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PubMed1995

[Effects of azithromycin on the virulence of Pseudomonas aeruginosa].

Pseudomonas aeruginosa is a saprophyte opportunistic bacteria which frequently colonizes the respiratory tract of patients presenting a severe chronic bronchitis pathology. Secreting a number of exotoxins and enzymes inducing an inflammation and necrosing of the surrounding tissues, it provokes irreversible pulmonary lesions. Different experimental in vitro works evidenced macrolides activity on the production and/or secretion of these factors, with a diminution of elastase, protease, lecithinase and D-nase synthesis. Among the macrolides, azithromycin seems to have the most pronounced activity. In vivo, some patients suffering from bronchiolitis or cystic fibrosis have been clinically improved with a treatment using erythromycin, or clarithromycin or azithromycin. These very preliminary results demand to be confirmed but the macrolides could allow a decrease of Pseudomonas aeruginosa pathogenicity and thus stop the deterioration of pulmonary functions.

Anti-Bacterial Agents↗
PubMed1999

Amino acid-mediated induction of the basic amino acid-specific outer membrane porin OprD from Pseudomonas aeruginosa.

Pseudomonas aeruginosa can utilize arginine and other amino acids as both carbon and nitrogen sources. Earlier studies have shown that the specific porin OprD facilitates the diffusion of basic amino acids as well as the structurally analogous beta-lactam antibiotic imipenem. The studies reported here showed that the expression of OprD was strongly induced when arginine, histidine, glutamate, or alanine served as the sole source of carbon. The addition of succinate exerted a negative effect on induction of oprD, likely due to catabolite repression. The arginine-mediated induction was dependent on the regulatory protein ArgR, and binding of purified ArgR to its operator upstream of the oprD gene was demonstrated by gel mobility shift and DNase assays. The expression of OprD induced by glutamate as the carbon source, however, was independent of ArgR, indicating the presence of more than a single activation mechanism. In addition, it was observed that the levels of OprD responded strongly to glutamate and alanine as the sole sources of nitrogen. Thus, that the expression of oprD is linked to both carbon and nitrogen metabolism of Pseudomonas aeruginosa.

Amino Acids↗
PubMed1993

Cloning and nucleotide sequence analysis of the ferripyoverdine receptor gene fpvA of Pseudomonas aeruginosa.

Pseudomonas aeruginosa K437 lacks the ferripyoverdine receptor and, as a result, grows poorly on an iron-deficient minimal medium supplemented with ethylenediamine-di(o-hydroxyphenylacetic acid) (EDDHA) and pyroverdine. By using a phagemid-based in vivo cloning system, attempts were made to clone the receptor gene by complementing this growth defect. Several recombinant phagemids carrying P. aeruginosa chromosomal DNA which provided for good growth on EDDHA-pyoverdine-containing medium and which concomitantly restored production of the ferripyroverdine receptor in strain K437 were isolated. These phagemids contained a common 4.6-kb SphI fragment which similarly restored production of the receptor in K437. Nucleotide sequencing of the SphI fragment revealed a single large open reading frame, designated fpvA (ferripyoverdine uptake), of 2439 bp. The predicted translation product of fpvA has a molecular mass of 89,395 Da. N-terminal amino acid sequence analysis of the purified ferripyoverdine receptor confirmed fpvA as the receptor gene. Moreover, it indicated that the receptor is initially synthesized as a precursor with a signal sequence of 27 amino acids which is cleaved to yield the mature protein. The deduced FpvA polypeptide exhibited homology to regions shown to be conserved in TonB-dependent receptor proteins. FpvA also shared strong homology (41.3% identity) with the PupA protein of Pseudomonas putida WCS358. This protein is the receptor for the iron-bound form of pseudobactin, a compound structurally very similar to pyoverdine.

