Emergence of extensive-drug-resistant Pseudomonas aeruginosa in a French university hospital

Development and Evaluation of Bacteriophage Cocktail to Eradicate Biofilms Formed by an Extensively Drug-Resistant (XDR) Pseudomonas aeruginosa

Extensive and multiple drug resistance in P. aeruginosa combined with the formation of biofilms is responsible for its high persistence in nosocomial infections. A sequential method to devise a suitable phage cocktail with a broad host range and high lytic efficiency against a biofilm forming XDR P. aeruginosa strain is presented here. Out of a total thirteen phages isolated against P. aeruginosa, five were selected on the basis of their high lytic spectra assessed using spot assay and productivity by efficiency of plating assay. Phages, after selection, were tested individually and in combinations of two-, three-, four-, and five-phage cocktails using liquid infection model. Out of total 22 combinations tested, the cocktail comprising four phages viz. φPA170, φPA172, φPA177, and φPA180 significantly inhibited the bacterial growth in liquid infection model (p < 0.0001). The minimal inhibitory dose of each phage in a cocktail was effectively reduced to >10 times than the individual dose in the inhibition of XDR P. aeruginosa host. Field emission-scanning electron microscopy was used to visualize phage cocktail mediated eradication of 4-day-old multi-layers of XDR P. aeruginosa biofilms from urinary catheters and glass cover slips, and was confirmed by absence of any viable cells. Differential bacterial inhibition was observed with different phage combinations where multiple phages were found to enhance the cocktail's lytic range, but the addition of too many phages reduced the overall inhibition. This study elaborates an effective and sequential method for the preparation of a phage cocktail and evaluates its antimicrobial potential against biofilm forming XDR strains of P. aeruginosa.

Essential Oil and Hydrophilic Antibiotic Co-Encapsulation in Multiple Lipid Nanoparticles: Proof of Concept and In Vitro Activity against Pseudomonas aeruginosa

In the worldwide context of an impending emergence of multidrug-resistant bacteria, this research combined the advantages of multiple lipid nanoparticles (MLNs) and the promising therapeutic use of essential oils (EOs) as a strategy to fight the antibiotic resistance of three Pseudomonas aeruginosa strains with different cefepime (FEP) resistance profiles. MLNs were prepared by ultrasonication using glyceryl trioleate (GTO) and glyceryl tristearate (GTS) as a liquid and a solid lipid, respectively. Rosemary EO (REO) was selected as the model EO. REO/FEP-loaded MLNs were characterized by their small size (~110 nm), important encapsulation efficiency, and high physical stability over time (60 days). An assessment of the antimicrobial activity was performed using antimicrobial susceptibility testing assays against selected P. aeruginosa strains. The assays showed a considerable increase in the antibacterial property of REO-loaded MLNs compared with the effect of crude EO, especially against P. aeruginosa ATCC 9027, in which the minimum inhibitory concentration (MIC) value decreased from 80 to 0.6 mg/mL upon encapsulation. Furthermore, the incorporation of FEP in MLNs stabilized the drug without affecting its antipseudomonal activity. Thus, the ability to co-encapsulate an essential oil and a hydrophilic antibiotic into MLN has been successfully proved, opening new possibilities for the treatment of serious antimicrobial infections.

Clinical Status of Efflux Resistance Mechanisms in Gram-Negative Bacteria

Antibiotic efflux is a mechanism that is well-documented in the phenotype of multidrug resistance in bacteria. Efflux is considered as an early facilitating mechanism in the bacterial adaptation face to the concentration of antibiotics at the infectious site, which is involved in the acquirement of complementary efficient mechanisms, such as enzymatic resistance or target mutation. Various efflux pumps have been described in the Gram-negative bacteria most often encountered in infectious diseases and, in healthcare-associated infections. Some are more often involved than others and expel virtually all families of antibiotics and antibacterials. Numerous studies report the contribution of these pumps in resistant strains previously identified from their phenotypes. The authors characterize the pumps involved, the facilitating antibiotics and those mainly concerned by the efflux. However, today no study describes a process for the real-time quantification of efflux in resistant clinical strains. It is currently necessary to have at hospital level a reliable and easy method to quantify the efflux in routine and contribute to a rational choice of antibiotics. This review provides a recent overview of the prevalence of the main efflux pumps observed in clinical practice and provides an idea of the prevalence of this mechanism in the multidrug resistant Gram-negative bacteria. The development of a routine diagnostic tool is now an emergency need for the proper application of current recommendations regarding a rational use of antibiotics.

