Pseudomonas aeruginosa strains obtained from patients with tracheal, urinary tract and wound infection: variations in virulence factors and virulence genes

Pseudomonas aeruginosa Quorum Sensing

Pseudomonas aeruginosa, like many bacteria, uses chemical signals to communicate between cells in a process called quorum sensing (QS). QS allows groups of bacteria to sense population density and, in response to changing cell densities, to coordinate behaviors. The P. aeruginosa QS system consists of two complete circuits that involve acyl-homoserine lactone signals and a third system that uses quinolone signals. Together, these three QS circuits regulate the expression of hundreds of genes, many of which code for virulence factors. P. aeruginosa has become a model for studying the molecular biology of QS and the ecology and evolution of group behaviors in bacteria. In this chapter, we recount the history of discovery of QS systems in P. aeruginosa, discuss how QS relates to virulence and the ecology of this bacterium, and explore strategies to inhibit QS. Finally, we discuss future directions for research in P. aeruginosa QS.

The Prevalence of Exoenzyme S Gene in Multidrug-Sensitive and Multidrug-Resistant Pseudomonas aeruginosa Clinical Strains

Pseudomonas aeruginosa rods are one of the most commonly isolated microorganisms from clinical specimens, usually responsible for nosocomial infections. Antibiotic-resistant P. aeruginosa strains may present reduced expression of virulence factors. This fact may be caused by appropriate genome management to adapt to changing conditions of the hospital environment. Virulence factors genes may be replaced by those crucial to survive, like antimicrobial resistance genes. The aim of this study was to evaluate, using PCR, the occurrence of exoenzyme S-coding gene (exoS) in two distinct groups of P. aeruginosa strains: 83 multidrug-sensitive (MDS) and 65 multidrug-resistant (MDR) isolates. ExoS gene was noted in 72 (48.7%) of the examined strains: 44 (53.0%) MDS and 28 (43.1%) MDR. The observed differences were not statistically significant (p = 0.1505). P. aeruginosa strains virulence is rather determined by the expression regulation of the possessed genes than the difference in genes frequency amongst strains with different antimicrobial susceptibility patterns.

Host suppression of quorum sensing during catheter-associated urinary tract infections

Chronic bacterial infections on medical devices, including catheter-associated urinary tract infections (CAUTI), are associated with bacterial biofilm communities that are refractory to antibiotic therapy and resistant to host immunity. Previously, we have shown that Pseudomonas aeruginosa can cause CAUTI by forming a device-associated biofilm that is independent of known biofilm exopolysaccharides. Here, we show by RNA-seq that host urine alters the transcriptome of P. aeruginosa by suppressing quorum sensing regulated genes. P. aeruginosa produces acyl homoserine lactones (AHLs) in the presence of urea, but cannot perceive AHLs. Repression of quorum sensing by urine implies that quorum sensing should be dispensable during infection of the urinary tract. Indeed, mutants defective in quorum sensing are able to colonize similarly to wild-type in a murine model of CAUTI. Quorum sensing-regulated processes in clinical isolates are also inhibited by urea. These data show that urea in urine is a natural anti-quorum sensing mechanism in mammals.

LasR Variant Cystic Fibrosis Isolates Reveal an Adaptable Quorum-Sensing Hierarchy in Pseudomonas aeruginosa

Chronic Pseudomonas aeruginosa infections cause significant morbidity in patients with cystic fibrosis (CF). Over years to decades, P. aeruginosa adapts genetically as it establishes chronic lung infections. Nonsynonymous mutations in lasR, the quorum-sensing (QS) master regulator, are common in CF. In laboratory strains of P. aeruginosa, LasR activates transcription of dozens of genes, including that for another QS regulator, RhlR. Despite the frequency with which lasR coding variants have been reported to occur in P. aeruginosa CF isolates, little is known about their consequences for QS. We sequenced lasR from 2,583 P. aeruginosa CF isolates. The lasR sequences of 580 isolates (22%) coded for polypeptides that differed from the conserved LasR polypeptides of well-studied laboratory strains. This collection included 173 unique lasR coding variants, 116 of which were either missense or nonsense mutations. We studied 31 of these variants. About one-sixth of the variant LasR proteins were functional, including 3 with nonsense mutations, and in some LasR-null isolates, genes that are LasR dependent in laboratory strains were nonetheless expressed. Furthermore, about half of the LasR-null isolates retained RhlR activity. Therefore, in some CF isolates the QS hierarchy is altered such that RhlR quorum sensing is independent of LasR regulation. Our analysis challenges the view that QS-silent P. aeruginosa is selected during the course of a chronic CF lung infection. Rather, some lasR sequence variants retain functionality, and many employ an alternate QS strategy involving RhlR.

