Influence of culture conditions on expression of the mucoid mode of growth of Pseudomonas aeruginosa

Nitrate respiration occurs throughout the depth of mucoid and non-mucoid Pseudomonas aeruginosa submerged agar colony biofilms including the oxic zone

Pseudomonas aeruginosa is an opportunistic pathogen and well characterized biofilm former. P. aeruginosa forms strong oxygen gradients inside biofilms due to rapid oxygen respiration in the top layers and the poor solubility of oxygen coupled with diffusion limited transport. Transcriptomic evidence from in vitro and ex vivo sampling suggests that denitrification is occurring in biofilms in ostensibly oxic environments. It is hypothesized that in the presence of nitrate there is stratification with aerobic respiration occurring in the outer oxic layer and denitrification in the lower anoxic zone. We used submerged agar colony biofilms grown from mucoid (FRD1) and non-mucoid (PAO1) strains to simultaneously measure depth microprofiles of oxygen and nitrous oxide in the same colony with microelectrodes. Oxygen respiration occurred at the top of the colony as expected but denitrification occurred throughout the entire depth, even in the oxic region. Local denitrification rates were highly variable suggesting heterogenous metabolic activity within the colony. We also assessed the short-term influence of tobramycin on aerobic respiration within a PAO1 colony. Although there was an immediate reduction in respiration it was never completely arrested over a 2 h period. On tobramycin removal the oxygen gradient steadily reestablished, demonstrating immediate recovery of metabolic activity.

Current Advances in Plant Growth Promoting Bacteria Alleviating Salt Stress for Sustainable Agriculture

Humanity in the modern world is confronted with diverse problems at several levels. The environmental concern is probably the most important as it threatens different ecosystems, food, and farming as well as humans, animals, and plants. More specifically, salinization of agricultural soils is a global concern because of on one side, the permanent increase of the areas affected, and on the other side, the disastrous damage caused to various plants affecting hugely crop productivity and yields. Currently, great attention is directed towards the use of Plant Growth Promoting Bacteria (PGPB). This alternative method, which is healthy, safe, and ecological, seems to be very promising in terms of simultaneous salinity alleviation and improving crop productivity. This review attempts to deal with different aspects of the current advances concerning the use of PGPBs for saline stress alleviation. The objective is to explain, discuss, and present the current progress in this area of research. We firstly discuss the implication of PGPB on soil desalinization. We present the impacts of salinity on crops. We look for the different salinity origin and its impacts on plants. We discuss the impacts of salinity on soil. Then, we review various recent progress of hemophilic PGPB for sustainable agriculture. We categorize the mechanisms of PGPB toward salinity tolerance. We discuss the use of PGPB inoculants under salinity that can reduce chemical fertilization. Finally, we present some possible directions for future investigation. It seems that PGPBs use for saline stress alleviation gain more importance, investigations, and applications. Regarding the complexity of the mechanisms implicated in this domain, various aspects remain to be elucidated.

Control of Pseudomonas mastitis on a large dairy farm by using slightly acidic electrolyzed water

The disinfection effect of slightly acidic electrolyzed water (SAEW) use in a farm where Pseudomonas mastitis has spread was evaluated. Despite the application of antibiotic therapy and complete cessation of milking infected quarters, numerous new and recurrent Pseudomonas aeruginosa clinical mastitis infections (5.8-7.1% of clinical mastitis cases) occurred on the farm from 2003 to 2005. Procedural changes and equipment modifications did not improve environmental contamination or the incidence of Pseudomonas mastitis. To more thoroughly decontaminate the milking parlor, an SAEW system was installed in 2006. All milking equipment and the parlor environment were sterilized with SAEW (pH 5-6.5, available chlorine 12 parts per million) before and during milking time. After adopting the SAEW system, the incidence of clinical and subclinical Pseudomonas mastitis cases decreased significantly (P < 0.0001) and disappeared. These findings suggest that SAEW effectively reduced the incidence of mastitis in a herd contaminated by Pseudomonas species. This is the first report to demonstrate the effectiveness of disinfection by SAEW against mastitis pathogens in the environment.

