Ecology and Epidemiology of Pseudomonas aeruginosa

Genome-based typing reveals rare events of patient contamination with Pseudomonas aeruginosa from other patients and sink traps in a medical intensive care unit

AIM

We used genome-based typing data with the aim of identifying the routes of acquisition of Pseudomonas aeruginosa by patients hospitalized in a medical intensive care unit (MICU) over a long period in a non-epidemic context.

METHODS

This monocentric prospective study took place over 10 months in 2019 in a 15-bed MICU that applies standard precautions of hygiene. Lockable sink traps installed at all water points of use were bleach disinfected twice a week. We sampled all sink traps weekly to collect 404 P. aeruginosa environmental isolates and collected all P. aeruginosa isolates (N = 115) colonizing or infecting patients (N = 65). All isolates had their phenotypic resistance profile determined and their genome sequenced, from which we identified resistance determinants and assessed the population structure of the collection at the nucleotide level to identify events of P. aeruginosa transmission.

FINDINGS

All sink traps were positive for P. aeruginosa, each sink trap being colonized for several months by one or more clones. The combination of genomic and spatiotemporal data identified one potential event of P. aeruginosa transmission from a sink trap to a patient (1/65, 1.5%) and six events of patient cross-transmission, leading to the contamination of five patients (5/65, 7.7%). All transmitted isolates were fully susceptible to β-lactams and aminoglycosides.

CONCLUSIONS

Genome-based typing revealed the contamination of patients by P. aeruginosa originating from sink traps to be infrequent (1.5%) in an MICU with sink trap-bleaching measures, and that only 7.7% of the patients acquired P. aeruginosa originating from another patient.

Rhizospheric and endophytic Pseudomonas aeruginosa in edible vegetable plants share molecular and metabolic traits with clinical isolates

AIM

Pseudomonas aeruginosa, a leading opportunistic pathogen causing hospital-acquired infections, is also commonly found in agricultural settings. However, there are minimal attempts to examine the molecular and functional attributes shared by agricultural and clinical strains of P. aeruginosa. This study investigates the presence of P. aeruginosa in edible vegetable plants (including salad vegetables) and analyses the evolutionary and metabolic relatedness of the agricultural and clinical strains.

METHODS AND RESULTS

Eighteen rhizospheric and endophytic P. aeruginosa strains were isolated from cucumber, tomato, eggplant, and chili directly from the farms. The identity of these strains was confirmed using biochemical and molecular assays. The genetic and metabolic traits of these plant-associated P. aeruginosa isolates were compared with clinical strains. DNA fingerprinting and 16S rDNA-based phylogenetic analyses revealed that the plant- and human-associated strains are evolutionarily related. Both agricultural and clinical isolates possessed plant-beneficial properties, including mineral solubilization to release essential nutrients (phosphorous, potassium, and zinc), ammonification, and the ability to release extracellular pyocyanin, siderophore, and indole-3 acetic acid.

CONCLUSION

These findings suggest that rhizospheric and endophytic P. aeruginosa strains are genetically and functionally analogous to the clinical isolates. In addition, the genotypic and phenotypic traits do not correlate with plant sources or ecosystems.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study reconfirms that edible plants are the potential source for human and animal transmission of P. aeruginosa.

Cataloguing the bacterial diversity in the active ectomycorrhizal zone of Astraeus from a dry deciduous forest of Shorea

The plant microbiome has been considered one of the most researched areas of microbial biodiversity, yet very little information is available on the microbial communities prevailing in the mushroom's ectomycorrhizosphere. Ectomycorrhizal symbioses often result in the formation of a favourable niche which enables the thriving of various microbial symbionts where these symbionts endorse functions, such as quorum sensing, biofilm formation, volatile microbial compound (VOC) production, regulation of microbial gene expression, symbiosis and virulence. The identification of hidden uncultured microbial communities around the active ectomycorrhizal zone of Astraeus from dry deciduous sal forest of Jharkhand, India was carried out using MinION Oxford Nanopore sequencing of 16S rRNA amplicons genes. High richness of Operational Taxonomic Units (1,905 OTUs) was observed. We recorded 25 distinct phyla. Proteobacteria (36%) was the most abundant phylum, followed by Firmicutes (28%), Actinobacteria (10%) and Bacteroidetes (6%), whereas Gammaproteobacteria was the most abundant class of bacterial communities in the active ectomycorrhizal zone. The ectomycorrhizosphere soil has abundant phosphate-solubilising bacteria (PSB). This is the first report of the ectomycorrhizosphere microbiome associated with Astraeus.

