Application of a timing protocol to the reduction of inter-plate variability in the indirect enzyme immunoassay for detection of anti-Brucella antibody

Risk of infection with Brucella abortus and Escherichia coli O157:H7 associated with marketing of unpasteurized milk in Kenya

As part of a study to assess zoonotic milk-borne health risks, seasonal survey data and unpasteurized milk samples were collected between January 1999 and February 2000 from randomly selected informal milk market agents (220 and 236 samples in the dry and wet seasons, respectively) and from households purchasing raw milk (213 and 219 samples in the dry and wet seasons, respectively) in rural and urban locations in central Kenya and screened for antibodies to Brucella abortus (B. abortus) and presence of Escherichia coli (E. coli) O157:H7. The latter was assessed based on samples from consumer households only. Antibodies to B. abortus were screened using the indirect antibody Enzyme Linked Immunosorbent Assay (ELISA) and the Milk Ring Test (MRT). The presence of E. coli O157:H7 was assessed by culture, biochemical characterisation, serological testing for production of verocytotoxin one (VT1) and two (VT2) and polymerase chain reaction (PCR) analysis for the presence of genes encoding for the toxins. The prevalence of antibodies to B. abortus varied considerably ranging from none in milk sold in small units and originating from intensive production systems to over 10% in samples that were bulked or originating from extensive production systems. E. coli O157:H7 was isolated from two samples (0.8%), one of which produced VT1. All urban consumers (100%) and nearly all rural consumers (96%) of marketed milk boiled the milk before consumption, mainly in tea, thus greatly reducing chances of exposure to live pathogens and potential health risks.

Development of a competitive ELISA using a truncated E2 recombinant protein as antigen for detection of antibodies to classical swine fever virus

The sequence encoding a truncated E2 glycoprotein of the Alfort/187 strain of classical swine fever virus (CSFV) was expressed in Escherichia coli using the pET expression system and the recombinant product purified by Ni-NTA agarose affinity chromatography. The antigenicity of this recombinant protein was demonstrated by immunoblot using anti- CSFV-specific antibodies. A monoclonal antibody was produced against the truncated E2 protein and used as competitor in an ELISA for the detection of antibodies to CSFV. Specific antibodies were demonstrated by competitive ELISA (C-ELISA) as early as 21 days post-infection (dpi) in experimentally infected pigs. Seroconversion was demonstrated by C-ELISA and neutralising peroxidase-linked assay (NPLA) in all infected animals by 4 weeks. No cross-reaction with antibodies to bovine viral diarrhoea virus (BVDV) was seen in the C-ELISA using sera from experimentally infected pigs. The C-ELISA is not intended as a substitute for the NPLA. However, it is expected it will be useful for monitoring and prevalence studies. It will also assist in testing a large number of samples in the event of an outbreak.

Evaluation of an indirect ELISA for the diagnosis of bovine brucellosis in milk and serum samples in dairy cattle in Argentina

An indirect enzyme-linked immunosorbent assay (ELISA) for Brucella abortus antibodies detection in bovine milk and serum samples was validated. The assay use B. abortus smooth lipopolysaccharide as antigen, immobilized on a polystyrene matrix; milk diluted 1:2 or serum diluted 1:50, in a buffer containing divalent cation chelating agents EDTA and EGTA (ethyleneglycol-bis-aminoether-N,N,N',N'-tetraacetic acid) to reduce non-specific reactions; and a mouse monoclonal antibody specific for an epitope of bovine IgG1, conjugated with horseradish peroxidase. A total of 2646 sera and 2119 milk samples from cows older than 24 months were obtained from 12 brucellosis-free herds for at least the previous 5 years. Milk samples were obtained in parallel with serum samples. The remaining 527 serum samples were from dry cows. All cattle were vaccinated with B. abortus strain 19 between 3-10 months of age. Five hundred and fifty-two milk samples and 562 serum samples were obtained from 6 infected herds with abortions where B. abortus was isolated at least once no more than 6 months before sampling. The complement-fixation test (CFT) on serum samples was considered the gold standard. Serum samples were also tested with the official screening test: the buffered plate antigen (BPA) test. The cut-off point was determined using receiver-operating characteristic (ROC) analysis. For milk samples, it was fixed at 36 percent positivity (PP) giving a sensitivity of 99.6% with a 95% confidence interval (CI) of 98.6-99.9%. The specificity was 99.1% (CI 98.9-99.4%). For serum samples, the cut-off was fixed at 53 PP giving a sensitivity of 99.6% (CI 98.6-99.9%) and a specificity 98.6% (CI 98-99%). The BPA test showed a relative sensitivity of 99.6% (CI 98.6-99.9%) and a relative specificity of 98.6% (CI 98.1-99%). Our results indicate that the indirect ELISA is a highly sensitive and specific test and can be adapted to process a large number of samples.

