Impact of In-Feed versus In-Water Chlortetracycline and Tiamulin Administrations on Fecal Prevalence and Antimicrobial Susceptibilities of Campylobacter in a Population of Nursery Pigs

Antimicrobial resistance (AMR) in bacteria is a major public health concern in the US and around the world. Campylobacter is an important foodborne pathogen that resides in the gut of pigs and is shed in feces, with the potential to be transmitted to humans. In pigs, the oral route, either in-feed or in-water, is by far the most common route of administration of antimicrobials. Because the distribution of the antibiotic in the gut and the dosages are different, the impact of in-feed vs. in-water administration of antibiotics on the development of AMR is likely to be different. Therefore, a study was conducted to compare in-feed vs. in-water administrations of chlortetracycline (CTC) and/or tiamulin on fecal prevalence and AMR profiles of Campylobacter among weaned nursery piglets. A total of 1,296 weaned piglets, allocated into 48 pens (27 piglets per pen), were assigned randomly to six treatment groups: Control (no antibiotic), in-feed CTC, in-water CTC, in-feed tiamulin, in-water tiamulin, or in-feed CTC and tiamulin. Fecal samples were collected randomly from 5 piglets from each pen during the pre-treatment (days 0, 7), treatment (days 14, 21), and post-treatment (days 28, 35) phases. Bacterial isolations and species identifications were conducted by culture and PCR, respectively. The microbroth dilution method with SensititreTM plates was used to determine the antimicrobial susceptibility and resistance of Campylobacter isolates. The results on resistance were interpreted based on the European Committee on Antimicrobial Susceptibility Testing (EUCAST) epidemiological cutoff values for Campylobacter. The overall prevalence of Campylobacter was 18.2% (262/1440). Speciation of Campylobacter isolates by PCR indicated the prevalence of only two species: Campylobacter hyointestinalis (17.9%; 258/1440) and C. coli (0.3%; 4/1440). Campylobacter isolates were resistant to tetracycline (98.5%), ciprofloxacin (89.3%), and nalidixic acid (60.3%). Neither the antibiotic nor the route of administration had an effect (p > 0.05) on the prevalence of AMR Campylobacter in the feces of piglets.

28 In-feed or In-water Antibiotic Administration Did Not Influence the Fecal Prevalence and Antimicrobial Susceptibility Profiles of Salmonella in Piglets

A total of 1,296 weaned piglets were used in a 35-d study to assess the impact of in-feed vs in-water administrations of chlortetracycline (CTC) and or tiamulin on prevalence and antimicrobial resistance (AMR) profiles of Salmonella enterica. Piglets were allocated to 48 pens (27 pigs per pen) and pens were assigned randomly to six treatment groups: control (no antibiotic), in-feed CTC, in-water CTC, in-feed tiamulin, in-water tiamulin, and in feed CTC and tiamulin. Fresh fecal samples were collected randomly from 5 of 27 piglets from each pen on days -7, 0 (pre-treatment), 7, 14 (treatment), 21, and 28 (post-treatment). Salmonella isolation and identification were done by enrichment, plating on selective medium, and species confirmation of putative colonies by PCR. Antimicrobial susceptibility and resistance of the isolates were determined using premade antibiotic panel (SensititreTM CMV3AGNF and BOPO7F) and results were interpreted based on the Clinical and Laboratory Standards Institute guidelines. All Salmonella isolates were identified as serotype Typhimurium. The overall prevalence of Salmonella was 3.0% (43/1,440) with no treatment effect (P > 0.05). All isolates were resistant (100%) to tetracycline and tiamulin. Additionally, the isolates were resistant to ampicillin (100%), streptomycin (100%), sulfisoxazole (100), ciprofloxacin (95.4%) and nalidixic acid (74.4%). Only a few isolates were resistant to trimethoprim/sulphamethoxazole (4.7%), ceftriaxone (7.0%), and ceftiofur (7.0%). PCR assays indicated the presence of tetB gene in all isolates, while 11 (25.6%) and 4 (9.3%) isolates were positive for tetD and tetA genes, respectively. Neither in-feed nor in-water administration of CTC or tiamulin impacted the fecal prevalence and antimicrobial susceptibility of Salmonella in nursery piglets.