Malonate utilization by Pseudomonas aeruginosa affects quorum-sensing and virulence and leads to formation of mineralized biofilm-like structures

Pseudomonas aeruginosa is an opportunistic pathogen that uses malonate among its many carbon sources. We recently reported that, when grown in blood from trauma patients, P. aeruginosa expression of malonate utilization genes was upregulated. In this study, we explored the role of malonate utilization and its contribution to P. aeruginosa virulence. We grew P. aeruginosa strain PA14 in M9 minimal medium containing malonate (MM9) or glycerol (GM9) as a sole carbon source and assessed the effect of the growth on quorum sensing, virulence factors, and antibiotic resistance. Growth of PA14 in MM9, compared to GM9, reduced the production of elastases, rhamnolipids, and pyoverdine; enhanced the production of pyocyanin and catalase; and increased its sensitivity to norfloxacin. Growth in MM9 decreased extracellular levels of N-acylhomoserine lactone autoinducers, an effect likely associated with increased pH of the culture medium; but had little effect on extracellular levels of PQS. At 18 hr of growth in MM9, PA14 formed biofilm-like structures or aggregates that were associated with biomineralization, which was related to increased pH of the culture medium. These results suggest that malonate significantly impacts P. aeruginosa pathogenesis by influencing the quorum sensing systems, the production of virulence factors, biofilm formation, and antibiotic resistance.

Mechanism of Action of Isolated Caffeic Acid and Epicatechin 3-gallate from Euphorbia hirta against Pseudomonas aeruginosa

BACKGROUND

The escalating dominance of resistant Pseudomonas aeruginosa strains as infectious pathogen had urged the researchers to look for alternative and complementary drugs.

OBJECTIVE

The objective of this study is to address the biological targets and probable mechanisms of action underlying the potent antibacterial effect of the isolated compounds from Euphorbia hirta (L.) against P. aeruginosa.

MATERIALS AND METHODS

The action mechanisms of caffeic acid (CA) and epicatechin 3-gallate (ECG) on P. aeruginosa cells were investigated by several bacterial physiological manifestations involving outer membrane permeabilization, intracellular potassium ion efflux, and nucleotide leakage.

RESULTS

The findings revealed that ECG and CA targeted both cell wall and cytoplasmic membrane of P. aeruginosa. The cellular membrane destruction and ensuing membrane permeability perturbation of P. aeruginosa had led to the ascending access of hydrophobic antibiotics, release of potassium ions, and leakages of nucleotides.

CONCLUSION

The overall study concludes that ECG and CA isolated from E. hirta possess remarkable anti-infective potentials which can be exploited as drug template for the development of new antibacterial agent against resistant P. aeruginosa pathogen.

SUMMARY

Epicatechin 3-gallate (ECG) and caffeic acid (CA) exhibited remarkable bactericidal abilities by increasing the outer membrane and plasma membrane permeability of Pseudomonas aeruginosa pathogenECG and CA had facilitated the entry of hydrophobic antibiotics into P. aeruginosa by disintegrating the lipopolysaccharides layer of the outer membraneECG-induced potassium efflux with efficiency close to that obtained with cefepime suggesting mode of action through membrane disruptionBoth ECG and CA had caused consistent leakage of intracellular nucleotide content with the increase in time. Abbreviations used: ECG: Epicatechin 3-gallate; CA: Caffeic acid; E. hirta: Euphoria hirta.

Pseudomonas aeruginosa in premise plumbing of large buildings

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that is widely occurring in the environment and is recognized for its capacity to form or join biofilms. The present review consolidates current knowledge on P. aeruginosa ecology and its implication in healthcare facilities premise plumbing. The adaptability of P. aeruginosa and its capacity to integrate the biofilm from the faucet and the drain highlight the role premise plumbing devices can play in promoting growth and persistence. A meta‐analysis of P. aeruginosa prevalence in faucets (manual and electronic) and drains reveals the large variation in device positivity reported and suggest the high variability in the sampling approach and context as the main reason for this variation. The effects of the operating conditions that prevail within water distribution systems (disinfection, temperature, and hydraulic regime) on the persistence of P. aeruginosa are summarized. As a result from the review, recommendations for proactive control measures of water contamination by P. aeruginosa are presented. A better understanding of the ecology of P. aeruginosa and key influencing factors in premise plumbing are essential to identify culprit areas and implement effective control measures.

