Susceptibility Monitoring
Bayer carefully watches the development of resistance.
Our specialists not only test the susceptibility of various pathogens as part of a continuing resistance monitoring programme, but also review publications on resistance to antibiotics worldwide.
Because published data on bacterial resistance are mostly obtained from diagnostic laboratories (sick animals and necropsy material), the findings will not always be congruent with the level of resistance of bacteria in the field. Surveys on resistance must therefore also cover bacterial isolates obtained from untreated animals in the field or from samples taken from animals at slaughter to give a reliable view on the actual resistance situation. A short overview of the resistance situation for the most important pathogens in ruminants can be seen below.
Pasteurella multocida
In the years 1997 and 1998 the sensitivity of 527 strains of P.multocida was assessed in France (data on file) by the disk diffusion method. The susceptibility to Baytril was 100%.
The same results were obtained in Japan (Yoshimura et al.,2001), where 68 isolates from pigs were tested. The MIC50/MIC90 values were < = 0.025/0.05 µg/ml.
14 isolates of P.multocida from necropsy material and nasal as well as cervical swabs, obtained from different laboratrories in Germany, also were 100% susceptible to Baytril. The MIC50/MIC90 values were 0.008/0.03 µg/ml.
Actinobacillus pleuropneumoniae
In 1997 the susceptibility of 40 strains of APP was evaluated in Denmark (Aarestrup F.M., Jensen N.E., 1999). All strains had MIC values for Enrofloxacin of < = 0.03 µg/ml. Similar results were shown in isolates from Germany, where MIC50/MIC90 values were < = 0.03/0.125 µg/ml.(data on file).
Salmonella spp.
The in-vitro activity of Enrofloxacin was tested in various pathogens of animal origin in the US (Watts et al., 1997). Among the tested bacteria, Salmonella spp. (n=82) were highly susceptible to Enrofloxacin and showed MIC50/90 values of 0.03/0.06 µg/ml.
A study from Spain (Diaz et al., 2001) found all Salmonella isolates from pigs in region of Catalonia susceptible to Enrofloxacin.
Bayer's internal monitoring on 14 isolates of Salmonella of porcine origin from 1998 showed 100% susceptibility to Baytril and MIC50/MIC90 values were < = 0.03/0.06 µg/ml (data on file).
E.coli
E.coli isolates of porcine origin from 1997 and 1998 from France were tested for susceptibility by the disk diffusion test. These tests included E.coli from urinary tract (n=524) and post-weaning infections (n=458). Among the isolates from urinary tract infections 95.6% were sensitive, 3.1% classified as intermediate and 1.3% were found to be resistant. From the strains isolated from post-weaning infections 96.5% were sensitive, 1.75% intermediate and 1.75% resistant (data on file).
In a study for food safety from Austria (Province of Styria-Resistance Monitoring Programme 2001), 44 strains of E.coli isolated from pork in different slaughterhouses were isolated and found 100% susceptible. The MIC MIC50/MIC90 values were < = 0.03/0.03 µg/ml.
The in-vitro activity of Enrofloxacin was tested in various pathogens of animal origin in the US (Watts et al., 1997). Among the tested bacteria, E.coli (n=45) were highly susceptible to Enrofloxacin and showed MIC50/90 values of 0.015/0.03 µg/ml.
Mycoplasma spp.
Hannan et al. (1997) tested the susceptibility of 58 field isolates (20 M.hyopneumoniae, 20 M.hyorhinis and 18 M.hyosynoviae) from the UK, Germany, USA and Japan. MIC90 values were 0.05 µg/ml for M.hyopneumoniae, 0.25 µg/ml for M.hyosynoviae and 1 µg/ml for M.hyorhinis.
The continuing monitoring shows that after more than 10 years of use in veterinary medicine Baytril still shows very good efficacy against relevant bacteria that cause enteritis, mastitis and respiratory tract infections.
Responsible use will help to maintain Baytril's high efficacy in the future. | 