Development and validation of an indirect enzyme immunoassay for detection of ovine antibody to Brucella ovis

An indirect enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of Brucella ovis infection was developed. The assay uses a mouse monoclonal antibody to bovine IgG1 horseradish peroxidase (HRPO) conjugate that cross-reacts with immunoglobulin from sheep and a purified antigen from Brucella ovis. The ELISA data were read and analyzed according to a targeting procedure. The ELISA results were compared with a cold complement fixation test (CFT). Sera from 675 rams from three uninfected flocks were used to determine the ELISA cut-off value (O.D. 405 nm: 0.095) and the diagnostic specificity of the ELISA (100%) and the CFT (99.69% +/- 0.42). The ELISA cut-off value was corroborated by receiver operating characteristic (ROC) analysis. Six hundred and forty semen and serum samples from 419 rams from two naturally infected flocks were collected before and after mating-time during two consecutive years. All semen samples were cultured and Brucella ovis was isolated from 28 samples. Sera from the 28 rams with positive semen were used to determine the diagnostic sensitivity of the ELISA (96.43% +/- 6.8) and of the CFT (including suspected positive samples with titers of 1:5; 88.89% +/- 11.85). Considering the CFT suspicious and the anti-complementary reactions as positive resulted in a diagnostic sensitivity value of 89.28% +/- 11.46. Six hundred and ten serum samples from the 640 sera were used to determine relative sensitivity (excluding sera with 1:5) at: ELISA/CFT 97.26% +/- 3.74 and CFT/ELISA was 71.72% +/- 8.87. The percent agreement, beyond chance measured by the Kappa index was 79.7. Relative sensitivity ELISA/CFT (including 1:5 titers in the CFT as positive) was 94.9% +/- 4.83 and CFT/ELISA was 72.84% +/- 8.59. The Kappa index was 79.4.

Development and validation of an indirect enzyme immunoassay for detection of antibody to Brucella abortus in milk

An indirect enzyme immunoassay for detection of antibody to Brucella abortus in bovine milk was developed and validated using 6238 milk samples from Canadian herds (brucellosis free) and 202 samples from herds infected with B. abortus (from Argentina and Chile). The assay utilized lipopolysaccharide as the antigen, immobilized on the polystyrene matrix, whole milk to test and a mouse monoclonal antibody, specific for an epitope of bovine IgG1, conjugated with horseradish peroxidase. The sensitivity of the assay was 95.2% +/- 3.7% at a confidence limit of 95% for samples from B. abortus infected herds obtained from chile and 98.7% +/- 0.3% at a confidence limit of 95% for samples from similar herds in Argentina. Of the negative milk samples tested, 77 gave a result above the threshold value of 0.200 optical density units. When the 77 false positive samples were retested using 7.5 mM (final concentration) of EDTA and ethyleneglycol-bis-aminoether-N,N,N', N'-tetraacetic acid (EGTA), the number of false positive reactions was reduced to 3, giving a diagnostic specificity of 99.95%. The divalent cation chelating agents did not affect positive reactions and the sensitivity remained the same. Based on control samples included with each assay, the performance of the assay was consistent.

The use of divalent cation chelating agents (EDTA/EGTA) to reduce non-specific serum protein interaction in enzyme immunoassay

An indirect enzyme immunoassay (ELISA) for detection of bovine antibody to Brucella abortus was modified by the addition of divalent chelating agents to the serum diluent. This addition resulted in an increase in specificity from 96.0% in the regular assay to 99.4% in the modified procedure. Of the 15,715 sera initially tested by the indirect ELISA, 691 that had given positive reactions were selected for retesting in the indirect ELISA with EDTA/EGTA added. The buffered plate antigen test (BPAT) correctly identified 98.6% of the samples as negative. The addition of chelating agents did not alter the sensitivity of the indirect ELISA, which correctly classified 609 sera from animals from which B. abortus had been isolated as positive. The sensitivity of the BPAT was 97.8%.