Novobiocin binding to NalD induces the expression of the MexAB-OprM pump in Pseudomonas aeruginosa

NalD was reported to be the secondary repressor of the MexAB-OprM multidrug efflux pump, the major system contributing to intrinsic multidrug resistance in Pseudomonas aeruginosa. Here, we show that novobiocin binds directly to NalD, which leads NalD to dissociate from the DNA promoter, and thus de-represses the expression of the MexAB-OprM pump. In addition, we have solved the crystal structure of NalD at a resolution of 2.90 Å. The structural alignment of NalD to its homologue TtgR reveals that the residues N129 and H167 in NalD are involved in its novobiocin-binding ability. We have confirmed the function of these two amino acids by EMSA and plate assay. The results presented here highlight the importance and diversity of regulatory mechanism in bacterial antibiotic resistance, and provide further insight for novel antimicrobial development.

Antibacterial Properties of Alkaloid Extracts from Callistemon citrinus and Vernonia adoensis against Staphylococcus aureus and Pseudomonas aeruginosa

The development of new antibiotics from new chemical entities is becoming more and more expensive, time-consuming, and compounded by emerging strains that are drug resistant. Alkaloids are plant secondary metabolites which have been shown to have potent pharmacological activities. The effect of alkaloids from Callistemon citrinus and Vernonia adoensis leaves on bacterial growth and efflux pump activity was evaluated on Staphylococcus aureus and Pseudomonas aeruginosa. At a concentration of 1.67 mg/mL, the alkaloids inhibited bacterial growth with comparable effects to ampicillin, a standard antibiotic. The alkaloids from C. citrinus were the most potent against S. aureus with an MIC of 0.0025 mg/mL and MBC of 0.835 mg/mL. It was shown that effects on P. aeruginosa by both plant alkaloids were bacteriostatic. P. aeruginosa was most susceptible to drug efflux pump inhibition by C. citrinus alkaloids which caused an accumulation of Rhodamine 6G of 121% compared to the control. Thus, C. citrinus alkaloids showed antibacterial activity as well as inhibiting ATP-dependent transport of compounds across the cell membrane. These alkaloids may serve as potential courses of compounds that can act as lead compounds for the development of plant-based antibacterials and/or their adjunct compounds.

Evaluation of an MPN test for the rapid enumeration of Pseudomonas aeruginosa in hospital waters

In this study, the performance of a new most probable number (MPN) test (Pseudalert(®)/Quanti-Tray(®)) for the enumeration of Pseudomonas aeruginosa from hospital waters was compared with both international and national membrane filtration-based culture methods for P. aeruginosa: ISO 16266:2006 and UK The Microbiology of Drinking Water - Part 8 (MoDW Part 8), which both use Pseudomonas CN agar. The comparison based on the calculation of mean relative differences between the two methods was conducted according to ISO 17994:2014. Using both routine hospital water samples (80 from six laboratories) and artificially contaminated samples (192 from five laboratories), paired counts from each sample and the enumeration method were analysed. For routine samples, there were insufficient data for a conclusive assessment, but the data do indicate at least equivalent performance of Pseudalert(®)/Quanti-Tray(®). For the artificially contaminated samples, the data revealed higher counts of P. aeruginosa being recorded by Pseudalert(®)/Quanti-Tray(®). The Pseudalert(®)/Quanti-Tray(®) method does not require confirmation testing for atypical strains of P. aeruginosa, saving up to 6 days of additional analysis, and has the added advantage of providing confirmed counts within 24-28 hours incubation compared to 40-48 hours or longer for the ISO 16266 and MoDW Part 8 methods.

Biofilm streamers cause catastrophic disruption of flow with consequences for environmental and medical systems

Biofilms are antibiotic-resistant, sessile bacterial communities that occupy most moist surfaces on Earth and cause chronic and medical device-associated infections. Despite their importance, basic information about biofilm dynamics in common ecological environments is lacking. Here, we demonstrate that flow through soil-like porous materials, industrial filters, and medical stents dramatically modifies the morphology of Pseudomonas aeruginosa biofilms to form 3D streamers, which, over time, bridge the spaces between obstacles and corners in nonuniform environments. We discovered that accumulation of surface-attached biofilm has little effect on flow through such environments, whereas biofilm streamers cause sudden and rapid clogging. We demonstrate that flow-induced shedding of extracellular matrix from surface-attached biofilms generates a sieve-like network that captures cells and other biomass, which add to the existing network, causing exponentially fast clogging independent of growth. These results suggest that biofilm streamers are ubiquitous in nature and strongly affect flow through porous materials in environmental, industrial, and medical systems.