Bacterial exopolysaccharide and biofilm formation stimulate chickpea growth and soil aggregation under salt stress

To compensate for stress imposed by salinity, biofilm formation and exopolysaccharide production are significant strategies of salt tolerant bacteria to assist metabolism. We hypothesized that two previously isolated salt-tolerant strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) have an ability to improve plant growth, These strains can form biofilm and accumulate exopolysacharides at increasing salt stress. These results showed that bacteria might be involved in developing microbial communities under salt stress and helpful in colonizing of bacterial strains to plant roots and soil particles. Eventually, it can add to the plant growth and soil structure. We investigated the comparative effect of exopolysacharide and biofilm formation in two bacterial strains Halomonas variabilis (HT1) and Planococcus rifietoensis (RT4) in response to varying salt stress. We found that biofilm formation and exopolysaccharide accumulation increased at higher salinity. To check the effect of bacterial inoculation on the plant (Cicer arietinum Var. CM-98) growth and soil aggregation, pot experiment was conducted by growing seedlings under salt stress. Inoculation of both strains increased plant growth at elevated salt stress. Weight of soil aggregates attached with roots and present in soil were added at higher salt concentrations compared to untreated controls. Soil aggregation was higher at plant roots under salinity. These results suggest the feasibility of using above strains in improving plant growth and soil fertility under salinity.

MudPIT analysis of released proteins in Pseudomonas aeruginosa laboratory and clinical strains in relation to pro-inflammatory effects

Pseudomonas aeruginosa (Pa) is the most common virulent pathogen contributing to the pathogenesis of cystic fibrosis (CF). During bacterial lung colonization, the products of its metabolism are released in the extracellular space contributing to the pathogenic events associated with its presence. To gain insights on the mechanisms involved in the Pa pathogenesis we focused our attention on proteins released by Pa using a MudPIT approach combined with cell biology assays. Conditioned medium (CM) collected under aerobic and microaerobic conditions from Pa clinical strains (in early and late colonization), unlike the laboratory strain, induced expression of IL-8 mRNA in CF airway epithelial cells. We have identified proteins released by clinically relevant Pa strains, focusing on the pro-inflammatory effects as metalloproteases (MMPs). In fact, their expression pattern was associated with the highest pro-inflammatory activity measured in the early clinically isolated strain. The relation was further supported by the result of the analysis of a larger and independent set of Pa isolates derived from sporadically and chronically infected CF patients: 76% of sporadic samples expressed protease activity (n = 44), while only 27% scored positive in the chronically infected individuals (n = 38, p < 0.0001, Fisher's exact test). Finally, looking for a possible mechanism of action of bacterial MMPs, we found that CM from early clinical isolates can cleave CXCR1 on the surface of human neutrophils, suggesting a potential role for the bacterially released MMPs in the protection of the pathogen from the host's response.

Characterization of exopolysaccharides produced by plant-associated fluorescent pseudomonads

A total of 214 strains of plant-associated fluorescent pseudomonads were screened for the ability to produce the acidic exopolysaccharide (EPS) alginate on various solid media. The fluorescent pseudomonads studied were saprophytic, saprophytic with known biocontrol potential, or plant pathogenic. Approximately 10% of these strains exhibited mucoid growth under the conditions used. The EPSs produced by 20 strains were isolated, purified, and characterized. Of the 20 strains examined, 6 produced acetylated alginate as an acidic EPS. These strains included a Pseudomonas aeruginosa strain reported to cause a dry rot of onion, a strain of P. viridiflava with soft-rotting ability, and four strains of P. fluorescens. However, 12 strains of P. fluorescens produced a novel acidic EPS (marginalan) composed of glucose and galactose (1:1 molar ratio) substituted with pyruvate and succinate. Three of these strains were soft-rotting agents. Two additional soft-rotting strains of P. fluorescens produced a third acidic novel EPS composed of rhamnose, mannose, and glucose (1:1:1 molar ratio) substituted with pyruvate and acetate. When sucrose was present as the primary carbon source, certain strains produced the neutral polymer levan (a fructan) rather than an acidic EPS. Levan was produced by most strains capable of synthesizing alginate or the novel acidic EPS containing rhamnose, mannose, and glucose but not by strains capable of marginalan production. It is now evident that the group of bacteria belonging to the fluorescent pseudomonads is capable of elaborating a diverse array of acidic EPSs rather than solely alginate.

