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Clinical and Diagnostic Laboratory Immunology, November 2001, p. 1049-1055, Vol. 8, No. 6
1071-412X/01/$04.00+0   DOI: 10.1128/CDLI.8.6.1049-1055.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Evaluation of Two Enzyme-Linked Immunosorbent Assays for Detecting Salmonella enterica subsp. enterica Serovar Dublin Antibodies in Bulk Milk

J. Veling,1,* F. G. van Zijderveld,2 A. M. van Zijderveld-van Bemmel,2 Y. H. Schukken,3 and H. W. Barkema1

Animal Health Service, 7400 AA Deventer,1 and Department of Bacteriology, Institute for Animal Science and Health, ID Lelystad, 8200 AB, Lelystad,2 The Netherlands, and Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York 148533

Received 20 February 2001/Returned for modification 24 April 2001/Accepted 23 July 2001

Two enzyme-linked immunosorbent assays (ELISAs) for the detecting Salmonella enterica subsp. enterica serovar Dublin antibodies in bulk milk were developed and evaluated for potential use in control programs. The ELISAs were based on either lipopolysacharide (LPS ELISA) or flagellar antigen (GP ELISA). Sensitivity was determined with 79 case herds with a wide range of clinical signs. Specificity was determined with 125 Dutch and 200 Swedish control herds. The relation between antibodies in bulk milk, antibodies in serum, and the level of milk production of individual cows was studied with 61 case herds. The optimal optical density (OD) values of the LPS ELISA and the GP ELISA were determined to be 0.2 and 0.5, respectively. The sensitivities of the LPS ELISA and the GP ELISA were 54 and 63%, respectively, with a specificity of 98% for both ELISAs with samples from the Dutch control herds. The specificities for samples from the Swedish herds were 100% for the LPS ELISA and 95% for the GP ELISA. The sensitivity of the combination of tests was 65% when samples were run in parallel, and the specificity was 100% when samples were run in series, irrespective of whether the samples came from Dutch or Swedish control herds. The variance (R2) in the OD value for bulk milk samples could be explained by the percentage of seropositive lactating cows in a herd with the LPS ELISA for 51% of the samples and with the GP ELISA for 72%. The variance in the OD value was best explained by the combination of the percentage of seropositive lactating cows in the herd and the mean log10 serum antibody titer for that herd (R2 = 62% for the LPS ELISA and R2 = 75% for the GP ELISA). Case herds more often tested negative by the ELISA with bulk milk when the percentage of seropositive lactating cows was less than 5%. It is concluded that both ELISAs with bulk milk can be used in control programs to distinguish between infected and noninfected herds. Specificity can be increased by using the two tests in combination. Sensitivity was relatively low for both single tests and both tests combined.


* Corresponding author. Mailing address: Animal Health Service, P.O. Box 9, 7400 AA Deventer, The Netherlands. Phone: 31-570 660343. Fax: 31-570 660345. E-mail: j.veling{at}gdvdieren.nl.


Clinical and Diagnostic Laboratory Immunology, November 2001, p. 1049-1055, Vol. 8, No. 6
1071-412X/01/$04.00+0   DOI: 10.1128/CDLI.8.6.1049-1055.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.