Environmental reservoirs for exoS+ and exoU+ strains of Pseudomonas aeruginosa

Urinary tract infections and catheter-associated urinary tract infections caused by Pseudomonas aeruginosa

SUMMARYUrinary tract infection (UTI) is one of the most common infections in otherwise healthy individuals. UTI is also common in healthcare settings where patients often require urinary catheters to alleviate urinary retention. The placement of a urinary catheter often leads to catheter-associated urinary tract infection (CAUTI) caused by a broad range of opportunistic pathogens, commonly referred to as ESKAPE (Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, and Enterobacter) pathogens. Our understanding of CAUTI is complicated by the differences in pathogens, in initial microbial load, changes that occur due to the duration of catheterization, and the relationship between infection (colonization) and disease symptoms. To advance our understanding of CAUTI, we reviewed UTI and CAUTI caused by Pseudomonas aeruginosa which is unique in that it is not commonly found associated with human microbiomes. For this reason, the ability of P. aeruginosa to cause UTI and CAUTI requires the introduction of the bacteria to the bladder from catheterization. Once in the host, the virulence factors used by P. aeruginosa in these infections remain an area of ongoing research. In this review, we will discuss studies that focus on P. aeruginosa UTI and CAUTI to better understand the infection dynamics and outcome in clinical settings, virulence factors associated with P. aeruginosa isolated from the urinary tract, and animal studies to test which bacterial factors are required for this infection. Understanding how P. aeruginosa can cause UTI and CAUTI can provide an understanding of how these infections initiate and progress and may provide possible strategies to limit these infections.

Bloodstream infections: mechanisms of pathogenesis and opportunities for intervention

Bloodstream infections (BSIs) are common in hospitals, often life-threatening and increasing in prevalence. Microorganisms in the blood are usually rapidly cleared by the immune system and filtering organs but, in some cases, they can cause an acute infection and trigger sepsis, a systemic response to infection that leads to circulatory collapse, multiorgan dysfunction and death. Most BSIs are caused by bacteria, although fungi also contribute to a substantial portion of cases. Escherichia coli, Staphylococcus aureus, coagulase-negative Staphylococcus, Klebsiella pneumoniae and Candida albicans are leading causes of BSIs, although their prevalence depends on patient demographics and geographical region. Each species is equipped with unique factors that aid in the colonization of initial sites and dissemination and survival in the blood, and these factors represent potential opportunities for interventions. As many pathogens become increasingly resistant to antimicrobials, new approaches to diagnose and treat BSIs at all stages of infection are urgently needed. In this Review, we explore the prevalence of major BSI pathogens, prominent mechanisms of BSI pathogenesis, opportunities for prevention and diagnosis, and treatment options.

ESKAPE pathogens: antimicrobial resistance, epidemiology, clinical impact and therapeutics

The rise of antibiotic resistance and a dwindling antimicrobial pipeline have been recognized as emerging threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria for which effective therapies were rapidly needed. Now, entering the third decade of the twenty-first century, and despite the introduction of several new antibiotics and antibiotic adjuvants, such as novel β-lactamase inhibitors, these organisms continue to represent major therapeutic challenges. These bacteria share several key biological features, including adaptations for survival in the modern health-care setting, diverse methods for acquiring resistance determinants and the dissemination of successful high-risk clones around the world. With the advent of next-generation sequencing, novel tools to track and combat the spread of these organisms have rapidly evolved, as well as renewed interest in non-traditional antibiotic approaches. In this Review, we explore the current epidemiology and clinical impact of this important group of bacterial pathogens and discuss relevant mechanisms of resistance to recently introduced antibiotics that affect their use in clinical settings. Furthermore, we discuss emerging therapeutic strategies needed for effective patient care in the era of widespread antimicrobial resistance.

