Epidemiology of infections due to Pseudomonas aeruginosa

A long-chain flavodoxin protects Pseudomonas aeruginosa from oxidative stress and host bacterial clearance

Long-chain flavodoxins, ubiquitous electron shuttles containing flavin mononucleotide (FMN) as prosthetic group, play an important protective role against reactive oxygen species (ROS) in various microorganisms. Pseudomonas aeruginosa is an opportunistic pathogen which frequently has to face ROS toxicity in the environment as well as within the host. We identified a single ORF, hereafter referred to as fldP (for flavodoxin from P. aeruginosa), displaying the highest similarity in length, sequence identity and predicted secondary structure with typical long-chain flavodoxins. The gene was cloned and expressed in Escherichia coli. The recombinant product (FldP) could bind FMN and exhibited flavodoxin activity in vitro. Expression of fldP in P. aeruginosa was induced by oxidative stress conditions through an OxyR-independent mechanism, and an fldP-null mutant accumulated higher intracellular ROS levels and exhibited decreased tolerance to H₂O₂ toxicity compared to wild-type siblings. The mutant phenotype could be complemented by expression of a cyanobacterial flavodoxin. Overexpression of FldP in a mutT-deficient P. aeruginosa strain decreased H₂O₂-induced cell death and the hypermutability caused by DNA oxidative damage. FldP contributed to the survival of P. aeruginosa within cultured mammalian macrophages and in infected Drosophila melanogaster, which led in turn to accelerated death of the flies. Interestingly, the fldP gene is present in some but not all P. aeruginosa strains, constituting a component of the P. aeruginosa accessory genome. It is located in a genomic island as part of a self-regulated polycistronic operon containing a suite of stress-associated genes. The collected results indicate that the fldP gene encodes a long-chain flavodoxin, which protects the cell from oxidative stress, thereby expanding the capabilities of P. aeruginosa to thrive in hostile environments.

Coping with toxic reactive oxygen species (ROS) generated as by-products of aerobic metabolism is a major challenge for O₂-thriving organisms, which deploy multilevel responses to prevent ROS-triggered damage, including membrane modifications, induction of antioxidant and repair systems and/or replacement of ROS-sensitive targets by resistant isofunctional versions, among others. The opportunistic pathogen Pseudomonas aeruginosa is frequently exposed to ROS in the environment as well as within the host, and we describe herein a new response by which this microorganism can deal with oxidative stress. This pathway depends on a previously uncharacterized gene that we named fldP (for flavodoxin from P. aeruginosa), which encodes a flavoprotein that belongs to the family of long-chain flavodoxins. FldP exhibited a protective role against ROS-dependent physiological and mutational damage, and contributed to the survival of P. aeruginosa during in vivo infection of flies as well as within mammalian macrophagic cells. Thus, fldP increases the adaptive repertoire of P. aeruginosa to face oxidative stress.

Effect of long-term voluntary exercise wheel running on susceptibility to bacterial pulmonary infections in a mouse model

Regular moderate exercise has been suggested to exert anti-inflammatory effects and improve immune effector functions, resulting in reduced disease incidence and viral infection susceptibility. Whether regular exercise also affects bacterial infection susceptibility is unknown. The aim of this study was to investigate whether regular voluntary exercise wheel running prior to a pulmonary infection with bacteria (P. aeruginosa) affects lung bacteriology, sickness severity and phagocyte immune function in mice. Balb/c mice were randomly placed in a cage with or without a running wheel. After 28 days, mice were intranasally infected with P. aeruginosa. Our study showed that regular exercise resulted in a higher sickness severity score and bacterial (P. aeruginosa) loads in the lungs. The phagocytic capacity of monocytes and neutrophils from spleen and lungs was not affected. Although regular moderate exercise has many health benefits, healthy mice showed increased bacterial (P. aeruginosa) load and symptoms, after regular voluntary exercise, with perseverance of the phagocytic capacity of monocytes and neutrophils. Whether patients, suffering from bacterial infectious diseases, should be encouraged to engage in exercise and physical activities with caution requires further research.

Deep sequencing analyses expands the Pseudomonas aeruginosa AmpR regulon to include small RNA-mediated regulation of iron acquisition, heat shock and oxidative stress response

Pathogenicity of Pseudomonas aeruginosa, a major cause of many acute and chronic human infections, is determined by tightly regulated expression of multiple virulence factors. Quorum sensing (QS) controls expression of many of these pathogenic determinants. Previous microarray studies have shown that the AmpC β-lactamase regulator AmpR, a member of the LysR family of transcription factors, also controls non-β-lactam resistance and multiple virulence mechanisms. Using RNA-Seq and complementary assays, this study further expands the AmpR regulon to include diverse processes such as oxidative stress, heat shock and iron uptake. Importantly, AmpR affects many of these phenotypes, in part, by regulating expression of non-coding RNAs such as rgP32, asRgsA, asPrrF1 and rgRsmZ. AmpR positively regulates expression of the major QS regulators LasR, RhlR and MvfR, and genes of the Pseudomonas quinolone system. Chromatin immunoprecipitation (ChIP)-Seq and ChIP–quantitative real-time polymerase chain reaction studies show that AmpR binds to the ampC promoter both in the absence and presence of β-lactams. In addition, AmpR directly binds the lasR promoter, encoding the QS master regulator. Comparison of the AmpR-binding sequences from the transcriptome and ChIP-Seq analyses identified an AT-rich consensus-binding motif. This study further attests to the role of AmpR in regulating virulence and physiological processes in P. aeruginosa.

Twitching motility activity, biofilm formation, and genetic typing for clinical isolates of Pseudomonas aeruginosa by random amplified DNA PCR

A total of 44 Pseudomonas aeruginosa clinical strains were studied by random amplified polymorphic DNA PCR. (RAPD)-PCR analysis determined the presence of 15 genotypes, with the most frequent genotype A detected in 27.3% of the strains. It was observed that clonally related strains were isolated from patients within the same ward and among different wards of two hospitals. The collection of P. aeruginosa was also screened in microtiter plates made of polystyrene to test for their ability to form a biofilm on an abiotic surface. Generally most of the strains (88.6%) showed a significant ability to form biofilm. We found a correlation between twitching motility activity and between biofilm production and source of isolation of strains. No correlation was observed between P. aeruginosa strain genotypes and biofilm formation, as well as source and place of isolation.

