Hervé Le Bris

Complete sequence of the floR-carrying multiresistance plasmid pAB5S9 from freshwater Aeromonas bestiarum

OBJECTIVES A multiresistant Aeromonas bestiarum strain, shown to be persistent and spreading in a freshwater stream, was investigated for the presence, location and organization of antimicrobial resistance genes. METHODS The plasmid pAB5S9 was transferred by electroporation into Escherichia coli TG1. The resistance phenotype mediated by pAB5S9 was determined. Moreover, the plasmid was sequenced completely and analysed for its structure and organization of reading frames. RESULTS Plasmid pAB5S9 mediated resistances to phenicols, sulphonamides, streptomycin and tetracycline. The analysis of the 24.7 kb sequence revealed the presence of 20 predicted coding sequences (CDSs), which included the floR, sul2 and strA-strB resistance genes and a tetR-tet(Y) determinant. Approximately 7.5 kb of pAB5S9 showed 100% nucleotide sequence identity to three non-contiguous segments of the SXT element of Vibrio cholerae. Regions identical to SXT comprised the floR gene, flanked upstream by a complete and downstream by a truncated ISCR2 element, and the region of the sul2 and strA-strB genes. Other CDSs of pAB5S9 related to plasmid replication and partitioning, metabolic and gene regulation functions as well as conjugative transfer showed homology to sequences from diverse bacterial species, indicating a mosaic structure. CONCLUSIONS This study provides the first report of a floR-carrying plasmid in the genus Aeromonas and the first description of a tetR-tet(Y) determinant. The analysis of the multiresistant A. bestiarum strain indicates that strains of this species, some of which are opportunistic pathogens for fish, might also act as a resistance gene reservoir in the freshwater environment.

Comparison of water, sediment, and plants for the monitoring of antibiotics: A case study on a river dedicated to fish farming

Oxolinic acid, flumequine, oxytetracycline, and florfenicol are antibiotics commonly used in farming. Because an important percentage of these antibiotics given to fish and cattle ends up, directly or indirectly, in the freshwater environment, suitable tools for the monitoring of these antibiotics are needed. A French river was chosen because of the location of four fish farms and a sewage plant on its main course. First, a passive monitoring program involving water, sediment, and autochthonous bryophytes was performed at 25 sampling sites tested once every three months for one year. Second, an active monitoring method was performed using moss bags for a one-month exposure period, both upstream and downstream of each potential source of antibiotics. Sediment and bryophyte samples, but not water samples, were found to be useful for monitoring environmental contamination by oxolinic acid, flumequine, oxytetracycline, and florfenicol. Sediments and bryophytes also appeared to be complementary media for dating the rivers contamination by antibiotics. Data collected by both active and passive monitoring methods confirmed contamination of the river, mainly by flumequine and oxytetracycline, attributable to fish farming but also to terrestrial animal farming and perhaps human pharmaceuticals.

Functional roles of an engineer species for coastal benthic invertebrates and demersal fish

Abstract Through their tissues or activities, engineer species create, modify, or maintain habitats and alter the distribution and abundance of many plants and animals. This study investigates key ecological functions performed by an engineer species that colonizes coastal ecosystems. The gregarious tubiculous amphipod Haploops nirae is used as a biological model. According to previous studies, the habitat engineered by H. nirae (i.e., Haploops habitat) could provide food and natural shelter for several benthic species such as benthic diatoms belonging to the gender Navicula, the micrograzer Geitodoris planata, or the bivalve Polititapes virgineus. Using data from scientific surveys conducted in two bays, this study explored whether (1) the Haploops sandy‐mud community modifies invertebrate and ichthyologic community structure (diversity and biomass); (2) H. nirae creates a preferential feeding ground; and (3) this habitat serves as a refuge for juvenile fish. Available Benthic Energy Coefficients, coupled with more traditional diversity indices, indicated higher energy available in Haploops habitat than in two nearby habitats (i.e., Sternaspis scutata and Amphiura filiformis/Owenia fusiformis habitats). The use of isotopic functional indices (IFIs) indicated (1) a higher functional richness in the Haploops habitat, related to greater diversity in food sources and longer food chains; and (2) a higher functional divergence, associated with greater consumption of a secondary food source. At the invertebrate‐prey level, IFIs indicated little specialization and little trophic redundancy in the engineered habitat, as expected for homogenous habitats. Our results partly support empirical knowledge about engineered versus nonengineered habitats and also add new perspectives on habitat use by fish and invertebrate species. Our analyses validated the refuge‐area hypothesis for a few fish species. Although unique benthic prey assemblages are associated with Haploops habitat, the hypothesis that it is a preferential feeding area was not verified. However, specialist feeding behavior was observed for predators, which calls for further investigation.