Amino Acid Sequence↗
PubMed2000

Influence of deletions within domain II of exotoxin A on its extracellular secretion from Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a gram-negative bacterium that secretes many proteins into the extracellular medium via the Xcp machinery. This pathway, conserved in gram-negative bacteria, is called the type II pathway. The exoproteins contain information in their amino acid sequence to allow targeting to their secretion machinery. This information may be present within a conformational motif. The nature of this signal has been examined for P. aeruginosa exotoxin A (PE). Previous studies failed to identify a common minimal motif required for Xcp-dependent recognition and secretion of PE. One study identified a motif at the N terminus of the protein, whereas another one found additional information at the C terminus. In this study, we assess the role of the central PE domain II composed of six alpha-helices (A to F). The secretion behavior of PE derivatives, individually deleted for each helix, was analyzed. Helix E deletion has a drastic effect on secretion of PE, which accumulates within the periplasm. The conformational rearrangement induced in this variant is predicted from the three-dimensional PE structure, and the molecular modification is confirmed by gel filtration experiments. Helix E is in the core of the molecule and creates close contact with other domains (I and III). Deletion of the surface-exposed helix F has no effect on secretion, indicating that no secretion information is contained in this helix. Finally, we concluded that disruption of a structured domain II yields an extended form of the molecule and prevents formation of the conformational secretion motif.

ADP Ribose Transferases↗
PubMed1977

Catabolism of L-lysine by Pseudomonas aeruginosa.

Pseudomonas aeruginosa PACI grows poorly on L-lysine as sole source of carbon but mutant derivatives which grow rapidly were readily isolated. Studies with one such mutant, P. aeruginosa PAC586, supported the existence of a route for L-lysine catabolism which differes from those reported previously in other species of Pseudomonas. The postulated route, the cadaverine or decarboxylase pathway, is initiated by the decarboxylation of L-lysine and involves the following steps: L-lysine leads to cadverine leads to I-piperideine leads 5-aminovalerate leads to glutarate semialdehyde leads glutarate. Evidence for this pathway is based on the characterization of the pathway reactions and the induction of the corresponding enzymes by growth on L-lysine. The first three enzymes were also induced by growth on cadaverine and to a lesser extent by 5-aminovalerate. No evidence was obtained for the presence of pathways involving L-lysine 2-monooxygenase or L-pipecolate dehydrogenase, but another potential route for L-lysine catabolism initiated by L-lysine 6-aminotransferase was detected. Studies with mutants unable to grow on L-lysine supported the existence of more than one catabolic pathway for L-lysine in this organism and indicated that all routes converge on a pathway for glutarate catabolism which generates acetyl-CoA. Pipecolate catabolism also appeared to converge on the glutarate pathway in P. AERUGINOSA. The results suggested that the growth rate of the parental strain is limited by the rate of transport and/or decarboxylation of L-lysine. The cadaverine pathway was present, but not so highly induced, in the parental strain P. aeruginosa PACI. Pseudomonas fluorescens contained enzymes of both the cadaverine (decarboxylase) and oxygenase pathways, strains of P. putida (biotypes A and B) contained enzymes of the oxygenase pathway but not the decarboxylase pathway and P. multivorans appeared deficient in both. All these species possessed L-lysine aminotransferase activity.

Cadaverine↗
PubMed1985

The contribution of exoproducts to virulence of Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces a large number of extracellular products which may contribute to its virulence. We have employed a genetic approach to determine the contribution of toxin A, exoenzyme S, elastase and alkaline protease to the pathogenesis of P. aeruginosa. Mutations have been introduced with chemicals or transposons. Mutants have been identified using immunological, chemical, or toxicity assays. Mutants were extensively characterized in vitro to ascertain that they were identical to their parent strain except for the production of the desired product. Appropriate mutants were compared with their parent strains in several animal models: the burned mouse model, the mouse corneal infection model, and a rat model of chronic lung infection. The data indicate that virulence of P. aeruginosa is multifactorial. Further, the relative contribution of a given P. aeruginosa product may vary with the type of infection.

ADP Ribose Transferases↗
PubMed1991

Mechanisms involved in the evasion of the host defence by Pseudomonas aeruginosa.