Resistance of Gram-Negative Bacilli in Lebanon

Several studies have reported the isolation of resistant Gram-Negative Bacilli in Lebanon. However, those studies are new and scarce as compared to worldwide data and mostly restricted to single center studies. In this review, we attempt to provide a reliable and comprehensive report describing the current situation and providing prospects for bacterial resistance in Lebanon. Several studies have shown that Extended Spectrum β-Lactamase-producing E. coli and K. pneumoniae strains are being increasingly reported. Moreover, 2.15% of E. coli and 7.84% of K. pneumoniae isolates have shown carbapenem resistance and up to 30% of isolated E. coli strains were found to be Multi-Drug Resistant. Molecular studies showed that the most widespread β-Lactamases in Lebanon are of the CTX-M-15 and SHV types. In addition, K. pneumoniae strains producing metallo-β-Lactamase and Klebsiella pneumoniae Carbapenemase have been reported. Resistant Pseudomonas aeruginosa and Acinetobacter baumannii caused several nosocomial infections and some Acinetobacter baumannii strains were found to produce OXA-58 type ESBL. The few data addressing the rate of antibiotic consumption in Lebanon show a high rate of antibiotic misuse and abuse. In conclusion, there is a need for antibiotic stewardship programs and additional studies that go beyond the scope of single-center studies in Lebanon.

Risk factors for pan-resistant Pseudomonas aeruginosa bacteremia and the adequacy of antibiotic therapy

INTRODUCTION

The aim of this study was to determine risk factors for acquiring carbapenem-resistant Pseudomonas aeruginosa bacteremia (CR-PA) and factors associated with in-hospital mortality.

METHODS

Seventy-seven cases of bacteremia caused by P. aeruginosa were evaluated in a hospital with high incidence of CR-PA. Clinical and laboratorial factors, and previous use of antibiotics were also evaluated. In one analysis, CR-PA and carbapenem-susceptible P. aeruginosa (CS-PA) bacteremia were compared. A second analysis compared patients who died with survivors.

RESULTS

Among 77 P. aeruginosa bacteremia, 29 were caused by CR-PA. Admission to the intensive care unit, higher number of total leukocytes, and previous use of carbapenem were statistically associated with CR-PA. In the multivariate analysis, only previous use of carbapenem (including ertapenem) turned out to be a risk factor for CR-PA (p=0.014). The 30-day mortality of patients with P. aeruginosa bloodstream infection was 44.8% for CS-PA and 54.2% for patients with CR-PA (p=0.288). Chronic renal failure, admission to the intensive care unit, mechanical ventilation, and central venous catheter were risk factors for mortality. Incorrect treatment increased mortality of patients with bacteremia caused by CS-PA, but not for CR-SA. The odd ratio of mortality associated with incorrect therapy in patients with CS-PA was 3.30 (1.01-10.82; p=0.043). The mortality of patients with bacteremia caused by CR-PA was unexpectedly similar regardless of antimicrobial treatment adequacy.

CONCLUSION

Appropriate treatment for CS-PA bacteremia initiated within the first 24 hours was associated with lower mortality, but this cannot be extrapolated for CR-PA.

Bacteriophages in the experimental treatment of Pseudomonas aeruginosa infections in mice

The regular increase of drug-resistant pathogens has been a major force in the renewed interest in the use of bacteriophages as therapeutics. In addition to experience acquired in eastern Europe where bacteriophages have been used to treat bacterial infections in humans, in Western countries only experimental models have been developed until recently. The Gram-negative bacterium Pseudomonas aeruginosa is an opportunistic pathogen causing particularly severe infections in cystic fibrosis patients. Several experimental models in mice have yielded encouraging results for the use of bacteriophages to treat or prevent septicemia, skin and lungs infections caused by P. aeruginosa. Now, a phase II clinical trial conducted in the United Kingdom provides evidence for the efficacy of bacteriophage treatments in chronic otitis due to antibiotic-resistant P. aeruginosa strains. Together with experimental models, these results provide an incentive to develop more research and clinical studies to fully appreciate the benefits of the use of bacteriophages in medicine.

Phenotypic and genotypic diversity of Pseudomonas aeruginosa strains isolated from hospitals in siedlce (Poland)

A total of 62 Pseudomonas aeruginosa strains isolated from two hospitals in Siedlce (Poland) were studied by repetitive element based PCR (rep-PCR) using BOX primer. BOX-PCR results revealed the presence of 7 numerous genotypes and 31 unique patterns among isolates. Generally, the strains of P. aeruginosa were characterized by resistance to many antibiotics tested and by differences in serogroups and types of growth on cetrimide agar medium. However, the P. aeruginosa strains isolated from faeces showed much lower phenotypic and genotypic variations in comparison with strains obtained from other clinical specimens. It was observed that genetic techniques supported by phenotypic tests have enabled to conduct a detailed characterization of P. aeruginosa strains isolated from a particular environment at a particular time.

The deceased organ donor with an "open abdomen": proceed with caution

In solid organ transplantation, the disparity between donor supply and patients awaiting transplant continues to increase. The organ shortage has led to relaxation of historic contraindications to organ donation. A large percentage of deceased organ donors have been subjected to traumatic injuries, which can often result in intervention that leads to abdominal packing and intensive care unit resuscitation. The donor with this "open abdomen" (OA) presents a situation in which the risk of organ utilization is difficult to quantify. There exists a concern for the potential of a higher risk for both bacterial and fungal infections, including multidrug-resistant (MDR) pathogens because of the prevalence of antibiotic use and critical illness in this population. No recommendations have been established for utilization of organs from these OA donors, because data are limited. Herein, we report a case of a 21-year-old donor who had sustained a gunshot wound to his abdomen, resulting in a damage-control laparotomy and abdominal packing. The donor subsequently suffered brain death, and the family consented to organ donation. A multiorgan procurement was performed with respective transplantation of the procured organs (heart, liver, and both kidneys) into 4 separate recipients. Peritoneal swab cultures performed at the time of organ recovery grew out MDR Pseudomonas aeruginosa on the day after procurement, subsequently followed by positive blood and sputum cultures as well. All 4 transplant recipients subsequently developed infections with MDR P. aeruginosa, which appeared to be donor-derived with similar resistance patterns. Appropriate antibiotic coverage was initiated in all of the patients. Although 2 of the recipients died, mortality did not appear to be clearly associated with the donor-derived infections. This case illustrates the potential infectious risk associated with organs from donors with an OA, and suggests that aggressive surveillance for occult infections should be pursued.