Chronic Pseudomonas aeruginosa infections, such as those in patients with the genetic disease cystic fibrosis, are notable in that mutants with defects in the quorum-sensing transcription factor LasR frequently arise. In laboratory strains of P. aeruginosa, quorum sensing activates transcription of dozens of genes, many of which encode virulence factors, such as secreted proteases and hydrogen cyanide synthases. In well-studied laboratory strains, LasR-null mutants have a quorum-sensing-deficient phenotype. Therefore, the presence of LasR variants in chronic infections has been interpreted to indicate that quorum-sensing-regulated products are not important for those infections. We report that some P. aeruginosa LasR variant clinical isolates are not LasR-null mutants, and others have uncoupled a second quorum-sensing system, the RhlR system, from LasR regulation. In these uncoupled isolates, RhlR independently activates at least some quorum-sensing-dependent genes. Our findings suggest that quorum sensing plays a role in chronic P. aeruginosa infections, despite the emergence of LasR coding variants.

Urinary tract infections caused by Pseudomonas aeruginosa among children in Southern Poland: Virulence factors and antibiotic resistance

OBJECTIVE

The aim of this study was to analyze antibiotic resistance and virulence patterns in Pseudomonas aeruginosa (PAR) isolates from urinary tract infections among children in Southern Poland.

MATERIALS AND METHODS

This study comprised consecutive, non-repetitive PAR isolates sent from two collaborative laboratories. The study group consisted of children aged up to 17 years from Southern Poland with culture-proven PAR UTIs. Relevant information about patients with UTIs, such as age, sex, and type of infection (polymicrobial or monomicrobial), was collected. Isolates were screened for major virulence factors found in uropathogenic PAR strains. Multidrug-resistant (MDR) strains were defined as strains not susceptible to one antimicrobial in at least three different antimicrobial classes. Extensively drug resistant (XDR) strains were defined as strains susceptible to no more than two antimicrobial classes.

RESULTS

The total prevalence of PAR UTIs was 2.1%, and in children <5 years of age it was 3.0%. A total of 26 isolates was tested: 21 from outpatients and five from inpatients. Most infections (80.8%) occurred in children ≤ 4 years of age. The most prevalent virulence gene was exoY (96.2%). The prevalence of other effector proteins was 88.5% for exoT, 92.3% for exoS, and 19.2% for exoU. The gene for LasB was present in 80.8% of isolates; the gene for AprA in 61.5%; the gene for PilA in 19.2%; and the gene for PilB was not detected. The PAR isolates were generally susceptible to beta-lactam and aminoglycoside antimicrobials. All isolates were also susceptible to colistin. A large proportion of isolates were resistant to carbapenems and fluoroquinolones (Fig. 1). No significant differences were found in antimicrobial resistance between males and females or inpatients and outpatients (p > 0.05 for all tested antimicrobials), or in antimicrobial resistance between younger (≤ 5 years old, n = 21) and older (> 5 years old, n = 5) children (p > 0.05 for all tested antimicrobials). Two isolates were classified as XDR and none as MDR. The EDTA test yielded one MBL-positive isolate (3.8%), from a 17-year-old patient in home care. No isolates with genes for the KPC, IMP, or VIM were identified.

CONCLUSION

As data on UTIs in children with Pseudomonas etiology are scarce, this paper provides useful information for clinicians and allows for comparison between Poland and other countries. Our findings have important implications for clinicians treating UTIs empirically, because the success of empiric treatment is based on knowledge of pathogen antimicrobial susceptibility patterns.

Robustness and plasticity of metabolic pathway flux among uropathogenic isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a human pathogen that frequently causes urinary tract and catheter-associated urinary tract infections. Here, using ¹³C-metabolic flux analysis, we conducted quantitative analysis of metabolic fluxes in the model strain P. aeruginosa PAO1 and 17 clinical isolates. All P. aeruginosa strains catabolized glucose through the Entner-Doudoroff pathway with fully respiratory metabolism and no overflow. Together with other NADPH supplying reactions, this high-flux pathway provided by far more NADPH than needed for anabolism: a benefit for the pathogen to counteract oxidative stress imposed by the host. P. aeruginosa recruited the pentose phosphate pathway exclusively for biosynthesis. In contrast to glycolytic metabolism, which was conserved among all isolates, the flux through pyruvate metabolism, the tricarboxylic acid cycle, and the glyoxylate shunt was highly variable, likely caused by adaptive processes in individual strains during infection. This aspect of metabolism was niche-specific with respect to the corresponding flux because strains isolated from the urinary tract clustered separately from those originating from catheter-associated infections. Interestingly, most glucose-grown strains exhibited significant flux through the glyoxylate shunt. Projection into the theoretical flux space, which was computed using elementary flux-mode analysis, indicated that P. aeruginosa metabolism is optimized for efficient growth and exhibits significant potential for increasing NADPH supply to drive oxidative stress response.