Potent antibacterial antisense peptide-peptide nucleic acid conjugates against Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen causing severe infections in hospital settings, especially with immune compromised patients, and the increasing prevalence of multidrug resistant strains urges search for new drugs with novel mechanisms of action. In this study we introduce antisense peptide-peptide nucleic acid (PNA) conjugates as antibacterial agents against P. aeruginosa. We have designed and optimized antisense peptide-PNA conjugates targeting the translation initiation region of the ftsZ gene (an essential bacterial gene involved in cell division) or the acpP gene (an essential bacterial gene involved in fatty acid synthesis) of P. aeruginosa (PA01) and characterized these compounds according to their antimicrobial activity and mode of action. Four antisense PNA oligomers conjugated to the H-(R-Ahx-R)(4)-Ahx-βala or the H-(R-Ahx)(6)-βala peptide exhibited complete growth inhibition of P. aeruginosa strains PA01, PA14, and LESB58 at 1-2 μM concentrations without any indication of bacterial membrane disruption (even at 20 μM), and resulted in specific reduction of the targeted mRNA levels. One of the four compounds showed clear bactericidal activity while the other significantly reduced bacterial survival. These results open the possibility of development of antisense antibacterials for treatment of Pseudomonas infections.

Comparison of octenidine dihydrochloride (Octenisept®), polihexanide (Prontosan®) and povidon iodine (Betadine®) for topical antibacterial effects in Pseudomonas aeruginosa-contaminated, full-skin thickness burn wounds in rats

Pseudomonas aeruginosa is one of the most frequently isolated organisms from infected burn wounds and a significant cause of nosocomial infection and septic mortality among burn patients. In this animal study, three antiseptic agents which were Octenidine dihydrochloride (Octenisept®, Schülke & Mayr, Norderstedt, Germany), polyhexanide (Prontosan®, B. Braun, Melsungen AG, Germany) and povidon iodine (Betadine, Purdue Pharma L.P, Stamford, USA) were compared to assess the antiseptic effect of their applications on experimental burn wounds in in rats contaiminated with P. aeruginosa. All treatment modalities were effective against P. aeruginosa because there were significant differences between treatment groups and control groups. The mean eschar concentrations were not different between polyhexanide and povidon iodine groups, but there were significant differences between the octenidine dihydrochloride group and the other treatment groups, indicating that the Octenidine dihydrochloride significantly eliminated P. aeruginosa more effectively in the tissues compared to the to other agents. All treatment modalities were sufficient to prevent the P. aeruginosa invasion into the muscle and to cause systemic infection. In conclusion, Octenidine dihydrochloride is the most effective antiseptic agent in the treatment of the P. aeruginosa-contaminated burn wounds; Octenidine dihydrochloride can be considered as a treatment choice because of its peculiar ability of limit the frequency of replacing wound dressings.

Grazing resistance of Pseudomonas aeruginosa biofilms depends on type of protective mechanism, developmental stage and protozoan feeding mode

In a previous study we identified microcolony formation and inhibitor production as the major protective mechanisms of Pseudomonas aeruginosa biofilms against flagellate grazing. Here we compared the efficacy of these two key protective mechanisms by exposing biofilms of the non-toxic alginate overproducing strain PDO300 and the wild-type toxic strain PAO1 to a range of feeding types commonly found in the succession of protozoans associated with natural biofilms. Alginate-mediated microcolony formation conferred effective protection for strain PDO300 against the suspension feeding flagellate Bodo saltans and, as reported earlier, the surface feeding flagellate Rhynchomonas nasuta, both of which are considered as early biofilm colonizers. However, microcolonies of mature PDO300 biofilms were highly susceptible to late biofilm colonizers, the surface-feeding amoeba Acanthamoeba polyphaga and the planktonic ciliate Tetrahymena sp., resulting in a significant reduction of biofilm biomass. Mature biofilms of strain PAO1 inhibited growth of flagellates and A. polyphaga while the grazing activity of Tetrahymena sp. remained unaffected. Our findings suggest that inhibitor production of mature P. aeruginosa biofilms is effective against a wider range of biofilm-feeding predators while microcolony-mediated protection is only beneficial in the early stages of biofilm formation.

Microcolonies, quorum sensing and cytotoxicity determine the survival of Pseudomonas aeruginosa biofilms exposed to protozoan grazing

This study was based on the hypothesis that biofilms of the opportunistic pathogen Pseudomonas aeruginosa are successfully adapted to situations of protozoan grazing. We tested P. aeruginosa wild type and strains that were genetically altered, in structural and regulatory features of biofilm development, in response to the common surface-feeding flagellate Rhynchomonas nasuta. Early biofilms of the wild type showed the formation of grazing resistant microcolonies in the presence of the flagellate, whereas biofilms without the predator were undifferentiated. Grazing on biofilms of quorum sensing mutants (lasR and rhlR/lasR) also resulted in the formation of microcolonies, however, in lower numbers and size compared to the wild type. Considerably fewer microcolonies than the wild type were formed by mutant cells lacking type IV pili, whereas no microcolonies were formed by flagella-deficient cells. The alginate-overproducing strain PDO300 developed larger microcolonies in response to grazing. These observations suggest a role of quorum sensing in early biofilms and involvement of flagella, type IV pili, and alginate in microcolony formation in the presence of grazing. More mature biofilms of the wild type exhibited acute toxicity to the flagellate R. nasuta. Rapid growth of the flagellate on rhlR/lasR mutant biofilms indicated a key role of quorum sensing in the upregulation of lethal factors and in grazing protection of late biofilms. Both the formation of microcolonies and the production of toxins are effective mechanisms that may allow P. aeruginosa biofilms to resist protozoan grazing and to persist in the environment.

