Use of phages against antibiotic-resistant Staphylococcus aureus isolated from bovine mastitis.

Bovine mastitis is the primary disease of dairy cattle worldwide and it causes large economic losses. Among several microorganisms that are the causative agents of this disease, Staphylococcus aureus is the most prevalent. Although antibiotic therapy is still the most widely used procedure for the treatment of bovine mastitis, alternative means of treatment are necessary due to the presence of antibiotic residues in milk, which is a growing concern because of its interference with the production of milk derivatives and the selection of resistant bacterial strains. The use of bacteriophages as a tool for the control of pathogens is an alternative treatment to antibiotic therapy. In this work, to obtain phages with the potential for use in phage therapy as a treatment for mastitis, we isolated and identified the bacteria from the milk of mastitis-positive cows. A total of 19% of the animals from small and medium farms of the Zona da Mata Mineira, Brazil, was positive for bovine mastitis, and bacteria of the genus Staphylococcus were the most prevalent pathogens. The majority of the S. aureus isolates tested was resistant to penicillin and ampicillin. In parallel, we isolated 10 bacteriophages able to infect some of these S. aureus isolates. We determined that these phages contained DNA genomes of approximately 175 kb in length, and the protein profiles indicated the presence of 4 major proteins. Electron microscopy revealed that the phages are caudate and belong to the Myoviridae family. The isolates exhibited interesting features for their use in phage therapy such as a high lytic potential, a wide range of hosts, and thermostability, all of which favor their use in the field.

Molecular characterization of a new lytic bacteriophage isolated from cheese whey.

In this study, we isolated and characterized a lytic Lactococcus lactis bacteriophage from the sera of a failed fermentation. The phage was isolated and cultured in L. lactis subsp. cremoris in M17 medium. The isolated bacteriophage was characterized by multiplex PCR, pulsed-field electrophoresis, DNA restriction digestion, analysis of the N-terminal sequence of the phage major structural protein, transmission electron microscopy and sequencing and analysis of a conserved fragment of its genome. Analysis of the viral genome indicates that its genome is composed of a DNA strand of approximately 48 kb in length, and PCR and microscopy confirmed that IL-P1 belongs to the group of 936-type phages in the family Siphoviridae, which is the most abundant type of lactococcal virus in dairy products worldwide. To our knowledge, this is the first report of a virus within this family that has a presumptive genome larger than 40 kb.