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

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

doi:10.1111/jam.14309

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

J Appl Microbiol. 2019 Aug;127(2):406-417. doi: 10.1111/jam.14309. Epub 2019 Jun 3.

Authors

Y S Mahmmod^{1

2}, L Svennesen¹, J Katholm³, K Pedersen⁴, I C Klaas¹

Affiliations

¹ Department of Veterinary and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Frederiksberg C, Denmark.
² Infectious Diseases, Department of Animal Medicine, Faculty of Veterinary Medicine, Zagazig University, Zagazig, Sharkia Province, Egypt.
³ DNA Diagnostic A/S, Risskov, Denmark.
⁴ National Veterinary Institute, Technical University of Denmark, Kongens Lyngby, Denmark.

PMID: 31077513
DOI: 10.1111/jam.14309

Abstract

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 BC_Se in diagnosis of IMI, however; the Sp of BC was higher than qPCR_Sp . BC_Se and BC_Sp showed no substantial difference between the tested BC cut-offs. In contrast to IMI, estimates of BC and qPCR in diagnosing TAC were different. BC_Se was higher than qPCR_Se at all tested cut-offs, however; qPCR_Sp was higher than BC_Sp .

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.

Keywords: bovine mastitis; diagnostic test evaluation; latent class analysis; nonaureus staphylococci; sensitivity and specificity; teat skin colonization.

MeSH terms

Animals
Bayes Theorem
Cattle
Female
Mammary Glands, Animal / microbiology
Mastitis, Bovine / diagnosis*
Mastitis, Bovine / microbiology
Milk / microbiology
Real-Time Polymerase Chain Reaction*
Sensitivity and Specificity
Staphylococcal Infections / diagnosis
Staphylococcal Infections / microbiology
Staphylococcal Infections / veterinary*
Staphylococcus / isolation & purification