Risk factors for acquisition of carbapenem-resistance during treatment with carbapenem in the intensive care unit: a prospective study

The emergence of carbapenemases in gram-negative aerobes is worrying. The aim of this prospective study was to estimate the incidence of acquisition of carbapenem-resistance during treatment in ICU and to identify the risk factors. This was a prospective, observational, cohort study. This study was conducted at intensive care unit, academic medical center, Toulouse Rangueil University Hospital. Patients were included if they received antibiotic treatment with carbapenem for more than 48 h. Biological samples were taken in accordance with current practice in the unit. The main endpoint was the occurrence of bacterial resistance to carbapenems occurring between the onset of treatment and the patient’s exit from the ICU. Uni- and multi-variate analyses were carried out. Of the 364 patients admitted to the unit between May and November 2014, 78 were included in our study and 16 (20.51%) developed resistance. The two main risk factors were a length of stay in ICU of more than 29 days (HR = 3.61, p = 0.01) and the presence of Pseudomonas aeruginosa in the samples taken before the start of treatment (HR = 5.31, p = 0.002). No resistance due to carbapenemase production was observed in this study. The prescription of carbapenems in the ICU setting must adhere to the expert guidelines. In light of our results, special attention must be paid to patients whose stay in intensive care is prolonged, and those in whom Pseudomonas aeruginosa is isolated from bacteriological samples taken before the beginning of antibiotic therapy.

Risk factors and the resistance mechanisms involved in Pseudomonas aeruginosa mutation in critically ill patients

Background

The objective of this study was to determine the main risk factors of Pseudomonas aeruginosa mutation as well as the mechanisms of acquired resistance.

Methods

We conducted a 2-year prospective study in patients who were carriers of a Pseudomonas aeruginosa strain and who had been admitted to a medical/surgical ICU.

Results

Of the 153 patients who were included, 34 had a mutation in their strain. In a multivariate analysis, a duration of ventilation > 24 days was a risk factor for mutation (risk ratio 4.29; CI 95% 1.94-9.49) while initial resistance was a protective factor (RR 0.36; CI 95% 0.18-0.71). In a univariate analysis, exposure of P. aeruginosa to ceftazidime was associated with an over-production of AmpC cephalosporinase and exposure to meropenem was associated with impermeability. A segmentation method based on the duration of ventilation (> 24 days), initial resistance, and exposure of strains to ceftazidime made it possible to predict at 83% the occurrence of mutation.

Conclusion

The duration of ventilation and the presence of resistance as soon as P. aeruginosa is identified are predictive factors of mutation in ICU patients.

The prophylactic effects of human IgG derived from sera containing high anti-PcrV titers against pneumonia-causing Pseudomonas aeruginosa

The PcrV cap structure of the type III secretory apparatus of Pseudomonas aeruginosa is a vaccine target. Human immunoglobulin G (IgG) molecules extracted from sera containing high or low anti-PcrV titers were tested for their effects against P. aeruginosa pneumonia in a mouse model. Among 198 volunteers, we selected the top 10 high anti-PcrV titer sera and the bottom 10 low anti-PcrV titer sera and extracted the IgG fraction from each serum sample. First, we examined the effects of the IgG against virulent P. aeruginosa. A lethal dose of P. aeruginosa premixed with saline, low titer human IgG, high titer human IgG, or rabbit-derived polyclonal anti-PcrV IgG was intratracheally administered into the lungs of mice, and their survival and lung inflammation were evaluated for 24 h. The high anti-PcrV titer human IgG had a prophylactic effect. Next, the prophylactic effects of intravenous administration of extracted and pooled high or low anti-PcrV titer human IgG were examined. Here, prophylactic intravenous administration of pooled high anti-PcrV titer human IgG, which showed binding capacity to P. aeruginosa PcrV, was more effective than the administration of its low titer pooled equivalent, and the measured physiological and inflammatory parameters correlated with the anti-PcrV titer levels. This result indirectly implies that high anti-PcrV titers in blood can help to protect against virulent P. aeruginosa infections. In addition, the IgG fractions from such high titer sera have potential to be a source of specific intravenous immunoglobulin products for passive vaccination against virulent P. aeruginosa infections.

