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Dynamics of antimicrobial resistance and virulence genes in Enterococcus faecalis during swine manure storage

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Abstract:

In this study we used 2 experimental approaches to evaluate the stability of antimicrobial resistance (AMR) phenotypes, selected AMR genes, and selected virulence genes in Enterococcus faecalis during manure storage on a commercial swine farm. Isolates of E. faecalis were obtained directly from fresh fecal material (n = 120) and from the manure storage facility (n = 85) and compared. Tetracycline resistance and the virulence genes cob, esp, eep, and ccf were detected at lower frequency in manure isolates than in fecal isolates. A second approach consisted of immersing in diffusion chambers pure cultures of E. faecalis that varied in their AMR phenotypes and virulence genotypes in the swine manure storage facility for 8 weeks, sampling periodically, and evaluating the recovered strains for changes in their genotypic or phenotypic characteristics. Enterococcus faecalis populations declined exponentially, with rate constants ranging from 0.011 to 0.022 h-1. Among the AMR and virulence genes examined, 1 AMR gene (sat4) and 7 virulence genes (agrBfs, cob, cpd, cylB, efaAfs, enlA, and esp) were lost at low frequencies in the recovered strains. The AMR phenotypes were stable during the incubation, with minimal loss (P > 0.05) of the streptomycin-resistance phenotype. Overall, these results suggest that some attributes of public health significance in populations of E. faecalis decrease in frequency during manure storage.

Dans cette étude, nous avons utilisé 2 approches expérimentales afin d’évaluer la stabilité des phénotypes de résistance aux agents antimicrobiens (RAM), d’une sélection de gènes de RAM sélectionnés, et de virulence chez Enterococcus faecalis lors de l’entreposage de lisier de porc d'une ferme commerciale. Des souches de E. faecalis directement isolées de matières fécales fraiches (n = 120) ou d’une installation d’entreposage du lisier (n = 85) ont été comparées. La résistance à la tétracycline, et les gènes de virulence cob, esp, eep, et ccf ont été détectés moins fréquemment chez les isolats du lisier que chez ceux provenant des matières fécales. Une deuxième approche consistait à immerger des chambres de diffusion contenant des cultures pures de E. faecalis de phénotypes de RAM et de génotype de virulence variés dans l’installation d’entreposage de lisier pendant 8 semaines. Les échantillons ont été obtenus périodiquement pour récupérer les souches, et évaluer leurs changements phénotypiques ou génotypiques. Les populations de E. faecalis déclinaient de façon exponentielle, avec une constante de vitesse variant de 0,011 à 0,022 h-1. Parmi les gènes de RAM et de virulence examinés, seulement le gène sat4 de RAM et 7 gènes de virulence (agrBfs, cob, cpd, cylB, efaAfs, enlA et esp) disparaissaient à une faible fréquence chez les souches récupérées. Les phénotypes de RAM restaient stables durant l’incubation, avec une perte minimale de résistance à la streptomycine (P > 0,05). En somme, les résultats suggèrent que certaines propriétés des populations de E. faecalis pertinentes en santé publique s'atténuent lors d’entreposage du lisier de porc.

Document Type: Research Article

Publication date: August 1, 2010

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  • Published since 1954, this monthly journal contains new research in the field of microbiology including applied microbiology and biotechnology; microbial structure and function; fungi and other eucaryotic protists; infection and immunity; microbial ecology; physiology, metabolism and enzymology; and virology, genetics, and molecular biology. It also publishes review articles and notes on an occasional basis, contributed by recognized scientists worldwide.
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