The protection of calves against infection with Salmonella typhimurium by means of a vaccine prepared from Salmonella dublin (strain 51)

Bacterial Causes of Intestinal Disease in Dairy Calves: Acceptable Control Measures

Although diarrhea in dairy calves is common, it is not always due to bacteria. Escherichia coli, Salmonella, and Clostridium perfringens are the most commonly implicated bacteria, but an etiologic diagnosis should be sought before specific treatment is instituted. Nonspecific treatment such as fluid, electrolyte, and nutritional support should be accomplished while diagnostics are pending. Antimicrobials should not be a first-line therapy for calf diarrhea. Control measures are discussed.

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.

Salmonella in calves

Salmonellae are endemic on most large intensive farms and salmonellosis is a common cause of neonatal morbidity and mortality. Disease and mortality usually reflect a variety of management events and environmental stressors that contribute to compromised host immunity and increased pathogen exposure. The diversity of salmonella serovars present on farms, and the potential for different serovars to possess different virulence factors, require the implementation of broad prophylactic strategies that are efficacious for all salmonellae. This article discusses strategies to promote host immunity and minimize pathogen exposure at the farm level. The benefits of control include a reduction in disease incidence and mortality, reduced drug and labor costs, and improved growth rates.

Protection against oral challenge three months after i.v. immunization of BALB/c mice with live Aro Salmonella typhimurium and Salmonella enteritidis vaccines is serotype (species)-dependent and only partially determined by the main LPS O antigen

The role of the main LPS O antigen in the specificity of protection as mediated by systemic mechanisms following immunization with live attenuated Aro Salmonella vaccines was studied in mice. Innately Salmonella-susceptible (Itys) BALB/c mice were immunized intravenously with a single dose of either Salmonella typhimurium SL3261 aroA (LPS O4,5,12) or Salmonella enteritidis Se795aroA (LPS O1,9,12), and challenged orally 2-3 months later with either S. typhimurium C5 or S. enteritidis Thirsk. Nearly isogenic transductants of the two challenge strains expressing either their own LPS or that of the other serotype (S. typhimurium C5 O4 or O9, and S. enteritidis Thirsk O9 or O4) were also used. Both vaccines conferred similar high protection against the virulent strain of the homologous serotype expressing its own LPS. There was no protection against the heterologous serotype expressing its own LPS. However, when vaccinated mice were challenged with either the same serotype as the vaccine but expressing the heterologous LPS, or with the heterologous serotype expressing the LPS of the vaccine, protection was always lower than protection against the fully homologous serotype. Anti-smooth LPS antibodies showed higher titres against the homologous LPS, but with significant crossreactivity with the heterologous LPS. Antibodies to O-rough S. typhimurium and S. enteritidis LPS were present following immunization with either of the two vaccine strains. The LPS alone cannot fully account for the specificity of protection in this model; other (protein) antigens may be responsible. It remains to be seen whether there is a T-cell mediated component to the specificity of protection conferred by live Salmonella vaccines.

Current perspectives in salmonellosis

Salmonellosis remains an important human and animal problem worldwide and, despite extensive research effort, many of the details of its pathogenesis are not known. While there have been recent advances in some aspects of pathogenesis, other areas are not understood. The host adaptation shown by several serotypes and the recent dramatic changes in the predominance of particular serotypes are examples. Molecular techniques using in vitro model systems have identified several genes involved in adhesion and invasion, though their function and even their relevance to disease remain poorly defined. Similarly, several potential toxins have been identified and the genes cloned, although their significance is far from clear. Some of the essential genes on the large virulence plasmids have been defined, and these are known to be necessary for the establishment of systemic infection. Two of these genes are regulatory, but the function of the other genes is unknown. A general theme has been the identification of gene systems involved in regulation of virulence. New vaccines, based on 'rational attenuation' are being designed, and these have also been used to carry heterologous antigens; such vaccines are currently undergoing trials. The improved understanding of the pathogenesis of salmonellosis may also provide a model of wide applicability to a more general understanding of bacterial pathogenesis. New techniques, including the polymerase chain reaction, are being applied to diagnose salmonellosis.