Genomic Insights into Vietnamese Extended-Spectrum β-Lactamase-9-Producing Extensively Drug-Resistant Pseudomonas aeruginosa Isolates Belonging to the High-Risk Clone ST357 Obtained from Bulgarian Intensive Care Unit Patients

Extensively drug-resistant P. aeruginosa (XDR-PA) has been highlighted as a serious public health threat. The present study aimed to explore the genomic characteristics of two Vietnamese extended-spectrum β-lactamase-9 (VEB-9)-producing XDR-PA isolates from Bulgaria in comparison to all blaVEB-9-positive strains with available genomes. The isolates designated Pae51 and Pae52 were obtained from tracheobronchial aspirates of intensive care unit (ICU) patients. Antimicrobial susceptibility testing, whole-genome sequencing, RT-qPCR, and phylogenomic analysis were performed. Pae51 and Pae52 were resistant to most antipseudomonal β-lactams including carbapenems, aminoglycosides, and fluoroquinolones but remained susceptible to colistin and cefiderocol. Numerous resistance determinants were detected: blaVEB-9, blaPDC-3, blaOXA-10, blaOXA-50, aac(6')-II, ant(2″)-Ia, ant(3″)-IIa, aph(3')-IIb, cprP, catB7, dfrB2, sul1, fosA, and tet(A). Both isolates carried complex integrons with blaVEB-9 and tet(A) embedded next to the conservative 3' end sequences. A variety of virulence factors were also identified, including the type III secretion system exotoxin U. Pae51 and Pae52 differed by only four SNPs and belonged to the high-risk clone ST357. To our knowledge, this is the first report of blaVEB-9-positive XDR-PA isolates in Bulgaria presenting a detailed genomic analysis. The development of novel antimicrobial strategies for such pathogens should be an essential part of infection control stewardship practices in ICU wards.

Pseudomonas aeruginosa from river water: antimicrobial resistance, virulence and molecular typing

Pseudomonas aeruginosa isolates were recovered from surface river water samples in La Rioja region (Spain) to characterise their antibiotic resistance, molecular typing and virulence mechanisms. Fifty-two P. aeruginosa isolates were isolated from 15 different water samples (45.4%) and belonged to 23 different pulsed-field electrophoresis (PFGE) patterns. All isolates were susceptible to all antibiotics tested, except one carbapenem-resistant P. aeruginosa that showed a premature stop codon in OprD porin. Twenty-two sequence types (STs) (six new ones) were detected among 29 selected P. aeruginosa (one strain with a different PFGE pattern per sample), with ST274 (14%) being the most frequent one. O:6 and O:3 were the predominant serotypes (31%). Seven virulotypes were detected, being 59% exoS-exoY-exoT-exoA-lasA-lasB-lasI-lasR-rhlAB-rhlI-rhlR-aprA-positive P. aeruginosa. It is noteworthy that the exlA gene was identified in three strains (10.3%), and the exoU gene in seven (24.1%), exoS in 18 (62.1%), and both exoS and exoU genes in one strain. High motility ranges were found in these strains. Twenty-seven per cent of strains produced more biofilm biomass, 90% more pyorubin, 83% more pyocyanin and 65.5% more than twice the elastase activity compared with the PAO1 strain. These results highlight the importance of rivers as temporary reservoirs and sources of P. aeruginosa transmission, and show the importance of their epidemiological surveillance in the environment.

Diversity loss from multiple interacting disturbances is regime-dependent

Anthropogenic activities expose many ecosystems to multiple novel disturbances simultaneously. Despite this, how biodiversity responds to simultaneous disturbances remains unclear, with conflicting empirical results on their interactive effects. Here, we experimentally test how one disturbance (an invasive species) affects the diversity of a community over multiple levels of another disturbance regime (pulse mortality). Specifically, we invade stably coexisting bacterial communities under four different pulse frequencies, and compare their final resident diversity to uninvaded communities under the same pulse mortality regimes. Our experiment shows that the disturbances synergistically interact, such that the invader significantly reduces resident diversity at high pulse frequency, but not at low. This work therefore highlights the need to study simultaneous disturbance effects over multiple disturbance regimes as well as to carefully document unmanipulated disturbances, and may help explain the conflicting results seen in previous multiple-disturbance work.

