Efficacy of Bacteriophages Against Staphylococcus aureus Isolates from Bovine Mastitis

Abstract

The lytic efficacy of bacteriophages against Staphylococcus aureus isolates from bovine milk was investigated in vitro, regarding possible applications in the therapy of udder inflammation caused by bacterial infections (mastitis). The host range of sequenced, lytic bacteriophages was determined against a collection of 92 Staphylococcus (S.) aureus isolates. The isolates originated from quarter foremilk samples of clinical and subclinical mastitis cases. A spot test and a subsequent plaque assay were used to determine the phage host range. According to their host range, propagation and storage properties, three phages, STA1.ST29, EB1.ST11, and EB1.ST27, were selected for preparing a bacteriophage mixture (1:1:1), which was examined for its lytic activity against S. aureus in pasteurized and raw milk. It was found that almost two thirds of the isolates could be lysed by at least one of the tested phages. The bacteriophage mixture was able to reduce the S. aureus germ density in pasteurized milk and its reduction ability was maintained in raw milk, with only a moderate decrease compared to the results in pasteurized milk. The significant reduction ability of the phage mixture in raw milk promotes further in vivo investigation.

Antimicrobial Activity of a Phage Mixture and a Lactic Acid Bacterium against Staphylococcus aureus from Bovine Mastitis

“…The present in vitro examinations were conducted with regard to a combined use in mastitis therapy. The S. aureus isolates used for inoculation were already investigated in a previous study and the PM also used in the present study was able to significantly reduce the S. aureus isolates in pasteurized and raw milk [52].…”

“…In the present study, we used a mixture of obligately lytic, sequenced phages to fulfil functional and safety requirements. The phages of the mixture were already investigated in a previous study, resulting in a broad host spectrum against S. aureus isolates from mastitis cases [52].…”

“…plantarum 118/37) at a concentration of 6.6 × 10 6 cfu/mL or c) a combination of PM and LAB was added, resulting in a total amount of 7 mL for each approach. Previous examinations [52] have shown the best reduction ability for the concentrations of S. aureus isolates (7142; 10614) and PM, which were also used in the present trials. For the application of S. aureus and LAB, a ratio of 1:10 was used according to the findings of previous studies [53,54].…”

“…Phage EB1 is an isolate from pig manure and is closely related to the phage PSa3, which was isolated and characterized by Kraushaar et al in 2013 [50]. The genetically distinct phages were grown on different host strains (ST29; ST11 or ST27), which might have led to epigenetic modifications [51] that resulted in a different host range in previous examinations [52].…”

“…It contained phages STA1.ST29, EB1.ST11 and EB1.ST27 in equal quantities and a final concentration of 7.4 × 10 9 pfu/mL. The phages were selected according to previously examined criteria including a broad host range against S. aureus isolates from mastitis cases, good propagation properties and adequate storage stabilities [52]. All phages of the mixture showed lytic activity against the S. aureus isolates 7142 and 10614 in the plaque assay and the phage mixture (PM) showed antimicrobial activity against the S. aureus isolates in pasteurized and raw milk in previous examinations [52].…”