IV Immunoglobulin for Acute Lung Injury and Bacteremia in Pseudomonas aeruginosa Pneumonia

OBJECTIVES

Virulent and multidrug-resistant Pseudomonas aeruginosa causes a lethal pneumonia, especially in patients who are artificially ventilated. It has been reported that the virulence mechanism used by P. aeruginosa, which is linked to acute lung injury, is strongly associated with the type III secretion system, and specific antibodies targeting this system have shown a protective effect in both experimental and clinical settings. We investigated the effect of administering IV immunoglobulins on P. aeruginosa pneumonia, including its associated bacteremia and mortality, although focusing especially on type III secretion system-associated P. aeruginosa virulence.

DESIGN

Prospective randomized and controlled animal study.

SETTING

University laboratory.

SUBJECTS

Male ICR mice.

INTERVENTIONS

Mice were infected intratracheally with a lethal dose of the virulent P. aeruginosa PA103 strain. IV immunoglobulin administration was examined in three different settings: 1) premixed; 2) pre-IV, prophylactic administration before bacterial infection; and 3) post-IV, therapeutic administration after bacterial infection. The effect of specific antigen titer depletion of IV immunoglobulins was also examined.

MEASUREMENTS AND MAIN RESULTS

Survival and body temperature were monitored for 24 hours. Bacteremia, cytokine concentration, myeloperoxidase activity, WBC counts in the blood, and lung bacterial load were evaluated. Survival improved significantly in mice that received IV immunoglobulins (p < 0.05). Lung edema, lung bacteriologic load, and bacteremia decreased significantly in the IV immunoglobulin-treated mice (p < 0.05). The mechanism of protection was associated with the presence of antibodies against both PcrV and some bacterial surface antigens in the IV immunoglobulins.

CONCLUSIONS

IV immunoglobulin administration had a significantly protective effect against lethal infection from virulent P. aeruginosa. Prophylactic IV immunoglobulin administration at the highest dose was comparable with that achieved by administrating a specific anti-PcrV polyclonal IgG into the mice. The mechanism of protection is likely to involve the synergic action of anti-PcrV titers and antibodies against some surface antigen(s) that block the type III secretion system-associated virulence of P. aeruginosa.

Prevalence and risk factors associated with colonization and infection of extensively drug-resistant Pseudomonas aeruginosa: a systematic review

Pseudomonas aeruginosa is a Gram-negative human pathogen with extensively drug-resistant (XDR) strains emerging in hospitals across the globe. This systematic review is focused on the worldwide prevalence of XDR P. aeruginosa (XDR-PA) and on the risk factors associated with its colonization and infection, based on literature available through PubMed, Web of Science and BioMed Central databases. An overview of surveillance systems is provided as well as a synopsis on the prevalence of XDR-PA, showing an increase in recent reports. Risk factors independently associated with XDR-PA colonization or infections are described in four groups with reference to antimicrobial therapy, medical devices as well as patient- and hospital environment-related factors.

Emergence of imipenem-resistant gram-negative bacilli in intestinal flora of intensive care patients