Private link between signal and response in Bacillus subtilis quorum sensing

Bacteria coordinate their behavior using quorum sensing (QS), whereby cells secrete diffusible signals that generate phenotypic responses associated with group living. The canonical model of QS is one of extracellular signaling, where signal molecules bind to cognate receptors and cause a coordinated response across many cells. Here we study the link between QS input (signaling) and QS output (response) in the ComQXPA QS system of Bacillus subtilis by characterizing the phenotype and fitness of comQ null mutants. These lack the enzyme to produce the ComX signal and do not activate the ComQXPA QS system in other cells. In addition to the activation effect of the signal, however, we find evidence of a second, repressive effect of signal production on the QS system. Unlike activation, which can affect other cells, repression acts privately: the de-repression of QS in comQ cells is intracellular and only affects mutant cells lacking ComQ. As a result, the QS signal mutants have an overly responsive QS system and overproduce the secondary metabolite surfactin in the presence of the signal. This surfactin overproduction is associated with a strong fitness cost, as resources are diverted away from primary metabolism. Therefore, by acting as a private QS repressor, ComQ may be protected against evolutionary competition from loss-of-function mutations. Additionally, we find that surfactin participates in a social selection mechanism that targets signal null mutants in coculture with signal producers. Our study shows that by pleiotropically combining intracellular and extracellular signaling, bacteria may generate evolutionarily stable QS systems.

Regulatory and metabolic networks for the adaptation of Pseudomonas aeruginosa biofilms to urinary tract-like conditions

Biofilms of the Gram-negative bacterium Pseudomonas aeruginosa are one of the major causes of complicated urinary tract infections with detrimental outcome. To develop novel therapeutic strategies the molecular adaption strategies of P. aeruginosa biofilms to the conditions of the urinary tract were investigated thoroughly at the systems level using transcriptome, proteome, metabolome and enzyme activity analyses. For this purpose biofilms were grown anaerobically in artificial urine medium (AUM). Obtained data were integrated bioinformatically into gene regulatory and metabolic networks. The dominating response at the transcriptome and proteome level was the adaptation to iron limitation via the broad Fur regulon including 19 sigma factors and up to 80 regulated target genes or operons. In agreement, reduction of the iron cofactor-dependent nitrate respiratory metabolism was detected. An adaptation of the central metabolism to lactate, citrate and amino acid as carbon sources with the induction of the glyoxylate bypass was observed, while other components of AUM like urea and creatinine were not used. Amino acid utilization pathways were found induced, while fatty acid biosynthesis was reduced. The high amounts of phosphate found in AUM explain the reduction of phosphate assimilation systems. Increased quorum sensing activity with the parallel reduction of chemotaxis and flagellum assembly underscored the importance of the biofilm life style. However, reduced formation of the extracellular polysaccharide alginate, typical for P. aeruginosa biofilms in lungs, indicated a different biofilm type for urinary tract infections. Furthermore, the obtained quorum sensing response results in an increased production of virulence factors like the extracellular lipase LipA and protease LasB and AprA explaining the harmful cause of these infections.

Pseudomonas aeruginosa PA1006, which plays a role in molybdenum homeostasis, is required for nitrate utilization, biofilm formation, and virulence

Pseudomonas aeruginosa (Pae) is a clinically important opportunistic pathogen. Herein, we demonstrate that the PA1006 protein is critical for all nitrate reductase activities, growth as a biofilm in a continuous flow system, as well as virulence in mouse burn and rat lung model systems. Microarray analysis revealed that ΔPA1006 cells displayed extensive alterations in gene expression including nitrate-responsive, quorum sensing (including PQS production), and iron-regulated genes, as well as molybdenum cofactor and Fe-S cluster biosynthesis factors, members of the TCA cycle, and Type VI Secretion System components. Phenotype Microarray™ profiles of ΔPA1006 aerobic cultures using Biolog plates also revealed a reduced ability to utilize a number of TCA cycle intermediates as well as a failure to utilize xanthine as a sole source of nitrogen. As a whole, these data indicate that the loss of PA1006 confers extensive changes in Pae metabolism. Based upon homology of PA1006 to the E. coli YhhP protein and data from the accompanying study, loss of PA1006 persulfuration and/or molybdenum homeostasis are likely the cause of extensive metabolic alterations that impact biofilm development and virulence in the ΔPA1006 mutant.

