CONTROL OF STAPHYLOCOCCUS AUREUS BY BACTERIOPHAGES – A PROGRESS REPORT ON THE RESEARCH PROJECT.

Principal researcher: Dr Iona Basdew, UKZN

Introduction: The primary aim of the in vivo trial was to identify if a cocktail of lytic bacteriophages that are specific to mastitis caused by Staphylococcus aureus are effective in reducing and controlling mastitis. Studies have shown that commonly used control measures (antibiotics, cultural measures, culling, vaccines) are now becoming ineffective, the primary reason being increasing antibiotic resistance. As a result, new sustainable measures for the control of the disease should be investigated, one being bacteriophages. The treatment here aimed to reduce and gradually eradicate S. aureus numbers so that the disease does not progress to clinical mastitis.

Methodology: The trail was carried out at Southdown Dairy Farm, outside Mooi River. Twelve cows were assigned to the trial and they were split into two groups, the control group and a treated group. Before assignment, the cows were tested for S. aureus induced-mastitis using SCC and bacterial culturing. All cows tested positive. The six cows in the control group was treated with 40% glycerol, and the six cows in the treatment group with a cocktail of three potent bacteriophages (Sabp1, SaBp2 and SaBp3) (phages) in 40% glycerol suspension. Approximately 10ml of the phage suspension was sprayed onto each teat-end post-milking once per day for five consecutive days, whereas in the control group 10ml of 40% glycerine solution was similarly sprayed onto each teat-end post-milking. The procedure followed was: the cows were milked as normal; then, teat-ends were disinfected using cotton pads saturated with 70% iso-propanol. After cleaning of teat-ends, phage suspension was sprayed onto each teat, where after the cows were allowed back to their sheds. After treatment for five consecutive days and milk collection before treatment, raw milk samples were collected from each treated quarter using aseptic collection techniques. Collection was for days 1 to 5 and 8 to 12. The collected milk samples were screened for the presence of phage and cultured for S. aureus to determine bacteriological cure (CFU). The cell count (CFU/ml) and phage titre were performed as the major and direct measure of determining the effectiveness of the phages in controlling the S. aureus induced-mastitis. SCC was also determined.

Results: The application of the phage suspension on the cow teats reduced the S. aureus cell count from about 10.2 log CFU/ml to 8.8 log CFU/ml at day 16, whereas there was practically no reduction in the control cows. The results suggest that the phages were able to infect, multiply and inhibit the growth S. aureus. With respect to potency, the results showed that the phages were able to find their host (S. aureus) within one day and started to multiply immediately. In the control group there were also phages, which are indigenous (or natural). These natural phages were however unable to reduce the bacterial cells, therefore, they can be described as temperate phages and not lytic. The results therefore also suggest that it is important to isolate lytic phages which are able to kill the bacterial host.

To summarise, the results indicate that the isolated cocktail phages were able to kill S. aureus bacterial cells and they can now be evaluated on a larger scale to try and reduce mastitis in dairy herds.