DairyGuard is an innovative new molecular diagnostic system that can be used to identify bacterial DNA in a milk sample. It was developed by Safeguard Biosystems, and Valley Veterinarians (VVI) has been experimenting and using it since early 2024.
The DNA is exposed and isolated from the rest of the milk through a cell-lysis and wash protocol. Then the DNA is amplified using PCR (polymerase chain reaction), which greatly amplifies the amount of DNA present, and each new strand of DNA has flourophors added as the DNA strand is created. The flourophors allow for a measurement of the quantity of each specific strand of DNA, as it is bound to a proprietary assay plate. The process is very technical, very sensitive, and very specific…only DNA from that organism will bind to the binding site specific to that organism.
Results from the DairyGuard platform will be presented in a format with 7 different levels for each organism.
- Negative – No DNA present
- Scant – An extremely slight signal that may or may not be significant
- + – A very low amount of DNA present
- ++
- +++ – A moderate amount of DNA present
- ++++
- +++++ – A very large amount of DNA present
Here is a sample of a DairyGuard report with some significant positives.
Because of the amplification process, the presence of even a very small amount of bacterial DNA will produce a signal. Often with a contaminated sample, diagnosis through traditional plating methods is complicated or impossible. DairyGuard has the capability of reading through contamination, because all the DNA present is amplified. Then, due to the sensitivity and specificity of DNA binding, a signal will be produced for every organism present in that sample, allowing for identification of significant contagious pathogens such as S aureus and S agalactiae.
DairyGuard, when utilized for pooled milk samples (tanks, pens, strings or side-outs) compares very favorably with traditional plating methods on both a cost basis and with speed of diagnosis. With the additional accuracy and sensitivity, we at VVI have decided to make it the default method of processing pooled milk samples. The bulk of individual cow samples will be plated as we have always done due to the cost and logistics involved.
An additional benefit to the DairyGuard platform is that there are many more organisms in the array than can easily be identified through traditional plating methods. A summary of those organisms follows:
- Staphylococcus aureus
- Mycoplasma bovis
- Mycoplasma bovigenitalium
- Mycoplasma californicum
- Mycoplasma spp.
- Prototheca spp.
- Streptococcus agalactiae
Gram positive environmental organisms:
- Staphylococcus capitis, Staphylococcus hominis, Staphylococcus similans
- Staphylococcus hyicus, Staphylococcus chromogenes
- Micrococcus caseolyticus
- Staphylococcus xylosus, Staphylococcus equorum
- Staphylococcus haemolyticus
- Staphylococcus saprophyticus
- Staphylococcus sciuri
- Staphylococcus species
- Streptococcus dysgalactiae
- Streptococcus uberis
- Streptococcus species
- Bacillus cereus group
- Bacillus subtilis group
- Corynebacterium bovis
- Trueperella pyogenes
- Enterococcus species
- Aerococcus viridans
- Lactococcus lactis
Gram negative environmental organism:
- Escherichia coli
- Enterobacter/Klebsiella
- Pseudomonas aeruginosa
- Proteus spp.
- Citrobacter
- Serratia marcescens
- Salmonella
Organisms typically associated with dirty milking equipment:
- Acinetobacter spp.
- Enterobacteriaciae
- Pseudomonas spp.
- Stenotrophomonas maltophilia
Public Health/Food Quality bacteria:
- Acholeplasma spp.
- Clostridium spp.
- Listeria spp.
- Campylobacter jejuni
Results obtained through DairyGuard and are meant to stimulate and prompt an informed conversation with your herd veterinarian, and serve as a monitoring and surveillance tool for the health of your herd. Please do not make any management or herd decisions without discussing your concerns and your plan with your herd veterinarian, as that may lead to unnecessary culling decisions, unnecessary expense, or adverse herd health events.