Isolation, characterization and therapeutic potential assessment of bacteriophages virulent to Staphylococcus aureus associated with goat mastitis.

In the present study, the therapeutic potential of bacteriophages virulent to Staphylococcus aureus associated with goat mastitis were isolated, identified and assessed. Staphylococcus aureus (host or indicator bacterium) was isolated from a goat suffering from clinical mastitis. Based on cultural, morphological, biochemical tests and amplification of S. aureus specific thermonuclease gene in PCR, the identity of the organism was confirmed as S. aureus. Bacteriophages were isolated from soil and faecal samples (n=42) collected from different parts of the Mathura district in Uttar Pradesh (India), and their identity was confirmed by amplification of the bacteriophage-specific endolysin gene fragment in PCR. The thermal tolerance study revealed that all phage isolates were stable at 30 and 40°C with 100% lytic efficacy and their activities reduced to 62-80% at 50°C declining sharply at 60°C with less than 5% efficacy. Likewise, at pH = 6.5 and 7.5, the survivability of all isolates was 100% which reduced to 70-79% and 84-91% at pH = 5.5 and 8.5, respectively. All isolates were stable up to 3 months at 37°C, and for 16 months at 4°C but the stability of their respective endolysins only lasted for 12-23 days at 37°C and 6 months at 4°C. Three of the bacteriophage isolates, S. aureus phage/CIRG/1, S. aureus phage/CIRG/4 and S. aureus phage/CIRG/5 exhibited lytic activity against over 80% of the staphylococcal isolates. The results of the present study provide insight for the use of lytic bacteriophages for therapeutic interventions against multi-drug-resistant S. aureus inducing mastitis in goats.