Role of macrophage chemoattractant protein-1 in acute inflammation after lung contusion

Lung contusion (LC), commonly observed in patients with thoracic trauma is a leading risk factor for development of acute lung injury/acute respiratory distress syndrome. Previously, we have shown that CC chemokine ligand (CCL)-2, a monotactic chemokine abundant in the lungs, is significantly elevated in LC. This study investigated the nature of protection afforded by CCL-2 in acute lung injury/acute respiratory distress syndrome during LC, using rats and CC chemokine receptor (CCR) 2 knockout (CCR2(-/-)) mice. Rats injected with a polyclonal antibody to CCL-2 showed higher levels of albumin and IL-6 in the bronchoalveolar lavage and myeloperoxidase in the lung tissue after LC. Closed-chest bilateral LC demonstrated CCL-2 localization in alveolar macrophages (AMs) and epithelial cells. Subsequent experiments performed using a murine model of LC showed that the extent of injury, assessed by pulmonary compliance and albumin levels in the bronchoalveolar lavage, was higher in the CCR2(-/-) mice when compared with the wild-type (WT) mice. We also found increased release of IL-1β, IL-6, macrophage inflammatory protein-1, and keratinocyte chemoattractant, lower recruitment of AMs, and higher neutrophil infiltration and phagocytic activity in CCR2(-/-) mice at 24 hours. However, impaired phagocytic activity was observed at 48 hours compared with the WT. Production of CCL-2 and macrophage chemoattractant protein-5 was increased in the absence of CCR2, thus suggesting a negative feedback mechanism of regulation. Isolated AMs in the CCR2(-/-) mice showed a predominant M1 phenotype compared with the predominant M2 phenotype in WT mice. Taken together, the above results show that CCL-2 is functionally important in the down-modulation of injury and inflammation in LC.

Extrachromosomal DNA length and antibiograms of Staphylococcus aureus and Pseudomonas aeruginosa isolated from tears of HIV/AIDS patients after curing with sodium dodecyl sulphate

Staphylococcus aureus and Pseudomonas aeruginosa strains were isolated from eye swab samples randomly obtained from 100 seropositive HIV/AIDS patients who reported to various anti-retroviral treatment clinics at the University of Benin Teaching Hospital and Central Hospital both based in Benin City, Nigeria. Invitro antibiotic sensitivity patterns of strains before curing were determined by the Kirby-Bauer disc diffusion technique. Resistance plasmid DNA of multidrug resistant strains was cured with 0.1% sodium dodecyl sulphate and cured strains were again subjected to in vitro antibiotic sensitivity testing. EcoRI and Hind III restriction endonuclease enzymes were used to make cuts on extracted plasmid DNA whose length sizes were then determined. A total of 36 (36.0%) strains made up of 27 (75.0%) Staphylococcus. aureus and 9 (25.0%) Pseudomonas aeruginosa were isolated of which 7 (19.4%) strains showed multidrug resistance to ciprofloxacin, pefloxacin, ofloxacine, gentamycin, tetracycline, ampicillin, chloramphenicol, nitrofurantoin and erythromycin. All seven multidrug resistant strains before curing, recorded 85.7%, 42.9%, 14.3% and 14.3% sensitivity in that decreasing order to ciprofloxacin, pefloxacin, ofloxacin and gentamycin respectively. There was 0.0% sensitivity each to tetracycline and ampicillin. After curing, there was enhanced sensitivity of 100.0%, 85.7%, 28.6% and 71.4% respectively. There was also 28.6% and 57.1% improved sensitivity to tetracycline and ampicillin after curing. Before curing, there was 76.2% average resistance to all used antibiotics and this reduced to 47.6% after curing Staph. aureus plasmid DNA. In the case of Pseudomonas aeruginosa, there was an average resistance of 76.3% before curing which fell to 42.5% after curing. EcoRI restriction enzyme gave the plasmid DNA length of Staphylococcus aureus strain 04 as 4.0Kb and this size depended upon the distance between recognition sites. Isolation of 36 (36.0%) strains of both isolates from 100 eye swabs shows the danger these organisms portend to all categories of opticians. The cheapness and high sensitivity of gentamycin justifies its use as eye drops for treatment of some eye infections. Curing of plasmid DNA is an indication that if SDS is administered to the organisms in sublethal doses, it can lead to the elimination of plasmid DNA without adverse effect on the genomic DNA of the bacterial strains.

P. aeruginosa infection increases morbidity in experimental cholesteatomas

OBJECTIVES

Clinicians have long noted that infected cholesteatomas are more aggressive than uninfected ones without data to support these observations. The purpose of this study is to determine the etiological role of biofilm forming P. aeruginosa (PA) and the virulence factor, type IV pili (TFP), in the pathogenesis of experimental cholesteatomas.

DESIGN

We evaluated three different PA strains and one Escherichia coli strain in cholesteatoma progression: PA14, a well-characterized wound isolate, OPPA8, an otopathogenic strain from a human cholesteatoma, OPPA8-NP, an isogenic TFP deletion mutant, and DH5α, an E. coli strain.

METHODS

Cholesteatomas were induced in gerbils. We inoculated the right ear with bacteria and the left with vehicle. After 6 weeks their cholesteatomas were evaluated by micro-CT scanning. Cholesteatoma size and bone resorption were analyzed digitally.

RESULTS

Results demonstrate that PA infection increases cholesteatoma size when compared to uninfected controls: OPPA8 showed an 8.9-fold increase, PA14 a 2.6-fold increase, OPPA8-NP a 1.9-fold increase, while DH5α was not increased over controls. Additionally, infected bullae showed 10 to 50% more cholesteatoma-induced bone resorption.

CONCLUSIONS

In this model, PA infected cholesteatomas enlarge more rapidly and are more destructive than uninfected controls. OPPA8, the strain from a human cholesteatoma, showed the greatest enlargement and bone destruction. Additionally, we demonstrate that TFP is a virulence factor in this model because the nonpiliated isogenic mutant, OPPA8-NP, was significantly less aggressive than the wild-type OPPA8 indicating that type IV pili may be a virulence factor in this disease.