Evaluation of a saline boiled extract, capsular polysaccharides and long-chain lipopolysaccharides of Actinobacillus pleuropneumoniae serotype 1 as antigens for the serodiagnosis of swine pleuropneumonia

A saline boiled extract (SBE), capsular polysaccharides (CPS) and long-chain lipopolysaccharides (LC-LPS) of Actinobacillus pleuropneumoniae serotype 1 have been evaluated in ELISA for the serodiagnosis of swine pleuropneumonia caused by this serotype. Mean optical densities (ODs) obtained with the three antigens using sera from negative herds as well as from animals experimentally and naturally exposed to A. pleuropneumoniae serotypes 1, 9 or 11 were not significantly different. The positive ELISA reaction with anti-serotypes 9 and 11 was unexpected with the CPS, which are supposed to be serotype-specific; LPS, and to a lesser extent proteins, were present in the CPS and appeared to be responsible for this reaction. In addition, sera from animals exposed to a field strain of A. pleuropneumoniae serotype 3 and to Actinobacillus suis presented a significantly lower mean OD (P < 0.001) when LC-LPS were used. Cross-reacting antigens consisted mainly of LPS core-lipid A present in the SBE and CPS. The specificity and the sensitivity of the ELISA were evaluated using three different cut-off values (the OD plus two, three and four times the standard deviation or SD) obtained with 667 negative sera. The diagnostic sensitivity was of 81% with the three antigens and the different thresholds. The diagnostic specificity was of 84, 86 and 88% for the mean plus two, three and four times the SD respectively using the SBE and the CPS, while that obtained with the LC-LPS was of 96, 98 and 99% using the same thresholds. In conclusion, LC-LPS make an easily obtainable antigen and seem to retain the best specificity while minimizing losses of sensitivity.

Improvements to the competitive ELISA for detection of antibodies to Brucella abortus in cattle sera

This paper reports improvements in the competitive ELISA (cELISA) for the detection of serum antibodies to Brucella abortus through modification of the coating of antigen and of the enzyme labelling of the monoclonal antibody conjugate. The covalent linkage of poly-L-lysine to the o-polysaccharide antigen of Brucella abortus enhanced its binding to the polystyrene matrix which resulted in a more efficient and reliable cELISA. Optimal discrimination between vaccinated and infected cattle was achieved by adjustment of the ratio between the monoclonal antibody used in the cELISA and the horseradish peroxidase. Both modifications resulted in a refined, more efficient and reliable cELISA with potential as a routine serodiagnostic assay for Brucellosis.

Evaluation of long chain lipopolysaccharides (LC-LPS) of Actinobacillus pleuropneumoniae serotype 5 for the serodiagnosis of swine pleuropneumonia

Long chain lipopolysaccharides (LC-LPS) of Actinobacillus pleuropneumoniae serotype 5 have been evaluated and compared with a crude boiled extract (CBE) in ELISA for the serodiagnosis of swine pleuropneumonia caused by this serotype. The mean optical density (OD) obtained with the LC-LPS in ELISA using sera from negative herds as well as from animals experimentally and naturally exposed to A. pleuropneumoniae serotype 5 was not significantly different from that obtained with the CBE. However, sera from animals exposed to serotypes of A. pleuropneumoniae other than serotype 5 presented a significantly lower mean OD (P < 0.05) when the LC-LPS was used. As a consequence, it was demonstrated that a high percentage of non-specific cross-reactions were eliminated, without losing specificity. The specificity and the sensitivity of the LC-LPS- and CBE-ELISA were evaluated using two different cut-off values (the OD plus two and three standard deviations) (SD) obtained from 593 sera from negative herds. The LC-LPS appeared a more suitable antigen than the CBE, since the sensitivity and the specificity (obtained with both thresholds) were statistically improved (P < 0.01). A threshold of 0.244 (mean OD plus three SD) for the LC-LPS-ELISA seemed more suitable, since a sensitivity of 79% and a specificity of 97% was achieved. Nevertheless, it may be advisable to keep a buffer range (OD between 0.194 and 0.243) and to consider sera presenting values within this range as suspicious. In the present study, the complement fixation test presented a high specificity (97%) and a very low sensitivity (47%). A herd with animals presenting ELISA positive and CFT negative results in serology, along with the absence of suggestive lesions should not be considered as a non-infected herd.

