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Accuracy of qPCR and bacterial culture for the diagnosis of bovine intramammary infections and teat skin colonisation with Streptococcus agalactiae and Staphylococcus aureus using Bayesian analysis.

Authors :
Svennesen, Line
Mahmmod, Yasser S.
Skjølstrup, Nanna K.
Mathiasen, Louise R.
Katholm, Jørgen
Pedersen, Karl
Klaas, Ilka C.
Nielsen, Søren S.
Source :
Preventive Veterinary Medicine. Dec2018, Vol. 161, p69-74. 6p.
Publication Year :
2018

Abstract

Highlights • PCR and culture performance was evaluated for Staph. aureus and Strep. agalactiae. • The sensitivity was higher for PCR than bacterial culture for milk and teat skin. • The specificity of PCR and bacterial culture was generally high. • Different target conditions of culture and PCR probably affected the results. Abstract Streptococcus agalactiae (Strep. agalactiae) and Staphylococcus aureus (Staph. aureus) are originally regarded as contagious mastitis pathogens, however, both pathogens have recently been isolated from extramammary and environmental sites, indicating that other sites than the udder might contribute to the spread of these pathogens potentially causing intramammary infections. Diagnostic tools to identify pathogens at extramammary sites are available but still needs to be validated. The objective of this cross-sectional field study was to estimate the diagnostic sensitivity (Se) and specificity (Sp) of the commercially available Mastit4 qPCR assay and bacterial culture (BC) in identifying Strep. agalactiae and Staph. aureus from milk and teat skin samples. We randomly selected 30–40 cows with high somatic cell counts from eight Danish Strep. agalactiae- positive dairy herds with automatic milking systems. Teat skin samples and aseptic milk samples were collected from right rear quarters (n = 287) for BC and PCR analysis. Se and Sp were estimated in a Bayesian latent class analysis. For milk samples, the Se and Sp of qPCR for Strep. agalactiae were estimated to 0.97 and 0.99, respectively, whereas the Se and Sp of BC were 0.41 and 1.00, respectively. The Se and Sp of qPCR for Staph. aureus were estimated to 0.95 and 0.99, respectively, whereas the Se and Sp of BC were 0.54 and 0.77, respectively. For teat skin samples, the Se and Sp of qPCR for Strep. agalactiae were estimated to be 0.97 and 0.96, respectively, whereas the Se and Sp of BC were 0.33 and 1.00, respectively. The Se and Sp of qPCR for Staph. aureus were estimated to 0.94 and 0.98, respectively, whereas the Se and Sp of BC were 0.44 and 0.74, respectively. In conclusion, the Se for diagnosing Strep. agalactiae and Staph. aureus IMI was higher for qPCR than BC, suggesting that qPCR is a valuable method for detecting both pathogens from quarter-level milk samples. The performance of BC in the detection of Strep. agalactiae and Staph. aureus on teat skin was poor compared to qPCR, indicating that differences in the target condition of the two methods should be considered when implementing them as routine diagnostic tests for detecting teat skin colonisers. The low Se of BC may preclude the use of BC for skin testing, and qPCR is better for this task. [ABSTRACT FROM AUTHOR]

Details

Language :
English
ISSN :
01675877
Volume :
161
Database :
Academic Search Index
Journal :
Preventive Veterinary Medicine
Publication Type :
Academic Journal
Accession number :
133115441
Full Text :
https://doi.org/10.1016/j.prevetmed.2018.10.013