Effect of lactoferrin on biofilm formation of bovine mastitis-causing <i>Staphylococcus</i> species

The most common bovine mastitis pathogen is the Staphylococcus species, consisting of Staphylococcus aureus and non-aureus staphylococci (NAS). Lactoferrin (Lf) is an iron-binding protein with antimicrobial and antibiofilm properties. Lf has a metal-free form (apo-Lf) and a natural form (native-Lf), and their differences were reported to affect their activity against bacteria. However, its effects on bovine mastitis-causing Staphylococcus spp. remain unclear. Fifteen S. aureus and 49 NAS strains were isolated from bovine mastitis cases, and their growth and biofilm-forming abilities were observed. Bacterial growth and biofilm formation were observed by culturing each strain with/without bovine milk apo-/native-lactoferrin (200 μg/mL). Without Lf treatment, the growth and biofilm formation abilities of S. aureus were significantly higher and lower, respectively, than those of NAS. The growth of S. aureus and NAS significantly decreased during apo-Lf treatment and significantly reduced the total amount of biofilm produced by S. aureus whereas native-LF treatment did not affect the growth and biofilm formation of Staphylococcus species. These results confirmed the ability of Lf to act as an antimicrobial and antibiofilm substance against mastitis-causing Staphylococcus spp., although various responses from each strain were observed. Additionally, the iron-binding state of Lf affected growth but did not affect the biofilm formation ability. Differences in the responses of Staphylococcus strains to Lf may help explain their pathogenicity, requiring further research.