Experimental Staphylococcus aureus Mastitis Infection Model by Teat Dipping in Bacterial Culture Suspension in Dairy Cows

SIMPLE SUMMARY: Udder infection by bacteria such as Staphylococcus aureus cause economic losses to dairy production. An effective vaccine is required to control S. aureus mastitis. To develop an effective vaccine, a good experimental infection model is required. Infusion of bacteria into the udder can overwhelm the host because it bypasses physical barriers and defense mechanisms in the teat canal. The objective of this study was to develop Staphylococcus aureus mastitis challenge model that mimics natural infection. Eight Holstein dairy cows within 1st to 3rd parity at early non-milking period were randomly divided into experimental (n = 5) and control (n = 3) groups. All teats of experimental cows were challenged by dipping into S. aureus culture suspension, whereas those of control cows were dipped into phosphate-buffered saline. Bacteria in the mammary secretion was determined by bacteriological culture. The antibody titer in blood was tested by enzyme-linked immunosorbent assay (ELISA). Other analyses, which include somatic cell count, rectal body temperature, inflammatory changes in mammary secretion, and gland tissues, were assessed. Results showed that three and one of five experimental cows developed subclinical and clinical mastitis, respectively. The remaining cow was infected with Staphylococcus chromogenes. In conclusion, experimental S. aureus mastitis can be induced by teat dipping in the bacterial culture. ABSTRACT: Mastitis is inflammation of mammary glands usually caused by bacteria such as Staphylococcus aureus. Dairy cows are susceptible to mastitis during early dry and transition periods. Effective vaccine is needed during these periods. One of the limitations to develop an effective vaccine against S. aureus is the absence of good infection model. Intramammary infusion (IMIF) with S. aureus has been used as an infection model to test vaccine efficacy. IMIF is reliable in causing mastitis, but it bypasses physical barriers, non-specific natural defenses, and immunity in the teat canal. IMIF also transfers a large number of bacteria into the intramammary area at once. The objective of this study was to develop S. aureus IMIF model that mimics natural infection. Eight Holstein dairy cows were randomly divided into two groups of experimental (n = 5) and control (n = 3) cows. All teats of experimental cows were dipped in S. aureus culture suspension, whereas that of control cows were dipped in phosphate-buffered saline. Results showed that four of five cows were infected with challenge strain by day 3 of the challenge. The remaining cow was infected with Staphylococcus chromogenes. In conclusion, an experimental S. aureus intramammary infection can be induced by teat dipping into bacterial suspension.