Proceedings of the British Mastitis Conference (2001) Garstang, p 100 Institute for Animal Health/Milk Development Council
PRELIMINARY RESULTS OF A METHOD FOR THE RAPID
DETECTION OF STAPHYLOCOCCUS AUREUS IN MILK
E.M. Smith1, D.J. Mason2 , G.F. Medley1, C.S. Dow 2 , L.E. Green1
University of Warwick Department of Biological Sciences, Coventry, CV4 7AL
1 Ecology and Epidemiology Group
2 Microbiology Group
The presence of bacteria in milk is a major determining factor in its value to
both farmers and dairy companies. Several methods are available to
determine the microbiological content of milk, but suffer from significant
disadvantages such as time taken to produce results (up to 72 h for
traditional culture methods), operator fatigue or a lack of specificity.
The use of flow cytometry (FCM), or electrical impedance technology
(CellFacts) offers advantages of speed and, when coupled with the use of
fluorescent probes, sensitivity, for the detection of specific pathogenic
bacteria in foods. A method that allows rapid detection of Staphylococcus
aureus in milk would greatly benefit farmers with a known problem and help
to identify sub-clinically infected cattle.
This would facilitate earlier
treatment of the disease which has been shown to be much more effective at
eliminating the pathogens from the udder, benefiting milk yield and quality,
and the health of the cow.
The objective of this project is to develop a new diagnostic tool to quickly
identify clinical and sub-clinical mastitis in dairy cows. The presence of
protein and lipid particles in milk can interfere non-specifically with
fluorescent labelling techniques and in doing so, reduce the effectiveness of
the assay.
Enzymatic clearing using a number of protease enzymes

(Alcalase , Savinase  and Proteinase K) was investigated as a method for the
preparation of milk, to be used in combination with S. aureus specific,
fluorochrome-labelled monoclonal antibodies. Either FCM or CellFacts
analysers could then enumerate numbers of labelled bacteria.
Thus
enabling the rapid (≤ 2 h) detection of S. aureus in milk. Up to 100%
recovery of bacteria added to milk using the conventional plate count
method has been achieved.
The results of adaptation and validation of the technique indicate that this
method detects S. aureus in milk rapidly. The detection limit of a flow
cytometer and CellFacts analyser is approximately 104, and 105 bacteria/ml
of milk respectively. This level (104 bacteria/ml) should be sufficiently
sensitive to satisfy the requirements of the majority of the dairies in the UK.
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