High-resolution time series of Pseudomonas aeruginosa gene expression and rhamnolipid secretion through growth curve synchronization

Background

Online spectrophotometric measurements allow monitoring dynamic biological processes with high-time resolution. Contrastingly, numerous other methods require laborious treatment of samples and can only be carried out offline. Integrating both types of measurement would allow analyzing biological processes more comprehensively. A typical example of this problem is acquiring quantitative data on rhamnolipid secretion by the opportunistic pathogen Pseudomonas aeruginosa. P. aeruginosa cell growth can be measured by optical density (OD₆₀₀) and gene expression can be measured using reporter fusions with a fluorescent protein, allowing high time resolution monitoring. However, measuring the secreted rhamnolipid biosurfactants requires laborious sample processing, which makes this an offline measurement.

Results

Here, we propose a method to integrate growth curve data with endpoint measurements of secreted metabolites that is inspired by a model of exponential cell growth. If serial diluting an inoculum gives reproducible time series shifted in time, then time series of endpoint measurements can be reconstructed using calculated time shifts between dilutions. We illustrate the method using measured rhamnolipid secretion by P. aeruginosa as endpoint measurements and we integrate these measurements with high-resolution growth curves measured by OD₆₀₀ and expression of rhamnolipid synthesis genes monitored using a reporter fusion. Two-fold serial dilution allowed integrating rhamnolipid measurements at a ~0.4 h^-1 frequency with high-time resolved data measured at a 6 h^-1 frequency. We show how this simple method can be used in combination with mutants lacking specific genes in the rhamnolipid synthesis or quorum sensing regulation to acquire rich dynamic data on P. aeruginosa virulence regulation. Additionally, the linear relation between the ratio of inocula and the time-shift between curves produces high-precision measurements of maximum specific growth rates, which were determined with a precision of ~5.4%.

Conclusions

Growth curve synchronization allows integration of rich time-resolved data with endpoint measurements to produce time-resolved quantitative measurements. Such data can be valuable to unveil the dynamic regulation of virulence in P. aeruginosa. More generally, growth curve synchronization can be applied to many biological systems thus helping to overcome a key obstacle in dynamic regulation: the scarceness of quantitative time-resolved data.

Prevalence and antimicrobial-resistance of Pseudomonas aeruginosa in swimming pools and hot tubs

Pseudomonas aeruginosa is an important opportunistic pathogen in recreational waters and the primary cause of hot tub folliculitis and otitis externa. The aim of this surveillance study was to determine the background prevalence and antimicrobial resistance profile of P. aeruginosa in swimming pools and hot tubs. A convenience sample of 108 samples was obtained from three hot tubs and eight indoor swimming pools. Water and swab samples were processed using membrane filtration, followed by confirmation with polymerase chain reaction. Twenty-three samples (21%) were positive for P. aeruginosa, and 23 isolates underwent susceptibility testing using the microdilution method. Resistance was noted to several antibiotic agents, including amikacin (intermediate), aztreonam, ceftriaxone, gentamicin, imipenem, meropenem (intermediate), ticarcillin/clavulanic acid, tobramycin (intermediate), and trimethoprim/sulfamethoxazole. The results of this surveillance study indicate that 96% of P. aeruginosa isolates tested from swimming pools and hot tubs were multidrug resistant. These results may have important implications for cystic fibrosis patients and other immune-suppressed individuals, for whom infection with multidrug-resistant P. aeruginosa would have greater impact. Our results underlie the importance of rigorous facility maintenance, and provide prevalence data on the occurrence of antimicrobial resistant strains of this important recreational water-associated and nosocomial pathogen.

Differential attraction of malaria mosquitoes to volatile blends produced by human skin bacteria

The malaria mosquito Anopheles gambiae sensu stricto is mainly guided by human odour components to find its blood host. Skin bacteria play an important role in the production of human body odour and when grown in vitro, skin bacteria produce volatiles that are attractive to A. gambiae. The role of single skin bacterial species in the production of volatiles that mediate the host-seeking behaviour of mosquitoes has remained largely unknown and is the subject of the present study. Headspace samples were taken to identify volatiles that mediate this behaviour. These volatiles could be used as mosquito attractants or repellents. Five commonly occurring species of skin bacteria were tested in an olfactometer for the production of volatiles that attract A. gambiae. Odour blends produced by some bacterial species were more attractive than blends produced by other species. In contrast to odours from the other bacterial species tested, odours produced by Pseudomonas aeruginosa were not attractive to A. gambiae. Headspace analysis of bacterial volatiles in combination with behavioural assays led to the identification of six compounds that elicited a behavioural effect in A. gambiae. Our results provide, to our knowledge, the first evidence for a role of selected bacterial species, common on the human skin, in determining the attractiveness of humans to malaria mosquitoes. This information will be used in the further development of a blend of semiochemicals for the manipulation of mosquito behaviour.

What can Dictyostelium bring to the study of Pseudomonas infections?

Bacterial infections are complex events. They are studied in a variety of simple model systems, using mammalian or non-mammalian hosts, all of which fail to reproduce fully the situation in infected patients. Each model presents a combination of conceptual, practical, and ethical advantages and disadvantages. In this review, we detail the use of Dictyostelium discoideum amoebae as a model to study Pseudomonas aeruginosa. More specifically, our aim is to explore what this additional model system can bring to our understanding of Pseudomonas infections. The study of interactions between Dictyostelium amoebae and Pseudomonas provides a view of the selection pressures exerted by environmental predators on Pseudomonas. It also represents a unique system to assess the virulence of very large numbers of Pseudomonas strains.

Multilevel modelling of the prevalence of hospitalized patients infected with Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the leading nosocomial pathogens. The question of the respective contribution of endogenous and exogenous sources remains controversial. In this study, we shed new light on this issue by means of a multilevel logistic regression analysis which allowed a simultaneous investigation of factors associated with prevalence of patients infected with P. aeruginosa at two levels: patient and healthcare facility (HCF) in the eastern regions of France. A total of 25 533 in-patients from 51 HCFs were included in the analysis. The overall prevalence was 0·37% (range 0-1·65%). Multilevel modelling estimated that <14% of total variability of the outcome variable was explained by differences between HCFs and that after adjusting for patient-level variables, which explained 52% of HCF-level variance, the latter became non-significantly different from zero. A compositional effect (patient factors), rather than a contextual effect (ecological factors), explains heterogeneity of the prevalence of patients infected with P. aeruginosa in the eastern HCFs of France.