Immunity conferred by Aro- Salmonella live vaccines

The specificity of protection conferred by Aro- salmonellae was studied in BALB/c mice challenged 3 months after intravenous (i.v.) vaccination, more than 1 month after the vaccine had been cleared. Oral challenge showed better protection than i.v. challenge. Salmonella typhimurium aroA SL3261 conferred very good protection against wild-type S. typhimurium C5 (over 10,000 x LD50). Cross protection experiments were performed using S. typhimurium, S. enteritidis and S. dublin for vaccination and challenge, including variants of S. typhimurium and S. enteritidis of similar virulence differing in the main LPS antigen (O-4 or O-9). Salmonella typhimurium aroA conferred solid protection against S. typhimurium (O-4), but no protection against wild-type S. enteritidis (O-9). However challenge with LPS variant strains showed that although protection was generally better to strains of the homologous LPS type, specificity of protection was determined more by the parent strain background (S. typhimurium or S. enteritidis) of the challenge than by O-factors 4 or 9, suggesting that other antigens are involved. The nature of the protective antigen(s) in this model is unclear, but it does not appear to be the main O-specific antigen. A S. enteritidis Se795 aroA vaccine gave good protection against wild-type S. enteritidis Se795 2 weeks after vaccination, but much less at 3 months (approximately 10-200 x LD50), although the persistence of the S. enteritidis aroA vaccine in the liver and spleen was similar to that of the S. typhimurium vaccine, and the wild-type Se795 challenge strain was of similar virulence to S. typhimurium C5. A S. dublin aroA vaccine conferred similar protection against wild-type S. dublin (approximately 300 x LD50).

Immunity induced by live attenuated Salmonella vaccines

Studies on the degree and specificity of protection conferred by immunization with aroA salmonella live vaccines in BALB/c mice are described. Animals were immunized i.v. and challenged orally 3 months later to ensure that the vaccine had been cleared from the tissues. Vaccination with Salmonella typhimurium aroA SL3261 conferred very good protection against virulent S. typhimurium C5 (over 10,000 x LD50). The specificity of cross protection was studied using S. typhimurium, Salmonella enteritidis and Salmonella dublin for vaccination and challenge, including challenge with variants of S. typhimurium and S. enteritidis of similar virulence which differed in the main LPS (lipopolysaccharide) antigen (0-4 or 0-9). S. typhimurium SL3261 gave very good protection against S. typhimurium C5 (0-4), but no protection against S. enteritidis Se795 (0-9). However, challenge with strains differing in the main 0 antigens showed that, although protection was generally better to strains expressing the same LPS type as the vaccine, specificity of protection was determined more by the background (S. typhimurium or S. enteritidis) of the parent strain used for the challenge than by 0 factors 4 or 9, suggesting that other factors could be involved. The nature of the antigen(s) responsible for protection in this model is unclear, but it would not appear to be the main 0-specific antigen. An S. enteritidis Se795 aroA vaccine was far less effective than S. typhimurium SL3261; it conferred good protection against the homologous wild type at 2 weeks post-vaccination, but far less at three months (approx 10-200 x LD50). This was unexpected, as the persistence of the S. enteritidis vaccine in the liver and spleen was similar to that of S. typhimurium SL3261, and the S. enteritidis and S. typhimurium challenge strains were of similar virulence. An S. dublin aroA vaccine conferred similar protection against wild type S. dublin (approx 300 x LD50).

The serological responses of calves to live Salmonella dublin vaccine--a comparison of different serological tests

The serological responses to live Salmonella dublin vaccine was assessed in three groups of calves; three-day-old colostrum-deprived (3DO C-), three-day-old colostrum-fed (3DO C+) and three-month-old (3MO), by the following tests; serum agglutination test (SAT), indirect haemagglutination test (IHA), complement-fixation test (CFT) and antiglobulin test (AGT). Serological activity was detected by all the tests in the 3MO calves. In the 3DO C+ calves no serological activity was detected by either the somatic SAT or IHA but low levels of CF and somatic AGT antibodies were produced. In 3DO C- calves serological activity, often at low levels, was detected by all the tests except the somatic SAT. High levels of flagellar agglutinins were detected in both groups of 3DO calves. It was concluded that with the exception of the flagellar SAT the tests were affected by the age of the calf and in 3DO calves also by the presence of colostral antibodies. However, the use of the SAT in 3MO calves would provide an indication as to the potency of salmonella vaccines.

