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Prev Vet Med. 2019 Jun 1;167:80-84. doi: 10.1016/j.prevetmed.2019.03.026. Epub 2019 Mar 30.

Diagnostic value of composite milk sample vs single quarter milk sample for the detection of Staphylococcus aureus intra-mammary infections in cattle.

Author information

1
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Sezione Diagnostica di Lodi, Via Albert Einstein, 26900 Lodi, Italy. Electronic address: antoniomarco.maisano@yahoo.it.
2
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Sezione Diagnostica di Lodi, Via Albert Einstein, 26900 Lodi, Italy. Electronic address: mariovittorio.luini@izsler.it.
3
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Produzione primaria, Via Antonio Bianchi 9, 25124 Brescia, Italy. Electronic address: valentina.lorenzi@izsler.it.
4
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Unità Analisi del Rischio ed Epidemiologia Genomica, Via dei Mercati 13/A, 43100 Parma, Italy. Electronic address: luca.bolzoni@izsler.it.
5
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Sezione Diagnostica di Lodi, Via Albert Einstein, 26900 Lodi, Italy. Electronic address: alicia.romano@agroscope.admin.ch.
6
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Sezione Diagnostica di Lodi, Via Albert Einstein, 26900 Lodi, Italy. Electronic address: chspelta@icloud.com.
7
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Produzione primaria, Via Antonio Bianchi 9, 25124 Brescia, Italy. Electronic address: ale.angelucci@libero.it.
8
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Produzione primaria, Via Antonio Bianchi 9, 25124 Brescia, Italy. Electronic address: francesca.fusi@izsler.it.
9
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Produzione primaria, Via Antonio Bianchi 9, 25124 Brescia, Italy. Electronic address: giandomenico.ferrara@izsler.it.
10
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Sezione Diagnostica di Lodi, Via Albert Einstein, 26900 Lodi, Italy. Electronic address: fausto.vezzoli@izsler.it.
11
Istituto Zooprofilattico Sperimentale della Lombardia e dell'Emilia Romagna "Bruno Ubertini" - Produzione primaria, Via Antonio Bianchi 9, 25124 Brescia, Italy. Electronic address: luigi.bertocchi@izsler.it.

Abstract

Staphylococcus aureus (S. aureus) is one of the most important causes of mastitis in dairy cattle. Control and eradication programs of S. aureus intra-mammary infections (IMI) are based on different factors included the correct detection and management of the infected cows. The present study aimed at evaluating the efficacy of composite milk samples (CMS) analysis, compared to quarter milk samples (QMS) analysis, for the bacteriological detection of S. aureus intra-mammary infections. During 2016, 661 CMS (hygienically collected) and 2644 QMS (aseptically collected) were obtained from 661 cows in 5 herds. All the samples were submitted to S. aureus bacteriological culture and somatic cell count (SCC) analysis. QMS bacteriological analysis on blood agar plates was able to detect 236 cows excreting S. aureus, while the bacteriological analysis of CMS, using selective agar, identified 229 positive cows. The concordance was 95% with an excellent Cohen's κ (0.89). Relative sensitivity and specificity of CMS vs QMS, considered as the reference test, were 91.5% ± 2.1 and 96.9% ± 1.3 (CI 95%), respectively. In addition, the relative sensitivity of CMS improved as the number of infected quarters per cow and the number of colony forming units (cfu) per sample increased. The predictive value of CMS results was better when paired with SCC data, in particular CMS showed better negative predictive value when SCC was <200,000 cells/mL and better positive predictive value when SCC was>200,000 cells/mL. The probability for a cow to be S. aureus positive was 56.4% in case of SCC > 200,000 cells/mL, while it was 18.6% in case of SCC < 200,000 cells/mL. The average SCC in CMS was significantly higher in positive cows and the value rose as the number of infected quarters per cow increased. Given the intermittent excretion of S. aureus in milk from dairy cows, it could be more advantageous to carry out several serial CMS, rather than few QMS, being CMS an easier to collect and less expensive milk sampling method. Thus, bacteriological examination of CMS, combined with SCC data of the same sample, could be extremely useful for the success of S. aureus IMI control plans, because repeated CMS are easier to be performed and could be more easily proposed to the farmers.

KEYWORDS:

Composite milk sample; Dairy cow; Mastitis; Somatic cell count; Staphylococcus aureus

PMID:
31027725
DOI:
10.1016/j.prevetmed.2019.03.026
[Indexed for MEDLINE]

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