Lipopolysaccharide-specific IgG in egg yolk from two chicken flocks infected with Salmonella enteritidis

Surface plasmon resonance (BIACORE) detection of serum antibodies against Salmonella enteritidis and Salmonella typhimurium

We have used a surface plasmon resonance biosensor (BIACORE 3000) to detect serum antibodies in chickens having current or recent infections. Three well-defined Salmonella flagellar recombinant DNA antigens reflecting Salmonella enteritidis (H:g,m flagellin) and Salmonella typhimurium (H:i and H:1,2 flagellins) expressed in Escherichia coli were each immobilized in a single flow cell of a biosensor chip. Glutathione-S-transferase was immobilized on the surface of another flow cell to monitor non-specific binding. Sera collected from chickens with no history of Salmonella infection, and from chickens infected with Salmonella serotypes infantis, pullorum, gallinarum were used to test the performance of the system. The sensitivity exhibited to a range up to 900 arbitrary response units (RU) for the most positive S. typhimurium serum at a dilution of 1/40. Sera from Salmonella infantis, Salmonella pullorum and Salmonella gallinarum infected birds gave responses less than the cut-off point, which was determined as the averaged response of sera from specific pathogen-free chickens plus three times the standard deviation. A positive response was obtained when these sera and whole blood were fortified with S. enteritidis and S. typhimurium positive serum. The sensitivity, specificity, precision and reproducibility obtained suggested that this approach could be used for detecting past or present infection with a range of pathogens in animals.

World Health Organisation--supervised interlaboratory comparison of ELISAs for the serological detection of Salmonella enterica serotype Enteritidis in chickens

A collaborative exercise, supervised by the World Health Organisation, was set up to compare ELISAs used for the serological detection of Salmonella enteritica serotype Enteritidis in chickens. The aim was to ascertain how far agreement could be reached on the interpretation of optical density readings for high titre, intermediate titre and low titre sera. Two sets of sera were sent to 14 participants. The first set compared high, medium and low titre sera raised in specified-pathogen-free and commercial broiler breeder chickens. The second set comprised 20 sera of different antibody titres raised in commercial birds reared under laboratory conditions and sent blind. Both indirect and double-antibody sandwich blocking ELISAs were used with a number of different detecting antigens. With a few exceptions good agreement was reached on the interpretation of results obtained from high and low titre sera from the optical density obtained with a single serum dilution. Differences were observed in the interpretation of medium titre sera. The results suggested that most ELISAs produce reasonably comparable results and that practical problems may arise from interpretation of the results mainly as a result of the choice of the criteria used for differentiating sera obtained from infected and uninfected chickens. These problems are discussed.

Comparison between persisting anti-lipopolysaccharide antibodies and culture at postmortem in salmonella-infected cattle herds

Herds with recent clinical outbreaks of Salmonella dublin (7 herds) and S. typhimurium (4 herds) infections were followed serologically in O-antigen ELISAs over about one year, divided in four equal sampling phases. Animals found to be persistent high-reactors or seronegative at the end of the study were slaughtered and subsequently cultured for salmonella in a selected number of organ samples. Approximately 3% of all animals had high seroreactions up to 17 months after the outbreaks, and less than half of the seropositive animals in the S. dublin-infected herds were salmonella culture positive at slaughter (14/31). However, one persistently seronegative animal was also culture positive. Furthermore, as much as 70% of the male calves investigated at postmortem in the S. dublin-infected herds were high-reactors, among which approx. 56% were culture positive. Surprisingly, 2 of the 14 animals found culture positive turned out to be culture positive for S. typhimurium only. In the S. typhimurium study, none of the 17 animals investigated at postmortem were salmonella culture positive. All sera from these animals were negative in the O:9 blocking ELISA, and no serum sample was positive in the S. dublin ELISA, alone. In conclusion, although serology based on the O-antigens appears to be useful to identify salmonella-infected herds, it seems to be insufficient for identification of persistently infected animals.

Detection of antibodies to Salmonella enteritidis in sera and yolks from experimentally and naturally infected chickens

An indirect enzyme-linked immunosorbent assay (ELISA) based on the lipopolysaccharide (LPS) of Salmonella enteritidis phage type 4, was developed for the detection of antibodies to salmonella. Sera and yolks from chickens infected experimentally with S enteritidis showed strong positive reactions. Cross-reactions occurred with sera from chickens inoculated with S typhimurium or S gallinarum. Cross-reactions were weak with sera from chickens infected with five strains of other Enterobacteriaceae. The ELISA was tested with sera and yolks from commercial poultry flocks which were bacteriologically negative for salmonella or infected with salmonella serotypes belonging to serogroup D or to other serogroups. The serological reactions were strong in most flocks infected with S enteritidis and were weaker in flocks infected with S typhimurium. In some flocks infected with these serotypes no antibodies were detected. The correct setting of the cut-off value of the optical density in the ELISA makes it possible to discriminate between chickens which are infected with S enteritidis and chickens which are not infected with S enteritidis.