Pseudomonas spp. in Canine Otitis Externa

Canine otitis externa (OE) is a commonly diagnosed condition seen in veterinary practice worldwide. In this review, we discuss the mechanisms of the disease, with a particular focus on the biological characteristics of Pseudomonas aeruginosa and the impact that antibiotic resistance has on successful recovery from OE. We also consider potential alternatives to antimicrobial chemotherapy for the treatment of recalcitrant infections. P. aeruginosa is not a typical constituent of the canine ear microbiota, but is frequently isolated from cases of chronic OE, and the nature of this pathogen often makes treatment difficult. Biofilm formation is identified in 40-95% of P. aeruginosa from cases of OE and intrinsic and acquired antibiotic resistance, especially resistance to clinically important antibiotics, highlights the need for alternative treatments. The role of other virulence factors in OE remains relatively unexplored and further work is needed. The studies described in this work highlight several potential alternative treatments, including the use of bacteriophages. This review provides a summary of the aetiology of OE with particular reference to the dysbiosis that leads to colonisation by P. aeruginosa and highlights the need for novel treatments for the future management of P. aeruginosa otitis.

The effect of metal remediation on the virulence and antimicrobial resistance of the opportunistic pathogen Pseudomonas aeruginosa

Anthropogenic metal pollution can result in co-selection for antibiotic resistance and potentially select for increased virulence in bacterial pathogens. Metal-polluted environments can select for the increased production of siderophore molecules to detoxify non-ferrous metals. However, these same molecules also aid the uptake of ferric iron, a limiting factor for within-host pathogen growth, and are consequently a virulence factor. Anthropogenic methods to remediate environmental metal contamination commonly involve amendment with lime-containing materials. However, whether this reduces in situ co-selection for antibiotic resistance and siderophore-mediated virulence remains unknown. Here, using microcosms containing non-sterile metal-contaminated river water and sediment, we test whether liming reduces co-selection for these pathogenicity traits in the opportunistic pathogen Pseudomonas aeruginosa. To account for the effect of environmental structure, which is known to impact siderophore production, microcosms were incubated under either static or shaking conditions. Evolved P. aeruginosa populations had greater fitness in the presence of toxic concentrations of copper than the ancestral strain and showed increased resistance to the clinically relevant antibiotics apramycin, cefotaxime and trimethoprim, regardless of lime addition or environmental structure. Although we found virulence to be significantly associated with siderophore production, neither virulence nor siderophore production significantly differed between the four treatments. Furthermore, liming did not mitigate metal-imposed selection for antibiotic resistance or virulence in P. aeruginosa. Consequently, metal-contaminated environments may select for antibiotic resistance and virulence traits even when treated with lime.

Copper selects for siderophore-mediated virulence in Pseudomonas aeruginosa

BACKGROUND

Iron is essential for almost all bacterial pathogens and consequently it is actively withheld by their hosts. However, the production of extracellular siderophores enables iron sequestration by pathogens, increasing their virulence. Another function of siderophores is extracellular detoxification of non-ferrous metals. Here, we experimentally link the detoxification and virulence roles of siderophores by testing whether the opportunistic pathogen Pseudomonas aeruginosa displays greater virulence after exposure to copper. To do this, we incubated P. aeruginosa under different environmentally relevant copper regimes for either two or twelve days. Subsequent growth in a copper-free environment removed phenotypic effects, before we quantified pyoverdine production (the primary siderophore produced by P. aeruginosa), and virulence using the Galleria mellonella infection model.

