Stress sensitivity assays of bacteriophages associated with Staphylococcus aureus, causal organism of bovine mastitis

Abstract

Bacteriophages can provide an alternative measure for the control of Staphylococcus aureus, the major causal agent for bovine mastitis. This study looked at the sensitivity of six phages towards simulated environmental and formulation stresses. Phages Sabp-P1, Sabp-P2 and Sabp-P3 showed the most stable replication rates at increasing temperatures (45 to 70ºC), in comparison to phages Sabp-P4, Sabp-P5 and Sabp-P6. The effect of temperature on storage of phages showed that 4ºC was the minimum temperature at which phages could be stored without a significant reduction in their lytic and replication abilities. Furthermore, all phages showed varying levels of sensitivity to chloroform exposure, with Sabp-P5 exhibiting the highest level of reduction in activity (74.23%) in comparison to the other phages. All six phages showed optimal lytic ability at pH 6 to 7 and reduced activity at any pH above or below pH 6 to 7. Exposure of phages to varying glycerol concentrations (5 to 100%) produced variable results. All six phages were most stable at a glycerol concentration between 10 to 15%. Three of the six isolated phages, Sabp-P1, Sabp-P2 and Sabp-P3, performed optimally during the in vitro assays and have considerable potential for in vivo applications to treat mastitis-infected dairy cattle.