Antibacterial-resistant Pseudomonas aeruginosa: clinical impact and complex regulation of chromosomally encoded resistance mechanisms

Treatment of infectious diseases becomes more challenging with each passing year. This is especially true for infections caused by the opportunistic pathogen Pseudomonas aeruginosa, with its ability to rapidly develop resistance to multiple classes of antibiotics. Although the import of resistance mechanisms on mobile genetic elements is always a concern, the most difficult challenge we face with P. aeruginosa is its ability to rapidly develop resistance during the course of treating an infection. The chromosomally encoded AmpC cephalosporinase, the outer membrane porin OprD, and the multidrug efflux pumps are particularly relevant to this therapeutic challenge. The discussion presented in this review highlights the clinical significance of these chromosomally encoded resistance mechanisms, as well as the complex mechanisms/pathways by which P. aeruginosa regulates their expression. Although a great deal of knowledge has been gained toward understanding the regulation of AmpC, OprD, and efflux pumps in P. aeruginosa, it is clear that we have much to learn about how this resourceful pathogen coregulates different resistance mechanisms to overcome the antibacterial challenges it faces.

Molecular characterization of class 1 integrons in MDR Pseudomonas aeruginosa isolated from clinical settings in Iran, Tehran

Seven hundred and fifty nonreplicated clinical isolates of Pseudomonas aeruginosa were collected from five hospitals during March 2007 to May 2009. Forty-one isolates (5.46%) were characterized as multidrug-resistant P. aeruginosa (MDRPA). PCR assays were used to detect class 1 integrons. Amplifications of internal variable regions (IVRs) of class 1 integrons revealed three different arrays (0.8, 1.3, and 1.7 kb) with different distributions in clinical isolates. The amplified IVRs were sequenced and three gene cassette arrays including aadB (0.8 kb), aadA6-orfD (1.3 kb), and bla(OXA10)-aacA4 (1.7 kb) were identified. In conclusion, we confirmed the high prevalence of class 1 integons with limited diversity of gene cassette arrays in MDRPA clinical isolates found from five hospitals. This is the first report showing gene cassette contents of class 1 integrons in P. aeruginosa isolates in Iran.

Global transcriptomic response of Pseudomonas aeruginosa to chlorhexidine diacetate

Pseudomonas aeruginosa is implicated in nosocomial infections and chronic respiratory infections in cystic fibrosis patients. Chlorhexidine diacetate (CHX) is a biguanide disinfectant used for bacterial control in the hospital and agricultural and domestic environments. A better understanding of the mechanism of action of CHX and the resulting response elicited by P. aeruginosa to CHX will facilitate its effective utilization for P. aeruginosa control in these environments. This study presents, for the first time, the transcriptomic response of P. aeruginosa to 0.008 mM CHX after 10 and 60 min. Our results reveal that, after both treatment times, membrane transport, oxidative phosphorylation, and electron transport genes were downregulated. After 10 min, DNA repair was downregulated and the oprH gene that blocks the self-promoted uptake of antimicrobials was upregulated. After 60 min, outer membrane protein, flagellum, pilus, oxidative phosphorylation, and electron transport genes were downregulated. The mexC and mexD genes of the MexCD-OprJ multidrug efflux pump were significantly upregulated after both treatment times. The results of this study improve our understanding of the mode of action of CHX on P. aeruginosa and provide insights into the mechanism of action of other biguanide disinfectants which can be used for the development of more efficient disinfectants.

Antibacterial-resistant Pseudomonas aeruginosa: clinical impact and complex regulation of chromosomally encoded resistance mechanisms

Treatment of infectious diseases becomes more challenging with each passing year. This is especially true for infections caused by the opportunistic pathogen Pseudomonas aeruginosa, with its ability to rapidly develop resistance to multiple classes of antibiotics. Although the import of resistance mechanisms on mobile genetic elements is always a concern, the most difficult challenge we face with P. aeruginosa is its ability to rapidly develop resistance during the course of treating an infection. The chromosomally encoded AmpC cephalosporinase, the outer membrane porin OprD, and the multidrug efflux pumps are particularly relevant to this therapeutic challenge. The discussion presented in this review highlights the clinical significance of these chromosomally encoded resistance mechanisms, as well as the complex mechanisms/pathways by which P. aeruginosa regulates their expression. Although a great deal of knowledge has been gained toward understanding the regulation of AmpC, OprD, and efflux pumps in P. aeruginosa, it is clear that we have much to learn about how this resourceful pathogen coregulates different resistance mechanisms to overcome the antibacterial challenges it faces.

Determination of the efflux pump-mediated resistance prevalence in Pseudomonas aeruginosa, using an efflux pump inhibitor

In gram negative bacteria, fluoroquinolone resistance is acquired by target mutations in topoisomerase genes or by reducing the permeation of drugs due to the increase in expression of endogenous multidrug efflux pumps that expel structurally unrelated antimicrobial agents. An ongoing challenge is searching for new inhibitory substances in order to block efflux pumps and restore the antibiotic drugs susceptibility. In this research, we sought to investigate the interplay between ciprofloxacin and an efflux pump inhibitor (EPI), phenyl alanine arginyl beta-naphtylamide (PAbetaN), to determine the prevalence of efflux pump overexpression in clinical isolates of Pseudomonas aeruginosa. Ciprofloxacin was tested at different concentrations (256-0.25 microg/ml) with a fixed concentration of PAbetaN (50 microg/ml). The isolates susceptibility profiles were analyzed by disc diffusion and agar dilution methods using 10 antibiotic discs and 4 powders. It was found that in the presence of PAbetaN, resistance to ciprofloxacin was inhibited obviously and MIC values were decreased. The comparison between subgroups of P. aeruginosa isolates with different resistance profiles indicates that efflux pump overexpression (EPO) is present in 35% of ciprofloxacin resistant isolates with no cross resistance and in variable frequencies among isolates showing cross resistance to other tested antibiotics: gentamicin (31%), ceftazidime (29%), and imipenem (18%). Altogether, these results imply that PAbetaN maybe effective to restore the fluoroquinolone drugs susceptibility in clinical treatment procedures. Results also show that increased use of a fluoroquinolone drug such as ciprofloxacin can affect the susceptibility of P. aeruginosa to other different antipseudomonal agents.