RESULTS

Copper selected for increased pyoverdine production, which was positively correlated with virulence. This effect increased with time, such that populations incubated with high copper for twelve days were the most virulent. Replication of the experiment with a non-pyoverdine producing strain of P. aeruginosa demonstrated that pyoverdine production was largely responsible for the change in virulence.

CONCLUSIONS

We here show a direct link between metal stress and bacterial virulence, highlighting another dimension of the detrimental effects of metal pollution on human health.

Role of Host and Bacterial Lipids in Pseudomonas aeruginosa Respiratory Infections

The opportunistic pathogen Pseudomonas aeruginosa is one of the most common agents of respiratory infections and has been associated with high morbidity and mortality rates. The ability of P. aeruginosa to cause severe respiratory infections results from the coordinated action of a variety of virulence factors that promote bacterial persistence in the lungs. Several of these P. aeruginosa virulence mechanisms are mediated by bacterial lipids, mainly lipopolysaccharide, rhamnolipid, and outer membrane vesicles. Other mechanisms arise from the activity of P. aeruginosa enzymes, particularly ExoU, phospholipase C, and lipoxygenase A, which modulate host lipid signaling pathways. Moreover, host phospholipases, such as cPLA2α and sPLA2, are also activated during the infectious process and play important roles in P. aeruginosa pathogenesis. These mechanisms affect key points of the P. aeruginosa-host interaction, such as: i) biofilm formation that contributes to bacterial colonization and survival, ii) invasion of tissue barriers that allows bacterial dissemination, iii) modulation of inflammatory responses, and iv) escape from host defenses. In this mini-review, we present the lipid-based mechanism that interferes with the establishment of P. aeruginosa in the lungs and discuss how bacterial and host lipids can impact the outcome of P. aeruginosa respiratory infections.

Genome sequencing of Pseudomonas aeruginosa strain M2 illuminates traits of an opportunistic pathogen of burn wounds

Pseudomonas aeruginosa is a Gram-negative nosocomial pathogen and one of the most prevalent organisms isolated from burn wounds worldwide. Pseudomonas aeruginosa strain M2 (O5 serotype, type B flagella) is utilized for examining the murine model associated with burns. Pseudomonas aeruginosa M2 is similar in lethality to common laboratory P. aeruginosa strains when infecting CD-1 mice. Conversely, we recently showed that, relative to these strains, P. aeruginosa M2-infected mice are more susceptible to sepsis and demonstrate a 6-log reduction in LD50 from subcutaneous infection at the infection site directly after 10% total body surface area burn. To better understand this striking phenotypic difference from other P. aeruginosa strains employed in burn models, we sequenced the P. aeruginosa M2 genome. A total of 4,136,641 read pairs were obtained, providing an average genome coverage of 97.5X; subsequent assembly yielded a draft genome with 187 contigs comprising 6,360,304 bp with a G + C content of 66.45%. Genome-based phylogeny estimation of 92 P. aeruginosa strains placed P. aeruginosa M2 with P. aeruginosa-12-4-4(59), a nonairway clinical strain isolated from the blood culture of a burn patient. Phylogenomic analyses identified genes shared between P. aeruginosa M2 and P. aeruginosa 14, another strain exhibiting increased lethality in thermal tissues, as well as P. aeruginosa M2 unique genes with diverse functions like degradation of toxic aromatic compounds, iron scavenging, swarming motility and biofilm formation, defense against invasive DNA, and host assault. Predicted lateral gene transfers illuminate proteins heretofore uncharacterized for roles in P. aeruginosa biology. Our work yields a rich resource for assessing P. aeruginosa genes required for increased lethality in burn tissue seroma.

A panel of diverse Pseudomonas aeruginosa clinical isolates for research and development

Objectives

Pseudomonas aeruginosa is a leading cause of community- and hospital-acquired infections. Successful treatment is hampered by its remarkable ability to rapidly develop resistance to antimicrobial agents, primarily through mutation. In response, WHO listed carbapenem-resistant P. aeruginosa as a Priority 1 (Critical) pathogen for research and development of new treatments. A key resource in developing effective countermeasures is access to diverse and clinically relevant strains for testing. Herein we describe a panel of 100 diverse P. aeruginosa strains to support this endeavour.

