Detection of antibiotic resistant E. coli in weaned piglets

Evaluating the presence of antibiotic resistant (AR) bacteria in swine production is important to estimate the problems associated with bacterial antibiotic resistances on farms. Especially the prevalence of resistance in commensal E. coli is a useful indicator of antibiotic resistance in bacteria of different communities. This bacterium causes also diarrhea problems in weaned piglets. For this reason, E. coli and AR E. coli were assessed in weaned piglets of an Austrian farm in the first week after weaning.

The prevalence of total E. coli and AR E. coli was determined in fecal samples of piglets which did not receive antibiotics during the experiment. Experiment started on day 1 with forty weaning pigs, which were split into four groups (= replicates). Individual fecal samples of three pigs per replicate were collected on days 1 and 7 of the experiment. The colony count of E. coli, E. coli resistant to streptomycin (Str), tetracycline (Tet), sulfamethoxazole (Sul), amoxicillin (Amx), ampicillin (Amp) and extended spectrum ß-lactamases (ESBL)-producing E. coli were investigated within 24 hours after collecting the samples. MacConkey (Merck GmbH) agar was used for the detection of total E. coli, MacConkey agar supplemented with an antibiotic at the concentration of the CLSI breakpoint for AR E. coli and ChromlD^® ESBL medium for ESBL-producing E. coli.

Results showed that the level of E. coli in fecal samples was 1.4 x 10⁸ cfu/g feces on day 1. Approximately half of these E. coli were resistant to Str, whereas Tet-, Sul- or Amx-resistant E. coli conformed to one-third of the total E. coli count in each case. About 16% or 9.5% of the total E. coli count were resistant to Amp or produced ESBL. Thus, it is supposed that multi-resistant E. coli were present on the farm. Compared to day 1 a decrease of E. coli by 70% was found on day 7 (p˂0.05). Furthermore, the level of Str- and Tet-resistant E. coli on day 7 was reduced by 62% and 86%, respectively (p˂0.05). Although the colony counts of Sul- and Amx-resistant E. coli were numerically decreased by 41% and 18% on day 7, these results were not significant. The same applies to the levels of Amp-resistant and ESBL-producing E. coli, which numerically increased from day 1 to day 7 by 47% and 94%.

An increase of Amp-resistant as well as ESBL-producing E. coli within the first week after weaning was detected in feces of the piglets, while Str- and Tet-resistant E. coli numbers decreased. Follow up studies in weaned piglets should be carried out in order to identify reasons for the decrease or increase of resistant E. coli in this stressful period.

Disclosure of Interest: None Declared.