Inactivation of the hmgA gene of Pseudomonas aeruginosa leads to pyomelanin hyperproduction, stress resistance and increased persistence in chronic lung infection

Clinical isolates of Pseudomonas aeruginosa that hyperproduce a dark-brown pigment are quite often found in the lungs of chronically infected patients, suggesting that they may have an adaptive advantage in chronic infections. We have screened a library of random transposon insertions in P. aeruginosa. Transposon insertions resulting in the hyperproduction of a dark-brown pigment were found to be located in the hmgA gene, which putatively encodes the enzyme homogentisate-1,2-dioxygenase. Complementation studies indicate that hmgA disruption is responsible for the hyperproduction of pyomelanin in both laboratory and clinical isolates. A relationship between hmgA disruption and adaptation to chronic infection was explored and our results show that the inactivation of hmgA produces a slight reduction of killing ability in an acute murine model of lung infection. On the other hand, it also confers decreased clearance and increased persistence in chronic lung infections. Whether pyomelanin production is the cause of the increased adaptation to chronicity or just a side effect of hmgA inactivation is a question to be studied in future; however, this adaptation is consistent with the higher resistance to oxidative stress conferred in vitro by the pyomelanin pigment. Our results clearly demonstrate that hmgA inactivation leads to a better adaptation to chronic infection, and strongly suggest that this mechanism may be exploited in naturally occurring P. aeruginosa strains.

Contaminated feeding bottles: the source of an outbreak of Pseudomonas aeruginosa infections in a neonatal intensive care unit

BACKGROUND

Outbreaks of Pseudomonas aeruginosa have been reported in relationship with contamination of staff fingernails, hands, water baths, hand lotions and others. To our knowledge, contamination of milk and feeding bottles as a source of an outbreak of P aeruginosa infections has not been reported. The incidence of P aeruginosa infection/colonization in our neonatal intensive care unit increased from 1.9 per 1000 patient-days in August 2004 to 8.8 per 1000 patient-days in September 2004.

METHODS

Samples were collected including hand and body lotions, water from the incubator humidifying system, the health care worker hands, and the feeding bottle preparation room. Strains were epidemiologically characterized by pulsed-field gel electrophoresis of SpeI-digested genomic DNA. P aeruginosa was isolated from a total of 30 neonates during the period September 2004 to December 2004.

RESULTS

All cultures (139) of hand and body lotions, water from the incubator humidifying system, and hands of health care personnel were negative. Nine out of 48 samples collected from the feeding bottle preparation room were positive for P aeruginosa (6 samples of in-house prepared milk and 3 samples of water from dishwashers). Pulsed-field gel electrophoresis with SpeI showed that the strains isolated from neonates and from environmental samples were identical. Discontinuation of in-house preparation of feeding bottles and incorporation of unidose milk bottles stopped the outbreak.

CONCLUSION

The preparation and solution of milk from multidose powder preparation may be a source of P aeruginosa infections in a neonatal intensive care unit. The use of manufactured, nonmanipulated, unidose feeding bottles should be considered more adequate.

The Pseudomonas aeruginosa pfpI gene plays an antimutator role and provides general stress protection

Hypermutator Pseudomonas aeruginosa strains, characterized by an increased spontaneous-mutation rate, are found at high frequencies in chronic lung infections. Hypermutability is associated with the loss of antimutator genes related to DNA repair or damage avoidance systems. Only a few antimutator genes have been described in P. aeruginosa, although there is some evidence that additional genes may be involved in naturally occurring hypermutability. In order to find new P. aeruginosa antimutator genes, we constructed and screened a library of random insertions in the PA14 strain. Some previously described P. aeruginosa and/or Escherichia coli antimutator genes, such as mutS, mutL, uvrD, mutT, ung, and mutY, were detected, indicating a good coverage of our insertional library. One additional mutant contained an insertion in the P. aeruginosa PA14-04650 (pfpI) gene, putatively encoding a member of the DJ-1/ThiJ/PfpI superfamily, which includes chaperones, peptidases, and the Parkinson's disease protein DJ-1a. The pfpI-defective mutants in both PAO1 and PA14 showed higher spontaneous mutation rates than the wild-type strains, suggesting that PfpI plays a key role in DNA protection under nonstress conditions. Moreover, the inactivation of pfpI resulted in a dramatic increase in the H(2)O(2)-induced mutant frequency. Global transcription studies showed the induction of bacteriophage Pf1 genes and the repression of genes related to iron metabolism, suggesting that the increased spontaneous-mutant frequency may be due to reduced protection against the basal level of reactive oxygen species. Finally, pfpI mutants are more sensitive to different types of stress and are affected in biofilm formation.

Persistent infection with Pseudomonas aeruginosa in ventilator-associated pneumonia

RATIONALE

Pseudomonas aeruginosa is one of the leading causes of gram-negative ventilator-associated pneumonia (VAP) associated with a mortality rate of 34 to 68%. Recent evidence suggests that P. aeruginosa in patients with VAP may persist in the alveolar space despite adequate antimicrobial therapy. We hypothesized that failure to eradicate P. aeruginosa from the lung is linked to type III secretory system (TTSS) isolates.

OBJECTIVES

To determine the mechanism by which infection with P. aeruginosa in patients with VAP may evade the host immune response.

METHODS

Thirty-four patients with P. aeruginosa VAP underwent noninvasive bronchoalveolar lavage (BAL) at the onset of VAP and on Day 8 after initiation of antibiotic therapy. Isolated pathogens were analyzed for secretion of type III cytotoxins. Neutrophil apoptosis in BAL fluid was quantified by assessment of nuclear morphology on Giemsa-stained cytocentrifuge preparations. Neutrophil elastase was assessed by immunoenzymatic assay.

MEASUREMENTS AND MAIN RESULTS

Twenty-five out of the 34 patients with VAP secreted at least one of type III proteins. There was a significant difference in apoptotic rate of neutrophils at VAP onset between those strains that secreted cytotoxins and those that did not. Neutrophil elastase levels were positively correlated with the rate of apoptosis (r = 0.43, P < 0.01). Despite adequate antimicrobial therapy, 13 out of 25 TTSS(+) isolates were recovered at Day 8 post-VAP, whereas eradication was achieved in all patients who had undetectable levels of type III secretion proteins.

CONCLUSIONS

The increased apoptosis in neutrophils by the TTSS(+) isolates may explain the delay in eradication of Pseudomonas strains in patients with VAP. Short-course antimicrobial therapy may not be adequate in clearing the infection with a TTSS secretory phenotype.