Detection of Salmonella enteritidis in eggs and chicken with enzyme-linked immunosorbent assay

An ELISA previously developed for the rapid detection of Salmonella enteritidis (SE) in environmental samples was modified and applied to food samples. A sandwich ELISA was designed that employs affinity-purified rabbit polyclonal antibodies for the capture stage and highly specific monoclonal antibodies for the detection stage. Thirty-nine species of bacteria other than SE, including 32 Salmonella species, were included in cross-reactivity testing with ELISA. Results showed no reactivity with any species tested besides SE. Salmonella enteritidis was added to homogenized food samples (chicken skin, meat, and eggs) to test ELISA sensitivity. The lower limit for ELISA detection of SE was 10(4) cells/mL for pure cultures and in 10% meat (wt/vol), 10(5) cells/mL in 10% skin (wt/vol), and 10(7) cells/mL in 10% eggs (wt/vol). Salmonella enteritidis detection with ELISA was confirmed with the Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) method. Results were obtained within 24 h for ELISA method compared to 96 h for the BAM procedure. Results show that sensitivity of ELISA can vary with the type of food tested for detection of SE.

Salmonella enteritidis: the egg and I

The world-wide clinical incidence of Salmonella Enteritidis has increased markedly. The increase is associated with the enhanced ability of the bacterium to systemically colonise layer chickens. Subsequent contamination and consumption of intact shell eggs from colonised layer hens, either directly or in foods containing raw or lightly cooked eggs, causes human disease. Despite investigation, no change in the biology of the bacterium has been correlated with increased colonisation in chickens. To date, no method of control at the production level has proven effective; consumer education is the best means of minimising the public health risk.

Serological diagnosis of Salmonella serotype enteritidis infections in poultry by ELISA and other tests

Serological methods have increasingly been used for the detection of invasive Salmonella serotypes including enteritidis in poultry. Different types of ELISA, particularly indirect or double antibody-blocking assays using a variety of antigens such as lipopolysaccharide, flagella and SEF14 fimbrial antigen are used as part of control programmes in a number of countries. There are many advantages to using such assays for preliminary screening of flocks prior to using bacteriological culture methods.

Enzyme-linked immunosorbent assay (ELISA) for the detection of antibodies against Salmonella enteritidis in chicken blood or egg yolk

Tracing of flock infection remains one of the most serious unsolved problems of controlling salmonellosis in poultry. In order to overcome this problem, a serological test kit for the detection of antibody to Salmonella enteritidis (1, 9, 12:[f], g, m, [p]:[1, 7]) in chicken flocks was developed. In this study, samples of antisera and the yolk of eggs from different chicken flocks were tested with the ELISA kit, and the resulting flock profiles were compared. The test system clearly allowed a differentiation between flocks which were positive and flocks which were negative for S. enteritidis. Sera from stocks infected with S. typhimurium (1, 4, (5), 12:i:1, 2) or S. heidelberg (1, 4, (5), 12:r, 1, 2) were also analysed in order to determine the relative cross-reactivity in the test. No false-positive results could be shown in the case of S. heidelberg; cross-reactions with antibodies against S. typhimurium were found in 2.5% to 10% of the samples from a particular flock. The test kit could also be used for the analysis of egg yolk samples without time-consuming purification procedures. Specific antibodies were detected in high dilutions of positive egg yolks, thus enabling a rapid screening for S. enteritidis-positive chicken flocks.

Cost-benefit analysis of a screening strategy for Salmonella enteritidis in poultry

Salmonella enteritidis is an emerging problem in several industrial countries. Outbreaks caused by this organism are almost always associated with the consumption of eggs and egg-products originating from infected poultry flocks. To reduce human infection, elimination of contaminated flocks could be considered. In this study we estimated the effectiveness of such a measure to reduce human infections. If poultry flocks are screened for S. enteritidis only once during their laying period, there is a 43.7% reduction in contaminated eggs. The effectiveness increases if the frequency of screening is increased, resulting in a 65.4% reduction in contaminated eggs after three screenings. The costs of this intervention strategy are determined by both the costs of screening and the economic losses of destroying poultry flocks.

The identification of Salmonella enteritidis-infected poultry flocks associated with an outbreak of human salmonellosis

In the summer of 1991 a human outbreak of Salmonella enteritidis infection occurred following a barbecue in which about 100 persons were involved. Eggs, supplied by one or more of 10 different layer farms, were the most probable source of the infection. To identify the S. enteritidis-positive flocks, an immunoassay was used to detect salmonella serogroup D-specific antibodies in the yolk of hens eggs. Antibody titres in the eggs from two layer farms, farm A and B, clearly exceeded the titres found in randomly collected eggs. Further investigation on farm A and B yielded high antibody titres in the eggs from flocks A1, A2 and B2, and low titres in the eggs from flock B1. S. enteritidis was isolated from the faecal samples of flocks A1, A2 and B2, whereas no salmonella was detected in the faecal samples of flock B1. The flocks present on both farms originated from the same breeder flock.

ELISAs and the serological analysis of Salmonella infections in poultry: a review

Large increases in the number of cases of human food-poisoning caused by salmonella have occurred in several countries in recent years. In England and Wales the annual number of bacteriologically confirmed cases rose from 10665 in 1981 to 30112 in 1990 and it is generally accepted that these figures are underestimates. The reasons for the unprecedented increase are largely unknown but may include increases in the consumption of convenience foods, poultry, and poultry products, together with a dramatic increase inSalmonella enteritidisinfections in poultry.S. enteritidisandS. typhimuriumare now the predominant serotypes both in human disease and in poultry.