A total of 50 Staphylococcus intermedius strains isolated in France from canine pyodermas in 2002 were investigated for their susceptibility to various antimicrobial drugs. Antimicrobial susceptibility was assessed using a 2-fold serial dilution method in Mueller-Hinton agar, and the minimal inhibitory concentrations (MICs) were determined. About 62% of the 50 strains tested were producers of beta-lactamase and categorized as penicillin-resistant. About 26% demonstrated resistance to sulphonamides, 46% to oxytetracycline, 30% to chloramphenicol, 28% to streptomycin, kanamycin, neomycin or erythromycin, 22% to clindamycin, 6% to doxycycline, 2% to gentamicin, enrofloxacin, marbofloxacin or pradofloxacin. Acquired resistance was not observed to a clavulanic acid-amoxicillin combination, oxacillin, cephalosporins (cephalexin, ceftiofur and cefquinome), trimethoprim, a sulphamethoxazole-trimethoprim combination and florfenicol. About 42% were simultaneously resistant to three or more antimicrobial classes (multiresistance). All isolates with acquired resistance to erythromycin were also resistant to streptomycin and neomycin/kanamycin. About 22% of isolates exhibited cross-resistance between erythromycin and clindamycin and all clindamycin-resistant isolates also exhibited resistance to erythromycin. Resistance to penicillin, oxytetracycline and chloramphenicol was also positively associated with resistance to erythromycin and streptomycin.

Aims:  The aims of this study were: (i) to determine the proportions of Aeromonas spp. resistant to florfenicol (FC), oxolinic acid (OA) and oxytetracycline (OTC) along a river receiving effluents from fish farms, and (ii) to assess the relevance of using this bacterial group as an indicator for studying the consequences of the use and release of these aquacultural antimicrobials in the freshwater environment, as compared with performing antimicrobial measurements in sediments. Methods and results:  Sediment interstitial waters sampled along a river during two distinct climatic seasons were plated on an Aeromonas‐selective medium supplemented or not with OA, OTC or FC. The October 2004 campaign showed an enrichment of OA‐ and OTC‐resistant Aeromonas immediately downstream of the fish farms and a wastewater treatment plant. Two fish farms showed similar results in March 2005. In contrast, only 10 FC‐resistant Aeromonas strains could be isolated, which revealed that minimum inhibitory concentrations of FC were greater than 64 μg ml−1 and multiple antimicrobial resistances. Contamination of sediments by antimicrobials was detected but was not always co‐localized with resistance peaks or known point sources of contamination. Conclusions:  Aeromonas could be valuable indicators of OA, OTC and FC resistance in the freshwater environment. Fish farms contribute to the contamination of the river by antimicrobials and resistant bacteria. Significance and Impact of the Study:  Considering the still very low proportion of FC‐resistant Aeromonas, this study can be considered as a reference for further studies about this recently introduced veterinary antimicrobial agent.

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