In the Republic of Ireland, the Department of Agriculture, Food and the Marine (DAFM) operates a group of six veterinary diagnostic laboratories: one large central laboratory on the outskirts of Dublin city and five smaller regional laboratories near Athlone, Cork, Kilkenny, Limerick and Sligo.
Each regional laboratory, (Figure 1), typically has a complement of three veterinary research officers, four laboratory analysts, two clerical officers and two laboratory attendants. The laboratories support DAFM’s role in the surveillance, control and eradication of exotic, emerging and endemic animal diseases. They also have a role in public health and in the facilitation of trade. The provision of a veterinary diagnostic service strengthens the connections of DAFM with veterinary practicioners and farms in the catchment area of each laboratory (Figure 2), and thus facilitates the surveillance role.
Microbiological culture of milk samples and antimicrobial sensitivity testing are amongst the tests offered as part of the diagnostic service, and these are carried out in all of the six laboratories.
The culture method used in all six laboratories follows the same standard operating procedure. Four agar plates (Blood, MacConkey, Edwards and Baird Parker or Manitol Salt agar) are inoculated with a sample of the milk under test (Figure 3), and then incubated aerobically at 37oC for 24 hours. Suspect colonies are sub-cultured to produce pure cultures and incubated for another 24 hours. After this, appropriate identification procedures are followed which include the use of gram stains, catalase, oxidase, API and CAMP tests.
Antimicrobial sensitivity testing is carried out if appropriate using the Kirby-Bauer disk diffusion method (Figure 4) and the results of all tests are recorded electronically using a laboratory information management system (LIMS). At the same time a qualitative inhibitory substance test is carried out to detect whether or not the milk sample contains an antimicrobial substance.
In 2013 over 3,000 samples were received and tested. Typically, milk samples are submitted from clinical mastitis cases, sub-clinical mastitis cases flagged by high individual somatic cell counts at milk recording, and pre-drying-off cows (composite samples). Farmers may submit samples themselves or through the milk processor or veterinary practitioner. In all cases the report is issued to a nominated veterinary practice and the farmer can access the report there.
The biggest problem the laboratories have year-on-year is with contamination at time of sampling. Some 11.8 % of samples received in 2013 were considered to be contaminated. This percentage is reducing year-on-year through the building of awareness on proper sampling technique. Contamination is more common in the single sample submissions which typically involve clinical mastitis cases. More often than not the submission of multiple samples forms part of a mastitis investigation being carried out on a farm by a veterinary practitioner or milk quality advisor. In most of these cases the quality of the sample received is excellent.
Text & illustrations: Alan Johnson – Alan.Johnson@agriculture.gov.ie
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