Effects of Pseudomonas aeruginosa virulence factor pyocyanin on human urothelial cell function and viability

PURPOSE

We determined the effects of Pseudomonas aeruginosa virulence factor pyocyanin on human urothelial cell viability and function in vitro.

MATERIALS AND METHODS

RT4 urothelial cells were treated with pyocyanin (1 to 100 μM) for 24 hours. After exposure the treatment effects were measured according to certain end points, including changes in urothelial cell viability, reactive oxygen species formation, caspase-3 activity, basal and stimulated adenosine triphosphate release, SA-β-gal activity and detection of acidic vesicular organelles.

RESULTS

The 24-hour pyocyanin treatment resulted in a concentration dependent decrease in cell viability at concentrations of 25 μM or greater, and increases in reactive oxygen species formation and caspase-3 activity at 25 μM or greater. Basal adenosine triphosphate release was significantly decreased at all tested pyocyanin concentrations while stimulated adenosine triphosphate release was significantly inhibited at pyocyanin concentrations of 12.5 μM or greater with no significant stimulated release at 100 μM. Pyocyanin treated RT4 cells showed morphological characteristics associated with cellular senescence, including SA-β-gal expression. This effect was not evident at 100 μM pyocyanin and may have been due to apoptotic cell death, as indicated by increased caspase-3 activity. An increase in acridine orange stained vesicular-like organelles was observed in RT4 urothelial cells after pyocyanin treatment.

CONCLUSIONS

Exposure to pyocyanin alters urothelial cell viability, reactive oxygen species production and caspase-3 activity. Treatment also results in cellular senescence, which may affect the ability of urothelium to repair during infection. The virulence factor depressed stimulated adenosine triphosphate release, which to our knowledge is a novel finding with implications for awareness of bladder filling in patients with P. aeruginosa urinary tract infection.

Evaluation of microorganisms cultured from injured and repressed tissue regeneration sites in endangered giant aquatic Ozark Hellbender salamanders

Investigation into the causes underlying the rapid, global amphibian decline provides critical insight into the effects of changing ecosystems. Hypothesized and confirmed links between amphibian declines, disease, and environmental changes are increasingly represented in published literature. However, there are few long-term amphibian studies that include data on population size, abnormality/injury rates, disease, and habitat variables to adequately assess changes through time. We cultured and identified microorganisms isolated from abnormal/injured and repressed tissue regeneration sites of the endangered Ozark Hellbender, Cryptobranchus alleganiensis bishopi, to discover potential causative agents responsible for their significant decline in health and population. This organism and our study site were chosen because the population and habitat of C. a. bishopi have been intensively studied from 1969–2009, and the abnormality/injury rate and apparent lack of regeneration were established. Although many bacterial and fungal isolates recovered were common environmental organisms, several opportunistic pathogens were identified in association with only the injured tissues of C.a. bishopi. Bacterial isolates included Aeromonas hydrophila, a known amphibian pathogen, Granulicetella adiacens, Gordonai terrae, Stenotrophomonas maltophilia, Aerococcus viridans, Streptococcus pneumoniae and a variety of Pseudomonads, including Pseudomonas aeruginosa, P. stutzeri, and P. alcaligenes. Fungal isolates included species in the genera Penicillium, Acremonium, Cladosporium, Curvularia, Fusarium, Streptomycetes, and the Class Hyphomycetes. Many of the opportunistic pathogens identified are known to form biofilms. Lack of isolation of the same organism from all wounds suggests that the etiological agent responsible for the damage to C. a. bishopi may not be a single organism. To our knowledge, this is the first study to profile the external microbial consortia cultured from a Cryptobranchid salamander. The incidence of abnormalities/injury and retarded regeneration in C. a. bishopi may have many contributing factors including disease and habitat degradation. Results from this study may provide insight into other amphibian population declines.