Methods

WGS was performed on 3785 P. aeruginosa isolates in our repository. Isolates were cultured from clinical samples collected from healthcare facilities around the world between 2003 and 2017. Core-genome MLST and high-resolution SNP-based phylogenetic analyses were used to select a panel of 100 strains that captured the genetic diversity of this collection. Antibiotic susceptibility testing was also performed using 14 clinically relevant antibiotics.

Results

This 100-strain diversity panel contained representative strains from 91 different STs, including genetically distinct strains from major epidemic clones ST-111, ST-235, ST-244 and ST-253. Seventy-one distinct antibiotic susceptibility profiles were identified ranging from pan-susceptible to pan-resistant. Known resistance alleles as well as the most prevalent mutations underlying the antibiotic susceptibilities were characterized for all isolates.

Conclusions

This panel provides a diverse and comprehensive set of P. aeruginosa strains for use in developing solutions to antibiotic resistance. The isolates and available metadata, including genome sequences, are available to industry, academia, federal and other laboratories at no additional cost.

Groundwater, soil and compost, as possible sources of virulent and antibiotic-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major public health concern all around the world. In the frame of this work, a set of diverse environmental P. aeruginosa isolates with various antibiotic resistance profiles were examined in a Galleria mellonella virulence model. Motility, serotypes, virulence factors and biofilm-forming ability were also examined. Molecular types were determined by pulsed-field gel electrophoresis (PFGE). Based on our results, the majority of environmental isolates were virulent in the G. mellonella test and twitching showed a positive correlation with mortality. Resistance against several antibiotic agents such as Imipenem correlated with a lower virulence in the applied G. mellonella model. PFGE revealed that five examined environmental isolates were closely related to clinically detected pulsed-field types. Our study demonstrated that industrial wastewater effluents, composts, and hydrocarbon-contaminated sites should be considered as hot spots of high-risk clones of P. aeruginosa.

Antimicrobial Resistance and Type III Secretion System Virulotypes of Pseudomonas aeruginosa Isolates from Dogs and Cats in Primary Veterinary Hospitals in Japan: Identification of the International High-Risk Clone Sequence Type 235

This study aimed to investigate the current trends in antimicrobial resistance among Pseudomonas aeruginosa clinical isolates of canine and feline origin and the prevalence of their sequence types (STs) and type III secretion system (T3SS) virulotypes, which remains unknown in Japan. A total of 240 nonduplicate clinical isolates of P. aeruginosa from dogs (n = 206) and cats (n = 34) collected from 152 primary care animal hospitals between August 2017 and October 2019 were examined. PCR detection of T3SS genes (exoU and exoS) and carbapenemase genes, multilocus sequence typing, and whole-genome sequencing of the representative carbapenem-resistant isolates were performed. Resistance rates to imipenem and meropenem were 6.67% and 2.08%, respectively. A high resistance rate (17.92%) was encountered with ciprofloxacin. The exoU−/exoS+ was the predominant T3SS virulotype (195 isolates, 81.3%), followed by exoU+/exoS− (35 isolates, 14.6%), exoU−/exoS− (7 isolates, 2.9%), and exoU+/exoS+ (3 isolates, 1.3%). A high frequency of the high-risk clones ST235 and clonal complex 235 (CC 235) (28.9%), followed by ST357 (21.1%), were noted among these 38 exoU+ isolates. Seventeen carbapenem-resistant isolates comprising 2 exoU+ isolates, including an ST235 isolate, and 15 exoU−/exoS+ isolates belonging to non-ST235/CC235 were detected, of which all were carbapenemase negative. Different combinations of mutations among oprD, efflux pump regulatory genes, and AmpC β-lactamase regulatory genes were identified among representative isolates with high-level resistance to imipenem. This study emphasizes the occurrence of ST235 isolates among companion animals, which may represent a threat to public health because of the ability of this clone to acquire and spread resistance elements, including carbapenemase genes.