Suitability of autoclaved tap water for preparation of ELISA reagents and washing buffer

The suitability of autoclaved tap water for the preparation of ELISA reagents and washing buffer was compared with that of ultrapure water, in a standard indirect ELISA for the detection of antibodies to pseudorabies virus (PRV). The performance of the assay, using autoclaved tap water (AT-ELISA) compared favourably to that of the standard assay, using ultrapure water (UP-ELISA) in detecting anti-PRV antibodies in sequential serum samples from a pig experimentally infected with PRV. While both the UP-ELISA and AT-ELISA proved reliable in detecting anti-PRV antibodies in a coded proficiency serum panel (n = 60), the AT-ELISA detected fewer positive sera than the UP-ELISA in evaluating a limited number (n = 80) of field samples. The results suggest that autoclaved tap water may be substituted for ultrapure water for the preparation of ELISA reagents when or where ultrapure water may not be available.

Development of a competitive enzyme-linked immunosorbent assay for detection of bovine, ovine, porcine, and equine antibodies to vesicular stomatitis virus

Two competitive (C) enzyme-linked immunosorbent assays (ELISAs) were developed for the detection of antibodies to vesicular stomatitis virus (VSV) in animal sera. The assays are based upon the availability of polyclonal antibodies (PAbs) from mouse ascitic fluids prepared against the New Jersey (NJ) and the Indiana (IN) VSV serotypes. The assays were performed by the immobilization of VSV-NJ and VSV-IN antigens on a solid phase (microtiter plate). Appropriately diluted test serum mixed with an equal volume of serotype-specific PAb was allowed to incubate in the presence of the relevant VSV antigen and finally with an enzyme-conjugated anti-mouse immunoglobulin. In the absence of anti-VSV antibodies in the test serum, the VSV antigen sites are reactive with the relevant PAb (NJ or IN) as indicated by color development after enzyme degradation of substrate. If the test serum contains the homologous VSV-NJ or VSV-IN antibodies, they compete with the relevant PAb for immobilized antigen sites and quantitatively block and inhibit the PAb reaction and subsequent color development. The performance of C-ELISAs in detecting anti-VSV antibodies in serum samples from four calves, two horses, four sheep, and seven pigs experimentally infected with VSV-NJ and VSV-IN was evaluated. The sensitivity and specificity of the C-ELISAs were compared with those of the standard microtiter serum neutralization (MTSN) tests. Homologous antibodies were demonstrable by C-ELISAs as early as 5 days postinfection (DPI) in one horse and one sheep infected with VSV-IN serotype. Seroconversion was demonstrable by C-ELISAs and MTSN tests in all animals by 9 DPI except in one sheep that received VSV-NJ and one horse inoculated with VSV-IN serotype which, on the basis of the MTSN test results, did not seroconvert until 14 and 11 DPI, respectively. The dynamics of homologous antibody response in all animals as revealed by the corresponding type-specific C-ELISAs paralleled the results of the MTSN tests. The type-specific antibodies to VSV serotypes increased exponentially during the first 2 to 4 weeks postinfection and remained relatively stable for about 6 months in some animals. The results suggest that the C-ELISAs offer many advantages over the MTSN tests and have potential applications as rapid and inexpensive tests in serodiagnosis of VSV infections in animals.

Application of indirect ELISA for detection of bovine antibodies against vesicular stomatitis viruses