Infection control in cystic fibrosis

Over the past 20 years there has been a greater interest in infection control in cystic fibrosis (CF) as patient-to-patient transmission of pathogens has been increasingly demonstrated in this unique patient population. The CF Foundation sponsored a consensus conference to craft recommendations for infection control practices for CF care providers. This review provides a summary of the literature addressing infection control in CF. Burkholderia cepacia complex, Pseudomonas aeruginosa, and Staphylococcus aureus have all been shown to spread between patients with CF. Standard precautions, transmission-based precautions including contact and droplet precautions, appropriate hand hygiene for health care workers, patients, and their families, and care of respiratory tract equipment to prevent the transmission of infectious agents serve as the foundations of infection control and prevent the acquisition of potential pathogens by patients with CF. The respiratory secretions of all CF patients potentially harbor clinically and epidemiologically important microorganisms, even if they have not yet been detected in cultures from the respiratory tract. CF patients should be educated to contain their secretions and maintain a distance of >3 ft from other CF patients to avoid the transmission of potential pathogens, even if culture results are unavailable or negative. To prevent the acquisition of pathogens from respiratory therapy equipment used in health care settings as well as in the home, such equipment should be cleaned and disinfected. It will be critical to measure the dissemination, implementation, and potential impact of these guidelines to monitor changes in practice and reduction in infections.

Comparison of the exoS gene and protein expression in soil and clinical isolates of Pseudomonas aeruginosa

Exoenzyme S (ExoS) is translocated into eukaryotic cells by the type III secretory process and has been hypothesized to function in conjunction with other virulence factors in the pathogenesis of Pseudomonas aeruginosa. To gain further understanding of how ExoS might contribute to P. aeruginosa survival and virulence, ExoS expression and the structural gene sequence were determined in P. aeruginosa soil isolates and compared with ExoS of clinical isolates. Significantly higher levels of ExoS ADP-ribosyltransferase (ADPRT) activity were detected in culture supernatants of soil isolates compared to those of clinical isolates. The higher levels of ADPRT activity of soil isolates reflected both the increased production of ExoS and the production of ExoS having a higher specific activity. ExoS structural gene sequence comparisons found the gene to be highly conserved among soil and clinical isolates, with the greatest number of nonsynonymous substitutions occurring within the region of ExoS encoding GAP function. The lack of amino acid changes in the ADPRT region in association with a higher specific activity implies that other factors produced by P. aeruginosa or residues outside the ADPRT region are affecting ExoS ADPRT activity. The data are consistent with ExoS being integral to P. aeruginosa survival in the soil and suggest that, in the transition of P. aeruginosa from the soil to certain clinical settings, the loss of ExoS expression is favored.

Outbreak of severe Pseudomonas aeruginosa infections caused by a contaminated drain in a whirlpool bathtub

During a 14-month period, 7 patients with hematological malignancies acquired serious infections caused by a single strain of multiply resistant Pseudomonas aeruginosa. A case-control study, culture surveys, and pulsed-field gel electrophoresis implicated a whirlpool bathtub on the unit as the reservoir. All case patients and 32% of control patients used this bathtub (P=.003). The epidemic strain was found only in cultures of samples taken from the bathtub. The drain of the whirlpool bathtub, which was contaminated with the epidemic strain, closed approximately 2.54 cm below the drain's strainer. Water from the faucet, which was not contaminated, became contaminated with P. aeruginosa from the drain when the tub was filled. The design of the drain allowed the epidemic strain to be transmitted to immunocompromised patients who used the whirlpool bathtub. Such tubs are used in many hospitals, and they may be an unrecognized source of nosocomial infections. This potential source of infection could be eliminated by using whirlpool bathtubs with drains that seal at the top.