Alginate production by plant-pathogenic pseudomonads

Eighteen plant-pathogenic and three non-plant-pathogenic pseudomonads were tested for the ability to produce alginic acid as an exopolysaccharide in vitro. Alginate production was demonstrated for 10 of 13 fluorescent plant-pathogenic pseudomonads tested with glucose or gluconate as the carbon source, but not for all 5 nonfluorescent plant pathogens and all 3 non-plant pathogens tested. With sucrose as the carbon source, some strains produced alginate while others produced both polyfructan (levan) and alginate. Alginates ranged from <1 to 28% guluronic acid, were acetylated, and had number-average molecular weights of 11.3 x 10 to 47.1 x 10. Polyfructans and alginates were not elicitors of the soybean phytoalexin glyceollin when applied to wounded cotyledon surfaces and did not induce prolonged water soaking of soybean leaf tissues. All or most pseudomonads in rRNA-DNA homology group I may be capable of synthesizing alginate as an exopolysaccharide.

Corynebacterium diphtheriae as an emerging pathogen in nephrostomy catheter-related infection: evaluation of traits associated with bacterial virulence

Corynebacterium diphtheriae still represents a global medical challenge, particularly due to the significant number of individuals susceptible to diphtheria and the emergence of non-toxigenic strains as the causative agents of invasive infections. In this study, we characterized the clinical and microbiological features of what we believe to be the first case of C. diphtheriae infection of a percutaneous nephrostomy catheter insertion site in an elderly patient with a fatal bladder cancer. Moreover, we demonstrated the potential role of adherence, biofilm formation and fibrin deposition traits in C. diphtheriae from the catheter-related infection. Non-toxigenic C. diphtheriae isolated from the purulent discharge (named strain BR-CAT5003748) was identified by the API Coryne system (code 1 010 324) and a multiplex PCR for detection of dtxR and tox genes. Strain BR-CAT5003748 showed resistance to oxacillin, ceftazidime and ciprofloxacin. In experiments performed in vitro, the catheter isolate was classified as moderately hydrophobic and as moderately adherent to polystyrene surfaces. Glass provided a more effective surface for biofilm formation than polystyrene. Micro-organisms adhered to (>1.5 x 10(6) c.f.u.) and multiplied on surfaces of polyurethane catheters. Microcolony formation (a hallmark of biofilm formation) and amorphous accretions were observed by scanning electron microscopy on both external and luminal catheter surfaces. Micro-organisms yielded simultaneous expression of localized adherence-like and aggregative-like (LAL/AAL) adherence patterns to HEp-2 cells. Interestingly, the coagulase tube test resulted in the formation of a thin layer of fibrin embedded in rabbit plasma by the non-toxigenic BR-CAT5003748 strain. In conclusion, C. diphtheriae should be recognized as a potential cause of catheter-related infections in at-risk populations such as elderly and cancer patients. LAL/AAL strains may be associated with virulence traits that enable C. diphtheriae to effectively produce biofilms on catheter surfaces. Biofilm formation and fibrin deposition could have contributed to the persistence of C. diphtheriae at the infected insertion site and the obstruction of the nephrostomy catheter.

Erythromycin increases bactericidal activity of surface liquid in human airway epithelial cells

Macrolide antibiotics have clinical benefits in patients with diffuse panbronchiolitis and in patients with cystic fibrosis. Although many mechanisms have been proposed, the precise mechanisms are still uncertain. We examined the effects of erythromycin on bactericidal activity of airway surface liquid secreted by cultured human tracheal epithelial cells. Airway surface liquid was collected by washing the surface of human tracheal epithelial cells with a sodium solution (40 meq/l). Methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa were incubated with airway surface liquid, and the number of surviving bacteria was examined. The number of bacteria in airway surface liquid from the cells cultured in medium alone was significantly lower than that in the sodium solution. Furthermore, the number of bacteria in airway surface liquid from the cells treated with erythromycin was significantly lower than that in airway surface liquid from the cells treated with solvent alone. The production of mRNA and protein of human beta-defensin-1 and human beta-defensin-2 was significantly increased by erythromycin. Bactericidal activity of airway surface liquid was observed at low concentrations (40 meq/l) of sodium but not at higher concentrations (> or =80 meq/l). Airway surface liquid did not contain significant amounts of antibiotics supplemented in the culture medium. Erythromycin at the levels in airway surface liquid and in culture medium did not inhibit bacterial growth. These results suggest that erythromycin may increase bactericidal activity of airway surface liquid in human airway epithelial cells through human beta-defensins production and reduce susceptibility of the airway to bacterial infection.