Two indirect enzyme-linked immunosorbent assays (I-ELISAs) are described for the detection of bovine serum antibody to the New Jersey (NJ) and Indiana (IN) vesicular stomatitis viruses (VSV). Serum samples at a dilution of 1:200 were incubated with binary ethylenimine-inactivated VSV-NJ and VSV-IN type-specific antigens preadsorbed to microtiter plates. Bound antibodies were detected by a murine monoclonal antibody to bovine IgG1 conjugated with horseradish peroxidase. The performance of each I-ELISA in detecting homotypic and heterotypic antibodies to VSV-NJ and VSV-IN in sequential serum samples from calves experimentally infected with VSV-NJ or VSV-IN was evaluated. The I-ELISAs detected serotype-specific antibodies to either VSV-NJ or VSV-IN in calves infected with the homologous serotype. Homotypic but not heterotypic anti-VSV-NJ antibodies were first demonstrable by the VSV-NJ I-ELISA during the second week postinfection and remained at an elevated level for a period of 11 weeks, with a gradual decrease thereafter. Similar homotypic antibody profiles measured by the VSV-IN I-ELISA in calves inoculated with VSV-IN were observed. The performances of the I-ELISAs were compared using 1,495 microtiter serum neutralization (MTSN) test-negative bovine field sera collected from cattle in Canada (VS free) and 429 samples collected from cattle in the USA and Mexico (VS-epidemic and VS-endemic areas). The diagnostic specificities of the VSV-NJ and VSV-IN I-ELISAs for the Canadian samples relative to the MTSN test results were in the range of 99.8% and 99.7%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Competitive ELISA for serodiagnosis of bluetongue: evaluation of group-specific monoclonal antibodies and expressed VP7 antigen

The performance of 2 competitive enzyme-linked immunosorbent assays (C-ELISA) was compared with the reference C-ELISA I for the detection of antibodies to bluetongue virus (BTV). One of the assays (C-ELISA II) used a group-specific monoclonal antibody (MAb) to BTV, obtained from the American Type Culture Collection (8A3B-6) and tissue culture (TC)-derived BTV antigen (Ag), and the other assay (C-ELISA III) used BTV core protein VP7 (expressed in yeast) and the reference MAb (Pirbright Laboratory, 3-17-A3). Test sera were obtained by sequential blood samples from 22 calves, each inoculated with a different serotype (T) of BTV (South African [SA] T-1-T-16 and T-18-T-20 and USA T-11, T-13, and T-17). Sera were also obtained from 4 calves and 4 sheep inoculated with USA BTV T-10 and from several groups of calves exposed to single or multiple doses of epizootic hemorrhagic disease virus (EHDV) T-1-T-4 grown in TC (BHK-21) or suckling mouse brain (SMB). A total of 618 bovine and ovine field sera collected from BT-free and BT-endemic areas were also tested. The C-ELISA III was more sensitive than the C-ELISA II in the detection of anti-BTV antibody in sera from cattle and sheep early after infection with BTV. Seroconversion was demonstrated by the 3 C-ELISAs in all animals inoculated with BTV by 20 days postinfection (DPI), except in calves that received SA T-3 or USA T-13, which became positive at 40 DPI.(ABSTRACT TRUNCATED AT 250 WORDS)

Simultaneous screening of bovine sera for antibodies to bluetongue and epizootic hemorrhagic disease of deer viruses by enzyme-linked immunosorbent assay

An indirect enzyme-linked immunosorbent assay (I-ELISA) is described for simultaneous screening of bovine sera for detection of antibodies to bluetongue (BT) and epizootic hemorrhagic disease of deer (EHD) viruses (V). Optimal dilutions of BTV and EHDV antigens were combined and allowed to absorb on to the wells of microtiter plates. Appropriately diluted (1:100) bovine sera were allowed to incubate and the bound antibodies were detected by a murine monoclonal antibody (MAb) to bovine immunoglobulin (H-Chain) conjugated with horseradish peroxidase. The performance of the combined (C) I-ELISA in detecting antibodies to BTV and EHDV in sequential serum samples from calves experimentally inoculated with BTV, serotype 10, EHDV, serotype 1 (New Jersey) or EHDV serotype 2 (Alberta) was evaluated. Comparable antibody profiles were demonstrable by the CI-ELISA and separate I-ELISAs using either BTV or EHDV antigens. The results suggest that the CI-ELISA offers many advantages over the standard agar gel immunodiffusion (AGID) test and has potential application as a rapid, sensitive, inter-group-specific and inexpensive test for simultaneous screening of bovine sera for antibodies to BTV and/or EHDV.

