Bayesian estimation of qPCR and bacterial culture accuracy for detection of bovine coagulase-negative staphylococci from milk and teat apex at different test cut-off points

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Y. S. Mahmmod, L. Svennesen, J. Katholm, K. Pedersen, I. C. Klaas

Aim: To primarily estimate the sensitivity (Se) and specificity (Sp) of the commercially available Mastit4 quantitative PCR (qPCR) assay and bacterial culture (BC) for diagnosis of intramammary infections (IMI) and teat apex colonization (TAC) with coagulase-negative staphylococci (CNS) at different cut-offs for qPCR cycle threshold values using Bayesian latent class analysis. A secondary objective was to evaluate two cut-offs of BC for diagnosis of IMI and TAC with CNS. Methods and Results: We randomly selected 13–20 cows with subclinical mastitis from eight dairy herds. Teat skin samples and aseptically collected foremilk samples were collected from the right hindquarters (n = 149) for BC and qPCR analysis. The Se of qPCR was always higher than BCSein diagnosis of IMI, however; the Sp of BC was higher than qPCRSp. BCSeand BCSp showed no substantial difference between the tested BC cut-offs. In contrast to IMI, estimates of BC and qPCR in diagnosing TAC were different. BCSe was higher than qPCRSe at all tested cut-offs, however; qPCRSp was higher than BCSp. Conclusion: The overall performance of qPCR is higher than BC in the diagnosis of IMI; however, the performance of BC is better than qPCR in diagnosis of TAC. The qPCR and BC are valid diagnostics for bovine IMI with CNS. However, for TAC, both techniques require further investigation to reduce the uncertainty of the true status of the quarter and teat skin. Significance and Impact of the Study: We reported, for the first time, the diagnostic performance of new mastitis technology (Mastit4 PCR) and culture for detection of CNS in milk and nonmilk samples in dairy herds with automatic milking systems. Our findings will improve the interpretation of the test results of culture and qPCR assay and subsequently, will strengthen the control of IMI with CNS in dairy cows.

Original languageEnglish
JournalJournal of Applied Microbiology
Issue number2
Pages (from-to)406-417
Number of pages12
Publication statusPublished - 2019

    Research areas

  • bovine mastitis, diagnostic test evaluation, latent class analysis, nonaureus staphylococci, sensitivity and specificity, teat skin colonization

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