A megaplasmid family driving dissemination of multidrug resistance in Pseudomonas

Evolution of Subfamily I.1 Lipases in Pseudomonas aeruginosa

The gram-negative Pseudomonas aeruginosa is an opportunistic human pathogen that contains two different types of strains: the "classical" and the "outlier". In the "classical" strain, its bacterial subfamily I.1 lipases, such as LipA and LipC in P. aeruginosa PAO1, play critical roles in its pathogenicity. However, less is known about the subfamily I.1 lipases in the "outlier" strain, nor the evolution paths of those lipases in both types of P. aeruginosa strains. Our genome-scale investigation on I.1 lipases across different bacterial strains demonstrates the presence of one LipA-like and one new type of I.1 lipase (LipC2) in those "outlier" strains. The related genomic islands analyses further suggest that the LipC counterpart gene in the "outlier" strain was lost by gene truncation. In addition, the evolutionary analyses also indicates the horizontal LipC2 gene transfer from other gammaproteobacterial species, as well as the horizontal LipA gene transfer between two different phyla, both suggesting that the gene transfer of bacterial I.1 lipases might occur in different taxonomical levels. Our results not only provide an evidence to understand the pathogenicity among different P. aeruginosa strains, but add to the knowledge of I.1 lipase evolution in bacteria.

The Gut Microbiome as a Reservoir for Antimicrobial Resistance

This review will consider the gut as a reservoir for antimicrobial resistance, colonization resistance, and how disruption of the microbiome can lead to colonization by pathogenic organisms. There is a focus on the gut as a reservoir for β-lactam and plasmid-mediated quinolone resistance. Finally, the role of functional metagenomics and long-read sequencing technologies to detect and understand antimicrobial resistance genes within the gut microbiome is discussed, along with the potential for future microbiome-directed methods to detect and prevent infection.

Pseudomonas aeruginosa: a clinical and genomics update

Antimicrobial resistance (AMR) has become a global medical priority that needs urgent resolution. Pseudomonas aeruginosa is a versatile, adaptable bacterial species with widespread environmental occurrence, strong medical relevance, a diverse set of virulence genes and a multitude of intrinsic and possibly acquired antibiotic resistance traits. P. aeruginosa causes a wide variety of infections and has an epidemic-clonal population structure. Several of its dominant global clones have collected a wide variety of resistance genes rendering them multi-drug resistant (MDR) and particularly threatening groups of vulnerable individuals including surgical patients, immunocompromised patients, Caucasians suffering from cystic fibrosis (CF) and more. AMR and MDR especially are particularly problematic in P. aeruginosa significantly complicating successful antibiotic treatment. In addition, antimicrobial susceptibility testing (AST) of P. aeruginosa can be cumbersome due to its slow growth or the massive production of exopolysaccharides and other extracellular compounds. For that reason, phenotypic AST is progressively challenged by genotypic methods using whole genome sequences (WGS) and large-scale phenotype databases as a framework of reference. We here summarize the state of affairs and the quality level of WGS-based AST for P. aeruginosa mostly from clinical origin.

CRISPR-Cas systems restrict horizontal gene transfer in Pseudomonas aeruginosa

CRISPR-Cas systems provide bacteria and archaea with an adaptive immune system that targets foreign DNA. However, the xenogenic nature of immunity provided by CRISPR-Cas raises the possibility that these systems may constrain horizontal gene transfer. Here we test this hypothesis in the opportunistic pathogen Pseudomonas aeruginosa, which has emerged as an important model system for understanding CRISPR-Cas function. Across the diversity of P. aeruginosa, active CRISPR-Cas systems are associated with smaller genomes and higher GC content, suggesting that CRISPR-Cas inhibits the acquisition of foreign DNA. Although phage is the major target of CRISPR-Cas spacers, more than 80% of isolates with an active CRISPR-Cas system have spacers that target integrative conjugative elements (ICE) or the conserved conjugative transfer machinery used by plasmids and ICE. Consistent with these results, genomes containing active CRISPR-Cas systems harbour a lower abundance of both prophage and ICE. Crucially, spacers in genomes with active CRISPR-Cas systems map to ICE and phage that are integrated into the chromosomes of closely related genomes lacking CRISPR-Cas immunity. We propose that CRISPR-Cas acts as an important constraint to horizontal gene transfer, and the evolutionary mechanisms that ensure its maintenance or drive its loss are key to the ability of this pathogen to adapt to new niches and stressors.

