Combined parenteral and intramammary treatment of
mastitis caused by Staphylococcus aureus was compared to parenteral treatment only. Cows with clinical
mastitis (166 mastitic quarters) caused by S. aureus treated by veterinarians of the Ambulatory Clinic of the Faculty of Veterinary Medicine during routine farm calls were included. Treatment was based on in vitro susceptibility testing of the bacterial isolate.
Procaine penicillin G (86 cases due to
beta-lactamase negative strains) or
amoxycillin-clavulanic acid (24 cases due to
beta-lactamase positive strains) was administered parenterally and intramammarily for 5 days. Efficacy of treatments was assessed 2 and 4 weeks later by physical examination, bacteriological culture, determination of CMT, somatic cell count and
NAGase activity in milk. Quarters with growth of S. aureus in at least one post-treatment sample were classified as non-cured. As controls we used 41 clinical
mastitis cases caused by
penicillin-susceptible S. aureus isolates treated with
procaine penicillin G parenterally for 5 days and 15 cases due to
penicillin-resistant isolates treated with
spiramycin parenterally for 5 days from the same practice area. Bacteriological cure rate after the combination treatment was 75.6% for quarters infected with
penicillin-susceptible S. aureus isolates, and 29.2% for quarters infected with
penicillin-resistant isolates. Cure rate for quarters treated only parenterally with
procaine penicillin G was 56.1% and that for quarters treated with
spiramycin 33.3%. The difference in cure rates between
mastitis due to
penicillin-susceptible and
penicillin-resistant S. aureus was highly significant. Combined treatment was superior over systemic treatment only in the
beta-lactamase negative group.