Pseudomonas aeruginosa, an extracellular opportunistic pathogen, utilizes two major mechanisms to evade the host defence system. One of these mechanisms is the production of a large number of extracellular products, such as proteases, toxins, and lipases. The two proteases, alkaline protease and elastase, inhibit the function of the cells of the immune system (phagocytes, NK cells, T cells), inactivate several cytokines (IL-1, IL-2, IFN-r, TNF), cleave immunoglobulins and inactivate complement. Inhibition of the local immune response by bacterial proteases provides an environment for the colonization and establishment of chronic infection. The other mechanism by which P. aeruginosa evades the host defence system is the biofilm mode of growth of the bacteria in chronic infections. The biofilm-grown bacteria induce a low phagocyte response, and provide a barrier for the bacteria against antibodies, complement, and the cells of the immune system. Protection from the host defence system combined with increased antibiotic resistance of the bacteria in the biofilm are the major reasons for the persistence of P. aeruginosa in chronic infections.

Animals↗
PubMed1988

Antigenicity and immunogenicity of the polyagglutinable antigen of Pseudomonas aeruginosa.

Pseudomonas aeruginosa strains isolated from cystic fibrosis patients agglutinate in antisera against anti-polyagglutinable antigen (PA). Anti-PA antibodies were formed in rabbits when immunization was carried out with bacteria possessing core-bound PA, independently of whether the strains were of S or R phenotype. For bacterial agglutination with anti-PA antibodies two prerequisites are essential: the bacterial cell must be of R phenotype and must possess the core-linked PA. In contrast, the PA in the isolated LPS's can be demonstrated in passive haemagglutination for both (S or R) phenotypes, provided the PA is core-linked. Two PA forms have been recognized, one found only in P. aeruginosa species, both in free and bound form. The other one is shared by all members of Pseudomonas genus but is present only in a free, unbound form.

Antigens, Bacterial↗
PubMed1955

Studies on susceptibility to infection following ionizing radiation. III. Susceptibility of the intestinal tract to oral inoculation with Pseudomonas aeruginosa.

Pseudomonas aeruginosa introduced directly into the stomach established itself more regularly in the intestinal tract of irradiated mice than of unirradiated mice. The irradiated mice had been exposed to 550 r total body x-irradiation 5 days before inoculation. This difference between irradiated and unirradiated mice could not be explained by differences in pH of gastric or duodenal contents, propulsive motility of the intestinal tract, or the ability of the intestinal contents to support growth of Pseudomonas in vitro.

Animals↗
PubMed2004

Characterization of a rhodanese from the cyanogenic bacterium Pseudomonas aeruginosa.

Pseudomonas aeruginosa, the rRNA group I type species of genus Pseudomonas, is a Gram-negative, aerobic bacterium responsible for serious infection in humans. P. aeruginosa pathogenicity has been associated with the production of several virulence factors, including cyanide. Here, the biochemical characterization of recombinant P. aeruginosa rhodanese (Pa RhdA), catalyzing the sulfur transfer from thiosulfate to a thiophilic acceptor, e.g., cyanide, is reported. Sequence homology analysis of Pa RhdA predicts the sulfur-transfer reaction to occur through persulfuration of the conserved catalytic Cys230 residue. Accordingly, the titration of active Pa RhdA with cyanide indicates the presence of one extra sulfur bound to the Cys230 Sgamma atom per active enzyme molecule. Values of K(m) for thiosulfate binding to Pa RhdA are 1.0 and 7.4mM at pH 7.3 and 8.6, respectively, and 25 degrees C. However, the value of K(m) for cyanide binding to Pa RhdA (=14 mM, at 25 degrees C) and the value of V(max) (=750 micromol min(-1)mg(-1), at 25 degrees C) for the Pa RhdA-catalyzed sulfur-transfer reaction are essentially pH- and substrate-independent. Therefore, the thiosulfate-dependent Pa RhdA persulfuration is favored at pH 7.3 (i.e., the cytosolic pH of the bacterial cell) rather than pH 8.6 (i.e., the standard pH for rhodanese activity assay). Within this pH range, conformational change(s) occur at the Pa RhdA active site during the catalytic cycle. As a whole, rhodanese may participate in multiple detoxification mechanisms protecting P. aeruginosa from endogenous and environmental cyanide.

Amino Acid Sequence↗
PubMed1975

Extracellular deoxyribonuclease activity of Pseudomonas aeruginosa.