Evaluation of a simple method for improving the precision of an ELISA detecting antibody in serum

A method of correcting OD values to improve between-assay precision (PCF4 method) was evaluated using an ELISA detecting anti-Dichelobacter nodosus antibody in ovine serum. Four control sera with pre-defined target OD were included on each plate and used to calculate a correction factor. The mean between-plate CV for eight reference sera tested over a period of 6 months was reduced from 15.2% to 9.4% in a polyclonal conjugate assay (114 plates) and from 13.3% to 9.8% in a monoclonal conjugate assay (128 plates) using this method. The PCF4 method was compared with an existing method that uses only one control serum and was found to be superior. Time course plots of PCF4 values were useful for laboratory quality control. The mean within-plate coefficients of variation for four reference sera tested in paired wells were 8.2% and 5.1% in the polyclonal and monoclonal conjugate assays respectively. Marked changes in OD due to experimental manipulation of antigen dilution, serum dilution and incubation time, conjugate dilution and chromogen-substrate incubation time were corrected by the method.

Optimization and standardization of an enzyme-linked immunosorbent assay protocol for serodiagnosis of Actinobacillus pleuropneumoniae serotype 5

An indirect enzyme-linked immunosorbent assay protocol has been optimized with special emphasis given to assay standardization and quality control. Technical aspects such as choice of a microplate, antigen immobilization, buffer composition, optimal screening dilution of sera, and kinetics of the enzymatic reaction were studied and evaluated in order to design a standard protocol offering maximal analytical sensitivity and specificity, as well as to obtain minimal within- and between-plate variability. Among the 27 plates tested, the Nunc 475-094 and 269-620 immunoplates were found to be the best in terms of high positive-to-negative ratio and low variability. No significant differences in antigen immobilization were found by using buffers of various compositions or pHs; however, the presence of magnesium ions (Mg2+; 0.02 M) resulted in a twofold increase in nonspecific background. An optimal screening dilution of sera was established at 1:200. A 1-h incubation period for test serum was found to be optimal. Maximum enzymatic activity for peroxidase was obtained by adjusting both substrate (H2O2) and hydrogen donor [2,2' -azinobis(3-ethylbenz-thiazoline sulfonic acid)] concentrations to 4 and 1 mM, respectively. To control between-plate variability, a timing protocol was adopted. Within-plate variability was also controlled by using a sample placement configuration pattern. Sliding scales were determined by repeated testing of a cross section of samples to set acceptance limits for both within- and between-plate variability. These limits were used in a quality control program to monitor assay performance. The results obtained suggest that this standardized protocol might be useful in the serodiagnosis of Actinobacillus pleuropneumoniae serotype 5.

Chromatographic purification and characterization of antigens A and D from Mycobacterium paratuberculosis and their use in enzyme-linked immunosorbent assays for diagnosis of paratuberculosis in sheep

The protein antigens A and D were purified from culture filtrates and sonic extracts of laboratory strains of Mycobacterium paratuberculosis by salt precipitation and chromatography. The characterization of antigen A is shown here, and both antigens were evaluated along with lipoarabinomannan antigen in indirect enzyme-linked immunosorbent assays (ELISA) for the serodiagnosis of ovine paratuberculosis. After anion-exchange (DEAE-5PW) and hydrophobic (phenyl-5PW) chromatography using high-performance liquid chromatography, antigen A showed a prominant band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) at 31 kDa with small amounts of low-molecular-mass proteins but with no evidence of antigen D. A single precipitin arc was evident with purified antigen A in crossed immunoelectrophoresis. The determination of the N-terminal amino acid sequence showed a high degree of homology between the 31-kDa component of antigen A and antigens of the BCG85 complex of Mycobacterium bovis BCG, a total of 24 of 26 residues being identical to those of BCG85C. A prominant SDS-PAGE band at 400 kDa and a single crossed-immunoelectrophoresis arc was also evident for antigen D after gel filtration (Sephacryl S-200), anion-exchange (DEAE-Sephacel), and concanavalin A-Sepharose affinity chromatography. By ELISA, purified antigen A detected antibody in the sera of 18 of 22 paratuberculosis-infected sheep (82% sensitivity), whereas the purified antigen D detected antibody in all 22 infected animals (100% sensitivity). Combined ELISA results showed increased specificity with some loss in sensitivity.

