Pen-level agreement of antimicrobial resistance from pooled faecal samples at pen level and diarrhoeic pigs

Antimicrobial resistance testing of enterotoxic Escherichia coli (ETEC) is used as a diagnostic decision tool for selecting classes of antibiotics for treatment in pigs. Resistance testing is often done on isolates from faecal samples collected from diseased case pigs with the advantage of high certainty of analysing E. coli stains that has caused disease in the individual pig. The objective of this current study was to investigate pen-level agreement of antimicrobial resistance testing of E. coli isolates sampled from diarrhoeic pigs and from pooled faecal pen floor samples (PFP).

Faecal samples from diarrhoeic pigs two to four week post weaning and from PFP were collected from three commercial nursery facilities in the eastern part of Denmark. The samples were cultured on blood agar and E. coli isolates were analysed by PCR for adhesion factor, and toxin genes. Isolates possessing genes for both adhesion factors and toxins were classified as virulent and resistance testing by Sensititre for Tetracycline (TET), MIC=16 µg/ml; Ampicilline (AMP), MIC=32 µg/ml; Sulphamethoxazole (SUL), MIC=512 µg/ml; Trimethoprim (TMP), MIC=16 µg/ml; Streptomycin (STREP), MIC=32 µg/ml; and Spectinomycin (SPEC), MIC=128 µg/ml was performed. In the data analysis a pen was classified as antibiotic resistance positive against a specific antimicrobial compound if one virulent E. coli strain from minimum one pig in the pen were resistant. Similar a PFP sample were classified as antibiotic resistance positive if one virulent E. coli strain from the sample were resistant. Agreement was calculated by comparing the pen classification with the results from the PFP sample.

A total of 89 virulent E. coli isolates were cultures from 22 (26%) of 86 sampled diarrheic pigs and from in 13 (41%) of 31 pooled faecal samples from the pen floor. The overall prevalence of antimicrobial resistance in isolates for TET, AMP, SUL, TMP, STREP and SPEC was; 47.2 %, 60.7 %, 69.7 %, 69.7 %, 34.8 % and 18.0 %. It was possible to compare pen-level results from pig faecal samples and pen floor samples in 10 pens. Complete agreement was obtained for all antibiotic classes except for STREP where agreement was found in 8 of 10 pens.

The agreement of antimicrobial resistance testing of virulent E. coli strains was high between PFP samples and pigs samples. This study indicates that antimicrobial resistance testing can be performed on pooled faecal pen samples, as a tool for selecting classes of antibiotics for treatment of pigs at the pen level. However, these results should be confirmed in a larger study.

Disclosure of Interest: None Declared.