Extracellular enzymes affect biofilm formation of mucoid Pseudomonas aeruginosa

Pseudomonas aeruginosa secretes a variety of hydrolases, many of which contribute to virulence or are thought to play a role in the nutrition of the bacterium. As most studies concerning extracellular enzymes have been performed on planktonic cultures of non-mucoid P. aeruginosa strains, knowledge of the potential role of these enzymes in biofilm formation in mucoid (alginate-producing) P. aeruginosa remains limited. Here we show that mucoid P. aeruginosa produces extracellular hydrolases during biofilm growth. Overexpression of the extracellular lipases LipA and LipC, the esterase EstA and the proteolytic elastase LasB from plasmids revealed that some of these hydrolases affected the composition and physicochemical properties of the extracellular polymeric substances (EPS). While no influence of LipA was observed, the overexpression of estA and lasB led to increased concentrations of extracellular rhamnolipids with enhanced levels of mono-rhamnolipids, elevated amounts of total carbohydrates and decreased alginate concentrations, resulting in increased EPS hydrophobicity and viscosity. Moreover, we observed an influence of the enzymes on cellular motility. Overexpression of estA resulted in a loss of twitching motility, although it enhanced the ability to swim and swarm. The lasB-overexpression strain showed an overall enhanced motility compared with the parent strain. Moreover, the EstA- and LasB-overproduction strains completely lost the ability to form 3D biofilms, whereas the overproduction of LipC increased cell aggregation and the heterogeneity of the biofilms formed. Overall, these findings indicate that directly or indirectly, the secreted enzymes EstA, LasB and LipC can influence the formation and architecture of mucoid P. aeruginosa biofilms as a result of changes in EPS composition and properties, as well as the motility of the cells.

Urinary tract infections caused by Pseudomonas aeruginosa: a minireview

Urinary tract infections (UTIs) are a serious health problem affecting millions of people each year. Infections of the urinary tract are the second most common type of infection in the body. Catheterization of the urinary tract is the most common factor, which predisposes the host to these infections. Catheter-associated UTI (CAUTI) is responsible for 40% of nosocomial infections, making it the most common cause of nosocomial infection. CAUTI accounts for more than 1 million cases in hospitals and nursing homes annually and often involve uropathogens other than Escherichia coli. While the epidemiology and pathogenic mechanisms of uropathogenic Escherichia coli have been extensively studied, little is known about the pathogenesis of UTIs caused by other organisms like Pseudomonas aeruginosa. Scanty available information regarding pathogenesis of UTIs caused by P. aeruginosa is an important bottleneck in developing effective preventive approaches. The aim of this review is to summarize some of the advances made in the field of P. aeruginosa induced UTIs and draws attention of the workers that more basic research at the level of pathogenesis is needed so that novel strategies can be designed.

Comparison of virulence factors in Pseudomonas aeruginosa strains isolated from contact lens- and non-contact lens-related keratitis

Pseudomonas aeruginosa is one of the common pathogens associated with corneal infection, particularly in contact lens-related keratitis events. The pathogenesis of P. aeruginosa in keratitis is attributed to the production of virulence factors under certain environmental conditions. The aim of this study was to determine differences in the virulence factors of P. aeruginosa isolated from contact lens- and non-contact lens-related keratitis. Associations were assessed between type III secretion toxin-encoding genes, protease profiles, biofilm formation, serotypes and antibiotic-resistance patterns among 27 non-contact lens- and 28 contact lens-related P. aeruginosa keratitis isolates from Australia. Strains with a exoS +/exoU − genotype and a type I protease profile predominated in the non-contact lens-related keratitis isolates, whereas the exoS −/exoU + and a type II protease profile was associated with contact lens-related isolates (P<0.05). A strong biofilm formation phenotype was found to be associated with the possession of the exoU gene, and serotypes E, I and C. The exoS gene was strongly associated with serotypes G, A and B, while exoU was associated with serotypes E and C. Six out of fifty-five (11 %) clinical isolates were non-susceptible (intermediate-resistant or resistant) to ofloxacin and moxifloxacin. All resistant isolates were from non-contact lens-related keratitis. The results suggest that P. aeruginosa isolates from different infection origins may have different characteristics. A better understanding of these differences may lead to further development of evidence-based clinical guidelines for the management of keratitis.

Characterization of N-butanoyl-L-homoserine lactone (C4-HSL) deficient clinical isolates of Pseudomonas aeruginosa

In the opportunistic pathogen Pseudomonas aeruginosa, the production of several virulence factors such as elastase, rhamnolipids and pyocyanin depends on cell-to-cell signaling or quorum sensing (QS) involving N-acylhomoserine lactone (AHL) signal molecules. In vitro studies with laboratory strains and virulence studies in animals with these same strains have demonstrated the contribution of QS to the pathogenesis of P. aeruginosa. However, the importance of P. aeruginosa QS systems in the development of human infections is not clearly known. In order to determine if deficiency within the QS system compromises the ability of P. aeruginosa to cause infections in humans, we collected 50 P. aeruginosa clinical isolates. Phenotypic characterization showed that isolates I-457, I-458, I-459 and I-461 were defective in the production of N-butanoyl-l-homoserine lactone (C4-HSL) signaling molecule and virulence factors elastase, protease, pyocyanin and rhamnolipids. Analysis of the sequences of the lasR, lasI, rhlR and rhlI genes of these four isolates showed that two of the four isolates had mutational defects in both rhlR and rhlI genes while other two isolates were only mutated in the rhlI gene. The combination of rhlR and rhlI mutations or only rhlI mutation probably explains their C4-HSL and virulence factors deficiencies. These observations suggest that QS deficient P. aeruginosa clinical isolates are able to cause infections and that in addition to known virulence factors, factors yet unidentified may contribute to the pathogenesis of P. aeruginosa.