The Building Blocks of Antimicrobial Resistance in Pseudomonas aeruginosa: Implications for Current Resistance-Breaking Therapies

P. aeruginosa is classified as a priority one pathogen by the World Health Organisation, and new drugs are urgently needed, due to the emergence of multidrug-resistant (MDR) strains. Antimicrobial-resistant nosocomial pathogens such as P. aeruginosa pose unwavering and increasing threats. Antimicrobial stewardship has been a challenge during the COVID-19 pandemic, with a majority of those hospitalized with SARS-CoV2 infection given antibiotics as a safeguard against secondary bacterial infection. This increased usage, along with increased handling of sanitizers and disinfectants globally, may further accelerate the development and spread of cross-resistance to antibiotics. In addition, P. aeruginosa is the primary causative agent of morbidity and mortality in people with the life-shortening genetic disease cystic fibrosis (CF). Prolonged periods of selective pressure, associated with extended antibiotic treatment and the actions of host immune effectors, results in widespread adaptive and acquired resistance in P. aeruginosa found colonizing the lungs of people with CF. This review discusses the arsenal of resistance mechanisms utilized by P. aeruginosa, how these operate under high-stress environments such as the CF lung and how their interconnectedness can result in resistance to multiple antibiotic classes. Intrinsic, adaptive and acquired resistance mechanisms will be described, with a focus on how each layer of resistance can serve as a building block, contributing to multi-tiered resistance to antimicrobial activity. Recent progress in the development of anti-resistance adjuvant therapies, targeting one or more of these building blocks, should lead to novel strategies for combatting multidrug resistant P. aeruginosa. Anti-resistance adjuvant therapy holds great promise, not least because resistance against such therapeutics is predicted to be rare. The non-bactericidal nature of anti-resistance adjuvants reduce the selective pressures that drive resistance. Anti-resistance adjuvant therapy may also be advantageous in facilitating efficacious use of traditional antimicrobials, through enhanced penetration of the antibiotic into the bacterial cell. Promising anti-resistance adjuvant therapeutics and targets will be described, and key remaining challenges highlighted. As antimicrobial stewardship becomes more challenging in an era of emerging and re-emerging infectious diseases and global conflict, innovation in antibiotic adjuvant therapy can play an important role in extending the shelf-life of our existing antimicrobial therapeutic agents.

Disinfectant resistance in bacteria: Mechanisms, spread, and resolution strategies

Disinfectants are widely acknowledged for removing microorganisms from the surface of the objects and transmission media. However, the emergence of disinfectant resistance has become a severe threat to the safety of life and health and the rational allocation of resources due to the reduced disinfectant effectiveness. The horizontal gene transfer (HGT) of disinfectant resistance genes has also expanded the resistant flora, making the situation worse. This review focused on the resistance mechanisms of disinfectant resistant bacteria on biofilms, cell membrane permeability, efflux pumps, degradable enzymes, and disinfectant targets. Efflux can be the fastest and most effective resistance mechanism for bacteria to respond to stress. The qac genes, located on some plasmids which can transmit resistance through conjugative transfer, are the most commonly reported in the study of disinfectant resistance genes. Whether the qac genes can be transferred through transformation or transduction is still unclear. Studying the factors affecting the resistance of bacteria to disinfectants can find breakthrough methods to more adequately deal with the problem of reduced disinfectant effectiveness. It has been confirmed that the interaction of probiotics and bacteria or the addition of 4-oxazolidinone can inhibit the formation of biofilms. Chemicals such as eugenol and indole derivatives can increase bacterial sensitivity by reducing the expression of efflux pumps. The role of these findings in anti-disinfectant resistance has proved invaluable.