Pseudomonas aeruginosa cultured on deoxyribonucleic acid (DNA) media containing Nissan's heart extract or chicken heart extract could produce extracellular deoxyribonuclease, while on other DNA media with heart extracts from cow, pig and mouse could not. Variation in the kind of peptones in the DNA media did not make significant difference in this activity, although some peptones caused cloudiness of the media. P. aeruginosa did not need cation activators of chloride compounds to produce extracellular deoxyribonuclease. On the modified Eiken's DNA medium, gram negative bacilli other than P. aeruginosa and Serratia marcescens, i.e. Klebsiella, Salmonella, Shigella, Escherichia coli and Alcaligenes did not produce deoxyribonuclease. The production of extracellular deoxyribonuclease activity on the modified Eiken's DNA medium can be used as a supporting test for biochemical identification of P. aeruginosa.

Culture Media↗
PubMed1981

An outbreak of otitis externa in competitive swimmers due to Pseudomonas aeruginosa.

Pseudomonas aeruginosa was isolated from the ears of 18 of the 25 members of a team of competitive swimmers who complained of painful discharging ears. This group of swimmers trained twice daily in the pool, in the early morning and late afternoon. In contrast swabbing of the ears of a similar group of 54 competitive swimmers who used the pool only in the afternoon revealed only one swimmer with P. aeruginosa. Investigation of the swimming pool revealed that chlorination was often inadequate when the first group of swimmers were training in the early morning. Strains of P. aeruginosa were isolated from various sites around the pool and from the bag of a vacuum used to clean the pool. Pyocin typing, serotyping and phage typing were performed on all isolates. The dominant strain recovered from the swimmers' ears was found to be almost identical to that from the vacuum bag and belonged to serotype 0--11 which has been particularly associated with outbreaks of P. aeruginosa infection in whirlpools in the United States. These results support the hypothesis that there is a direct correlation between the development of otitis externa and swimming in water contaminated with P. aeruginosa.

Adolescent↗
PubMed2005

Treatment and control of severe infections caused by multiresistant Pseudomonas aeruginosa.

Pseudomonas aeruginosa is one of the leading causes of nosocomial infections. Severe infections, such as pneumonia or bacteraemia, are associated with high mortality rates and are often difficult to treat, as the repertoire of useful anti-pseudomonal agents is limited (some beta-lactams, fluoroquinolones and aminoglycosides, and the polymyxins as last-resort drugs); moreover, P. aeruginosa exhibits remarkable ability to acquire resistance to these agents. Acquired resistance arises by mutation or acquisition of exogenous resistance determinants and can be mediated by several mechanisms (degrading enzymes, reduced permeability, active efflux and target modification). Overall, resistance rates are on the increase, and may be different in different settings, so that surveillance of P. aeruginosa susceptibility is essential for the definition of empirical regimens. Multidrug resistance is frequent, and clinical isolates resistant to virtually all anti-pseudomonal agents are increasingly being reported. Monotherapy is usually recommended for uncomplicated urinary tract infections, while combination therapy is normally recommended for severe infections, such as bacteraemia and pneumonia, although, at least in some cases, the advantage of combination therapy remains a matter of debate. Antimicrobial use is a risk factor for P. aeruginosa resistance, especially with some agents (fluoroquinolones and carbapenems), and interventions based on antimicrobial rotation and restriction of certain agents can be useful to control the spread of resistance. Similar measures, together with the prudent use of antibiotics and compliance with infection control measures, are essential to preserve the efficacy of the currently available anti-pseudomonal agents, in view of the dearth, in the near future, of new options against multidrug-resistant P. aeruginosa strains.

Anti-Bacterial Agents↗
PubMed1990

Proteolytic inactivation of cytokines by Pseudomonas aeruginosa.

Pseudomonas aeruginosa alkaline protease and elastase are thought to contribute to bacterial invasiveness, tissue damage, and immune suppression in animals and patients infected with the bacterium. This study examined the ability of the two proteases to inactivate a number of cytokines that mediate immune and inflammatory responses. Human recombinant gamma interferon (rIFN-gamma) and human recombinant tumor necrosis factor alpha were inactivated by both proteases. Murine rIFN-gamma was relatively resistant to alkaline protease but was inactivated by elastase, and human recombinant interleukin-1 alpha and recombinant interleukin-1 beta were resistant to the effects of both proteases. Western immunoblots suggested that cytokine inactivation by these proteases, where it occurred, required only limited proteolysis of the polypeptides. The ability of different P. aeruginosa strains to inactivate IFN-gamma appeared to require the production of both proteases for optimum activity. These results indicate that in vitro cytokine inactivation by Pseudomonas proteases is selective, requires only limited proteolysis, and in certain instances reflects the cooperative effects of both proteases.