265 Evaluating the route of antibiotic administration and its effect on nursery pig growth performance

A total of 2,592 pigs (L337×1050, PIC, Hendersonville, TN; initially 5.58 kg BW) were used in a 28-d study to evaluate the route of antibiotic administration (in-feed vs in-water) on pig performance. Pigs were weaned at 21 d of age and placed in a commercial research facility with 27 pigs per pen. After a 7-d pre-trial period, pens of pigs were assigned to weight blocks in a randomized complete block design. There were 12 replications per treatment with pen as experimental unit for in-feed medication treatments and a pairs of pens as the experimental unit for water medication treatments. Treatments included a control (no medication), chlortetracycline (CTC) provided via feed or water to achieve 22 mg/kg BW, tiamulin in feed (5 to10 mg/kg BW) or water (23 mg/kg BW), or a combination of CTC and tiamulin in feed. Experimental treatments were provided for 14-d followed by a 14-d period without medication. Data were analyzed using R Studio (Version 3.5.2). From d 0 to 14, there was an antibiotic×route of administration interaction for ADG and G:F. For ADG, pigs fed diets containing CTC had increased (P< 0.05) ADG compared with those fed tiamulin in feed, with pigs provided CTC or tiamulin in the water intermediate. For G:F, pigs provided tiamulin in feed had decreased G:F compared to pigs fed CTC in feed or CTC or tiamulin supplied in water. Pigs fed CTC in the diet had increased ADFI compared to the control with pigs provided antibiotics in the water or tiamulin in feed intermediate (P< 0.05). Pigs provided the combination of CTC and tiamulin in feed were not different than those provided CTC in feed. There was no evidence of difference among treatments in subsequent performance. In summary, providing CTC in feed with or without tiamulin improved nursery pig growth performance.

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18 Impact of in-feed vs. in-water antibiotic administrations on the fecal prevalence and antimicrobial susceptibilities of Campylobacter and Salmonella in piglets

Campylobacter and Salmonella are common food borne pathogens in the gut of pigs and are shed in the feces. The control of these bacteria in pigs is of importance in reducing the potential for transmission to humans. In swine, oral route, either in-feed or in-water, is by far the most common route of administration of antibiotics. Because the distribution of the antibiotic in the gut and the dosage are different, the impact of in-feed vs. in-water administration of antibiotics on the fecal shedding of food borne pathogens, Campylobacter and Salmonella, and on the development of antimicrobial resistance (AMR) in gut bacteria is a largely unexplored area. Therefore, a study was conducted to compare the effects of in-feed and in-water antibiotic administration on fecal prevalence of Campylobacter and Salmonella and AMR development in nursery piglets. A total of 1,296 weaned piglets were allocated into pens (48 pens; 27 pigs per pen) distributed in a single room. Pens were assigned randomly to six treatment groups; Control (No antibiotic), In-feed chlortetracycline (CTC), In-water CTC, In-feed tiamulin, In-water tiamulin, and a combination of CTC and tiamulin (In-feed). Fresh fecal samples were collected randomly from 5 of 27 piglets from each pen on pre-treatment (days -7, 0), treatment (days 7, 14) and post-treatment (days 21, 28) phases. Bacterial isolations and identifications were done by culture method and PCR, respectively. Overall prevalence of Campylobacter and Salmonella were 18.2% (262/1,440) and 3.9% (56/1,440) respectively. Speciation of Campylobacter isolates indicated C. hyointestinalis (17.9%; 258/1,440) and C. coli (0.3%; 4/1,440). Pigs from control group had a higher prevalence (P< 0.05) of both Campylobacter and Salmonella when compared to other treatment groups. Both treatment and post-treatment phases had a significant effect on the prevalence of Campylobacter and Salmonella (P< 0.05).