IMPORTANCEPseudomonas aeruginosa is an environmentally ubiquitous and important opportunistic human pathogen responsible for life-threatening health care-associated infections. Because of its extensive repertoire of virulence determinants and intrinsic and acquired resistance mechanisms, the organism could be one of the most clinically and epidemiologically important causes of morbidity and mortality. In recent years, worldwide spreading of multidrug-resistant high-risk clones, particularly sequence type 235 (ST235), has become a serious public health threat. Companion animals which share much of their living environment with humans could be important reservoirs and spreaders of antimicrobial-resistant bacteria and resistance genes of clinical importance in humans, such as extended-spectrum β-lactamase-producing Enterobacterales and methicillin-resistant Staphylococcus aureus. However, antimicrobial resistance, virulence, and genotyping of P. aeruginosa in companion animals remain largely unknown. This work sheds light on the potential spread of high-risk clones in companion animals.

Pathogenesis of Gram-Negative Bacteremia

Gram-negative bacteremia is a devastating public health threat, with high mortality in vulnerable populations and significant costs to the global economy. Concerningly, rates of both Gram-negative bacteremia and antimicrobial resistance in the causative species are increasing. Gram-negative bacteremia develops in three phases. First, bacteria invade or colonize initial sites of infection. Second, bacteria overcome host barriers, such as immune responses, and disseminate from initial body sites to the bloodstream. Third, bacteria adapt to survive in the blood and blood-filtering organs. To develop new therapies, it is critical to define species-specific and multispecies fitness factors required for bacteremia in model systems that are relevant to human infection. A small subset of species is responsible for the majority of Gram-negative bacteremia cases, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii The few bacteremia fitness factors identified in these prominent Gram-negative species demonstrate shared and unique pathogenic mechanisms at each phase of bacteremia progression. Capsule production, adhesins, and metabolic flexibility are common mediators, whereas only some species utilize toxins. This review provides an overview of Gram-negative bacteremia, compares animal models for bacteremia, and discusses prevalent Gram-negative bacteremia species.

Why? - Successful Pseudomonas aeruginosa clones with a focus on clone C

The environmental species Pseudomonas aeruginosa thrives in a variety of habitats. Within the epidemic population structure of P. aeruginosa, occassionally highly successful clones that are equally capable to succeed in the environment and the human host arise. Framed by a highly conserved core genome, individual members of successful clones are characterized by a high variability in their accessory genome. The abundance of successful clones might be funded in specific features of the core genome or, although not mutually exclusive, in the variability of the accessory genome. In clone C, one of the most predominant clones, the plasmid pKLC102 and the PACGI-1 genomic island are two ubiquitous accessory genetic elements. The conserved transmissible locus of protein quality control (TLPQC) at the border of PACGI-1 is a unique horizontally transferred compository element, which codes predominantly for stress-related cargo gene products such as involved in protein homeostasis. As a hallmark, most TLPQC xenologues possess a core genome equivalent. With elevated temperature tolerance as a characteristic of clone C strains, the unique P. aeruginosa and clone C specific disaggregase ClpG is a major contributor to tolerance. As other successful clones, such as PA14, do not encode the TLPQC locus, ubiquitous denominators of success, if existing, need to be identified.

Type 3 secretion system of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen, mainly affecting severe patients, such as those in intensive care units (ICUs). High levels of antibiotic resistance and a long battery of virulence factors characterise this pathogen. Among virulence factors, the T3SS (Type 3 Secretion Systems) are especially relevant, being one of the most important virulence factors in P. aeruginosa. T3SS are a complex "molecular syringe" able to inject different effectors in host cells, subverting cell machinery influencing immune responses, and increasing bacterial survival rates. While T3SS have been largely studied and the molecular structure and main effector functions have been established, a series of questions and further points remain to be clarified or established. The key role of T3SS in P. aeruginosa virulence has resulted in the search for T3SS-targeting molecules able to impair their functions and subsequently improve patient outcomes. This review aims to summarise the most relevant features of the P. aeruginosa T3SS.