Pseudomonas aeruginosa cross-infection among patients with cystic fibrosis during a winter camp

Twenty-seven patients with cystic fibrosis from our Danish Cystic Fibrosis Center went to a winter camp for 1 week in November of 1990. This study is based on 22 of these patients. Prior to attending camp, 17 out of 22 patients harbored Pseudomonas aeruginosa in their sputum, but 5 patients did not. After returning from camp, all 22 patients harbored P. aeruginosa in the sputum, including the 5 patients whose sputum was free of P. aeruginosa before they went. Epidemiological typing used pulsed-field gel electrophoresis of the P. aeruginosa isolates was performed. The typing results showed that the 5 cystic fibrosis patients who were free of P. aeruginosa in their sputum prior to the winter camp had acquired P. aeruginosa isolates identical to the P. aeruginosa strains isolated from the other 17 cystic fibrosis patients. This constitutes a cross-colonization rate of 100%, the highest rate ever detected among patients with cystic fibrosis. We conclude that separate holiday camps based on the infection status of the patients with cystic fibrosis are necessary to avoid cross-infection of patients not infected with P. aeruginosa.

In-vitro activity of cefepime and seven other antimicrobial agents against 1518 non-fermentative Gram-negative bacilli collected from 48 Canadian health care facilities. Canadian Afermenter Study Group

Non-fermentative bacilli are primarily nosocomial pathogens, and are also often resistant in vitro to a broad range of antimicrobial agents. In this large Canadian study, we collected 1466 clinical, non-repeat isolates of Pseudomonas aeruginosa, 21 of Acinetobacter spp. and 31 Stenotrophomas maltophilia. MICs of eight antibiotics were determined by the NCCLS microdilution method in a central laboratory. Tobramycin was the most active agent against P. aeruginosa (94.5% susceptible); amikacin and imipenem were the most active against Acetinobacter spp. (100%) and ceftazidime was the most active against S. maltophilia (40.6%). Against each group of isolates, cefepime was active against 87, 86.4 and 15.6%, respectively. This in-vitro study showed that cefepime may be a useful additional agent in the treatment of infections caused by P. aeruginosa and Acinetobacter spp., but not when S. maltophilia is considered pathogenic.

Glucose stimulates phagocytosis of unopsonized Pseudomonas aeruginosa by cultivated human alveolar macrophages

Glucose has previously been shown to increase the in vitro phagocytosis of unopsonized Pseudomonas aeruginosa by freshly explanted murine peritoneal macrophages (PM) and cultivated alveolar macrophages (AM). This study examined the effect of glucose on the same phagocytosis process in human AM in order to determine whether this phenomenon is conserved among species. Freshly explanted human AM phagocytosed unopsonized P. aeruginosa at a low level (2 bacteria/macrophage/30 min), whereas mouse AM ingested a negligible number of P. aeruginosa (0.01 bacterium/macrophage/30 min). Glucose had no effect on this or other phagocytic processes in freshly explanted mouse or human AM. However, following in vitro cultivation for 72 h, human AM phagocytosed three to four times more unopsonized P. aeruginosa than did freshly explanted cells, but only in the presence of glucose. This glucose-inducible phagocytic response had also been observed in cultivated murine AM. Although similar increases were also detected for the phagocytosis of latex particles and complement-coated sheep erythrocytes by cultivated human AM, these processes were not glucose dependent. The lack of response to glucose in freshly explanted mouse AM was attributed to insufficient glucose transport; however, freshly explanted human AM exhibited significant facilitative glucose transport activity that was inhibitable by cytochalasin B and phloretin. Taken together, these results suggest that the process of glucose-inducible phagocytosis of unopsonized P. aeruginosa is conserved among macrophages from different species, including humans, and that AM, but not PM, required cultivation for this glucose effect to occur. Glucose transport by AM appears to be necessary but not sufficient for phagocytosis of unopsonized P. aeruginosa.

Structural and functional implications of sequence diversity of Pseudomonas aeruginosa genes oriC, ampC and fliC

Sequence analysis of three representative gene loci, oriC, ampC and fliC, in 19 Pseudomonas aeruginosa strains revealed a low sequence diversity that does not correlate with the extensive diversity of P. aeruginosa habitats. Single point mutations lead to a mean sequence diversity of 0.40%, 0.38% and 0.59% for oriC, ampC and a-type fliC, respectively, but of only 0.05% for b-type flagellin genes. The analyzed genes encode highly conserved functions that are subject to strong selective pressure. The detected nucleotide substitutions of oriC, accumulating in a central 95 bp region, affect neither the putative DnaA binding sites nor the 13 bp direct repeats that presumably provide the sites to open oriC duplex DNA. Even in P. aeruginosa strain DSM 1128, which exhibits an unusually high sequence variability in several analyzed genes, the 9 bp and 13 bp motifs are conserved, reflecting their essential functional role in replication initiation. The two flagellin types, differing by 37-38% in their primary structure, exhibit pronounced structural and functional homology, as shown by alignment of flagellin variants by hydrophobicity index, probability of surface exposure, chain flexibility and antigenicity, and by cross-reactivity between both proteins using specific antisera. Five nonsynonymous nucleotide substitutions of ampC lead to beta-lactamase variants that differ in recognition and turnover of substrate, as deduced from the three-dimensional structure of the highly homologous Enterobacter cloacae beta-lactamase and confirmed by inhibition kinetics. The identified point mutations in the three genes are classified as selectively equivalent sequence variants indicating neutral genetic drift as a mechanism of molecular evolution in P. aeruginosa, rather than positive selection.