Novel Lytic Phages Protect Cells and Mice against Pseudomonas aeruginosa Infection

With the fast emergence of serious antibiotic resistance and the lagged discovery of novel antibacterial drugs, phage therapy for pathogenic bacterial infections has acquired great attention in the clinics. However, development of therapeutic phages also faces tough challenges, such as laborious screening and time to generate effective phage drugs since each phage may only lyse a narrow scope of bacterial strains. Identifying highly effective phages with broad host ranges is crucial for improving phage therapy. Here, we isolated and characterized several lytic phages from various environments specific for Pseudomonas aeruginosa by testing their growth, invasion, host ranges, and potential for killing targeted bacteria. Importantly, we identified several therapeutic phages (HX1, PPY9, and TH15) with broad host ranges to lyse laboratory strains and clinical isolates of P. aeruginosa with multi-drug resistance (MDR) both in vitro and in mouse models. In addition, we analyzed critical genetic traits related to the high-level broad host coverages by genome sequencing and subsequent computational analysis against known phages. Collectively, our findings establish that these novel phages may have potential for further development as therapeutic options for patients who fail to respond to conventional treatments.IMPORTANCE Novel lytic phages isolated from various environmental settings were systematically characterized for their critical genetic traits, morphology structures, host ranges against laboratory strains and clinical multi-drug resistant (MDR) Pseudomonas aeruginosa, and antibacterial capacity both in vitro and in mouse models. First, we characterized the genetic traits and compared with other existing phages. Furthermore, we utilized acute pneumonia induced by laboratorial strain PAO1, and W19, an MDR clinical isolate and chronic pneumonia by agar beads laden with FDR1, a mucoid phenotype strain isolated from the sputum of a cystic fibrosis (CF) patient. Consequently, we found that these phages not only suppress bacteria in vitro but also significantly reduce the infection symptom and disease progression in vivo, including lowered bug burdens, inflammatory responses and lung injury in mice, suggesting that they may be further developed as therapeutic agents against MDR P. aeruginosa.

Epidemic Territorial Spread of IncP-2-Type VIM-2 Carbapenemase-Encoding Megaplasmids in Nosocomial Pseudomonas aeruginosa Populations

In 2003 to 2004, the first five VIM-2 metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa (MPPA) isolates with an In4-like integron, In461 (aadB-blaVIM-2-aadA6), on conjugative plasmids were identified in three hospitals in Poland. In 2005 to 2015, MPPA expanded much in the country, and as many as 80 isolates in a collection of 454 MPPA (∼18%) had In461, one of the two most common MBL-encoding integrons. The organisms occurred in 49 hospitals in 33 cities of 11/16 main administrative regions. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) classified them into 55 pulsotypes and 35 sequence types (STs), respectively, revealing their remarkable genetic diversity overall, with only a few small clonal clusters. S1 nuclease/hybridization assays and mating of 63 representative isolates showed that ∼85% of these had large In461-carrying plasmids, ∼350 to 550 kb, usually self-transmitting with high efficiency (∼10-1 to 10-2 per donor cell). The plasmids from 19 isolates were sequenced and subjected to structural and single-nucleotide-polymorphism (SNP)-based phylogenetic analysis. These formed a subgroup within a family of IncP-2-type megaplasmids, observed worldwide in pseudomonads from various environments and conferring resistance/tolerance to multiple stress factors, including antibiotics. Their microdiversity in Poland arose mainly from acquisition of different accessory fragments, as well as new resistance genes and multiplication of these. Short-read sequence and/or PCR mapping confirmed the In461-carrying plasmids in the remaining isolates to be the IncP-2 types. The study demonstrated a large-scale epidemic spread of multidrug resistance plasmids in P. aeruginosa populations, creating an epidemiological threat. It contributes to the knowledge on IncP-2 types, which are interesting research objects in resistance epidemiology, environmental microbiology, and biotechnology.