Cloning, high yield overexpression, purification, and characterization of AlgH, a regulator of alginate biosynthesis in Pseudomonas aeruginosa

The most common cause of mortality among cystic fibrosis sufferers is infection by antibiotic resistant strains of Pseudomonas aeruginosa. Means to control these strains continue to be an important goal. An integral component of the ability of many of these strains to defy antibiotic therapies is the protection afforded by the mucoexopolysaccharide alginate. Production of alginate by P. aeruginosa is tightly regulated at the transcriptional level. AlgH, a putative transcriptional regulator, is involved in regulating alginate biosynthesis as well as nucleoside diphosphate kinase activity and succinyl coenzyme A synthetase activity in P. aeruginosa. Sequence homologues are found in many bacterial species. Here, we describe a method for high level overexpression and high yield/high purity production of AlgH for biophysical and functional studies. The algH gene was cloned and AlgH was overexpressed in Escherichia coli using a commercially available vector with an inducible T7 promoter. We purified the recombinantly produced protein using a rapid classical purification scheme. The yield of purified protein, either isotopically labeled for NMR studies or unlabeled, is excellent (30-37 mg of purified protein per liter of minimal media culture), as is the purity (>95% pure). Analysis of the secondary structure using circular dichroism and NMR indicates that the protein is comprised of both beta-sheet and alpha-helical secondary structural elements. Heteronuclear NMR spectra indicate that AlgH is a monodisperse, folded globular protein. This rapid, high yield, and high purity method for AlgH production will permit further biophysical characterization of this protein including high resolution structural studies.

Impacts of water quality on chlorine and chlorine dioxide efficacy in natural waters

The impact of disinfection efficacy in natural waters was evaluated by performing disinfection assays using four untreated surface waters of various qualities and ultra-pure buffered waters as a baseline condition for comparison. Bacillus subtilis spores were spiked in these waters and disinfection assays were conducted at 22 degrees C using either free chlorine or chlorine dioxide. Assays using indigenous aerobic spores were also completed. The inactivation kinetics in natural and ultra-pure buffered waters were not statistically different (at p = 0.05) while using free chlorine, as long as disinfectant decay was taken into account. Filtering natural waters through a 0.45 microm did not improve the sporicidal efficacy of chlorine. For three out of the four waters tested, the efficacy of chlorine dioxide was greater in natural waters compared to that observed in ultra-pure buffered waters. Such results are consistent with previous observations using ultra-pure waters supplemented with NOM-extract from the Suwannee River. Similar to free chlorine results, the impact of filtration (0.45 microm) on the efficacy of chlorine dioxide was not statistically significant.

Screening for exopolysaccharide-producing bacteria from sub-tropical polluted groundwater

A selection of exopolysaccharide (EPS)--producing bacterial strains was conducted in groundwater adjacent to an old controlled landfill in the City of São Carlos (São Paulo, Brazil). The strains were isolated in P and E media under aerobic and microacrophilic conditions at 25 degrees C. A total of 26 strains were isolated and based on the mucoid mode of the colonies, 6 were selected and their morphological, physiological and biochemical aspects were characterized. All strains presented pigmentation, ranging from yellow to orange and from pink to salmon, with a shiny glistening aspect in all tested media. Strains Lb, Lc and Lg, which excelled the others with regard to the mucoid mode of the colonies, were selected to be cultured in E medium with alternate sucrose and glucose as carbon sources in anaerobiosis at 25 degrees C to analyze the production of EPS. Strains Lc and Lg were classified as being of order Actinomycelates, suborder Corynebacterineae. Lg strain was identified as Gordonia polyisoprenivorans and Lc strain did not correspond to a known description and therefore a more detailed study is under preparation. Considering all ecological aspects and the metabolic potential associated with the microorganisms of the environment studied, as well as the capacity to produce pigment and EPS, and the presence of G. polyisoprenivorans, a rubber degrader bacterium, the potential of the groundwater analyzed is evident as a source of microorganisms to be utilized in studies related to environmental remediation.

Spontaneous sequence duplication within an open reading frame of the pneumococcal type 3 capsule locus causes high-frequency phase variation

The molecular genetic basis of high-frequency serotype 3 capsule phase variation in Streptococcus pneumoniae (the pneumococcus) was investigated. Pneumococci were grown in sorbarod biofilms at 34 degrees C to mimic nasopharyngeal carriage. Different type 3 pneumococci commonly associated with invasive disease generated apparently random tandem duplications of 11-239 bp segments within the cap3A gene of the type 3 capsule locus. These duplications alone were found to be responsible for high-frequency capsule phase variation, in which (phase off) acapsular variants possessed duplications within cap3A, and (phase on) capsular revertants possessed wild-type cap3A genes, indicating the precise excision of the duplication. Additionally, the frequency of phase reversion (off to on) was found to exhibit a linear relationship between (log) frequency of reversion and (log) length of duplication. This apparently random duplication giving rise to phase variation is in stark contrast to the 'preprogrammed' contingency genes in many Gram-negative organisms that possess homopolymeric sequence repeats or motifs for site-specific recombination.

