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. Key words: Bacteriophage, biological control, bovine mastitis, sensitivity assays, Staphylococcus aureus.
Highlights
Staphylococcus aureus-induced bovine mastitis in dairy herds is one of the most widespread and destructive diseases of dairy cows
Bacteriophages can provide an alternative measure for the control of Staphylococcus aureus, the major causal agent for bovine mastitis
Strain identification to distinguish S. aureus from other staphylococcal strains was confirmed by hemolysis on blood agar, catalase reaction, Gram reaction and arrangement of bacterial cells upon Gram staining
Summary
Staphylococcus aureus-induced bovine mastitis in dairy herds is one of the most widespread and destructive diseases of dairy cows. It has far reaching consequences that affect milk quality and yield, health of the dairy cow, and the economics associated with the processing of milk and milk products. The natural defence mechanisms of the cow itself, in conjunction with cultural control measures, may prove adequate in curbing disease onset and severity. The real problem arises when these intrinsic defences and cultural measures are compromised by infection. Antibiotic therapy has traditionally served as the option to achieve effective control of the disease. Overall benefits of antibiotic therapy include a more rapid elimination of bacterial pathogens than self-cure, a reduced probability of chronic recurrent infections, a reduced depression in milk yield and a more rapid return to an acceptable somatic cell count and to saleable milk (Barkema et al, 2006; Nickerson, 2009)
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