Diversity of biofilms produced by quorum-sensing-deficient clinical isolates of Pseudomonas aeruginosa

The quorum-sensing (QS) systems control several virulence attributes of Pseudomonas aeruginosa. Five QS-deficient P. aeruginosa clinical isolates (CI) that were obtained from wound (CI-1), tracheal (CI-2, CI-3, CI-4) and urinary tract (CI-5) infections had previously been characterized. In this study, a flow-through continuous-culture system was utilized to examine in detail the biofilms formed by these isolates in comparison with the P. aeruginosa prototrophic strain PAO1. Analysis of the biofilms by confocal laser scanning microscopy and COMSTAT image analysis at 1 and 7 days post-inoculation showed that the isolates produced diverse biofilms. In comparison with PAO1, the CI produced biofilms that scarcely or partially covered the surface at day 1, although CI-1 produced larger microcolonies. At day 7, CI-2 and CI-4 produced mature biofilms denser than that produced by PAO1, while the biofilm formed by CI-1 changed very little from day 1. CI-1 was defective in both swarming and twitching motilities, and immunoblotting analysis confirmed that it produced a reduced level of PilA protein. The twitching-motility defect of CI-1 was not complemented by a plasmid carrying intact pilA. In the 48 h colony biofilm assay, the CI varied in susceptibility to imipenem, gentamicin and piperacillin/tazobactam. These results suggest that: (1) the isolates produced biofilms with different structures and densities from that of PAO1; (2) biofilm formation by the isolates was not influenced by either the isolation site or the QS deficiencies of the isolates; (3) the behaviour of CI-1 in the different biofilm systems may be due to its lack of swarming motility and type IV pilus-related twitching motility.

Type III secretion system-associated toxins, proteases, serotypes, and antibiotic resistance of Pseudomonas aeruginosa isolates associated with keratitis

The association between possession of toxin gene-related type III secretory system, protease profiles, O serotypes, and antibiotic resistance patterns was characterized genetically and phenotypically in 46 keratitis isolates of Pseudomonas aeruginosa. There was no significant difference in exoU or exoS prevalence among the keratitis strains. Distinct protease profiles were seen in isolates harboring either exoU or exoS genes. One hundred percent (13/13) of serotype E (O:11) strains contained type III secretion system-associated cytotoxin gene exoU. Multidrug resistance was identified in 4% of Australian and 29% of Indian isolates. None of the Australian isolates was resistant to ciprofloxacin. In general, the rate of multidrug resistance in the exoU positive cytotoxic and serotype E (O:11) strains was significantly higher than in exoS positive invasive strains (p < 0.01). The results suggest that multidrug resistance may be more commonly associated with the corneal isolates of P. aeruginosa having type III secretion system-associated cytotoxin gene exoU and belonging to serotype E (O:11) group.

Clinical, microbiologic, and epidemiologic characteristics of Pseudomonas aeruginosa infections in a University Hospital, Malatya, Turkey

BACKGROUND

Pseudomonas aeruginosa strains are generally resistant to many antibiotics, and nosocomial infections because of this species are one of the major problems in many hospitals. Molecular typing provides very useful information about origin and transmission of the strains. The aims of the present study were to investigate clinical and microbiologic characteristics of the nosocomial infections caused by P aeruginosa strains in a medical center and to bring up the cross-transmission level of this opportunistic pathogen in a university hospital by analyzing the clonal relationship among the isolates.

METHODS

A total of 105 P aeruginosa strains had been identified among the 80 inpatients in a 1-year period from August 2003 to August 2004. Demographic, clinical, and epidemiologic data of the patients were prospectively recorded. The standardized disk-diffusion method was used to determine resistance of the strains to imipenem, ceftazidime, aztreonam, amikacin, gentamicin, mezlocillin, cefepime, tobramycin, meropenem, ceftriaxone, and ciprofloxacin. Clonal relatedness of the strains was investigated by pulsed-field gel electrophoresis (PFGE).

