Quinolone Resistance in Gallibacterium anatis Determined by Mutations in Quinolone Resistance-Determining Region.

Control of the important pathogen, Gallibacterium anatis, which causes salpingitis and peritonitis in poultry, relies on treatment using antimicrobial compounds. Among these, quinolones and fluoroquinolones have been used extensively, leading to a rise in the prevalence of resistant strains. The molecular mechanisms leading to quinolone resistance, however, have not previously been described for G. anatis, which is the aim of this study. The present study combines phenotypic antimicrobial resistance data with genomic sequence data from a collection of G. anatis strains isolated from avian hosts between 1979 and 2020. Minimum inhibitory concentrations were determined for nalidixic acid, as well as for enrofloxacin for each included strain. In silico analyses included genome-wide queries for genes known to convey resistance towards quinolones, identification of variable positions in the primary structure of quinolone protein targets and structural prediction models. No resistance genes known to confer resistance to quinolones were identified. Yet, a total of nine positions in the quinolone target protein subunits (GyrA, GyrB, ParC and ParE) displayed substantial variation and were further analyzed. By combining variation patterns with observed resistance patterns, positions 83 and 87 in GyrA, as well as position 88 in ParC, appeared to be linked to increased resistance towards both quinolones included. As no notable differences in tertiary structure were observed between subunits of resistant and sensitive strains, the mechanism behind the observed resistance is likely due to subtle shifts in amino acid side chain properties.

Addressing a Rule of Thumb: Modeling the Effects of Meteorological Conditions on Prescription of Antimicrobials in Aquaculture.

Meteorological phenomena such as warm summer temperatures and increased numbers of sunlight hours have repeatedly been hypothesized to be associated with infectious diseases and an increased prescription of antimicrobial compounds in Danish aquaculture. To address this hypothesis, we prepared statistical models incorporating aquaculture production data from Danish Aquaculture, detailed records on prescription of antimicrobials from the Danish VETSTAT program, and meteorological data from 2001 to 2019 from the Danish Meteorological Institute. Separate series of models were made and refined for land-based and marine production, respectively. For both production forms, the models identify summer sunlight hours as having a significant influence on antimicrobial use. In addition to summer sunlight, spring sunlight and water temperature were integral, although not statistically significant, parameters when modeling antimicrobial use in marine production. Although the extensive availability and accuracy of relevant data are associated with Danish production, we believe the results allow for more general conclusions on the influence of meteorological parameters on outbreaks of bacterial pathogens in international aquaculture. Such insights could have a substantial impact on prophylactic strategies, fish husbandry, and our understanding of how increasing temperatures may affect future antimicrobial usage in the global aquaculture industry. IMPORTANCE Global aquaculture production has been rapidly increasing for decades and is set to play a pivotal role in feeding a growing human population. Along with the growth in aquaculture production, the annual global use of antimicrobials is estimated to increase by one-third between 2017 and 2030. Using detailed antimicrobial prescription records as a proxy for outbreaks, we were able to evaluate the effects of a variety of meteorological parameters through statistical modeling. Our results lend scientific support to informal observations from the industry, but more importantly, this study provides novel, essential information on the importance of abiotic factors that can, in turn, lead to improved prophylactic efforts and thus help to reduce antimicrobial use in global aquaculture.

Citrus flavonoids, ß-Glucan and organic acid feed additives decrease relative risk during Yersinia ruckeri O1 biotype 2 infection of rainbow trout (Oncorhynchus mykiss).

Whether through direct supplementation of bacteria or by prebiotic supplementation thought to favour subsets of bacteria, modulation of gut microbiota constitutes an important and promising alternative to the use of prophylactic and growth promoting antibiotics in worldwide aquaculture. We fed a commercial base feed, alone or supplemented with either proprietary ß-glucan, ß-glucan and organic acids, citrus flavonoid or yeast cell wall supplements, to rainbow trout over a period of four weeks. Fish from each feed group were then subjected to experimental, waterborne infection with Yersinia ruckeri O1 biotype 2. Following experimental feeding, the ß-glucan and organic acids supplemented group showed significantly improved feed conversion and lipid efficiency ratios. Furthermore, the ß-glucan, ß-glucan and organic acids and citrus flavonoid supplements proved to significantly reduce the risk of mortality in rainbow trout during experimental infection as shown by hazard ratio analysis. Resulting in 33.2%, 30.6% and 30.5% reduction in risk relative to the non-supplemented base feed, respectively, these three supplements show a promising potential either as stand-alone feed supplements, or as components in complex feed formulations.

Potential role of specific antibodies as important vaccine induced protective mechanism against Aeromonas salmonicida in rainbow trout.

Furunculosis caused by infection with Aeromonas salmonicida subsp. salmonicida has been a known threat to aquaculture for more than a century. Efficient prophylactic approaches against this disease are essential for continued growth of salmonid aquaculture. Since the introduction of successful oil-adjuvanted vaccines in the early 1990's, a number of studies have been published on the protective as well as adverse effects of these vaccines. Most studies focus on vaccination of salmon (Salmo salar). However, rainbow trout (Oncorhynchus mykiss) are also very susceptible to infection and are vaccinated accordingly. In this study we have examined the protection against infection with a Danish strain of A. salmonicida in both vaccinated and non-vaccinated rainbow trout. A commercial and an experimental auto-vaccine were tested. The protective effects of the vaccines were evaluated through an A. salmonicida challenge 18 weeks post vaccination. Both vaccines resulted in a significantly increased survival in the vaccinated fish during a 28 day challenge period relative to non-vaccinated fish (P = 0.01 and P = 0.001 for the commercial and experimental vaccine, respectively). Throughout the entire experiment, the presence of specific antibodies in plasma was monitored using ELISA. A significant increase in specific antibody levels was seen in fish vaccinated with both vaccines during the 18 weeks between vaccination and challenge. Within 3 days post challenge, a significant decrease in specific antibodies occurred in vaccinated fish. A positive correlation was found between mean levels of specific antibodies pre challenge and overall survival. This correlation, along with the observed depletion of antibodies during the initial phase of infection, suggests that specific antibodies play an essential role in vaccine mediated protection against A. salmonicida in rainbow trout.