Metagenomics has rapidly advanced our inventory and appreciation of the genetic potential inherent to the gut microbiome. However it is widely accepted that two key constraints to further genetic dissection of the gut microbiota and host-microbe interactions have been our inability to recover new isolates from the human gut, and the paucity of genetically tractable gut microbes. To address this challenge we developed a modular RP4 mobilisable recombinant vector system and an approach termed metaparental mating to support the rapid and directed isolation of genetically tractable fastidious gut bacteria. Using this approach we isolated transconjugants affiliated with Clostridium cluster IV (Faecalibacterium and Oscillibacter spp.), Clostridium cluster XI (Anaerococcus) and Clostridium XIVa (Blautia spp.) and group 2 ruminococci amongst others, and demonstrated that the recombinant vectors were stably maintained in their recipient hosts. By a similar approach we constructed fluorescently labelled bacterial transconjugants affiliated with Clostridium cluster IV (including Flavonifractor and Pseudoflavonifractor spp.), Clostridium XIVa (Blautia spp.) and Clostridium cluster XVIII (Clostridium ramosum) that expressed a flavin mononucleotide-based reporter gene (evoglow-C-Bs2). Our approach will advance the integration of bacterial genetics with metagenomics and realize new directions to support a more mechanistic dissection of host-microbe associations relevant to human health and disease.

BackgroundPseudomonas aeruginosa is an opportunistic pathogen and a major cause of infections. Widespread resistance in human infections are increasing the use of last resort antimicrobials such as polymyxins. However, these have been used for decades in veterinary medicine. Companion animals are an understudied source of antimicrobial resistant P. aeruginosa isolates. This study evaluated the susceptibility of P. aeruginosa veterinary isolates to polymyxins to determine whether the veterinary niche represents a potential reservoir of resistance genes for pathogenic bacteria in both animals and humans.Methods and resultsClinical P. aeruginosa isolates (n=24) from UK companion animals were compared for antimicrobial susceptibility to a panel of human-associated isolates (n=37). Minimum inhibitory concentration (MIC) values for polymyxin B and colistin in the companion animals was significantly higher than in human isolates (P=0.033 and P=0.013, respectively). Genotyping revealed that the veterinary isolates were spread throughout the P. aeruginosa population, with shared array types from human infections such as keratitis and respiratory infections, suggesting the potential for zoonotic transmission. Whole genome sequencing revealed mutations in genes associated with polymyxin resistance and other antimicrobial resistance-related genes.ConclusionThe high levels of resistance to polymyxin shown here, along with genetic similarities between some human and animal isolates, together suggest a need for sustained surveillance of this veterinary niche as a potential reservoir for resistant, clinically relevant bacteria in both animals and humans.

While it is now accepted that the gut microbiota contribute to the genotype-environment-lifestyle interactions triggering inflammatory bowel disease (IBD) episodes, efforts to identify the pathogen(s) that cause these diseases have met with limited success. The advent of culture-independent techniques for characterizing the structure and/or function of microbial communities (hereafter referred to as metagenomics) has provided new insights into the events associated with the onset, remission and recurrence of IBD. A large number of observational and/or case-control studies of IBD patients have confirmed substantive changes in gut bacterial profiles (dysbiosis) associated with disease. These types of studies have been augmented by new profiling approaches that support the identification of more ‘colitogenic' bacteria from numerically predominant taxa. Evidence of alterations in lesser abundant taxa such as the methanogenic archaea, to favor types that are more immunogenic, has also been forthcoming. Several recent longitudinal studies of patients with Crohn's disease have produced additional insights, including evidence for the role of ‘anti-inflammatory' microbiota in providing a protective effect and/or promoting remission. In summation, the implications of dysbiosis and restoration of a ‘healthy microbiota' in IBD patients requires definition beyond a taxonomic assessment of the changes in the gut microbiota during disease course. The available evidence does suggest that specific members of the gut microbiota can contribute either pro- or anti-inflammatory effects, and their ecological fitness in the large bowel affects the onset and recurrence of IBD. While metagenomics and related approaches offer the potential to provide novel and important insights into these microbiota and thereby the pathophysiology of IBD, we also need to better understand factors affecting the ecological fitness of these microbes, if new treatment of IBD patients are to be delivered.

Pseudomonas aeruginosa undergoes diversification during infection of the cystic fibrosis (CF) lung. Understanding these changes requires model systems that capture the complexity of the CF lung environment. We previously identified loss-of-function mutations in the twocomponent regulatory system sensor kinase gene pmrB, in P. aeruginosa from CF and from experimental infection of mice. Here, we demonstrate that whilst such mutations lower in vitro MICs for multiple antimicrobial classes, this is not reflected in increased antibiotic susceptibility in vivo. Loss of PmrB impairs aminoarabinose modification of lipopolysaccharide, increasing the negative charge of the outer membrane and promoting uptake of cationic antimicrobials. However, in vivo, this can be offset by increased membrane binding of other positively charged molecules present in lungs. The polyamine spermidine readily coats the surface of PmrB-deficient P. aeruginosa, reducing susceptibility to antibiotics that rely on charge differences to bind the outer membrane and increasing biofilm formation. Spermidine is elevated in lungs during P. aeruginosa infection in mice and during episodes of antimicrobial treatment in people with CF. These findings highlight the need to study antimicrobial resistance under clinically relevant environmental conditions. Microbial mutations carrying fitness costs in vitro may be advantageous during infection, where host resources can be utilised.