RESULTS

Of the 105 P aeruginosa strains identified, 45 (43%) were isolated from the patients hospitalized in intensive care units. Thirteen patients had repeated pseudomonas infection (total 38 infections/13 patients); 26 of these repeated infections in 9 patients showed the same localization. Half of the patients had at least 1 underlying disease such as burn (48%), chronic illness (32%), and malignancy (20%). Fifty-seven patients (71%) had urinary and/or other catheterization. Urinary tract infection (35%) was the most frequent infection encountered, followed by respiratory tract infection (34%) and sepsis (13%). Resistance to the antibiotics tested was in the 12% to 88% range; amikacin was the most effective and ceftriaxone was the least effective antibiotic. The PFGE typing method showed that 28 of the 80 patients' isolates were clonally related, including 23 indistinguishable or closely related strains (29%), and 5 possibly related strains (6%). Epidemiologic data of the 16 patients (20% of the patients) confirmed a clonal relationship among the strains. Of the 26 isolates of the 9 patients having repeated infection in the same location, 18 (69%) were in the clonally related groups, whereas 11 of the 12 strains isolated from repeated infections on different body sites were clonally different.

CONCLUSION

Our results indicated that P aeruginosa infections in our hospital mainly affected the patients hospitalized in intensive care units and those having catheterization, burn, and/or chronic illness. Amikacin was the best antibiotic as far as bacterial resistance was considered. Although lack of major PFGE type confirmed no P aeruginosa outbreak, typing results showed that cross transmission and treatment failure are the 2 main problems, which should be consider together to prevent this bacterial infection in medical centers.

Impact of quorum sensing on fitness of Pseudomonas aeruginosa

In Pseudomonas aeruginosa, cell-cell communication based on N-acyl-homoserine lactone (AHL) signal molecules (termed quorum sensing) is known to control the production of extracellular virulence factors. Hence, in pathogenic interactions with host organisms, the quorum-sensing (QS) machinery can confer a selective advantage on P. aeruginosa. However, as shown by transcriptomic and proteomic studies, many intracellular metabolic functions are also regulated by quorum sensing. Some of these serve to regenerate the AHL precursors methionine and S-adenosyl-methionine and to degrade adenosine via inosine and hypoxanthine. The fact that a significant percentage of clinical and environmental isolates of P. aeruginosa is defective for QS because of mutation in the major QS regulatory gene lasR, raises the question of whether the QS machinery can have a negative impact on the organism's fitness. In vitro, lasR mutants have a higher probability to escape lytic death in stationary phase under alkaline conditions than has the QS-proficient wild type. Similar selective forces might also operate in natural environments.

Examination of the coordinate effects of Pseudomonas aeruginosa ExoS on Rac1

Exoenzyme S (ExoS) is a bifunctional toxin directly translocated into eukaryotic cells by the Pseudomonas aeruginosa type III secretory (TTS) process. The amino-terminal GTPase-activating (GAP) activity and the carboxy-terminal ADP-ribosyltransferase (ADPRT) activity of ExoS have been found to target but exert opposite effects on the same low-molecular-weight G protein, Rac1. ExoS ADP-ribosylation of Rac1 is cell line dependent. In HT-29 human epithelial cells, where Rac1 is ADP-ribosylated by TTS-ExoS, Rac1 was activated and relocalized to the membrane fraction. Arg66 and Arg68 within the GTPase-binding region of Rac1 were identified as preferred sites of ExoS ADP-ribosylation. The modification of these residues by ExoS would be predicted to interfere with Rac1 inactivation and explain the increase in active Rac1 caused by ExoS ADPRT activity. Using ExoS-GAP and ADPRT mutants to examine the coordinate effects of the two domains on Rac1 function, limited effects of ExoS-GAP on Rac1 inactivation were evident in HT-29 cells. In J774A.1 macrophages, where Rac1 was not ADP-ribosylated, ExoS caused a decrease in the levels of active Rac1, and this decrease was linked to ExoS-GAP. Using immunofluorescence staining of Rac1 to understand the cellular basis for the targeting of ExoS ADPRT activity to Rac1, an inverse relationship was observed between Rac1 plasma membrane localization and Rac1 ADP-ribosylation. The results obtained from these studies have allowed the development of a model to explain the differential targeting and coordinate effects of ExoS GAP and ADPRT activity on Rac1 within the host cell.

The Pseudomonas aeruginosa PA14 type III secretion system is expressed but not essential to virulence in the Caenorhabditis elegans-P. aeruginosa pathogenicity model

The Pseudomonas aeruginosa type III secretion system (TTSS), enabling direct injection of toxins into host cells, has been shown to be crucial to virulence in several models of P. aeruginosa pathogenesis. Using the strain PA14 and its isogenic mutant, PA14exsA, we investigated the role of the TTSS during infection of the nematode Caenorhabditis elegans. Although C. elegans N2 was killed by PA14 in an infection like process over 48 to 72 h the same effect was observed following infection with PA14exsA, implying that a functional TTSS was not essential for virulence. This was despite the TTSS being actively expressed during C. elegans infection as demonstrated by the use of green fluorescent reporter constructs and RT-PCR. However, compared to the wild type PA14, PA14exsA did display a reduced rate of killing of C. elegans strain AU1 which harbours a mutation in the sek-1 gene encoding a MAP kinase involved in nematode innate immunity. A fuller understanding of the mechanism of resistance to type III attack in C. elegans may lead to the identification and development of novel therapeutic targets affording protection to TTSS products in man.