Genomic Features of a Food-Derived Pseudomonas aeruginosa Strain PAEM and Biofilm-Associated Gene Expression under a Marine Bacterial α-Galactosidase

The biofilm-producing strains of P. aeruginosa colonize various surfaces, including food products and industry equipment that can cause serious human and animal health problems. The biofilms enable microorganisms to evolve the resistance to antibiotics and disinfectants. Analysis of the P. aeruginosa strain (serotype O6, sequence type 2502), isolated from an environment of meat processing (PAEM) during a ready-to-cook product storage (−20 °C), showed both the mosaic similarity and differences between free-living and clinical strains by their coding DNA sequences. Therefore, a cold shock protein (CspA) has been suggested for consideration of the evolution probability of the cold-adapted P. aeruginosa strains. In addition, the study of the action of cold-active enzymes from marine bacteria against the food-derived pathogen could contribute to the methods for controlling P. aeruginosa biofilms. The genes responsible for bacterial biofilm regulation are predominantly controlled by quorum sensing, and they directly or indirectly participate in the synthesis of extracellular polysaccharides, which are the main element of the intercellular matrix. The levels of expression for 14 biofilm-associated genes of the food-derived P. aeruginosa strain PAEM in the presence of different concentrations of the glycoside hydrolase of family 36, α-galactosidase α-PsGal, from the marine bacterium Pseudoalteromonas sp. KMM 701 were determined. The real-time PCR data clustered these genes into five groups according to the pattern of positive or negative regulation of their expression in response to the action of α-galactosidase. The results revealed a dose-dependent mechanism of the enzymatic effect on the PAEM biofilm synthesis and dispersal genes.

Characterization of Putative Virulence Factors of Pseudomonas aeruginosa Strain RBS Isolated from a Saltern, Tunisia: Effect of Metal Ion Cofactors on the Structure and the Activity of LasB

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium able to survive in diverse environments such as soil, plants, freshwater, and seawater. P. aeruginosa can be an opportunistic pathogen to humans when their immune system is deficient. Its pathogenicity may be linked to the production of virulence factors. We isolated P. aeruginosa strain RBS from the saltern of Sfax in Tunisia. In this study, we characterized the halotolerance, antibiotic susceptibility, and some virulence factors of strain RBS. High NaCl concentrations inhibited growth and motility. However, biofilm formation was enhanced to protect bacteria against salt stress. Among the 18 antibiotics tested, quinolones and tetracycline showed a significant inhibitory effect on growth, motility, and biofilm formation of strain RBS. β-Lactams, however, did not have any inhibitory effect on neither bacterial growth nor motility. In some cases, resistance was due, in part, to biofilm formation. We also showed that RBS produces two proteases, LasB and AprA, which have been shown to be implicated in host infection. LasB was further characterized to study the role of metal ions in enzyme stability. It possesses two distinct metal ion-binding sites coordinating a calcium and a zinc ion. The effect of metal ion chelation was evaluated as well as substitutions of residues involved in metal ion binding. Impairing metal ion binding of LasB led to a loss of activity and a sharp decrease of stability. Our findings suggest that the binding of both metal ions is interdependent as the two metal ions' binding sites are linked via a hydrogen bond network.

The Pseudomonas aeruginosa accessory genome elements influence virulence towards Caenorhabditis elegans

BACKGROUND

Multicellular animals and bacteria frequently engage in predator-prey and host-pathogen interactions, such as the well-studied relationship between Pseudomonas aeruginosa and the nematode Caenorhabditis elegans. This study investigates the genomic and genetic basis of bacterial-driven variability in P. aeruginosa virulence towards C. elegans to provide evolutionary insights into host-pathogen relationships.

