Baytril® Resistance Monitoring 2010-2015: Antimicrobial Susceptibility of Porcine Pathogens in Germany

Antimicrobial resistance is a concern in the antimicrobial therapy of both humans and animals. Knowledge on the actual susceptibility and its development over the years is important for ensuring long-term antimicrobial efficacy. Therefore, in the early nineties of the past century Bayer has established a susceptibility monitoring program for target animal pathogens obtained from food producing animals in Germany. Here, the susceptibility status for enrofloxacin, the active ingredient of Baytril®, is presented with regard to respiratory pathogens recovered from pigs.

Bacteria were isolated by three diagnostic laboratories from samples of diseased pigs during 2010-2015 across Germany. Per farm and outbreak only one isolate was included. The Minimum Inhibitory Concentrations (MICs) of enrofloxacin were determined by agar dilution methodology according to the Clinical and Laboratory Standards Institute (CLSI) in a central lab. Enrofloxacin resistance was calculated using the CLSI breakpoints of ≥ 1 µg/mL for Pasteurella multocida (PM) and Actinobacillus pleuropneumoniae (APP), and ≥ 2 µg/mL for Streptococcus suis (SS). For pathogens for which CLSI breakpoints have not been set (Bordetella bronchiseptica, BB and Haemophilus parasuis, HP), a tentative breakpoint of ≥ 2 µg/mL was applied.

In total, 606 isolates were tested. The most common species isolated from respiratory tract samples were PM (n=181), BB (n=120), SS (n=89), APP (n=79) and HP (n=41). In addition, other species (n=96) were found in lower numbers, e.g., Trueperella pyogenes, Staphylococcus spp., Klebsiella spp., Pseudomonas aeruginosa, Streptococcus spp. and Escherichia coli. Due to the low numbers per species, these isolates were not further analyzed. MIC50/90 values were 0.008/0.03 for PM, 0.5/1 for BB and SS, 0.06/0.125 for APP and 0.015/0.03 for HP. For PM, APP and HP no resistant isolates were found. For BB and SS the mean resistance rates were 1.7 % and 2.2%, respectively.

This survey demonstrates a high susceptibility of major respiratory pathogens obtained from German pigs to enrofloxacin after more than two decades of therapeutic use of fluoroquinolones in veterinary medicine. Results are consistent with findings of other national and European monitoring surveys, e.g. GERM-Vet (Germany) and VetPath (Europe). In spite of this high susceptibility, prudent and responsible use of fluoroquinolones as well as resistance monitoring are imperative.

Disclosure of Interest: C. Ludwig Conflict with: Employee of Bayer Animal Health GmbH, S. Fälker Conflict with: Employee of Bayer Animal Health GmbH, C. Bhushan Conflict with: Employee of Bayer Animal Health GmbH, A. de Jong Conflict with: Employee of Bayer Animal Health GmbH, S. Tennagels Conflict with: Employee of Bayer Animal Health GmbH, B. Stephan Conflict with: Employee of Bayer Animal Health GmbH.