Effect of nutrient limitation on adhesion characteristics of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes a variety of diseases in humans including lung and ocular infections. Infections of the cornea are usually associated with wearing contact lenses and can result in loss of vision. This study aimed to determine the effect of carbon or nitrogen limitation on the adhesion to contact lenses of a strain of Ps. aeruginosa isolated from contact lens-related corneal inflammation. Cells were grown in a continuous culture apparatus in varying levels of glucose or ammonia to effect nutrient limitation. Adhesion to contact lenses was measured as total counts and viable counts. The cell surface hydrophobicity and charge were measured using adhesion to surface-modified Sepharose. Changes in lipopolysaccharide were determined using 1D SDS-PAGE and changes in cell-surface proteins were measured using 2D gel electrophoresis. The more the cultures were nitrogen limited, the greater the increase in adhesion to unworn hydrogel contact lenses 0.3 x 10(3) - 2.2 x 10(3) cells/mm2 on Etafilon A lenses. Cells that were carbon limited showed a greater increase in adhesion to contact lenses when the lenses had been coated in artificial tears. It appeared that lipopolysaccharide may have been involved in the constitutive adhesion to unworn lenses that occurred during C-limitation, whereas changes in the outer membrane proteins contributed to the increased adhesion under nitrogen limitation, or the change in adhesion that occurred to carbon-limited cells using contact lenses coated in artificial tears. Nine cell-surface proteins appeared during nitrogen limitation with kDa/pI of 75/4.8, 4.9, 5.0; 62/5.6; 89/6.5; 38/6.4; 28/1.5; 18/6.4; 12/4.5. Any or all of these may have been involved in the increased adhesion and further experiments are underway to examine this possibility.

Copper as a signal for alginate synthesis in Pseudomonas syringae pv. syringae

Plant-associated pseudomonads are commonly exposed to copper bactericides, which are applied to reduce the disease incidence caused by these bacteria. Consequently, many of these bacteria have acquired resistance or tolerance to copper salts. We recently conducted a survey of 37 copper-resistant (Cur) Pseudomonas spp., including P. cepacia, P. fluorescens, P. syringae, and P. viridiflava, and found that a subset of the P. syringae strains showed a dramatic increase in exopolysaccharide (EPS) production on mannitol-glutamate medium containing CuSO4 at 250 micrograms/ml. A modified carbazole assay indicated that the EPS produced on copper-amended media contained high levels of uronic acids, suggesting that the EPS was primarily alginic acid. Uronic acids extracted from selected strains were further confirmed to be alginate by demonstrating their sensitivity to alginate lyase and by descending paper chromatography following acid hydrolysis. Subinhibitory levels of arsenate, cobalt, lithium, rubidium, molybdenum, and mercury did not induce EPS production, indicating that alginate biosynthesis is not induced in P. syringae cells exposed to these heavy metals. A 200-kb plasmid designated pPSR12 conferred a stably mucoid phenotype to several P. syringae recipients and also increased their resistance to cobalt and arsenate. A cosmid clone constructed from pPSR12 which conferred a stably mucoid phenotype to several P. syringae strains but not to Pseudomonas aeruginosa was obtained. Results obtained in this study indicate that some of the signals and regulatory genes for alginate production in P. syringae differ from those described for alginate production in P. aeruginosa.

Regulation of nucleoside diphosphate kinase and secretable virulence factors in Pseudomonas aeruginosa: roles of algR2 and algH

Alginate is an important virulence factor for Pseudomonas aeruginosa during infection of the lungs of cystic fibrosis patients. The genes encoding enzymes for alginate production by P. aeruginosa are normally silent. They are activated in response to several environmental conditions, including high osmolarity, exposure to ethanol, or long-term growth under conditions of nutrient deprivation. Several genes which participate in the activation of alginate gene promoters have been identified; among these is the algR2 (algQ) gene. AlgR2 is an 18-kDa protein which has been shown to regulate the critical algD gene encoding GDP-mannose dehydrogenase as well as to regulate the levels of a tricarboxylic acid cycle enzyme, i.e., succinyl coenzyme A synthetase, and nucleoside diphosphate kinase (Ndk), an enzyme involved in nucleoside triphosphate synthesis. Succinyl coenzyme A synthetase and Ndk form a complex in P. aeruginosa. While algR2 is required for alginate synthesis at 37 degrees C, an algR2 insertion mutant was still able to make alginate slowly at 37 or at 30 degrees C. We used this observation to identify and clone a gene, termed algH. A strain with mutations in both algR2 and algH is unable to produce alginate at either 37 or 30 degrees C, and it is fully defective in Ndk production.

