Effect of Tulathromycin on Colonization Resistance, Antimicrobial Resistance, and Virulence of Human Gut Microbiota in Chemostats

DSS treatment does not affect murine colonic microbiota in absence of the host

The prevalence of inflammatory bowel disease (IBD) is rising globally; however, its etiology is still not fully understood. Patient genetics, immune system, and intestinal microbiota are considered critical factors contributing to IBD. Preclinical animal models are crucial to better understand the importance of individual contributing factors. Among these, the dextran sodium sulfate (DSS) colitis model is the most widely used. DSS treatment induces gut inflammation and dysbiosis. However, its exact mode of action remains unclear. To determine whether DSS treatment induces pathogenic changes in the microbiota, we investigated the microbiota-modulating effects of DSS on murine microbiota in vitro. For this purpose, we cultured murine microbiota from the colon in six replicate continuous bioreactors. Three bioreactors were supplemented with 1% DSS and compared with the remaining PBS-treated control bioreactors by means of microbiota taxonomy and functionality. Using metaproteomics, we did not identify significant changes in microbial taxonomy, either at the phylum or genus levels. No differences in the metabolic pathways were observed. Furthermore, the global metabolome and targeted short-chain fatty acid (SCFA) quantification did not reveal any DSS-related changes. DSS had negligible effects on microbial functionality and taxonomy in vitro in the absence of the host environment. Our results underline that the DSS colitis mouse model is a suitable model to study host-microbiota interactions, which may help to understand how intestinal inflammation modulates the microbiota at the taxonomic and functional levels.

Impact of Chronic Tetracycline Exposure on Human Intestinal Microbiota in a Continuous Flow Bioreactor Model

Studying potential dietary exposure to antimicrobial drug residues via meat and dairy products is essential to ensure human health and consumer safety. When studying how antimicrobial residues in food impact the development of antimicrobial drug resistance and disrupt normal bacteria community structure in the intestine, there are diverse methodological challenges to overcome. In this study, traditional cultures and molecular analysis techniques were used to determine the effects of tetracycline at chronic subinhibitory exposure levels on human intestinal microbiota using an in vitro continuous flow bioreactor. Six bioreactor culture vessels containing human fecal suspensions were maintained at 37 °C for 7 days. After a steady state was achieved, the suspensions were dosed with 0, 0.015, 0.15, 1.5, 15, or 150 µg/mL tetracycline, respectively. Exposure to 150 µg/mL tetracycline resulted in a decrease of total anaerobic bacteria from 1.9 × 10⁷ ± 0.3 × 10⁷ down to 2 × 10⁶ ± 0.8 × 10⁶ CFU/mL. Dose-dependent effects of tetracycline were noted for perturbations of tetB and tetD gene expression and changes in acetate and propionate concentrations. Although no-observed-adverse-effect concentrations differed, depending on the traditional cultures and the molecular analysis techniques used, this in vitro continuous flow bioreactor study contributes to the knowledge base regarding the impact of chronic exposure of tetracycline on human intestinal microbiota.

A history of antimicrobial drugs in animals: Evolution and revolution

The evolutionary process of antimicrobial drug (AMD) uses in animals over a mere eight decades (1940-2020) has led to a revolutionary outcome, and both evolution and revolution are ongoing, with reports on a range of uses, misuses and abuses escalating logarithmically. As well as veterinary therapeutic perspectives (efficacy, safety, host toxicity, residues, selection of drug, determination of dose and measurement of outcome in treating animal diseases), there are also broader, nontherapeutic uses, some of which have been abandoned, whilst others hopefully will soon be discontinued, at least in more developed countries. Although AMD uses for treatment of animal diseases will continue, it must: (a) be sustainable within the One Health paradigm; and (b) devolve into more prudent, rationally based therapeutic uses. As this review on AMDs is published in a Journal of Pharmacology and Therapeutics, its scope has been made broader than most recent reviews in this field. Many reviews have focused on negative aspects of AMD actions and uses, especially on the question of antimicrobial resistance. This review recognizes these concerns but also emphasizes the many positive aspects deriving from the use of AMDs, including the major research-based advances underlying both the prudent and rational use of AMDs. It is structured in seven sections: (1) Introduction; (2) Sulfonamide history; (3) Nontherapeutic and empirical uses of AMDs (roles of agronomists and veterinarians); (4) Rational uses of AMDs (roles of pharmacologists, clinicians, industry and regulatory controls); (5) Prudent use (residue monitoring, antimicrobial resistance); (6) International and inter-disciplinary actions; and (7) Conclusions.

Antibiotic resistance in Escherichia coli from pigs from birth to slaughter and its association with antibiotic treatment

The purpose of this longitudinal study was to describe the occurrence of antibiotic resistance in faecal Escherichia coli isolated from pigs between birth and slaughter and its association with antibiotic treatment. Four objectives were addressed: comparison of antibiotic resistance in isolates from a) treated vs. non-treated pigs, b) follow-up vs. initial samples of treated and non-treated pigs, c) pigs receiving treatments via different administration routes and d) sows and their piglets. Each comparison addressed the following antibiotic groups used for treatment: beta-lactams, tetracyclines, polymyxins and macrolides, and the susceptibility of E. coli isolates to the respective agents: ampicillin, tetracycline, colistin and azithromycin. Between 2014 and 2016, 406 focal animals from 29 commercial breeding herds were followed from birth to the end of the relevant fattening periods. All antibiotic treatments in these pigs were documented. Faecal samples were collected from the focal pigs once while suckling, once after weaning and three times during fattening, and from their dams once around farrowing. Escherichia coli isolated from these samples was tested for antibiotic susceptibility. In total, 264 animals from 19 breeding herds were treated with an antibiotic at least once during their lifetime. Beta-lactams, tetracyclines and colistin were used most frequently. Piglets were treated individually by injection (n = 108 treatments) or via drench (9); weaners via feed (192) or water (56) and fatteners via feed (30) or injection (15). Resistance to ampicillin and tetracycline in E. coli was already common prior to antibiotic treatment. Resistance proportions were higher for beta-lactam-, tetracycline-, colistin- and macrolide-treated pigs compared to untreated pigs at different sampling periods (p < 0.05; Fisher's exact test). In the logistic analysis, the difference was confirmed for beta-lactam-treated vs. untreated pigs. In E. coli from macrolide-untreated pigs, resistance to azithromycin was more frequent compared to pre-treatment values. Route of application did not affect rates of antibiotic resistance in the logistic analysis even though Fisher's exact test indicated associations for beta-lactams (feed/water vs. injection), tetracyclines (feed/water vs. non-treatment) and macrolides (tulathromycin-injection vs. tylosin in feed). Piglets were more likely to carry an E. coli resistant to ampicillin or azithromycin if their dams did so as well. Our results suggest further research on resistance effects by administration routes is required. Reducing antibiotic resistance in sows might lead to a lower level of beta-lactam or macrolide-resistant E. coli among their progeny. To preserve treatment options for bacterial infections, antibiotic use should be restricted to necessary cases.