Absorption of non-specific antibodies with Salmonella Enteritidis and Salmonella Typhimurium suspensions from tested serum samples as a useful method in serodiagnosis of salmonellosis carried out by ELISA for epidemiological surveillance

Abstract

Introduction: Diagnosis of salmonellosis is usually made by stool culture however in many laboratories ELISA for the detection of human serum antibodies against mixture of LPS antigens of the two predominant serovars of Salmonella was developed. We present the method of absorbing non-specific antibodies with S. Enteritidis (serovars D) and S. Typhimurium (serovars B) suspensions from serum samples as a useful method in serodiagnosis of salmonellosis carried out by ELISA. This simple, cost-efficient and effective method of absorption may be used in the epidemiological investigations. Methods: We used in-house ELISA three different antigens: LPS of the S. Enteritidis, LPS of the S. Typhimurium and 1:1 mixture of LPS of both serovars. Serum samples collected from 14 patients with salmonellosis, were absorbed with 20% bacterial suspensions obtained from S. Enteritidis, S. Typhimurium and mixture of both serovars (serovars B+D). The non-absorbed sera and sera after particular absorptions were tested separately in ELISA with all three antigens. Results: The all 14 non-absorbed serum samples showed a high positive results in the IgA, IgG and IgM ELISA with all three LPS antigens. Absorption of the 13 from 14 tested samples with the Salmonella B suspension resulted in a significant decrease in the level of antibodies to Salmonella B antigen, but only a very slight decrease in the levels of Salmonella B + D and Salmonella D antigen. On the other hand, the absorption of the same sera with Salmonella D suspension, caused a significant decrease in the level of antibodies for serovars D, B and B + D antigens. Such a test result clearly shows that the 13 serum samples were obtained from patients with an infection caused by S. Enteritidis (serogroup D). A opposite picture of the humoral response was obtained in the case of one serum sample obtained from a subject with an infection caused by S. Typhimurium (serogroup B). Conclusions: The presented work demonstrates the usefulness of absorption of non-specific antibodies with S. Enteritidis and S. Typhimurium suspensions in serodiagnosis of salmonellosis carried out by ELISA.