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

Abstract

Aim:To primarily estimate the sensitivity (Se) and specificity (Sp) of thecommercially available Mastit4 quantitative PCR (qPCR) assay and bacterialculture (BC) for diagnosis of intramammary infections (IMI) and teat apexcolonization (TAC) with coagulase-negative staphylococci (CNS) at differentcut-offs for qPCR cycle threshold values using Bayesian latent class analysis. Asecondary objective was to evaluate two cut-offs of BC for diagnosis of IMIand TAC with CNS.Methods and Results:We randomly selected 13–20 cows with subclinicalmastitis from eight dairy herds. Teat skin samples and aseptically collectedforemilk samples were collected from the right hindquarters (n=149) for BCand qPCR analysis. The Se of qPCR was always higher than BCSein diagnosis ofIMI, however; the Sp of BC was higher than qPCRSp.BCSeand BCSpshowed nosubstantial difference between the tested BC cut-offs. In contrast to IMI,estimates of BC and qPCR in diagnosing TAC were different. BCSewas higherthan qPCRSeat all tested cut-offs, however; qPCRSpwas higher than BCSp.Conclusion:The overall performance of qPCR is higher than BC in thediagnosis of IMI; however, the performance of BC is better than qPCR indiagnosis of TAC. The qPCR and BC are valid diagnostics for bovine IMI withCNS. However, for TAC, both techniques require further investigation toreduce the uncertainty of the true status of the quarter and teat skin.Significance and Impact of the Study:We reported, for the first time, thediagnostic performance of new mastitis technology (Mastit4 PCR) and culturefor detection of CNS in milk and nonmilk samples in dairy herds withautomatic milking systems. Our findings will improve the interpretation of thetest results of culture and qPCR assay and subsequently, will strengthen thecontrol of IMI with CNS in dairy cows.