Pseudomonas aeruginosa: assessment of risk from drinking water

Pseudomonas aeruginosa is an ubiquitous environmental bacterium. It can be recovered, often in high numbers, in common food, especially vegetables. Moreover, it can be recovered in low numbers in drinking water. A small percentage of clones of P. aeruginosa possesses the required number of virulence factors to cause infection. However, P. aeruginosa will not proliferate on normal tissue but requires previously organs. Further narrowing the risk to human health is that only certain specific hosts are at risk, including patients with profound neutropenia, cystic fibrosis, severe burns, and those subject to foreign device installation. Other than these very well-defined groups, the general population is refractory to infection with P. aeruginosa. Because of its ubiquitous nature, it is not only not practical to eliminate P. aeruginosa from our food and drinking water, but attempts to do so would produce disinfection byproducts more hazardous than the species itself. Moreover, because there is no readily available sensitive and specific means to detect and identify P. aeruginosa available in the field, any potential regulation governing its control would not have a defined laboratory test measure of outcome. Accordingly, attempts to regulate P. aeruginosa in drinking water would not yield public health protection benefits and could, in fact, be counterproductive in this regard.

Genetic diversity of flagellins of Pseudomonas aeruginosa

Physical genome analysis of the virulence-associated fliC locus in 20 Pseudomonas aeruginosa strains by mapping and sequencing revealed groups of heterologous a-type (1164 bp; 1185 bp) and highly conserved b-type (1467 bp) flagellin genes. Whereas only two synonymous nucleotide substitutions were detected in eight b-type fliC sequences, the 12 a-type sequences exhibited 57 nucleotide substitutions, of which 39 occurred within a variable central region. Although a-type and b-type flagellins differ by 35% in their primary structure, they share strong homology in their predicted features, implying that the polymorphic proteins fold into similar structures during polymerization of the flagella.

Potential of preventing Pseudomonas aeruginosa lung infections in cystic fibrosis patients: experimental studies in animals

In patients with cystic fibrosis (CF), respiratory tract infections caused by Staphylococcus aureus and Haemophilus influenzae are followed by Pseudomonas aeruginosa with increasing age. Chronic endobronchial lung infection with P. aeruginosa is the leading cause of morbidity and mortality. In Danish CF patients we noted that both onset of initial colonization and chronic lung infection with P. aeruginosa peaked during the winter months which is the season for respiratory virus infections. Virus may therefore pave the way for P. aeruginosa. We established a chronic P. aeruginosa lung infection in rats by embedding mucoid bacteria in seaweed alginate and installing the beads intratracheally into the lower part of the left lung. Although the rats did not suffer from CF, the antibody responses and the pathologic changes of the lungs mimicked the findings in CF patients. By using this model in normal and athymic rats we showed that the T-cell response during the "natural" course of the infection played no major role. In a model of acute P. aeruginosa pneumonia we found that the macroscopic inflammatory response of the lungs was immense and that the natural capacity to clear P. aeruginosa was very efficient and could not be improved by immunization, although high serum levels of IgM, IgG and IgA antibodies to P. aeruginosa alginate, LPS, exotoxin A and sonicate were induced. We developed a method for collecting and measuring IgA in saliva and noted that mucosal IgA antibodies were induced by vaccination; they did not significantly prevent inflammation, however. In the chronic rat model we succeeded to improve the survival significantly and to change the inflammatory response subsequent to vaccination from an acute type inflammation dominated by polymorphonuclear leukocytes (PMNs) as in CF patients to a chronic type inflammation dominated by mononuclear leukocytes. Furthermore, we found that rats immunized with an alginate containing vaccine had a significantly earlier cellular shift to a chronic type inflammation as well as a significant reduction in the severity of the macroscopic inflammation compared to two other vaccine groups and to nonimmunized controls. Similar results were obtained in rats treated with the TH1 cytokine, interferon-gamma (IFN-gamma). Several authors have shown that the lung tissue damage during chronic infection in CF patients is caused by a type III hypersensitivity reaction leading to release of elastase by PMNs surrounding the bacterial microcolonies. The cellular shift we have induced by vaccination and by IFN-gamma treatment therefore offers a possible new strategy for improving the clinical course in chronically infected CF patients.

