Deoxyribonucleic Acid Fingerprinting of Staphylococcus aureus from Heifer Mammary Secretions and from Horn Flies

Staphylococcus aureus isolated from heifer mammary secretions, streak canals, and horn flies (Haematobia irritans) were evaluated by randomly amplified polymorphic DNA fingerprinting. The relationship between DNA fingerprint patterns of S. aureus isolated from horn flies and S. aureus isolated from heifer mammary glands was examined. Amplified DNA fragments were visualized by agarose gel electrophoresis and were analyzed by densitometry. Analysis of DNA fingerprint patterns of 56 S. aureus isolates that were obtained from heifer mammary secretions or streak canals resulted in three distinct subtypes of S. aureus. Of these, 31 isolates (55%) belonged to subtype 1, 22 isolates (39%) belonged to subtype 2, and 3 (5%) belonged to subtype 3. Eight of 10 S. aureus isolates from horn flies belonged to subtype 1, and 2 isolates belonged to subtype 2. Thus, all of the S. aureus isolates from horn flies had DNA fingerprint patterns identical to the majority (95%) of S. aureus isolates from heifer mammary secretions or streak canals. In addition, 10 S. aureus isolates from multiparous cows from the same herd were examined by randomly amplified polymorphic DNA. All S. aureus isolates from multiparous cows belonged to subtype 3. Results of this study suggest that horn flies may play an important role in the transmission of S. aureus to nulligravid and primigravid heifers. Furthermore, this study demonstrates the usefulness of randomly amplified polymorphic DNA fingerprinting to distinguish between different subtypes of S. aureus and to draw epidemiological inferences from the information it provides.