Intestinal flora contains a reservoir of Gram-negative bacilli (GNB) resistant to cephalosporins, which are potentially pathogenic for intensive care unit (ICU) patients; this has led to increasing use of carbapenems. The emergence of carbapenem resistance is a major concern for ICUs. Therefore, in this study, we aimed to assess the intestinal carriage of imipenem-resistant GNB (IR-GNB) in intensive care patients. For 6 months, 523 consecutive ICU patients were screened for rectal IR-GNB colonization upon admission and weekly thereafter. The phenotypes and genotypes of all isolates were determined, and a case control study was performed to identify risk factors for colonization. The IR-GNB colonization rate increased regularly from 5.6% after 1 week to 58.6% after 6 weeks in the ICU. In all, 56 IR-GNB strains were collected from 50 patients: 36 Pseudomonas aeruginosa strains, 12 Stenotrophomonas maltophilia strains, 6 Enterobacteriaceae strains, and 2 Acinetobacter baumannii strains. In P. aeruginosa, imipenem resistance was due to chromosomally encoded resistance (32 strains) or carbapenemase production (4 strains). In the Enterobacteriaceae strains, resistance was due to AmpC cephalosporinase and/or extended-spectrum β-lactamase production with porin loss. Genomic comparison showed that the strains were highly diverse, with 8 exceptions (4 VIM-2 carbapenemase-producing P. aeruginosa strains, 2 Klebsiella pneumoniae strains, and 2 S. maltophilia strains). The main risk factor for IR-GNB colonization was prior imipenem exposure. The odds ratio for colonization was already as high as 5.9 (95% confidence interval [95% CI], 1.5 to 25.7) after 1 to 3 days of exposure and increased to 7.8 (95% CI, 2.4 to 29.8) thereafter. In conclusion, even brief exposure to imipenem is a major risk factor for IR-GNB carriage.

Tracking down antibiotic-resistant Pseudomonas aeruginosa isolates in a wastewater network

The Pseudomonas aeruginosa-containing wastewater released by hospitals is treated by wastewater treatment plants (WWTPs), generating sludge, which is used as a fertilizer, and effluent, which is discharged into rivers. We evaluated the risk of dissemination of antibiotic-resistant P. aeruginosa (AR-PA) from the hospital to the environment via the wastewater network. Over a 10-week period, we sampled weekly 11 points (hospital and urban wastewater, untreated and treated water, sludge) of the wastewater network and the river upstream and downstream of the WWTP of a city in eastern France. We quantified the P. aeruginosa load by colony counting. We determined the susceptibility to 16 antibiotics of 225 isolates, which we sorted into three categories (wild-type, antibiotic-resistant and multidrug-resistant). Extended-spectrum β-lactamases (ESBLs) and metallo-β-lactamases (MBLs) were identified by gene sequencing. All non-wild-type isolates (n = 56) and a similar number of wild-type isolates (n = 54) were genotyped by pulsed-field gel electrophoresis and multilocus sequence typing. Almost all the samples (105/110, 95.5%) contained P. aeruginosa, with high loads in hospital wastewater and sludge (≥3×10⁶ CFU/l or/kg). Most of the multidrug-resistant isolates belonged to ST235, CC111 and ST395. They were found in hospital wastewater and some produced ESBLs such as PER-1 and MBLs such as IMP-29. The WWTP greatly reduced P. aeruginosa counts in effluent, but the P. aeruginosa load in the river was nonetheless higher downstream than upstream from the WWTP. We conclude that the antibiotic-resistant P. aeruginosa released by hospitals is found in the water downstream from the WWTP and in sludge, constituting a potential risk of environmental contamination.

MexXY multidrug efflux system of Pseudomonas aeruginosa

Anti-pseudomonas aminoglycosides, such as amikacin and tobramycin, are used in the treatment of Pseudomonas aeruginosa infections. However, their use is linked to the development of resistance. During the last decade, the MexXY multidrug efflux system has been comprehensively studied, and numerous reports of laboratory and clinical isolates have been published. This system has been increasingly recognized as one of the primary determinants of aminoglycoside resistance in P. aeruginosa. In P. aeruginosa cystic fibrosis isolates, upregulation of the pump is considered the most common mechanism of aminoglycoside resistance. Non-fermentative Gram-negative pathogens possessing very close MexXY orthologs such as Achromobacter xylosoxidans and various Burkholderia species (e.g., Burkholderia pseudomallei and B. cepacia complexes), but not B. gladioli, are intrinsically resistant to aminoglycosides. Here, we summarize the properties (e.g., discovery, mechanism, gene expression, clinical significance) of the P. aeruginosa MexXY pump and other aminoglycoside efflux pumps such as AcrD of Escherichia coli, AmrAB-OprA of B. pseudomallei, and AdeABC of Acinetobacter baumannii. MexXY inducibility of the PA5471 gene product, which is dependent on ribosome inhibition or oxidative stress, is noteworthy. Moreover, the discovery of the cognate outer membrane component (OprA) of MexXY in the multidrug-resistant clinical isolate PA7, serotype O12 deserves special attention.