Animals↗
PubMed2003

Need for cytochrome bc1 complex for dissimilatory nitrite reduction of Pseudomonas aeruginosa.

Pseudomonas aeruginosa strains deficient in the genes for cytochrome c1, a subunit of the cytochrome bc1 complex, or the tetraheme membrane protein NapC, which is similar to NirT of Pseudomonas stutzeri, were constructed and their growth was investigated. The cytochrome c1 mutant could not grow under anaerobic conditions with nitrite as an electron acceptor and did not reduce nitrite in spite of its producing active nitrite reductase. NirM (cytochrome c551) and azurin, which are the direct electron donors for nitrite reductase, were reduced by succinate in the presence of the membrane fraction from the wild-type strain as a mediator but not in the presence of that from the cytochrome c1 mutant. These results indicated that cytochrome bc1 complex was necessary for electron transfer from the membrane quinone pool to nitrite reductase. The NapC mutant grew anaerobically at the expense of nitrite, indicating that NapC was not necessary for nitrite reduction.

Aerobiosis↗
PubMed2005

Production of rhamnolipids by Pseudomonas aeruginosa.

Pseudomonas aeruginosa produces glycolipidic surface-active molecules (rhamnolipids) which have potential biotechnological applications. Rhamnolipids are produced by P. aeruginosa in a concerted manner with different virulence-associated traits. Here, we review the rhamnolipids biosynthetic pathway, showing that it has metabolic links with numerous bacterial products such as alginate, lipopolysaccharide, polyhydroxyalkanoates, and 4-hydroxy-2-alkylquinolines (HAQs). We also discuss the factors controlling the production of rhamnolipids and the proposed roles this biosurfactant plays in P. aeruginosa lifestyle.

Bacterial Proteins↗
PubMed2007

Oxygen, cyanide and energy generation in the cystic fibrosis pathogen Pseudomonas aeruginosa.

Pseudomonas aeruginosa is a gram-negative, rod-shaped bacterium that belongs to the gamma-proteobacteria. This clinically challenging, opportunistic pathogen occupies a wide range of niches from an almost ubiquitous environmental presence to causing infections in a wide range of animals and plants. P. aeruginosa is the single most important pathogen of the cystic fibrosis (CF) lung. It causes serious chronic infections following its colonisation of the dehydrated mucus of the CF lung, leading to it being the most important cause of morbidity and mortality in CF sufferers. The recent finding that steep O2 gradients exist across the mucus of the CF-lung indicates that P. aeruginosa will have to show metabolic adaptability to modify its energy metabolism as it moves from a high O2 to low O2 and on to anaerobic environments within the CF lung. Therefore, the starting point of this review is that an understanding of the diverse modes of energy metabolism available to P. aeruginosa and their regulation is important to understanding both its fundamental physiology and the factors significant in its pathogenicity. The main aim of this review is to appraise the current state of knowledge of the energy generating pathways of P. aeruginosa. We first look at the organisation of the aerobic respiratory chains of P. aeruginosa, focusing on the multiple primary dehydrogenases and terminal oxidases that make up the highly branched pathways. Next, we will discuss the denitrification pathways used during anaerobic respiration as well as considering the ability of P. aeruginosa to carry out aerobic denitrification. Attention is then directed to the limited fermentative capacity of P. aeruginosa with discussion of the arginine deiminase pathway and the role of pyruvate fermentation. In the final part of the review, we consider other aspects of the biology of P. aeruginosa that are linked to energy metabolism or affected by oxygen availability. These include cyanide synthesis, which is oxygen-regulated and can affect the operation of aerobic respiratory pathways, and alginate production leading to a mucoid phenotype, which is regulated by oxygen and energy availability, as well as having a role in the protection of P. aeruginosa against reactive oxygen species. Finally, we consider a possible link between cyanide synthesis and the mucoid switch that operates in P. aeruginosa during chronic CF lung infection.

Cystic Fibrosis↗