Identification of exopolysaccharides produced by fluorescent pseudomonads associated with commercial mushroom (Agaricus bisporus) production

The acidic exopolysaccharides (EPSs) from 63 strains of mushroom production-associated fluorescent pseudomonads which were mucoid on Pseudomonas agar F medium (PAF) were isolated, partially purified, and characterized. The strains were originally isolated from discolored lesion which developed postharvest on mushroom (Agaricus bisporus) caps or from commercial lots of mushroom casing medium. An acidic galactoglucan, previously named marginalan, was produced by mucoid strains of the saprophyte Pseudomonas putida and the majority of mucoid strains of saprophytic P. fluorescens (biovars III and V) isolated from casing medium. One biovar II strain (J1) of P. fluorescens produced alginate, a copolymer of mannuronic and guluronic acids, and one strain (H13) produced an apparently unique EPS containing neutral and amino sugars. Of 10 strains of the pathogen "P. gingeri," the causal agent of mushroom ginger blotch, 8 gave mucoid growth on PAF. The "P. gingeri" EPS also was unique in containing both neutral sugar and glucuronic acid. Mucoid, weakly virulent strains of "P. reactans" produced either alginate or marginalan. All 10 strains of the pathogen P. tolaasii, the causal agent of brown blotch of mushrooms were nonnmucoid on PAF. Production of EPS by these 10 strains plus the 2 nonmucoid strains of "P. gingeri" also was negative on several additional solid media as well as in two broth media tested. The results support our previous studies indicating that fluorescent pseudomonads are a rich source of novel EPSs.

Energy metabolism and alginate biosynthesis in Pseudomonas aeruginosa: role of the tricarboxylic acid cycle

Infection with mucoid, alginate-producing strains of Pseudomonas aeruginosa is the leading cause of mortality among patients with cystic fibrosis. Alginate production by P. aeruginosa is not constitutive but is triggered by stresses such as starvation. The algR2 (also termed algQ) gene has been previously identified as being necessary for mucoidy; an algR2 mutant strain is unable to produce alginate when grown at 37 degrees C. We show here that the levels of phosphorylated succinyl coenzyme A synthetase (Scs) and nucleoside diphosphate kinase (Ndk), which form a complex in P. aeruginosa, are reduced in the algR2 mutant. We were able to correlate the lower level of phosphorylated Scs with a decrease in Scs activity. Western blots (immunoblots) also showed a decreased level of Ndk in the algR2 mutant, but the presence of another kinase activity sensitive to Tween 20 provides the missing Ndk function. The effect of AlgR2 on tricarboxylic acid (TCA) cycle enzymes appears to be specific for Scs, since none of the other TCA cycle enzymes measured showed a significant decrease in activity. Furthermore, the ability of the algR2 mutant to grow on TCA cycle intermediates, but not glucose, is impaired. These data indicate that AlgR2 is responsible for maintaining proper operation of the TCA cycle and energy metabolism.

Alginate synthesis by Pseudomonas aeruginosa: a key pathogenic factor in chronic pulmonary infections of cystic fibrosis patients

Pulmonary infection by mucoid, alginate-producing Pseudomonas aeruginosa is the leading cause of mortality among patients suffering from cystic fibrosis. Alginate-producing P. aeruginosa is uniquely associated with the environment of the cystic fibrosis-affected lung, where alginate is believed to increase resistance to both the host immune system and antibiotic therapy. Recent evidence indicates that P. aeruginosa is most resistant to antibiotics when the infecting cells are present as a biofilm, as they appear to be in the lungs of cystic fibrosis patients. Inhibition of the protective alginate barrier with nontoxic compounds targeted against alginate biosynthetic and regulatory proteins may prove useful in eradicating P. aeruginosa from this environment. Our research has dealt with elucidating the biosynthetic pathway and regulatory mechanism(s) responsible for alginate synthesis by P. aeruginosa. This review summarizes reports on the role of alginate in cystic fibrosis-associated pulmonary infections caused by P. aeruginosa and provides details about the biosynthesis and regulation of this exopolysaccharide.