The serological response of cattle immunized with Yersinia enterocolitica O:9 or O:16 to Yersinia and Brucella abortus antigens in enzyme immunoassays

Sera from calves immunized with Yersinia enterocolitica serotypes O:9 or O:16 were tested by indirect enzyme linked immunosorbent assay (ELISA) using lipopolysaccharide (LPS) preparations from Brucella abortus or Y. enterocolitica O:9 or O:16 for their antibody content of the IgG1 or IgG2 subclasses. High IgG1 responses were present with the three antigens in both groups although some individual variations between animals were noted. The IgG2 responses were modest and in some cases not above background 'noise'. Thus IgG2 antibody was not measurable in sera from serotype O:9 injected calves when using serotype O:16 LPS or in serotype O:16 injected calves when using B. abortus or serotype O:9 LPSs. A competitive ELISA using B. abortus O-polysaccharide and a monoclonal antibody to B. abortus LPS (initially designed to differentiate the antibody responses of cattle naturally infected with B. abortus from those vaccinated with strain 19) was used on sera from both groups of calves. Using this test, no antibody was detected in the group immunized with serotype O:16 and except for one animal in the serotype O:9 immunized group, only low levels of antibody were transiently in evidence. One animal in this group responded with quite high levels of competing antibody which, however, declined towards the end of the test period. The competitive ELISA may prove a useful serological tool for differentiating vaccinal and field infection titers to B. abortus and also to eliminate cross-reactions observed with Y. enterocolitica serotypes.

Bovine monoclonal antibody specific for Brucella abortus lipopolysaccharide

The development of a bovine monoclonal antibody against Brucella abortus smooth lipopolysaccharide (BM-8) by interspecies fusion of bovine peripheral lymphocytes from an immunized cow and a murine plasmacytoma cell line is described. The twice cloned cell line secreted bovine IgG1 subclass antibody. Ascites fluid was prepared in pristane treated nu/nu mice by intraperitoneal injection. The pooled ascites fluid was purified by affinity chromatography and the functions of the antibody assessed in various serological tests. The BM-8 antibody did not agglutinate well at a neutral pH, however, under acid conditions it was efficient at agglutinating B. abortus cells. The antibody did not precipitate B. abortus LPS in double agar gel immunodiffusion but was very active in the direct complement fixation test and the indirect enzyme immunoassay, although it was unable to compete with a murine monoclonal antibody in a competitive enzyme immunoassay.

A review of enzyme immunoassay for detection of antibody to Brucella abortus in cattle

Enzyme immunoassay has gained wide acceptance for serological diagnosis of bovine brucellosis because of its ability to detect antibody of all isotypes unlike the conventional tests. The indirect enzyme immunoassay, however, presents several parameters that require careful analysis. These parameters include the choice of antigen and antiglobulin-enzyme conjugate reagents for use in the assay, dealing with the large amount of data the semi-automatic or automatic assay can generate and the inter- and intralaboratory standardization and quality control. This review considers the various methods described in the literature and, briefly, how some of the problems have been overcome or how they might be dealt with.

Brucella abortus 1119-3 O-chain polysaccharide to differentiate sera from B. abortus S-19-vaccinated and field-strain-infected cattle by agar gel immunodiffusion

Purified Brucella abortus 1119-3 and Brucella melitensis 16M lipopolysaccharide O-chain polysaccharides were not precipitated in agar gel immunodiffusion by any of 24 sera from vaccinated cattle but were precipitated by 18 of 24 sera from infected cattle. This difference can be used to differentiate sera of cattle vaccinated with B. abortus S-19 from sera of some field-strain-infected cattle.

Bovine IgM: does it fix guinea pig complement in the absence of bovine complement components?

Purified bovine isotypes IgM, IgG1, IgG2, and IgA (secretory), affinity purified with Brucella abortus, were tested in a complement fixation test (CFT) for their ability to activate guinea pig complement directly or in the presence of 'normal' bovine serum. Only IgG1 fixed guinea pig complement in the direct test and approximately 250 ng of antibody was required to activate 50% of 3 CH50 units with a standard amount of antigen. Addition of 'normal' bovine serum as an additional source of complement resulted in activation of guinea pig complement by IgM, IgG2 and secretory IgA at levels of approximately 1200, 700 and 2250 ng, respectively for 50% of 3 CH50 units. Addition of 'normal' bovine serum did not enhance complement activation by bovine IgG1.