Bacterial multidrug efflux pumps are antibiotic resistance determinants present in all microorganisms. With few exceptions, they are chromosomally encoded and present a conserved organization both at the genetic and at the protein levels. In addition, most, if not all, strains of a given bacterial species present the same chromosomally-encoded efflux pumps. Altogether this indicates that multidrug efflux pumps are ancient elements encoded in bacterial genomes long before the recent use of antibiotics for human and animal therapy. In this regard, it is worth mentioning that efflux pumps can extrude a wide range of substrates that include, besides antibiotics, heavy metals, organic pollutants, plant-produced compounds, quorum sensing signals or bacterial metabolites, among others. In the current review, we present information on the different functions that multidrug efflux pumps may have for the bacterial behaviour in different habitats as well as on their regulation by specific signals. Since, in addition to their function in non-clinical ecosystems, multidrug efflux pumps contribute to intrinsic, acquired, and phenotypic resistance of bacterial pathogens, the review also presents information on the search for inhibitors of multidrug efflux pumps, which are currently under development, in the aim of increasing the susceptibility of bacterial pathogens to antibiotics.

Determining the effect of wastewater treatment in water resistome is a topic of interest for water quality, mainly under re-use and One-Health perspectives. The resistome, the plasmidome, and the bacterial community composition of samples from influents and treated effluents from a wastewater treatment plant located in Northern Portugal were studied using metagenomic techniques. Wastewater treatment contributed to reduce the abundance of resistance genes and of plasmid replicons, coinciding with a decline in the number of intrinsic resistance genes from Enterobacteriaceae, as well as with a reduction in the relative abundance of Firmicutes and Proteobacteria after treatment. These taxons comprise bacterial pathogens, including those belonging to the ESKAPE group, which encompasses bacteria with the highest risk of acquiring antibiotic resistance, being the most relevant hosts of resistance genes acquired through horizontal gene transfer. Our results support that wastewater treatment efficiently removes the hosts of antibiotic resistance genes and, consequently, the harboured antibiotic resistance genes. Principal component analysis indicates that the resistome and the bacterial composition clustered together in influent samples, while did not cluster in final effluent samples. Our results suggest that wastewater treatment mitigates the environmental dissemination of urban resistome, through the removal of the hosts harbouring mobile resistance genes.

Most studies on bacterial virulence focus on the pathogen itself. However, it is important to recall that the in-host behavior and the virulence of bacterial pathogens constitute a complex situation that depends on both the microorganisms and the infected host. While healthy people (the community) is infected by classical pathogenic microorganisms, able to cope with the anti-infection defenses of the host, in the case of people with basal diseases, debilitated or immunodepressed, the range of pathogens able to cause infection is wider and includes the so-named opportunistic pathogens, which lack the inherent ability to cause disease in healthy hosts and rarely produce infections in the community. Some of the most relevant opportunistic pathogens, as Stenotrophomonas maltophilia, have an environmental origin and, in occasions present interesting biotechnological properties. Consequently, it is important knowing whether S. maltophilia isolates recovered from infections constitute a specific phylogenetic branch that has evolved towards acquiring a virulent phenotype as it happens in the case of classical pathogens or rather, any member of this bacterial species is capable of producing infection and its pathogenic behavior is mainly a consequence of the host situation. To address this question, we analyzed a set of environmental and clinical S. maltophilia strains. Our results indicate that this opportunistic pathogen presents a large core genome and that the distribution of genes in general and of known virulence determinants in particular, is similar among environmental and clinical isolates. The majority of genes not belonging to the S. maltophilia core genome are present in just one or two of the analyzed strains. This indicates that, more than speciation into different lineages (virulent and environmental), the evolution of S. maltophilia is based in the strain-specific acquisition of genes, likely involved in the adaptation of this bacterial species to different microniches. In addition, both environmental and clinical isolates present low susceptibility to several antimicrobials. Altogether our results support that S. maltophilia does not present a specific evolutionary branch towards virulence and most likely infection is mainly the consequence of the impaired anti-infective response of the infected patients.

Stenotrophomonas maltophilia is an opportunistic pathogen with an environmental origin, and it is an increasingly relevant cause of nosocomial infections. Here we present the whole-genome sequence of S. maltophilia strain D457, a clinical isolate that is being used as a model for studying antibiotic resistance in this bacterial species.

Antimicrobial resistance is a persistent problem in the public health sphere. However, recent attempts to find effective substitutes to combat infections have been directed at identifying natural antimicrobial peptides in order to circumvent resistance to commercial antibiotics. This study describes the development of synthetic peptides with antimicrobial activity, created in silico by site-directed mutation modeling using wild-type peptides as scaffolds for these mutations. Fragments of antimicrobial peptides were used for modeling with molecular modeling computational tools. To analyze these peptides, a decision tree model, which indicated the action range of peptides on the types of microorganisms on which they can exercise biological activity, was created. The decision tree model was processed using physicochemistry properties from known antimicrobial peptides available at the Antimicrobial Peptide Database (APD). The two most promising peptides were synthesized, and antimicrobial assays showed inhibitory activity against Gram-positive and Gram-negative bacteria. Colossomin C and colossomin D were the most inhibitory peptides at 5 μg/ml against Staphylococcus aureus and Escherichia coli . The methods described in this work and the results obtained are useful for the identification and development of new compounds with antimicrobial activity through the use of computational tools.

In this study we isolated 109 Enterococcus faecalis from chicken faecal samples in 6 provinces of China to investigate the prevalence and transmission mechanism of the bacitracin resistance locus bcrABDR in E. faecalis. Thirty-seven bcrABDR-positive E. faecalis were detected with 26 different PFGE clusters. The MLST of 14 positive strains belonged to ST16 and we also detected three new sequence types. S1-PFGE analysis indicated that the locus was located on plasmids presenting different sizes, with the most prevalent size being ~50 kb (13/37). Sequence analysis revealed that 17 out of the 37 strains harbored a 5400-bp central region, in which locus bcrABDR was bracketed by two ISEnfa1 of the same orientation. Two types of bcrABDR alleles, differing in around 10% of their sequence were found. In silico analysis showed that bcrABDR is present in a variety of bacteria including the chicken commensal Enterococcus cecorum. Our results indicate that the use of bacitracin at farms might trigger the emergence and spread of the bacitracin resistance determinant bcrABDR among human bacterial pathogens. The finding of bcrABDR in the chicken commensal E. cecorum indicates that farm animals microbiota can be an important reservoir of resistance genes with relevance for human health.