A Comparison of Antimicrobial-susceptibility Patterns of Escherichia coli Isolated from Cattle, Geese and Soil

Introduction:  Recent global reports indicate that Escherichia coli are rapidly expressing resistant to drugs of last resort.  This is particularly worrisome as no new antimicrobials are forthcoming.  In order to develop appropriate mitigation strategies, it is important that we understand pathogen transmission and the dissemination of resistance genes throughout ecological systems.  Branta canadensis (Canada goose) have previously been recognized as a reservoir for antimicrobial resistant organisms.  Cattle operations are an excellent model system in which to study the relatedness and persistence of microorganisms in cattle, Canadian geese, and their shared soil environment. 

Purpose:  The purpose of this study was to longitudinally follow the antimicrobial susceptibility patterns of E. coli isolates throughout an environment shared by dairy cattle and a transient population of Branta canadensis (Canada goose).

Methods: Over a 12 month period, samples (~5 g feces) were collected from dairy cattle (n=275) and Canada geese (n=242). Soil samples (n=220; 10g) from defined pasture plot areas were also collected. Selective culture was used to isolate Escherichia coli, and antimicrobial susceptibility was determined using broth microdilution (Vitek, BioMerieux, Marcy l'Etoile).  Interpretations were based on CLSI guidelines.  

Results: Antimicrobial susceptibility was determined for Escherichia coli isolated from cattle (n=230), geese (n=201), and soil (n=123).  The majority (81.4%) of isolates exhibited no resistances to the panel of antimicrobials evaluated.  Seven (1.2%) isolates exhibited extended spectrum beta-lactamase (ESBL) activity.  The most common resistance pattern (4.7% of isolates) was to ampicillin, piperacillin, and tetracycline; this pattern was found in E. coli from cattle, geese and soil.  

Significance:  We demonstrated the presence of multidrug resistant E. coli, including ESBLs over time in a shared environment of cattle and migratory geese. The possibility of further transmission from migratory birds warrants further study.