Molecular Epidemiology of Pseudomonas aeruginosa in the Intensive Care Units - A Review

Pseudomonas aeruginosa is one of the leading nosocomial pathogens in intensive care units (ICU). This opportunist pathogen is commonly recovered from moist environments, and is also found colonizing 2.6 to 24% of hospitalized patients. We reviewed the recent literature that used highly discriminatory typing methods to precisely identify the reservoirs and modes of transmission of this microorganism in the ICU setting. In most ICUs, the endogenous flora was suspected to be the main source of infection compared to exogenous sources (other patients, the contaminated environment such as sinks or taps). However, the percentage of endogenous versus exogenous sources might vary considerably from one setting to another. Reasons for this include the compliance of health care workers to infection control measures, the contamination of the environment, and probably also the biology of the pathogen (intrinsic fitness factors). As P. aerugi-nosa is ubiquitous in the environment and colonizes up to 15% of hospitalized patients, eradication of the reservoir is difficult, if not impossible. Therefore, efforts should primarily focus on reinforcement of infection control measures to limit its transmission.

Pseudomonas aeruginosa: resistance and therapeutic options at the turn of the new millennium

Pseudomonas aeruginosa is a major cause of nosocomial infections. This organism shows a remarkable capacity to resist antibiotics, either intrinsically (because of constitutive expression of beta-lactamases and efflux pumps, combined with low permeability of the outer-membrane) or following acquisition of resistance genes (e.g., genes for beta-lactamases, or enzymes inactivating aminoglycosides or modifying their target), over-expression of efflux pumps, decreased expression of porins, or mutations in quinolone targets. Worryingly, these mechanisms are often present simultaneously, thereby conferring multiresistant phenotypes. Susceptibility testing is therefore crucial in clinical practice. Empirical treatment usually involves combination therapy, selected on the basis of known local epidemiology (usually a beta-lactam plus an aminoglycoside or a fluoroquinolone). However, therapy should be simplified as soon as possible, based on susceptibility data and the patient's clinical evolution. Alternative drugs (e.g., colistin) have proven useful against multiresistant strains, but innovative therapeutic options for the future remain scarce, while attempts to develop vaccines have been unsuccessful to date. Among broad-spectrum antibiotics in development, ceftobiprole, sitafloxacin and doripenem show interesting in-vitro activity, although the first two molecules have been evaluated in clinics only against Gram-positive organisms. Doripenem has received a fast track designation from the US Food and Drug Administration for the treatment of nosocomial pneumonia. Pump inhibitors are undergoing phase I trials in cystic fibrosis patients. Therefore, selecting appropriate antibiotics and optimising their use on the basis of pharmacodynamic concepts currently remains the best way of coping with pseudomonal infections.

Increase of imipenem resistance among Pseudomonas aeruginosa isolates from a Polish paediatric hospital (1993-2002)

Analysis of the in vitro activity of imipenem and 13 other antibiotics against 2485 Pseudomonas aeruginosa isolates obtained from clinical specimens from children hospitalized during 1993-2002 was performed. In 2002, the percentage of P. aeruginosa isolates susceptible to all tested antibiotics, with the exception of imipenem, increased or remained on nearly the same level as in 1993. An increase of resistance to imipenem from 4.3% to 18.3% was observed. The MIC(90) value of imipenem increased from 2mg/L to 16 mg/L. Simultaneously, a four-fold increase of the usage of carbapenems imipenem and meropenem in the hospital was noted. In 2000-2001, a high incidence of imipenem-resistant strains was observed. The imipenem-resistant P. aeruginosa strains of serotype O6 from the general surgery ward and serotype O11 from the intensive care unit were shown to be clonally related by the pulsed-field gel electrophoresis method.

Pseudomonas aeruginosa infective endocarditis presenting as bacterial meningitis

Pseudomonas aeruginosa is a rare cause of infective endocarditis. The case of community-acquired P. aeruginosa infective endocarditis reported here is the first described in the literature to present as bacterial meningitis. Furthermore, new risk factors for P. aeruginosa infective endocarditis, including mitral annular calcification and re-use of insulin syringes, are proposed. Treatment of P. aeruginosa infective endocarditis complicated by bacterial meningitis is discussed.

The Epidemiological Profile of Infections with Multidrug-Resistant Pseudomonas aeruginosa and Acinetobacter Species

Isolates of Pseudomonas aeruginosa or Acinetobacter species that are resistant to all, or almost all, commercially available antibiotics are now prevalent worldwide. Typically, these strains are recovered from patients in intensive care units who have ventilator-associated pneumonia. "Panresistant" strains can be defined as strains that are resistant to all beta -lactam and quinolone antibiotics recommended as empirical therapy for ventilator-associated pneumonia. These strains are well adapted to the hospital environment--molecular epidemiological studies have frequently revealed that only 1 or 2 clones caused outbreaks in intensive care units. However, panresistant strains may also be selected by antibiotic use. Given the lack of antibiotic options to treat infection with panresistant strains, enhanced surveillance for these organisms is necessary at unit-specific, institutional, and national levels.

Exogenous sources of pseudomonas aeruginosa in intensive care unit patients: implementation of infection control measures and follow-up with molecular typing

BACKGROUND

In 1998, a study in the intensive care unit (ICU) of our institution suggested possible transmission of Pseudomonas aeruginosa from faucet to patient and from patient to patient. Infection-control measures were implemented to reduce the degree of P. aeruginosa colonization in faucets, to reduce the use of faucet water in certain patient care procedures, and to reduce the rate of transmission from patient to patient.

OBJECTIVE

To evaluate the effect of the control measures instituted in 1999 to prevent P. aeruginosa infection and colonization in ICU patients.

DESIGN

Prospective, molecular, epidemiological investigation.

SETTING

A 870-bed, university-affiliated, tertiary care teaching hospital.

METHODS

The investigation was performed in a manner identical to the 1998 investigation. ICU patients with a clinical specimen positive for P. aeruginosa were identified prospectively. Swab specimens from the inner part of the ICU faucets were obtained for the culture on 9 occasions between September 1997 and December 2000. All patients and environmental isolates were typed by pulsed-field gel electrophoresis (PFGE).