Cystic fibrosis. Infection and immunity to Pseudomonas

Chronic pulmonary infection with P. aeruginosa in CF may result from: 1. An initial failure of clearance mechanisms (increased adherence) leading to the development of a highly compartmentalized inflammatory reaction; 2. Inhibition of clearing mechanisms for bacteria present in the bronchial lumen; and 3. A largely ineffective, and possibly damaging, hyperactivity of inflammatory cells in the lumen and bronchial wall. The special relationship between the CF host and P. aeruginos, always long-term, and frequently subtle in its complexity, needs further understanding in order to develop new strategies for the treatment of chronic lung infections with this organism.

Microbiology of airway disease in patients with cystic fibrosis

Individuals with cystic fibrosis have abbreviated life spans primarily due to chronic airway infection. A limited number of types of organisms are responsible for these infections, with Staphylococcus aureus and Pseudomonas aeruginosa being of primary importance. In the pre-antibiotic era, greater than 90% of deaths due to infection were caused by S. aureus and death usually occurred in the first 2 years of life. With the advent of effective antistaphylococcal therapy, life spans increased and P. aeruginosa became the pathogen of primary importance. P. aeruginosa isolates recovered from patients with cystic fibrosis have a unique phenotypic characteristic referred to as "mucoid." The mucoid phenotype is due to the production of a mucoid exopolysaccharide. A mucoid exopolysaccharide is believed to play a central role in the establishment of chronic pseudomonal lung infection in these patients. A third organism, Pseudomonas cepacia, has recently been detected in the airways of older patients with cystic fibrosis and is associated with increased mortality. The virulence of P. cepacia is not understood, but the organism is extremely refractory to antimicrobial therapy. Other bacteria, including Haemophilus influenzae and members of the family Enterobacteriaceae, appear to play a secondary role in airway infection. Aspergillus fumigatus is the most important fungal agent causing allergic bronchopulmonary disease. The role of viruses has only recently been examined. At least in some patients with cystic fibrosis, respiratory syncytial virus may be important in predisposing to subsequent bacterial infections.

Comparison of the outer membrane protein and lipopolysaccharide profiles of mucoid and nonmucoid Pseudomonas aeruginosa

Laboratory-derived mucoid variants of Pseudomonas aeruginosa were selected by plating the standard PAO1 laboratory strain with bacteriophage. These mucoid variants formed two distinct groups of strains on the basis of phage typing. The first group had the same phage-typing pattern as the parent PAO1 strain, while the second group had a distinctly different phage-typing pattern. One strain from each group was assessed along with the parent PAO1 strain for its outer membrane protein (OMP) and lipopolysaccharide (LPS) profiles by sodium dodecyl sulfate-gel electrophoresis followed by appropriate staining. The mucoid derivatives were found to differ from the parent PAO1 nonmucoid strain in having lost a high-molecular-weight LPS species. Furthermore, the reversion of the mucoid strains to the nonmucoid phenotype was accompanied by a return of the missing high-molecular-weight LPS species. No observable difference between the mucoid derivatives and the parent nonmucoid strain was noted in the OMP profiles. The opposite was found in the case of four isolates of mucoid P. aeruginosa from patients with cystic fibrosis. Two OMP bands (of approximately 55 and 25 kilodaltons) were present in the mucoid isolates but missing in their sister nonmucoid strains. In the case of the cystic fibrosis isolates, no difference in the LPS profiles within mucoid-nonmucoid pairs was noted.

Visualization of Pseudomonas aeruginosa O antigens by using a protein A-dextran-colloidal gold conjugate with both immunoglobulin G and immunoglobulin M monoclonal antibodies