RESULTS

Natural isolates of P. aeruginosa that exhibit diverse genomes display a broad range of virulence towards C. elegans. Using gene association and genetic analysis, we identify accessory genome elements that correlate with virulence, including both known and novel virulence determinants. Among the novel genes, we find a viral-like mobile element, the teg block, that impairs virulence and whose acquisition is restricted by CRISPR-Cas systems. Further genetic and genomic evidence suggests that spacer-targeted elements preferentially associate with lower virulence while the presence of CRISPR-Cas associates with higher virulence.

CONCLUSIONS

Our analysis demonstrates substantial strain variation in P. aeruginosa virulence, mediated by specific accessory genome elements that promote increased or decreased virulence. We exemplify that viral-like accessory genome elements that decrease virulence can be restricted by bacterial CRISPR-Cas immune defense systems, and suggest a positive, albeit indirect, role for host CRISPR-Cas systems in virulence maintenance.

High frequency of the exoU+/exoS+ genotype associated with multidrug-resistant "high-risk clones" of Pseudomonas aeruginosa clinical isolates from Peruvian hospitals

The type III secretion system of Pseudomonas aeruginosa is an important virulence factor contributing to the cytotoxicity and the invasion process of this microorganism. The current study aimed to determine the presence of the exoU+/exoS+ genotype in P. aeruginosa clinical isolates. The presence of exoS, exoT, exoU and exoY was determined in 189 P. aeruginosa by PCR, and the presence/absence of exoU was analysed according to source infection, clonal relationships, biofilm formation, motility and antimicrobial susceptibility. The gyrA, parC, oprD, efflux pump regulators and β-lactamases genes were also analysed by PCR/sequencing. The exoS, exoT and exoY genes were found in 100% of the isolates. Meanwhile, exoU was present in 43/189 (22.8%) of the isolates, being significantly associated with multidrug resistance, extensively drug resistance as well as with higher level quinolone resistance. However, the presence of β-lactamases, mutations in gyrA and parC, and relevant modifications in efflux pumps and OprD were not significantly associated with exoU+ isolates. MLST analysis of a subset of 25 isolates showed 8 different STs displaying the exoU+/exoS+ genotype. The MDR basis of the exoU+ isolates remain to be elucidated. Furthermore, the clinical implications and spread of exoU+/exoS+ P. aeruginosa isolates need to be established.

The Population Structure of Pseudomonas aeruginosa Is Characterized by Genetic Isolation of exoU+ and exoS+ Lineages

The diversification of microbial populations may be driven by many factors including adaptation to distinct ecological niches and barriers to recombination. We examined the population structure of the bacterial pathogen Pseudomonas aeruginosa by analyzing whole-genome sequences of 739 isolates from diverse sources. We confirmed that the population structure of P. aeruginosa consists of two major groups (referred to as Groups A and B) and at least two minor groups (Groups C1 and C2). Evidence for frequent intragroup but limited intergroup recombination in the core genome was observed, consistent with sexual isolation of the groups. Likewise, accessory genome analysis demonstrated more gene flow within Groups A and B than between these groups, and a few accessory genomic elements were nearly specific to one or the other group. In particular, the exoS gene was highly overrepresented in Group A compared with Group B isolates (99.4% vs. 1.1%) and the exoU gene was highly overrepresented in Group B compared with Group A isolates (95.2% vs. 1.8%). The exoS and exoU genes encode effector proteins secreted by the P. aeruginosa type III secretion system. Together these results suggest that the major P. aeruginosa groups defined in part by the exoS and exoU genes are divergent from each other, and that these groups are genetically isolated and may be ecologically distinct. Although both groups were globally distributed and caused human infections, certain groups predominated in some clinical contexts.