Characterization of an ExoS Type III translocation-resistant cell line

Pseudomonas aeruginosa ExoS is a type III-secreted type III-secreted, bifunctional protein that causes diverse effects on eukaryotic cell function. The coculture of P. aeruginosa strains expressing ExoS with HL-60 myeloid cells revealed the cell line to be resistant to the toxic effects of ExoS. Differentiation of HL-60 cells with phorbol 12-myristate 13-acetate (TPA) rendered the cell line sensitive to ExoS. To understand the cellular basis for the alteration in sensitivity, undifferentiated and TPA-differentiated HL-60 cells were compared for differences in bacterial adherence, type III secretion induction, and ExoS translocation. These comparisons found that ExoS was translocated more efficiently in TPA-differentiated HL-60 cells than in undifferentiated cells. The studies support the ability of eukaryotic cells to influence P. aeruginosa TTS at the level of membrane translocation.

Analysis of quorum sensing-deficient clinical isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa produces multiple virulence factors and causes different types of infections. Previous clinical studies identified P. aeruginosa isolates that lack individual virulence factors. However, the impact of losing several virulence factors simultaneously on the in vivo virulence of P. aeruginosa is not completely understood. The P. aeruginosa cell-to-cell communication system, or quorum sensing (QS), controls the production of several virulence factors. Animal studies using constructed QS mutants indicated that loss of the QS system severely impacts the virulence of P. aeruginosa. In this study, we tried to determine if deficiency within the QS system compromises the ability of P. aeruginosa to establish infections in humans. We have identified five QS-deficient strains through screening 200 isolates from patients with urinary tract, lower respiratory tract and wound infections. These strains lacked LasB and LasA activities and produced either no or very low levels of the autoinducers N-(3-oxododecanoyl) homoserine lactone and N-butyryl homoserine lactone. PCR analysis revealed that three isolates contained all four QS genes (lasI, lasR, rhlI and rhlR) while two isolates lacked both the lasR and rhlR genes. We also examined the five isolates for other virulence factors. The isolates produced variable levels of exotoxin A and, with one exception, were deficient in pyocyanin production. One isolate produced the type III secretion system (TTSS) effector proteins ExoS and ExoT, two isolates produced ExoT only and two isolates produced no TTSS proteins. The isolates produced weak to moderate biofilms on abiotic surfaces. Analysis of the patients' data revealed that two of the isolates represented a single strain that was isolated twice from the same patient within a 1 month interval. One QS-deficient clinical isolate (CI-1) lacked all tested virulence factors and produced a weak biofilm. These results suggest that naturally occurring QS-deficient strains of P. aeruginosa do occur and are capable of causing infections; and, that besides the known virulence factors, additional factors may contribute to the ability of certain strains such as CI-1 to establish an infection.

Characterization of cell-to-cell signaling-deficient Pseudomonas aeruginosa strains colonizing intubated patients

Cell-to-cell signaling involving N-acyl-homoserine lactone compounds termed autoinducers (AIs) is instrumental to virulence factor production and biofilm development by Pseudomonas aeruginosa. In order to determine the importance of cell-to-cell signaling during the colonization of mechanically ventilated patients, we collected 442 P. aeruginosa pulmonary isolates from 13 patients. Phenotypic characterization showed that 81% of these isolates produced the AI-dependent virulence factors elastase, protease, and rhamnolipids. We identified nine genotypically distinct P. aeruginosa strains. Six of these strains produced AIs [N-butanoyl-homoserine lactone or N-(3-oxo-dodecanoyl)-homoserine lactone] and extracellular virulence factors (elastase, total exoprotease, rhamnolipid, hydrogen cyanide, or pyocyanin) in vitro. Three of the nine strains were defective in the production of both AIs and extracellular virulence factors. Two of these strains had mutational defects in both the lasR and rhlR genes, which encode the N-acyl-homoserine lactone-dependent transcriptional regulators LasR and RhlR, respectively. The third of these AI-deficient strains was only mutated in the lasR gene. Our observations suggest that most, but not all, strains colonizing intubated patients are able to produce virulence factors and that mutations affecting the cell-to-cell signaling circuit are preferentially located in the transcriptional regulator genes.

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.