Two lipopolysaccharide O-antigen-specific monoclonal antibodies, MA1-8 (an immunoglobulin G1 [IgG1]) and MF15-4 (an IgM), were used to localize the O antigen of the lipopolysaccharide of Pseudomonas aeruginosa PAO1. A protein A-dextran-gold conjugate with an average particle diameter of 12.5 nm was used to label bacterial cells treated with MA1-8, while a second antibody (goat anti-mouse IgM) was required before the same probe could interact with cells treated with the IgM antibody MF15-4. Both antibodies resulted in exclusive labeling of the surface of P. aeruginosa PAO1 but not that of an isogenic O-antigen-lacking rough mutant. When the monoclonal antibodies became attached to the cell surface of P. aeruginosa PAO1, resulting in an even coating, the foldings and other topographic details could not be discerned by negative staining. In thin sections of monoclonal-antibody-treated bacteria, a 20- and a 30- to 40-nm thick amorphous layer was observed around the outside of the outer membrane when MA1-8 (IgG) and MF15-4 (IgM) plus goat anti-mouse IgM antibodies were used, respectively. This amorphous layer presumably resulted from the stabilization of the lipopolysaccharide structure by the monoclonal antibodies which prevented the long O-antigen chains from collapsing owing to dehydration.

Contribution of hydrophobicity to hemagglutination reactions of Pseudomonas aeruginosa

Several strains of Pseudomonas aeruginosa exhibited the ability to hemagglutinate erythrocytes. Hydrophobic bond-breaking agents, but not sugars and saccharides, were effective inhibitors of hemagglutination. The results suggest the involvement of hydrophobic bonds in hemagglutination reactions of P. aeruginosa.

Staphylococci, in vitro and in vivo

Strains of Staphylococcus aureus were grown in broth and by the membrane technique; both drug-free media and media containing cloxacillin were used. The staphylococci grown in broth containing cloxacillin showed one thick cross wall and were larger than those grown in drug-free broth: 1.6 micron in diameter as opposed to 0.9 micron. The staphylococci grown on membranes placed on agar containing cloxacillin were 2-3 microns in diameter and contained three or more cross walls. Mice were infected intraperitoneally with staphylococci. After treatment with cloxacillin, the peritoneal fluid and spleens contained staphylococci that were 2-3 microns in diameter with three or more cross walls. A staphylococcal endocarditis was induced in rabbits that were then treated with cloxacillin. The staphylococci in the vegetation of the treated rabbits were 2-3 microns in diameter and contained multiple cross walls. Large staphylococci with multiple cross walls were observed in specimens from patients with respiratory infections treated with beta-lactam antibiotics. It appears, therefore, that the ultrastructure of staphylococci in vivo is comparable to that of staphylococci grown on a solid support medium such as a membrane, and different from that of staphylococci grown in a liquid medium.

The purification and chemical characterisation of the alginate present in extracellular material produced by mucoid strains of Pseudomonas aeruginosa

A rapid ion-exchange method has been used to purify the alginate from the extracellular material of mucoid strains of Pseudomonas aeruginosa isolated from the lungs of cystic fibrosis patients. The structure has been investigated by chemical analysis, infrared spectroscopy, paper chromatography, and gas-liquid chromatography. The alginates contain mainly random or poly(D-mannuronic acid) block structures, and are highly acetylated. The relative viscosity is not correlated with the ratio of D-mannuronic acid to L-guluronic acid residues, or the degree of acetylation. The chemical/physical properties of the alginate from P. aeruginosa are considered in the context of the growth of the organism in the lung.

Scanning electron microscopy of bacteria adherent to intravascular catheters

Scanning electron microscopy was used to assess the morphological features of coagulase-negative staphylococci adherent to polyvinylchloride intravascular catheter specimens. Clinical specimens were obtained by using patient catheters from which coagulase-negative staphylococci (greater than or equal to 15 colonies per catheter) grew on semiquantitative blood agar roll cultures. In vitro specimens were prepared by a previously published technique in which sterile polyvinylchloride catheters were immersed in 10(6) CFU of coagulase-negative staphylococci per ml suspended in phosphate-buffered saline. Unused sterile polyvinylchloride catheters were also examined. Scanning electron microscopy of unused sterile polyvinylchloride catheters demonstrated multiple linear surface irregularities. Scanning electron microscopy of infected patient catheters showed a diffuse amorphous material covering the entire surface and the presence of bacteria which appeared anchored to that surface by several different means. These included a slime layer, "foot" processes, and lodgement in surface irregularities. Scanning electron microscopy of in vitro specimens demonstrated no background surface coating, but it did show attachment of cocci to the surface by the same mechanisms as described for clinical specimens. These observations of similar means of attachment in clinical and in vitro specimens suggest that intrinsic catheter surface properties, bacterial surface features, and perhaps coating with host substances may all play a role in bacterial attachment to intravascular catheters. More sophisticated analysis of these interactions may clarify mechanisms of pathogenesis.