Reduced antimicrobial resistance in weaner pigs treated with Detach^® following natural challenge with F4 Escherichia coli

Aminoglycosides and zinc oxide (ZO) are used to prevent post-weaning diarrhoea (PWD) caused by Enterotoxigenic Escherichia coli (ETEC), but their use can lead to antibiotic resistance. Detach (Anatara Lifesciences Ltd, Brisbane, Qld, Australia) protects pigs from PWD but is not bactericidal. Detach^® acts by (1) inactivating host receptors, preventing ETEC colonisation and (2) inhibiting intestinal fluid secretion caused by ETEC toxins (Mynott et al. 1997; Chandler and Mynott 1998). This study tested the hypothesis that Detach^® could control PWD in weaner pigs without increasing the incidence of antimicrobial resistance (AMR) in E. coli.

Seventy-two weaner pigs (mixed gender) from nine gilt litters were randomly allocated into four treatment groups with two piglets from each litter per treatment. Each group, six pens of three pigs (n = 18 per group), were housed in separate rooms to avoid faecal contamination. Detach^® (4 mL) was administered orally (DT) the day before weaning (d –1) and on d 7. All pigs were acclimatised to non-medicated feed between d 0 and 7. Zinc oxide (2500 ppm) or neomycin sulphate (8 mg/kg, NS) was administered in feed between d 7 and 20. Non-medicated feed was supplied to Control (CT) and DT pigs from d 0 to 40, and to Zn and NS pigs from d 20 to 40. Pen feed intake and individual weight gains were recorded weekly and faeces were collected from each pig on d 6, 19 and 39 and faecal consistency scores recorded daily. Pathogenic F4 ETEC were quantified in d 6 faeces to compare infection levels between groups. Four E. coli isolates from each faecal sample were tested for AMR to seven commonly used antimicrobials. Differences in proportions of resistant E. coli between groups were analysed with a Kruskal–Wallis One-Way ANOVA (Genstat 18, VSN International, Hemel Hempstead, UK). Two NS pigs died on d 19 and 39 due to a Streptococcus suis infection and chronic pericarditis, respectively. Low numbers of F4 ETEC were detected at d 6 in all pigs (median = 280 ETEC), with a significantly higher proportion in CT relative to NS pigs (P = 0.042). During the treatment period, diarrhoea was numerically higher in CT piglets between d 7 and 19 (44% to 11% in other groups), but mean faecal consistency scores did not differ between treatments, and CT pigs recovered after d 20. Immediately following removal of ZO and NS, 25% of NS and ZO pigs had diarrhoea requiring electrolytes. Weight gains over the trial period (d 7 to 39) were NS, 23.13^a kg; ZO, 22.02^c kg; DT, 21.07^b kg and CT, 22.77^c kg (different superscripts indicate P < 0.05). Feed intake was NS, 25.77^a kg; ZO, 24.45^b kg; DT, 23.66^c kg and CT, 27.00^d kg. At d 6, E. coli AMR was not significantly different between groups, but by d 19 E. coli from DT pigs had reduced AMR to neomycin (1.4% compared to 12.7%), tetracycline, sulphamethoxazole/trimethoprim and lincospectin relative to NS pigs (Fig. 1). At Day 39, ZO pigs had significantly increased resistance to tetracycline.

Fig. 1.  Percentage of E. coli with resistance to tetracycline, sulphamethoxazole/trimethoprim (TMS) and lincospectin in NS, ZO, DT and CT pigs.

Detach^® effectively controlled diarrhoea following natural challenge without inducing resistance to antimicrobials in E. coli, but did not lead to the growth advantages observed in NS treated pigs.