Effect of Tetracycline Dose and Treatment Mode on Selection of Resistant Coliform Bacteria in Nursery Pigs

Abstract

This study describes the results of a randomized clinical trial investigating the effect of oxytetracycline treatment dose and mode of administration on the selection of antibiotic-resistant coliform bacteria in fecal samples from nursery pigs. Nursery pigs (pigs of 4 to 7 weeks of age) in five pig herds were treated with oxytetracycline for Lawsonia intracellularis-induced diarrhea. Each group was randomly allocated to one of five treatment groups: oral flock treatment with a (i) high (20 mg/kg of body weight), (ii) medium (10 mg/kg), or (iii) low (5 mg/kg) dose, (iv) oral pen-wise (small-group) treatment (10 mg/kg), and (v) individual intramuscular injection treatment (10 mg/kg). All groups were treated once a day for 5 days. In all groups, treatment caused a rise in the numbers and proportions of tetracyclineresistant coliform bacteria right after treatment, followed by a significant drop by the time that the pigs left the nursery unit. The counts and proportions of tetracyclineresistant coliforms did not vary significantly between treatment groups, except immediately after treatment, when the highest treatment dose resulted in the highest number of resistant coliforms. A control group treated with tiamulin did not show significant changes in the numbers or proportions of tetracycline-resistant coliforms. Selection for tetracycline-resistant coliforms was significantly correlated to selection for ampicillin-and sulfonamide-resistant strains but not to selection for cefotaximeresistant strains. In conclusion, the difference in the dose of oxytetracycline and the way in which the drug was applied did not cause significantly different levels of selection of tetracycline-resistant coliform bacteria under the conditions tested.IMPORTANCE Antimicrobial resistance is a global threat to human health. Treatment of livestock with antimicrobials has a direct impact on this problem, and there is a need to improve the ways that we use antimicrobials in livestock production. We hypothesized that antibiotic resistance development following treatment of diarrhea in nursery pigs could be reduced either by lowering the dose of oxytetracycline or by replacing the commonly used practice of flock treatment with individual or smallgroup treatments, since this would reduce the number of pigs treated. However, the study showed no significant difference between treatment groups with respect to the number or proportion of tetracycline-resistant coliforms selected. The most important conclusion is that under practical field conditions, there will be no added value, in terms of lowering resistance development, by exchanging flock treatment for individual or small-group treatment of nursery pigs. The reason for the lack of an

Phenotypic antimicrobial resistance in Escherichia coli strains isolated from swine husbandries in North Western Germany – temporal patterns in samples from laboratory practice from 2006 to 2017

“…Epidemiological studies revealed either an increase in antimicrobial resistance in populations treated more often with antibiotics [6,7], or a beneficial effect on resistance levels after the introduction of national antimicrobial usage (AMU) reduction campaigns [8]. Under defined experimental conditions, the effect of a selective pressure by antimicrobial usage on the frequency of phenotypically resistant bacteria in swine [9] or the total resistome of bacterial populations [10] was proven. In general, under field conditions, in livestock, the association between AMU and AMR is difficult to assess because additional factors such as vaccination, feed supplements, hygiene conditions and management characteristics also have an impact [11].…”

Effect of ampicillin, cephalexin, ceftiofur and tetracycline treatment on selection of resistant coliforms in a swine faecal microcosmos

“…Enumeration of dark red colonies with a size of >0Á5 mm was performed after 24 h of incubation at 37°C and proportions (%) of R strains were estimated. In a previous study, 100 such colonies were all confirmed to be E. coli (Graesboll et al 2017). Such a control was not carried out in the current work, and we will use the term coliforms, although they are likely to be E. coli.…”

“…5 g each. To determine pretreatment levels (T0) of R coliforms, samples were 10-fold diluted in DPBS, and 20 µl of each dilution were spotted in duplicate for CFU determination on McConkey agar (Oxoid, Roskilde, Denmark) plates with and without antimicrobials as described (Graesboll et al 2017;. Antimicrobials (Sigma) were added at concentrations corresponding to 29breakpoint concentration and 49breakpoint concentration (29 BPC and 49 BPC), respectively, of each specific antimicrobial according to EUCAST criteria (EUCAST 2019): ampicillin (Amp) at 16 and 32 lg ml À1 , cephalexin (Cpn) at 32 and 64 lg ml À1 , ceftiofur (Cef) at 2 and 4 lg ml À1 , and tetracycline (Tet) at 16 and 32 lg ml À1 .…”

“…Plates were incubated overnight at 37°C. Colonies growing on these plates were classified as resistant, based on growth (Vieira et al 2008;Graesboll et al 2017).…”

Tetracyclines: Insights and Updates of their Use in Human and Animal Pathology and their Potential Toxicity

“…In addition, it is worth noting that TCs have been employed also as healing agent for digital dermatitis treatment in dairy cattle [93]. For those reasons, pigs, livestock and poultry are still exposed to a huge range of antimicrobials while the long term effect on the environment, besides antibiotic resistance [94,95], or effects, when consumed by the animal or human species, on the overall individual health status have been partially investigated. As annual production and consumption increase, increasing volumes of antimicrobials will be used each year if nothing is done to reduce their usage with a consequent increase of antimicrobial resistant organisms.…”