Susceptibility profiles of Streptococci isolated from bovine milk samples in Italy

Bovine mastitis is the most economically important disease in dairy herds. Intramammary infections are caused by bacterial pathogens. Streptococci are frequently isolated from bovine mastitis in dairy farms, and they are generally very susceptible to \u3b2-lactam antibiotics. For that reason, susceptibility tests are usually not requested by veterinarians. We report susceptibility profiles observed in Streptococci isolated from milk samples from 12 different dairy herds in Lombardy region, Italy. We tested overall 25 strains: 7 of S. agalactiae, 1 of S. dysgalactiae, 6 of S. uberis, 3 of Streptococcus ssp. and 8 of Enterococcus faecalis. The antimicrobial susceptibility was determined using the disk diffusion test. We found resistance to penicillin in 52% of isolates, to ampicillin in 60%, to amoxicillin-clavulanic acid in 8%, to 1st generation cefalosporines in 36%, to 2nd generation cefalosporines in 12,5%, to 3rd generation cefalosporines in 40%, to 4th generation cefalosporines in 48%, to oxacillin in 80%, to nafcillin-penicillin-streptomicin in 16%, to tylosin in 41,6%, to erythromycin in 50%, to rifaximin in 36%, to norfloxacin in 65,2%, to tiamfenicol in 18,1%, and to kanamicin in 100%. Particularly, susceptibility profiles of S. agalactiae were surprising: 71,4% of the isolates showed resistance to penicillin, 85,7% to ampicillin, 14,2% to amoxicillin-clavulanic acid, 71,4% to 1st generation cefalosporines, 25% to 2nd generation cefalosporines, 42,8% to 3rd generation cefalosporines, 71,4% to 4th generation cefalosporines, 100% to oxacillin, 71,4% to nafcillin-penicillin-streptomicin, 57,1% to tylosin, 57,1% to erythromycin, 57,1% to rifaximin, 100% to norfloxacin, 40% to tiamfenicol and 100% to kanamicin. These results are quite different from those reported in different studies in our country. We believe this is the first report of extended resistance to \u3b2-lactam drugs of S. agalactiae isolated from milk samples in Italy. Therefore, frequent monitoring of Streptococci antibiotic susceptibility becomes a central point in the diagnosis of mastitis, in order to verify the spread of resistant strains among herds