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In Vitro Antimicrobial Susceptibility of Escherichia coli Isolates from Clinical Bovine Mastitis in Finland and Israel

T. Lehtolainen^*, A. Shwimmer, N. Y. Shpigel, T. Honkanen-Buzalski and S. Pyörälä^*

^* University of Helsinki, Faculty of Veterinary Medicine, FIN-04920 Saarentaus, Finland
Hebrew University of Jerusalem, Koret School of Veterinary Medicine, Rehovot 76100, Israel
National Veterinary and Food Research Institute, FIN-00580 Helsinki, Finland

Corresponding author: T. Lehtolainen; e-mail: tanja.lehtolainen{at}helsinki.fi.

Minimal inhibition concentration (MIC) values of 100 Finnish and 100 Israeli Escherichia coli isolated from clinical bovine mastitis were determined for ampicillin, cephalexin, ceftazidime, dihydrostreptomycin, gentamicin, tetracycline, trimethoprim-sulfadiazine, and ciprofloxacin by an agar dilution method. The in vitro antimicrobial susceptibility of the E. coli isolates was high; only 27% showed resistance to one or more tested antimicrobial agents. Fifteen percent of the Israeli isolates and 14% of the Finnish isolates were resistant to tetracycline, 3 and 16% to cephalexin, 10 and 7% to ampicillin, 13 and 9% to dihydrostreptomycin, and 4 and 2% to trimethoprim-sulfadiazine. No gentamicin–, ceftazidime-, or ciprofloxacin-resistant isolates were detected. Eleven percent of all the isolates were resistant to two or more antimicrobial agents. Tetracycline was most often associated with multiresistant patterns. Most of the multiresistant isolates had very high MIC values, whereas most of those that were resistant to only one tested antibiotic had MIC values close to the susceptibility breakpoint. Antimicrobial resistance appeared to pose no problem in E. coli isolated from mastitic milk of both countries. This is probably due to the controlled use of antimicrobial agents in the treatment of dairy herds. Some differences were present in the resistance patterns, which may reflect the different use of antimicrobial agents in these two countries.

Key Words: antimicrobials • Escherichia coli • mastitis • susceptibility

Abbreviation key: DHS = dihydrostreptomycin, MIC = minimal inhibition concentration, MIC₅₀ = minimal inhibition concentration for 50% of isolates tested, MIC₉₀ = minimal inhibition concentration for 90% of isolates tested, TS = trimethoprim-sulfadiazine

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