Interplay between mutational and horizontally acquired resistance mechanisms and its association with carbapenem resistance amongst extensively drug-resistant Pseudomonas aeruginosa (XDR-PA)

Between 2003 and 2009, the prevalence of extensively drug-resistant Pseudomonas aeruginosa (XDR-PA) increased significantly in northern Taiwan from 1.0% to 2.1%. Molecular methods were used to investigate the genetic relatedness and carbapenem resistance mechanisms of a collection of 203 non-repetitive XDR-PA isolates available for study. Using pulsed-field gel electrophoresis (PFGE), 52 genotypes were observed; one predominant genotype (pulsotype 1) was found in 57.6% of the isolates. Polymerase chain reaction (PCR), sequencing and quantitative reverse-transcriptase PCR analyses demonstrated that one horizontally acquired mechanism [metallo-β-lactamase (MBL) genes] and two mutational mechanisms (efflux and porins) accounted for the carbapenem resistance. The most predominant horizontally acquired mechanism was carriage of bla_VIM-3, which was found in 61.1% of isolates. Decreased expression of oprD was the most prevalent mutational mechanism and was found in 70.0% of the XDR-PA isolates, whereas overexpression of mexA was found in 27.6% of the isolates. The highlight of this study was the discovery of statistically significant relationships between certain horizontally acquired and mutational resistance mechanisms and their contribution to carbapenem susceptibility. MBL-producers expressed significantly lower MexAB and higher OprD than non-MBL-producers. Amongst isolates without an acquired β-lactamase gene, oprD expression was significantly reduced, whilst expression of efflux pumps was increased. Reduced OprD expression alone or the production of VIM-type MBLs showed similar contributions to a low to intermediate MIC₅₀ (minimum inhibitory concentration for 50% of the organisms) for carbapenems. Isolates with reduced OprD expression that simultaneously harboured bla_VIM exhibited high levels of resistance to carbapenems, which implied that these two mechanisms had a synergistic effect on the MICs.

Broad-specificity efflux pumps and their role in multidrug resistance of Gram-negative bacteria

Antibiotic resistance mechanisms reported in Gram-negative bacteria are causing a worldwide health problem. The continuous dissemination of 'multidrug-resistant' (MDR) bacteria drastically reduces the efficacy of our antibiotic 'arsenal' and consequently increases the frequency of therapeutic failure. In MDR bacteria, the overexpression of efflux pumps that expel structurally unrelated drugs contributes to the reduced susceptibility by decreasing the intracellular concentration of antibiotics. During the last decade, several clinical data have indicated an increasing involvement of efflux pumps in the emergence and dissemination of resistant Gram-negative bacteria. It is necessary to clearly define the molecular, functional and genetic bases of the efflux pump in order to understand the translocation of antibiotic molecules through the efflux transporter. The recent investigation on the efflux pump AcrB at its structural and physiological levels, including the identification of drug affinity sites and kinetic parameters for various antibiotics, may pave the way towards the rational development of an improved new generation of antibacterial agents as well as efflux inhibitors in order to efficiently combat efflux-based resistance mechanisms.

Pseudomonas aeruginosa: resistance to the max

Pseudomonas aeruginosa is intrinsically resistant to a variety of antimicrobials and can develop resistance during anti-pseudomonal chemotherapy both of which compromise treatment of infections caused by this organism. Resistance to multiple classes of antimicrobials (multidrug resistance) in particular is increasingly common in P. aeruginosa, with a number of reports of pan-resistant isolates treatable with a single agent, colistin. Acquired resistance in this organism is multifactorial and attributable to chromosomal mutations and the acquisition of resistance genes via horizontal gene transfer. Mutational changes impacting resistance include upregulation of multidrug efflux systems to promote antimicrobial expulsion, derepression of ampC, AmpC alterations that expand the enzyme's substrate specificity (i.e., extended-spectrum AmpC), alterations to outer membrane permeability to limit antimicrobial entry and alterations to antimicrobial targets. Acquired mechanisms contributing to resistance in P. aeruginosa include β-lactamases, notably the extended-spectrum β-lactamases and the carbapenemases that hydrolyze most β-lactams, aminoglycoside-modifying enzymes, and 16S rRNA methylases that provide high-level pan-aminoglycoside resistance. The organism's propensity to grow in vivo as antimicrobial-tolerant biofilms and the occurrence of hypermutator strains that yield antimicrobial resistant mutants at higher frequency also compromise anti-pseudomonal chemotherapy. With limited therapeutic options and increasing resistance will the untreatable P. aeruginosa infection soon be upon us?

