ELISA for measurement of antibody response to a killed Salmonella typhimurium vaccine in cattle

Characterization of Enzyme-Linked Immunosorbent Assay (ELISA) for Quantification of Antibodies against Salmonella Typhimurium and Salmonella Enteritidis O-Antigens in Human Sera

Nontyphoidal Salmonella (NTS) is a leading cause of morbidity and mortality caused by enteric pathogens worldwide in both children and adults, and vaccines are not yet available. The measurement of antigen-specific antibodies in the sera of vaccinated or convalescent individuals is crucial to understand the incidence of disease and the immunogenicity of vaccine candidates. A solid and standardized assay used to determine the level of specific anti-antigens IgG is therefore of paramount importance. In this work, we presented the characterization of a customized enzyme-linked immunosorbent assay (ELISA) with continuous readouts and a standardized definition of EU/mL. We assessed various performance parameters: standard curve accuracy, dilutional linearity, intermediate precision, specificity, limits of blanks, and quantification. The simplicity of the assay, its high sensitivity and specificity coupled with its low cost and the use of basic consumables and instruments without the need of high automation makes it suitable for transfer and application to different laboratories, including resource-limiting settings where the disease is endemic. This ELISA is, therefore, fit for purpose to be used for quantification of antibodies against Salmonella Typhimurium and Salmonella Enteritidis O-antigens in human samples, both for vaccine clinical trials and large sero-epidemiological studies.

Persistent experimental Salmonella dublin intramammary infection in dairy cows

Experimental intramammary infections were induced in five post-parturient Holstein cows by inoculation of low numbers (5000 colony forming units) of virulent Salmonella dublin via the teat canal of mammary gland quarters. Rectal temperature, pulse and respiratory rates, milk yield, and milk quality as assessed by the California Mastitis Test (CMT) and somatic cell counts (SCC) were recorded every 12 hours at milking. Bacteriologic cultures of foremilk quarter samples and feces were obtained daily, as were complete blood counts. ELISA titers for IgG and IgM recognizing S. dublin lipopolysaccharide (LPS) were obtained weekly on serum and quarter milk samples. All cows excreted S. dublin intermittently from infected quarters, but no changes were detected in rectal temperature, appearance of the mammary gland or secretions, CBC, milk yield, and pulse and respiratory rates. Somatic cell counts were modestly increased in infected quarters as compared with uninfected quarters (P = .015, paired t test); however, CMT scores after infection remained low, and were not significantly different from pre-infection scores (P greater than .10, sign test). After infection, administration of dexamethasone resulted in signs of clinical mastitis and increased excretion of S. dublin from mammary quarters (P = .0004, paired t test). One cow had necrotizing mastitis and S. dublin septicemia and was euthanatized. In the four surviving cows, clinical improvement was observed after systemic gentamicin therapy and intramammary infusion with polymyxin B, but all cows continued to excrete S. dublin intermittently from one or more quarters and occasionally from feces for the remaining period of observation. All infected cows demonstrated a rise in IgG and IgM ELISA titers recognizing S. dublin LPS in serum and milk. At necropsy (13-25 weeks postinfection), S. dublin was recovered only from the mammary tissue or supramammary lymph nodes in three of four cows. In one cow, mammary gland and lymph-node samples were negative for S. dublin despite positive milk cultures. In all cows, histopathologic examination revealed multifocal areas of chronic active mastitis. These lesions were similar to histopathologic findings from mammary gland carriers with naturally acquired S. dublin infection.

Diffusion in gel-enzyme linked immunosorbent assay (DIG-ELISA) to record the immunoglobulin response of calves vaccinated with Salmonella

A diffusion in gel-enzyme linked immunosorbent assay (DIG-ELISA) was used to record immunoglobulin development of colostrum-fed calves vaccinated with aromatic dependent (aro-) Salmonella and challenged with either the homologous as a heterologous serotype. IgG was detected by using a peroxidase conjugated rabbit antibovine IgG, whereas IgM and IgA were measured using a double sandwich technique. Although IgG levels to Salmonella endotoxins increased after exposure to Salmonella, they were found to be high in many calves prior to vaccination. However, IgM antibody levels were consistently low prior to vaccination, and their increase was a more reliable indicator of the vaccination and immune status of the calves. IgA levels were generally low and of less predictive value.

Quantification of bovine IgG, IgM and IgA antibodies to Clostridium perfringens B-toxin by enzyme immunoassay I. Preparturient immunization for enhancement of passive transfer of immunity

A quantitative competitive binding "triple-sandwich" enzyme immunoassay was developed and used to evaluated pathogen/class-specific antibody responses in Holstein-Friesian cows vaccinated against Clostridium perfringens B-toxin. Vaccination of cows at six weeks and again at two weeks prepartum increased pathogen-specific IgG levels in each dam's colostrum and respective calf's serum. Pathogen-specific IgG and IgM concentrations in dams' sera and colostra were related to subsequent pathogen-specific IgG and IgM neonatal sera concentrations. Only pathogen-specific IgA in dams' colostra was correlated to neonatal levels, possibly owing to a different origin and role of this immunoglobulin class. All class-specific colostral immunoglobulin levels were related to subsequent neonatal concentrations. Isotypic antibody responses against C. perfringens B-toxin were found with pathogen-specific IgM predominant in dams' sera and pathogen-specific IgA predominant in colostra and neonatal sera.

Salmonella typhimurium infection in calves: delayed specific skin reactions directed against the O-antigenic polysaccharide chain

Specific delayed skin reactions developed after intradermal injection of Salmonella typhimurium lipopolysaccharide in 12-week-old calves which had been orally infected with S. typhimurium 5 weeks earlier. Uninfected calves showed no delayed skin reactions. Skin biopsies from skin swellings showed a massive infiltration of mononuclear cells in the skin of infected calves but not in those of uninfected calves. Persistence of infection in infected calves was confirmed by isolation of S. typhimurium from fecal specimens. The delayed skin reactions could be shown to be specific and directed against the O-polysaccharide chain of the lipopolysaccharide since none of the lipopolysaccharide chain of the lipopolysaccharide since none of the lipopolysaccharide preparations from a rough mutant of S. typhimurium, two strains with different O-polysaccharide chains, or lipid A elicited skin reactivity. To cause a reaction, the O-polysaccharide had to be in a macromolecular complex, since skin swellings were seen only after injections of either O-polysaccharide chains cross-linked by 1,2,3,4-diepoxybutane or octasaccharides from the O chain covalently linked to a straight 12-carbon aliphatic chain forming an artificial glycolipid. Injection of the pure octasaccharides of O-polysaccharide chains failed to elicit delayed skin reactions.