RESULTS

Compared with the 1998 study, in 2000 we found that the annual incidence of ICU patients colonized or infected with P. aeruginosa had decreased by half (26.6 patients per 1,000 admissions in 2000 vs 59.0 patients per 1,000 admissions in 1998), although the populations of patients were comparable. This decrease was the result of the decreased incidence of cases in which an isolate had a PFGE pattern identical to that of an isolate from a faucet (7.0 cases per 1,000 admissions in 2000, vs 23.6 per 1,000 admissions in 1998) or from another patient (6.5 cases per 1,000 admissions in 2000 vs 16.5 cases per 1,000 admissions in 1998), whereas the incidence of cases in which the isolate had a unique PFGE pattern remained nearly unchanged (13.1 cases per 1,000 admissions in 2000 vs 15.6 cases per 1,000 admissions in 1998).

CONCLUSIONS

These results suggest that infection control measures were effective in decreasing the rate of P. aeruginosa colonization and infection in ICU patients, confirming that P. aeruginosa strains were of exogenous origin in a substantial proportion of patients during the preintervention period.

Multidrug-resistant Pseudomonas aeruginosa: risk factors and clinical impact

Pseudomonas aeruginosa, a leading nosocomial pathogen, may become multidrug resistant (MDR). Its rate of occurrence, the individual risk factors among affected patients, and the clinical impact of infection are undetermined. We conducted an epidemiologic evaluation and molecular typing using pulsed-field gel electrophoresis (PFGE) of 36 isolates for 82 patients with MDR P. aeruginosa and 82 controls matched by ward, length of hospital stay, and calendar time. A matched case-control study identified individual risk factors for having MDR P. aeruginosa, and a retrospective matched-cohort study examined clinical outcomes of such infections. The 36 isolates belonged to 12 PFGE clones. Two clones dominated, with one originating in an intensive care unit (ICU). Cases and controls had similar demographic characteristics and numbers of comorbid conditions. A multivariate model identified ICU stay, being bedridden, having high invasive devices scores, and being treated with broad-spectrum cephalosporins and with aminoglycosides as significant risk factors for isolating MDR P. aeruginosa. Having a malignant disease was a protective factor (odds ratio [OR] = 0.2; P = 0.03). MDR P. aeruginosa was associated with severe outcomes compared to controls, including increased mortality (OR = 4.4; P = 0.04), hospital stay (hazard ratio, 2; P = 0.001), and requirement for procedures (OR = 5.4; P = 0.001). The survivors functioned more poorly at discharge than the controls, and more of the survivors were discharged to rehabilitation centers or chronic care facilities. The epidemiology of MDR P. aeruginosa is complex. Critically ill patients that require intensive care and are treated with multiple antibiotic agents are at high risk. MDR P. aeruginosa infections are associated with severe adverse clinical outcomes.

Analysis of skin-graft loss due to infection: infection-related graft loss

This prospective study was performed to analyze the causes of infection-related skin-graft loss in a general population of plastic and reconstructive surgery patients. One hundred thirty-two patients who received either full- or split-thickness skin grafts to reconstruct soft-tissue defects were included. The tissue defects were grouped according to the cause as follows: vascular ulcers (9.2%), burns (14.5%), traumatic tissue defects (36.6%), and flap donor-site defects (39.7%). In all cases, the preoperative evaluation indicated an adequate wound-bed preparation. However, graft loss secondary to infection was recorded in 31 patients (23.5%). The microbiological cultures revealed Pseudomonas aeruginosa in 58.1% of the cases (P<0.05), followed by Staphylococcus aureus, Enterobacter, enterococci, and Acinetobacter; 58.3% of grafts in vascular ulcers, 47.4% of grafts in burns, 16.7% of grafts in traumatic-tissue defects; and 13.5% of grafts in donor-site defects were lost due to infection. Vascular ulcers and burns were more commonly associated with graft losses due to infection than other tissue defects (P<0.001). No correlation was found between the etiological cause of the defects and the microorganisms cultured. However, Pseudomonas infections were more fulminant and caused an increased reoperation rate 4.2 times (P<0.05). Full-thickness grafts were more resistant to infection than split-thickness grafts (P<0.05). Graft loss due to infection was also more common in grafts applied to the lower extremities or when performed at multiple sites. In conclusion, 23.7% of skin grafts were lost due to infection in a group of general plastic surgery patients. Infection-related graft loss was more commonly encountered in vascular ulcers and burn wounds, and the most common cause was Pseudomonas aeruginosa.

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.

Multiple-locus variable number tandem repeats analysis for genetic fingerprinting of pathogenic bacteria

DNA fingerprinting has attracted considerable interest as means for identifying, tracing and preventing the dissemination of infectious agents. Various methods have been developed for typing of pathogenic bacteria, which differ in discriminative power, reproducibility and ease of interpretation. During recent years a typing method, which uses the information provided by whole genome sequencing of bacterial species, has gained increased attention. Short sequence repeat (SSR) motifs are known to undergo frequent variation in the number of repeated units through cellular mechanisms most commonly active during chromosome replication. A class of SSRs, named variable number of tandem repeats (VNTRs), has proven to be a suitable target for assessing genetic polymorphisms within bacterial species. This review attempts to give an overview of bacterial agents where VNTR-based typing, or multiple-locus variant-repeat analysis (MLVA) has been developed for typing purposes, together with addressing advantages and drawbacks associated with the use of tandem repeated DNA motifs as targets for bacterial typing and identification.

[Surgical wound infections due to Pseudomonas aeruginosa in orthopedic surgery]

OBJECTIVE

The department of infection control carried out an investigation to search for the origin of 4 surgical site infections and 1 wound colonization by Pseudomonas aeruginosa in patients having undergone orthopedic surgery.

PATIENTS AND METHODS

The authors retrospectively reviewed the medical records, the clinical data of the operating units, as well as the bacteriological assessments of the infected patients. Multiple environmental samples were made to screen for P. aeruginosa and care giving was evaluated.

RESULTS

The 5 patients underwent surgery between August and September 2001 with various surgeons and were followed-up by various paramedics. The surgical procedures were varied and performed in different operating rooms. Various P. aeruginosa serotypes were isolated. No specific event could be related to the infections concerning the surgical procedures. In 3 of the 5 patients, non-sterile cotton jersey had been used, either normally (plaster or plaster splint) or after sterilization (wrapping of wounded limbs before surgical procedure). The culture samplings of non-sterile jersey were always contaminated by Enterobacteriaceae or Pseudomonas sp., with 2 positives cultures of P. aeruginosa. Only one water sample was positive, whereas other environmental samples remained negative. The reorganization of jersey supply put an end to this epidemic phenomenon.

CONCLUSION

The most probable hypothesis for surgical wound infection was the cotton jersey in 3 of the 5 cases.