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In the present study, a Lactococcus lactis strain was tested for its ability of growth inhibition of Staphylococcus aureus in-vitro, using a cocultivation method. Furthermore, the strain was used in a field trial as probiotic teat dip for dairy cows.
For the cocultivataion, a Lactococcus lactis strain and a Staphylococcus aureus strain were incubated in microtitre plates in different concentrations and their growth was observed by turbidity measurement. To evaluate the potential impact on bacterial growth, DNA was extracted from all incubates and the strains were quantified with qPCR. A minor inhibition of growth of S. aureus was detected when cocultivation was performed with the highest used concentration of L. lactis and the lowest used concentration of S. aureus. No other concentration led to the implication of a mutual impact of the strains.
During the field trial over the period of four months, a control group of 35 dairy cows was dipped with a teat dip based on iodine and an experimental group of 37 animals was treated with a teat dip based on Lactococcus lactis. Data of clinical parameters were collected to evaluate the impact of the application of the teat dips on the teat skin as well as the udder health.
Furthermore, the colonization of the teat canal by the applied Lactococcus lactis strain was evaluated, using microbiological and molecular biological methods after taking swab samples.
The evaluation of clinical parameters and selected characteristic values for udder health revealed few differences between the control and the experimental group. Accordingly, the application of the teat dip containing Lactococcus lactis can be classified as comparable to the teat dip used in the control group, containing iodine. The commercially available PathoProof™ Mastitis PCR Assay was quantified with extracts of culture strains, which lead to some false-positive results. Therefore, the samples of the
experimental animals could not be tested for all mastitis causing pathogens detectable with the test kit and a possible variation of the microflora of the teat canal could not be evaluated.
The establishment of the used Lactococcus lactis strain in the teat canal of dairy cows could be shown by microbiological as well as molecular biological methods.
With regard to the present results, the use of a probiotic teat dip seems to be comparable to conventional teat dips. However, further studies are needed to evaluate the effects of the probiotic teat dip under different conditions, including animal housing, hygiene and genetics.