Bradykinin generation triggered by Pseudomonas proteases facilitates invasion of the systemic circulation by Pseudomonas aeruginosa

To elucidate the mechanism of bacterial exoprotease in promotion of the intravascular dissemination of Pseudomonas aeruginosa, we examined the possible involvement of bradykinin (whose generation is induced by pseudomonal proteases in septic foci) in the invasion by bacteria, and in access of bacterial toxins to systemic blood circulation. P. aeruginosa 621 (PA 621), which produces very little protease, was injected intraperitoneally into mice together with pseudomonal exoproteases (elastase/alkaline protease). Dissemination of bacteria from the peritoneal septic foci to the blood was assessed by counting viable bacteria in the blood and spleen by use of the colony-forming assay. The results showed that pseudomonal proteases markedly enhanced (10- to 100-fold) intravascular dissemination of bacteria in mice. This enhancement was induced not only by pseudomonal proteases but also by bradykinin. More importantly, the increased spread of PA 621 induced by pseudomonal protease and bradykinin was significantly augmented by the addition of kininase inhibitors, indicating the direct involvement of bradykinin in bacterial dissemination. Similarly, bradykinin caused effective dissemination of pseudomonal toxins such as endotoxin (lipopolysaccharide) and exotoxin A when the toxins were injected into the peritoneal cavity with bradykinin. Furthermore, the lethality of the infection with PA 621 was strongly enhanced by pseudomonal proteases given i.p. simultaneously with PA 621. On the basis of these results, it is strongly suggested that pseudomonal proteases as well as bradykinin generated in infectious foci are involved in facilitation of bacterial dissemination in vivo.

Distribution and transmission of Pseudomonas aeruginosa and Burkholderia cepacia in a hospital ward

Genotyping and antibiotic susceptibility testing were used to analyze Pseudomonas aeruginosa and Burkholderia cepacia strains from sink drain from 14 pediatric patients with cystic fibrosis (CF) and from hospital personnel as part of a 4 week prospective study of strain transmission in a pediatric ward. A total of 87.5% of all washbasin drains were contaminated with P. aeruginosa [10(2) to 10(5) colony forming units (CFU)/ml sink fluid], whereas B. cepacia was found only once in a sink drain. From the eight CF patients already infected with P. aeruginosa upon entering the ward, we isolated six genotypes that were identical with strains found in sink drains of the ward. Four of the 16 members of the personnel had one positive P. aeruginosa hand culture. B. cepacia was never found in patients or on personnel hands. Hand washing in contaminated sinks (> or = 10(3) CFU/ml) led to positive P. aeruginosa or B. cepacia hand cultures. P. aeruginosa or B. cepacia embedded in sputum were transmissable by hand shaking for up to 180 min, whereas both pathogens suspended in physiological saline were transmissable to other hands only up to 30 min. Genotyping of P. aeruginosa revealed strain transmission from CF patients or the environment to other patients or the personnel, as well as one transmission from the environment to a CF patient. The ability of CF sputum to prolong survival of P. aeruginosa and B. cepacia may be important for strain transmission. The results suggest that improved hygienic measures are required to prevent routes of bacterial transmission via the hands and sink drains.

Host-microbe interaction in the gastrointestinal tract

In order for an infection to occur, the target organ must come in contact with sufficient microbes, the microbe must possess specific virulence factors, these virulence factors must be expressed, and the defenses of the organ system must be overcome. This dynamic process, which is ongoing in all living entities, can be described by the following relationship: [formula: see text] The establishment of infection first occurs in a particular organ. This phenomenon is known as tissue trophism and the association of microbes with organ systems governs the practice of clinical microbiology and infectious disease. With some microbes (e.g., Giardia, Cryptosporidium) the interaction with the particular organ is so specific that infections are almost always confined to one site; with others (e.g., Salmonella, enterovirus) the microbe has the potential to become systemic. When attempting to establish health risk assessment from microbes by contact with food and drinking water, one must therefore consider that the gastrointestinal tract is a complex organ system with a variety of specific host defense mechanisms. It is only when the microbe has particular virulence factors for sites in gastrointestinal tract, and the specific host defense mechanisms in the gastrointestinal tract are breached, that infection of this organ system occurs. Therefore, the general terms "immunosuppression" or "immunocompromise" are meaningless unless the specific immune defect is known. A description of the microbial virulence factors active against the gastrointestinal tract and the defense mechanisms of this organ system are reviewed to provide a biological basis health risk assessment and future food and drinking water regulations.