Growth responses of environmental mastitis pathogens to long-chain fatty acids

Streptococcus uberis, Streptococcus faecalis, Escherichia coli, and Klebsiella pneumoniae were tested for susceptibility to long-chain fatty acids predominant in teat canal keratin. Antibacterial activity of free fatty acids on each bacterial species was measured after 12 h in synthetic media. Growth responses of all three strains of Streptococcus uberis were completely inhibited by C18:3 and those of two of three strains by C18:2 at 1 micrograms/ml. None of the fatty acids tested were bactericidal to Streptococcus faecalis. Saturated fatty acids C14 and C16 were more bacteriostatic to Streptococcus faecalis than were polyene fatty acids. Growth responses of coliform species were not affected by long-chain fatty acids. In general, environmental mastitis pathogens were resistant to fatty acids predominant in teat canal keratin.