Most multidrug-resistant Pseudomonas aeruginosa isolates from hospitals in eastern France belong to a few clonal types

This study aimed to determine the genetic diversity of clinical multidrug-resistant Pseudomonas aeruginosa. We used pulsed-field gel electrophoresis and multilocus sequence typing to analyze 187 strains isolated in different French hospitals. To illustrate the diversity of resistance mechanisms to antibiotics in a given clone, we identified β-lactamases with an extended spectrum by using phenotypic and genotypic methods. Typing results showed that the majority of our multidrug-resistant isolates belong to a few clonal types (ST235, ST111, and ST175) that are already spreading worldwide. These successful international clones sporadically produced extended-spectrum β-lactamase-encoding genes but mostly became extensively resistant to β-lactams after derepression of intrinsic resistance mechanisms (i.e., AmpC cephalosporinase). Our results indicate that cross-transmission plays a major role in the spread of multidrug-resistant P. aeruginosa in hospital settings.

Pseudomonas aeruginosa: resistance to the max

Pseudomonas aeruginosa is intrinsically resistant to a variety of antimicrobials and can develop resistance during anti-pseudomonal chemotherapy both of which compromise treatment of infections caused by this organism. Resistance to multiple classes of antimicrobials (multidrug resistance) in particular is increasingly common in P. aeruginosa, with a number of reports of pan-resistant isolates treatable with a single agent, colistin. Acquired resistance in this organism is multifactorial and attributable to chromosomal mutations and the acquisition of resistance genes via horizontal gene transfer. Mutational changes impacting resistance include upregulation of multidrug efflux systems to promote antimicrobial expulsion, derepression of ampC, AmpC alterations that expand the enzyme's substrate specificity (i.e., extended-spectrum AmpC), alterations to outer membrane permeability to limit antimicrobial entry and alterations to antimicrobial targets. Acquired mechanisms contributing to resistance in P. aeruginosa include β-lactamases, notably the extended-spectrum β-lactamases and the carbapenemases that hydrolyze most β-lactams, aminoglycoside-modifying enzymes, and 16S rRNA methylases that provide high-level pan-aminoglycoside resistance. The organism's propensity to grow in vivo as antimicrobial-tolerant biofilms and the occurrence of hypermutator strains that yield antimicrobial resistant mutants at higher frequency also compromise anti-pseudomonal chemotherapy. With limited therapeutic options and increasing resistance will the untreatable P. aeruginosa infection soon be upon us?

Oxidative stress induction of the MexXY multidrug efflux genes and promotion of aminoglycoside resistance development in Pseudomonas aeruginosa

Exposure to reactive oxygen species (ROS) (e.g., peroxide) was shown to induce expression of the PA5471 gene, which was previously shown to be required for antimicrobial induction of the MexXY components of the MexXY-OprM multidrug efflux system and aminoglycoside resistance determinant in Pseudomonas aeruginosa. mexXY was also induced by peroxide exposure, and this too was PA5471 dependent. The prospect of ROS promoting mexXY expression and aminoglycoside resistance recalls P. aeruginosa infection of the chronically inflamed lungs of cystic fibrosis (CF) patients, where the organism is exposed to ROS and where MexXY-OprM predominates as the mechanism of aminoglycoside resistance. While ROS did not enhance aminoglycoside resistance in vitro, long-term (8-day) exposure of P. aeruginosa to peroxide (mimicking chronic in vivo ROS exposure) increased aminoglycoside resistance frequency, dependent upon PA5471 and mexXY. This enhanced resistance frequency was also seen in a mutant strain overexpressing PA5471, in the absence of peroxide, suggesting that induction of PA5471 by peroxide was key to peroxide enhancement of aminoglycoside resistance frequency. Resistant mutants selected following peroxide exposure were typically pan-aminoglycoside-resistant, with mexXY generally required for this resistance. Moreover, PA5471 was required for mexXY expression and aminoglycoside resistance in these as well as several CF isolates examined.

