Effects of bovine lactoferrin on the growth and biofilm formation of Escherichia coli and Klebsiella pneumoniae associated with bovine mastitis

Escherichia coli and Klebsiella pneumoniae are major causal pathogens of mastitis in dairy cows. In this study, we focus on bovine lactoferrin, an endogenous protein with antimicrobial and antibiofilm activities expressed in mammary glands. Given that the activity of lactoferrin against bovine mastitis-associated pathogens has yet to be fully elucidated, we sought to determine its effects on the growth and biofilm formation of E. coli and K. pneumoniae. We selected 24 and 20 isolates of E. coli and K. pneumoniae, respectively, including mastitis- and environmentally derived isolates, and examined the antimicrobial and antibiofilm effects of lactoferrin using a microdilution method and crystal violet staining, respectively. The percentages of E. coli and K. pneumoniae isolates for which we obtained lactoferrin minimum inhibitory concentration ≥ 4,000 µg/mL were 57% and 80%, respectively. At concentrations of 200 and 1,000 µg/mL, although lactoferrin caused significant reductions in the growth of both E. coli and K. pneumoniae, whereas biofilm formation by K. pneumoniae was inhibited, that of E. coli was paradoxically enhanced. These findings highlight that E. coli and K. pneumoniae, which have traditionally been grouped as coliforms in the context of bovine mastitis, have distinct responses when exposed to lactoferrin.