Draft genome sequence of the Chilean isolate Aeromonas salmonicida strain CBA100.

We report the draft genome sequence from Aeromonas salmonicida sp. strain CBA100, which was characterized as an antibiotic-resistant bacterium isolated from infected rainbow trout. The total size of the genome is 4,788,109 bp, with a G + C content of 60.55%. Comparison of its open reading frames shows that the closest homologue to one third of the genes of strain CBA100 are found in A. hydrophila. The strain contains several efflux pumps and putative genes that confer resistance to multiclass antibiotics, including macrolide, ß-lactamics, florfenicol and quinolones. The antibiogram profile suggests that efflux pumps are the main mechanism of resistance to non-ß-lactamic antibiotics. This is the first genome of a Chilean isolate of A. salmonicida, which should shed light on the design of strain-specific vaccines against this pathogen and reduce the use of antibiotics for preventive treatment in Chilean aquaculture.

The hydrocarbon-degrading marine bacterium Cobetia sp. strain MM1IDA2H-1 produces a biosurfactant that interferes with quorum sensing of fish pathogens by signal hijacking.

Biosurfactants are produced by hydrocarbon-degrading marine bacteria in response to the presence of water-insoluble hydrocarbons. This is believed to facilitate the uptake of hydrocarbons by bacteria. However, these diffusible amphiphilic surface-active molecules are involved in several other biological functions such as microbial competition and intra- or inter-species communication. We report the isolation and characterization of a marine bacterial strain identified as Cobetia sp. MM1IDA2H-1, which can grow using the sulfur-containing heterocyclic aromatic hydrocarbon dibenzothiophene (DBT). As with DBT, when the isolated strain is grown in the presence of a microbial competitor, it produces a biosurfactant. Because the obtained biosurfactant was formed by hydroxy fatty acids and extracellular lipidic structures were observed during bacterial growth, we investigated whether the biosurfactant at its critical micelle concentration can interfere with bacterial communication systems such as quorum sensing. We focused on Aeromonas salmonicida subsp. salmonicida, a fish pathogen whose virulence relies on quorum sensing signals. Using biosensors for quorum sensing based on Chromobacterium violaceum and Vibrio anguillarum, we showed that when the purified biosurfactant was mixed with N-acyl homoserine lactones produced by A. salmonicida, quorum sensing was inhibited, although bacterial growth was not affected. In addition, the transcriptional activities of A. salmonicida virulence genes that are controlled by quorum sensing were repressed by both the purified biosurfactant and the growth in the presence of Cobetia sp. MM1IDA2H-1. We propose that the biosurfactant, or the lipid structures interact with the N-acyl homoserine lactones, inhibiting their function. This could be used as a strategy to interfere with the quorum sensing systems of bacterial fish pathogens, which represents an attractive alternative to classical antimicrobial therapies in fish aquaculture.

Identification and modeling of a novel chloramphenicol resistance protein detected by functional metagenomics in a wetland of Lerma, Mexico.

The exploration of novel antibiotic resistance determinants in a particular environment may be limited because of the presence of uncultured microorganisms. In this work, a culture-independent approach based on functional metagenomics was applied to search for chloramphenicol resistance genes in agro-industrial wastewater in Lerma de Villada, Mexico. To this end, a metagenomic library was generated in Escherichia coli DH10B containing DNA isolated from environmental samples of the residual arsenic-enriched (10 mg/ml) effluent. One resistant clone was detected in this library and further analyzed. An open reading frame similar to a multidrug resistance protein from Aeromonas salmonicida and responsible for chloramphenicol resistance was identified, sequenced, and found to encode a member of the major facilitator superfamily (MFS). Our results also showed that the expression of this gene restored streptomycin sensitivity in E. coli DH10B cells. To gain further insight into the phenotype of this MFS family member, we developed a model of the membrane protein multiporter that, in addition, may serve as a template for developing new antibiotics.