or suppresses neutrophil function will rapidly make the animal more susceptible to infectious diseases. In vitro assays are used to detect and characterize defects in neutrophil function that may be induced by exposure to potential toxins. This paper focuses on important considerations in designing experiments for the evaluation of neutrophil function and interpretation of data.

Comparative analysis of using MTT and XTT in colorimetric assays for quantitating bovine neutrophil bactericidal activity

Two different tetrazolium compounds were compared for use in a colorimetric assay for quantitating bovine neutrophil bactericidal activity against Staphylococcus aureus, Escherichia coli, Listeria monocytogenes, and Brucella abortus. The tetrazolium compounds tested included 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and sodium 3,3'-[1[(phenylamino)carbonyl]-3,4- tetrazolium]-bis(4-methoxy-6-nitro) benzene sulfonic acid hydrate (XTT). The MTT and XTT colorimetric bactericidal assays were conducted by incubating antibody-opsonized bacteria with neutrophils in microtiter plates for 30 and 60 min at ratios of ten and 100 bacteria per neutrophil. Neutrophils were then lysed with saponin and samples were incubated 30 min with MTT or XTT plus coenzyme Q (CQ). Dead bacteria and lysed neutrophils did not react with MTT or XTT plus CQ. Live bacteria converted XTT to water soluble orange formazan in the presence of CQ and MTT to insoluble purple formazan. Absorption of formazan produced by bacteria from XTT was measured at 450 nm. Formazan produced by bacteria from MTT was solubilized by adding isopropanol and measured by absorption at 560 nm. Absorption of both types of formazan was directly related to viable bacteria cell number and used to determine the number of bacteria not killed by neutrophils. The percentage of bacteria killed by neutrophils was determined by extrapolation from a standard formazan curve that was derived by incubating MTT or XTT plus CQ with known numbers of bacteria. The XTT and MTT colorimetric bactericidal assays produced comparable results when used to measure bovine neutrophil bactericidal activity against S. aureus, E. coli, L. monocytogenes, and B. abortus. However, the assay using XTT was quicker and easier to perform because bacteria converted XTT to a formazan that did not need to be solubilized before measuring absorption.