Approaches for characterizing and tracking hospital-associated multidrug-resistant bacteria

Hospital-associated infections are a major concern for global public health. Infections with antibiotic-resistant pathogens can cause empiric treatment failure, and for infections with multidrug-resistant bacteria which can overcome antibiotics of "last resort" there exists no alternative treatments. Despite extensive sanitization protocols, the hospital environment is a potent reservoir and vector of antibiotic-resistant organisms. Pathogens can persist on hospital surfaces and plumbing for months to years, acquire new antibiotic resistance genes by horizontal gene transfer, and initiate outbreaks of hospital-associated infections by spreading to patients via healthcare workers and visitors. Advancements in next-generation sequencing of bacterial genomes and metagenomes have expanded our ability to (1) identify species and track distinct strains, (2) comprehensively profile antibiotic resistance genes, and (3) resolve the mobile elements that facilitate intra- and intercellular gene transfer. This information can, in turn, be used to characterize the population dynamics of hospital-associated microbiota, track outbreaks to their environmental reservoirs, and inform future interventions. This review provides a detailed overview of the approaches and bioinformatic tools available to study isolates and metagenomes of hospital-associated bacteria, and their multi-layered networks of transmission.

Tn6603, a Carrier of Tn5053 Family Transposons, Occurs in the Chromosome and in a Genomic Island of Pseudomonas aeruginosa Clinical Strains

Transposons of the Pseudomonasaeruginosa accessory gene pool contribute to phenotype and to genome plasticity. We studied local P. aeruginosa strains to ascertain the encroachment of mer-type res site hunter transposons into clinical settings and their associations with other functional modules. Five different Tn5053 family transposons were detected, all chromosomal. Some were solitary elements; one was in res of Tn1013^#, a relative of a reported carrier of int-type res site hunters (class 1 integrons), but most were in res of Tn6603, a new Tn501-related transposon of unknown phenotype. Most of the Tn6603::Tn elements, and some Tn6603 and Tn6603::Tn elements found in GenBank sequences, were at identical sites in an hypothetical gene of P. aeruginosa genomic island PAGI-5v. The island in clonally differing strains was at either of two tRNA^Lys loci, suggesting lateral transfer to these sites. This observation is consistent with the membership of the prototype PAGI-5 island to the ICE family of mobile genetic elements. Additionally, the res site hunters in the nested transposons occupied different positions in the Tn6603 carrier. This suggested independent insertion events on five occasions at least. Tn5053 family members that were mer-/tni-defective were found in Tn6603- and Tn501-like carriers in GenBank sequences of non-clinical Pseudomonas spp. The transposition events in these cases presumably utilized tni functions in trans, as can occur with class 1 integrons. We suggest that in the clinical context, P. aeruginosa strains that carry Tn6603 alone or in PAGI-5v can serve to disseminate functional res site hunters; these in turn can provide the requisite trans-acting tni functions to assist in the dissemination of class 1 integrons, and hence of their associated antibiotic resistance determinants.

A Novel Family of Acinetobacter Mega-Plasmids Are Disseminating Multi-Drug Resistance Across the Globe While Acquiring Location-Specific Accessory Genes

Acinetobacter species are emerging as major nosocomial pathogens, aided by their ability to acquire resistance to all classes of antibiotics. A key factor leading to their multi-drug resistance phenotypes is the acquisition of a wide variety of mobile genetic elements, particularly large conjugative plasmids. Here, we characterize a family of 21 multi-drug resistance mega-plasmids in 11 different Acinetobacter species isolated from various locations across the globe. The plasmid family exhibits a highly dynamic and diverse accessory genome, including 221 antibiotic resistance genes (ARGs) that confer resistance to 13 classes of antibiotics. We show that plasmids isolated within the same geographic region are often evolutionarily divergent members of this family based on their core-genome, yet they exhibit a more similar accessory genome. Individual plasmids, therefore, can disseminate to different locations around the globe, where they then appear to acquire diverse sets of accessory genes from their local surroundings. Further, we show that plasmids from several geographic regions were enriched with location-specific functional traits. Together, our findings show that these mega-plasmids can transmit across species boundaries, have the capacity for global dissemination, can accumulate a diverse suite of location-specific accessory genes, and can confer multi-drug resistance phenotypes of significant concern for human health. We therefore highlight this previously undescribed plasmid family as a serious threat to healthcare systems worldwide. These findings also add to the growing concern that mega-plasmids are key disseminators of antibiotic resistance and require global surveillance.