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.

Nationwide investigation of extended-spectrum beta-lactamases, metallo-beta-lactamases, and extended-spectrum oxacillinases produced by ceftazidime-resistant Pseudomonas aeruginosa strains in France

A nationwide study aimed to identify the extended-spectrum beta-lactamases (ESBLs), metallo-beta-lactamases (MBLs), and extended-spectrum oxacillinases (ES-OXAs) in a French collection of 140 clinical Pseudomonas aeruginosa isolates highly resistant to ceftazidime. Six ESBLs (PER-1, n=3; SHV-2a, n=2; VEB-1a, n=1), four MBLs (VIM-2, n=3; IMP-18, n=1), and five ES-OXAs (OXA-19, n=4; OXA-28, n=1) were identified in 13 isolates (9.3% of the collection). The prevalence of these enzymes is still low in French clinical P. aeruginosa isolates but deserves to be closely monitored.

Application of an inducible system to engineer unmarked conditional mutants of essential genes of Pseudomonas aeruginosa

The Phi CTX-based integration vector pYM101 harboring a tightly controlled modified phage T7 early gene promoter/LacI(q) repressor (T7/LacI) system was constructed for the generation of unmarked conditional mutants in Pseudomonas aeruginosa. Promoter activity of the T7/LacI system was demonstrated to be dependent on the presence of the inducer isopropyl -beta-D-1-thiogalactopyranoside (IPTG), as evaluated by measuring beta-galactosidase activity. In the absence of the inducer, the promoter was silent as its activity was lower than those of a promoter-less lacZ control. Unmarked conditional mutants of four predicted essential genes (lolCDE (PA2988-86), lpxC (PA4406), rho (PA5239), and def (PA0019)) were successfully constructed using this recombination system. In the absence of IPTG, the growth of all mutants was repressed; however, the addition of either 0.1 or 1mM IPTG restored growth rates to levels nearly identical to wild-type cells. It was therefore demonstrated that the inducible integration vector pYM101 is suitable for the creation of unmarked conditional mutants of P. aeruginosa, and is particularly useful for examining the function of essential genes.

[Evolution of antimicrobial resistance against Pseudomonas aeruginosa in a French university hospital between 2002 and 2006]

AIM OF STUDY

Monitor evolution of antibiotic resistance of Pseudomonas aeruginosa from 2002 to 2006 in our hospital to optimize antibiotherapy.

PATIENTS AND METHOD

The infections/colonizations with P. aeruginosa have been identified by the hospital's informatic database. Bacteriological samples realized 48hours after patient's admission was considered as nosocomial. A Cochran-Armitage test was conducted to assess the evolution of resistance.

RESULTS

During this period, 2098 infections/colonizations with P. aeruginosa have been identified. Bacteriological samples (68.5%) were nosocomial. Among the beta-lactam antibiotics, ceftazidime and imipenem were the most active (R=16.8% and 15.2%, respectively), followed by piperacillin and piperacillin-tazobactam (R=24.8%, 18.4%, respectively). Amikacin and tobramycin were more active than gentamicin (R=19.9%; 22.2% and 40.6%, respectively). 28.9% of strains were resistant to ciprofloxacin. Nosocomial strains were significantly more resistant than non-hospital strains: ceftazidime: 17.9% versus 14.2%, p=0.0346; ticarcillin-clavulanic acid: 47.5% versus 39.6%, p=0.0009; piperacillin-tazobactam: 20.0% versus 14.8%, p=0.0046; ciprofloxacin: 30.7% versus 25.2%, p=0.0112. A significant increase in the resistance of nosocomial strains to ceftazidime, ticarcillin-clavulanic acid and piperacillin-tazobactam was noted. Resistance from non-hospital strains to fluoroquinolones, aminoglycosides, ceftazidime, piperacillin and ticarcillin-clavulanic acid decreased significantly.

CONCLUSION

P. aeruginosa is a predominantly nosocomial microorganism. There is a decrease of resistance for non-hospital strains. But the resistance of nosocomial strains to antibiotics widely prescribed in hospital is worrying.