Salmonella typhimurium infection in calves: protection and survival of virulent challenge bacteria after immunization with live or inactivated vaccines

Salmonella typhimurium SL1479, an auxotrophic mutant strain having a complete block in the aromatic biosynthetic pathway and therefore requiring p-aminobenzoic acid and 2,3-dihydroxybenzoate not available in mammalian tissues, was given orally in a dose of 10(10) live bacteria to 4- to 5-week-old calves. Only a mild transient fever response was seen. Strain SL1479 was unable to colonize and persist in the calves for more than 2 weeks. In a vaccination experiment, groups of six calves were (i) orally vaccinated with the live S. typhimurium SL1479 strain, (ii) subcutaneously vaccinated with a heat-inactivated S. typhimurium SVA1232 strain with aluminum hydroxide as adjuvant, or (iii) not vaccinated, to serve as controls. Calves were orally challenged with the live, calf-virulent S. typhimurium SVA44 strain: either 10(6) bacteria (equivalent to 100 25% lethal doses [LD25S]) or 10(9) bacteria (100,000 LD25S doses). The live oral vaccine gave significantly better protection than the heat-vaccinated, subcutaneously injected vaccine since (i) only control calves and calves given the killed vaccine developed profuse diarrhea, (ii) clinically, the mild fever responses seen after challenge in calves given the live vaccine were significantly lower (P less than 0.0005), (iii) autopsies performed 21 days after the challenge infection revealed normal findings in calves given the live vaccine, whereas calves given the killed vaccine showed signs of acute enteritis and chronic salmonellosis, (iv) all 12 calves given either 100 X or 100,000 X the LD25 survived the 21-day observation period; the mean survival time in nonvaccinated calves was 8.0 days; in calves given heat-inactivated vaccine and 100 X the LD25 it was 21.0 days, and in calves given 100,000 X the LD25 it was 11.5 days, (v) the fecal bacterial counts of the challenge S. typhimurium SVA44 strain were significantly lower (P less than 0.0005) in both groups given the live vaccine, and (vi) upon autopsy followed by culture, the qualitative recovery of the challenge strain from the alimentary canals and tissues of calves given the live vaccine was significantly lower (P less than 0.005).

Salmonella typhimurium infection in calves: cell-mediated and humoral immune reactions before and after challenge with live virulent bacteria in calves given live or inactivated vaccines

Groups of six calves, 4 to 5 weeks old, were vaccinated either orally with a live auxotrophic Salmonella typhimurium (O-antigen 1,4,12) SL1479 vaccine (10(8) bacteria on day zero, 10(10) bacteria on days 7 and 14) or subcutaneously with a heat-inactivated (56 degrees C, 30 min) S. typhimurium SVA1232 vaccine (10(10) bacteria suspended in 30% [vol/vol] aluminum hydroxide on days zero, 7, and 14). The calves were then orally challenged with either 10(6) (approximately 100 X the 25% lethal dose) or 10(9) (approximately 100,000 X the 25% lethal dose) live bacteria of the calf-virulent S. typhimurium SVA44 strain. The immune reactivity of these calves and of nonvaccinated control calves was followed before and after the challenge infection up to 42 days by (i) intradermal injection of S. typhimurium crude extract, outer membrane protein preparation (porins), and lipopolysaccharide (LPS), (ii) in vitro stimulation of peripheral blood lymphocytes estimated by using uptake of [3H]thymidine, with S. typhimurium crude extract, porins, LPS, and polysaccharide (O-antigenic polysaccharide chain free of lipid A), and Salmonella sp. serotype thompson (O-antigen 6,7) strain IS40 LPS and polysaccharide, and (iii) estimation of the class-specific immunoglobulin G (IgG) and IgM antibody responses against S. typhimurium LPS and porins, and Salmonella sp. serotype thompson LPS. The immune studies showed that in calves given the live vaccine orally, the skin test reactivity and lymphocyte stimulation indices were significantly higher (P values ranging from less than 0.025 to less than 0.0005) against homologous, but not heterologous, antigens than those seen in calves given the heat-inactivated vaccine subcutaneously. In contrast, the IgG and IgM antibody titers against homologous LPS and porins were significantly higher (P less than 0.0005) in sera collected on day 21 from calves given the heat-inactivated vaccine than in calves given the live vaccine. After the oral challenge, calves given the live vaccine showed reduced cell-mediated immune reactions, in agreement with the observation that the host defense could eradicate the challenge organism, whereas calves given the heat-inactivated vaccine showed significantly increased cell-mediated immune reactions (P values ranging from less than 0.025 to less than 0.005), in agreement with the observation that in these calves, the challenge strain caused enteritis as well as systemic invasion. The increased cell-mediated immune reactivity in calves given the live vaccine correlated well with the excellent protection against challenge infection seen in these animals.