Identification of the Pseudomonas aeruginosa O17 and O15 O-Specific Antigen Biosynthesis Loci Reveals an ABC Transporter-Dependent Synthesis Pathway and Mechanisms of Genetic Diversity

Many bacterial cell surface glycans, such as the O antigen component of lipopolysaccharide (LPS), are produced via the so-called Wzx/Wzy- or ABC transporter-dependent pathways. O antigens are highly diverse polysaccharides that protect bacteria from their environment and engage in important host-pathogen interactions. The specific structure and composition of O antigens are the basis of classifying bacteria into O serotypes. In the opportunistic pathogen Pseudomonas aeruginosa, there are currently 20 known O-specific antigen (OSA) structures. The clusters of genes responsible for 18 of these O antigens have been identified, all of which follow the Wzx/Wzy-dependent pathway and are located at a common locus. In this study, we located the two unidentified O antigen biosynthesis clusters responsible for the synthesis of the O15 and the O17 OSA structures by analyzing published whole-genome sequence data. Intriguingly, these clusters were found outside the conserved OSA biosynthesis locus and were likely acquired through multiple horizontal gene transfer events. Based on data from knockout and overexpression studies, we determined that the synthesis of these O antigens follows an ABC transporter-dependent rather than a Wzx/Wzy-dependent pathway. In addition, we collected evidence to show that the O15 and O17 polysaccharide chain lengths are regulated by molecular rulers with distinct and variable domain architectures. The findings in this report are critical for a comprehensive understanding of O antigen biosynthesis in P. aeruginosa and provide a framework for future studies.IMPORTANCE P. aeruginosa is a problematic opportunistic pathogen that causes diseases in those with compromised host defenses, such as those suffering from cystic fibrosis. This bacterium produces a number of virulence factors, including a serotype-specific O antigen. Here, we identified and characterized the gene clusters that produce the O15 and O17 O antigens and show that they utilize a pathway for synthesis that is distinct from that of the 18 other known serotypes. We also provide evidence that these clusters have acquired mutations in specific biosynthesis genes and have undergone extensive horizontal gene transfer within the P. aeruginosa population. These findings expand on our understanding of O antigen biosynthesis in Gram-negative bacteria and the mechanisms that drive O antigen diversity.

oprC Impairs Host Defense by Increasing the Quorum-Sensing-Mediated Virulence of Pseudomonas aeruginosa

Pseudomonas aeruginosa, found widely in the wild, causes infections in the lungs and several other organs in healthy people but more often in immunocompromised individuals. P. aeruginosa infection leads to inflammasome assembly, pyroptosis, and cytokine release in the host. OprC is one of the bacterial porins abundant in the outer membrane vesicles responsible for channel-forming and copper binding. Recent research has revealed that OprC transports copper, an essential trace element involved in various physiological processes, into bacteria during copper deficiency. Here, we found that oprC deletion severely impaired bacterial motility and quorum-sensing systems, as well as lowered levels of lipopolysaccharide and pyocyanin in P. aeruginosa. In addition, oprC deficiency impeded the stimulation of TLR2 and TLR4 and inflammasome activation, resulting in decreases in proinflammatory cytokines and improved disease phenotypes, such as attenuated bacterial loads, lowered lung barrier damage, and longer mouse survival. Moreover, oprC deficiency significantly alleviated pyroptosis in macrophages. Mechanistically, oprC gene may impact quorum-sensing systems in P. aeruginosa to alter pyroptosis and inflammatory responses in cells and mice through the STAT3/NF-κB signaling pathway. Our findings characterize OprC as a critical virulence regulator, providing the groundwork for further dissection of the pathogenic mechanism of OprC as a potential therapeutic target of P. aeruginosa.

Current Knowledge and Future Directions in Developing Strategies to Combat Pseudomonas aeruginosa Infection

In the face of growing antimicrobial resistance, there is an urgent need for the development of effective strategies to target Pseudomonas aeruginosa. This metabolically versatile bacterium can cause a wide range of severe opportunistic infections in patients with serious underlying medical conditions, such as those with burns, surgical wounds or people with cystic fibrosis. Many of the key adaptations that arise in this organism during infection are centered on core metabolism and virulence factor synthesis. Interfering with these processes may provide a new strategy to combat infection which could be combined with conventional antibiotics. This review will provide an overview of the most recent work that has advanced our understanding of P. aeruginosa infection. Strategies that exploit this recent knowledge to combat infection will be highlighted alongside potential alternative therapeutic options and their limitations.