Prospective survey of beta-lactamases produced by ceftazidime- resistant Pseudomonas aeruginosa isolated in a French hospital in 2000

Enterobacter cloacae Complex and CTX-M Extended-Spectrum β-Lactamases in Algeria

We evaluated the β-lactam resistance phenotypes of clinical and environmental strains of the Enterobacter cloacae complex (ECC) isolated from three Algerian hospitals. The first combination of API 20E, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and hsp60 genetic clustering methodologies were carried out for the identification of ECC strains. Our research showed that API 20E and MALDI TOF MS are satisfactory in genus identification of ECC strains, but sequence-based methods are then necessary to discriminate the species and subspecies levels. Among 36 ECC strains, 94.44% belonged to Enterobacter hormaechei species. Twenty-five isolates clustered with the reference strain of E. hormaechei subsp. xiangfangensis, making it the most frequently isolated subspecies. Enterobacter kobei was found only once (2.77%). All ECC isolates were phenotypically extended-spectrum β-lactamase (ESBL) producers and were resistant to ticarcillin, piperacillin, cefoxitin, cefotaxime, ceftazidime, ceftriaxone, and aztreonam, but susceptible to ertapenem and imipenem. The genetic analyses only allowed the detection of resistance genes of the CTX-M-1 group (32 strains, 88.9%), including CTX-M-15 (30 strains), CTX-M-3 (1 strain), and CTX-M-22 (1 strain). We report for the first time the detection of CTX-M-22 among ECC strains in an Algerian hospital (Tlemcen hospital). None of the isolated strains harbored CTX-M-2, CTX-M-9, or CTX-M-8/25 group genes. In this review, we address recent comparison in the identification methods of multidrug-resistant E. cloacae complex in Algeria, focusing also on the CTX-M ESBLs. This represents a serious public health challenge, which requires the clarification of the current situation and warrants the reinforcement of hygiene measures in the Algerian hospitals.

Detection of Extended-Spectrum β-Lactamases among Acinetobacter Baumannii Isolated from Hospitals of Qazvin, Iran

Background

Acinetobacter baumannii is a major contributor to nosocomial infections. Extended-spectrum β-lactamase (ESBL)-producing A. baumannii is spreading worldwide. We aimed to determine the frequency of ESBL-encoding genes in clinical isolates of A. baumannii and to access their clonal relationship by repetitive extragenic palindromic-PCR (rep-PCR).

Methods

In this descriptive cross-sectional study, 203 isolates of A. baumannii were collected from Qazvin hospitals. The Identification of isolates was performed by standard laboratory methods. To verify ESBL production, all isolates were screened by disk agar diffusion and confirmed by the combined disk method. Subsequently, ESBL-encoding genes were detected by PCR and sequencing. Possible clonal association of ESBL-producing isolates was evaluated using rep-PCR.

Results

Two hundred (98.5%) isolates showed reduced susceptibility to one of the antibiotics used in the ESBL screening test, of which 127 isolates (62.6%) produced ESBL. PCR results showed bla_OXA-1 (20.5%) was the most prevalent gene followed by bla_TEM-1 (20%), bla_GES-1 (15.7%), bla_CTX-M-15 (7.9%), and bla_PER-1 (1.6%). Rep-PCR results revealed that ESBL-producing isolates belonged to clones A (85%), B (13.4%), and C (1.6%).

Conclusion

Our study showed the significant presence of bla_OXA-1, bla_TEM-1, bla_GES-1, bla_CTX-M-15, and bla_PER-1 genes in ESBL-producing A. baumannii isolates in the studied hospitals. This is the first report on the emergence of bla_OXA-1 gene in these isolates in Iran. The use of comprehensive antimicrobial treatment guidelines based on laboratory data and appropriate infection control interventions are essential.

Occurrence and distribution of antimicrobial resistance genes in the soil of an industrial park in China: A metagenomics survey

As zoned areas of industries, industrial parks have great impacts on the environment. Several studies have demonstrated that chemical compounds and heavy metals released from industrial parks can contaminate soil, water, and air. However, as an emerging pollutant, antimicrobial resistance genes (ARGs) in industrial parks have not yet been investigated. Here, we collected soil samples from 35 sites in an industrial park in China and applied a metagenomics strategy to profile the ARGs and virulence factors (VFs). We further compared the relative abundance of ARGs between the sites (TZ_31-35) located in a beta-lactam antimicrobial-producing factory and other sites (TZ_1-30) in this industrial park. Metagenomic sequencing and assembly generated 14, 383, 065 contigs and 17, 631, 051 open reading frames (ORFs). Taxonomy annotation revealed Proteobacteria and Actinobacteria as the most abundant phylum and class, respectively. The 32 pathogenic bacterial genera listed in the virulence factor database (VFDB) were all identified from the soil metagenomes in this industrial park. In total, 685,354 ARGs (3.89% of the ORFs) and 272,694 virulence factors (VFs) (1.55% of the ORFs) were annotated. These ARGs exhibited resistance to several critically important antimicrobials, such as rifampins, fluroquinolones, and beta-lactams. In addition, no significant difference in the relative abundance of ARGs was observed between sites TZ_31-35 and TZ_1-30, indicating that ARGs have already disseminated widely in this industrial park. The present study gave us a better understanding of the whole picture of the resistome and virulome in the soil of the industrial park and suggested that we should treat the industrial park as a whole in the surveillance and maintenance of ARGs.

A synthetic peptide sensitizes multi-drug resistant Pseudomonas aeruginosa to antibiotics for more than two hours and permeabilizes its envelope for twenty hours

BACKGROUND

Pseudomonas aeruginosa is a Gram-negative pathogen that frequently causes life-threatening infections in immunocompromised patients. We previously showed that subinhibitory concentrations of short synthetic peptides permeabilize P. aeruginosa and enhance the lethal action of co-administered antibiotics.

METHODS

Long-term permeabilization caused by exposure of multidrug-resistant P. aeruginosa strains to peptide P4-9 was investigated by measuring the uptake of several antibiotics and fluorescent probes and by using confocal imaging and atomic force microscopy.

RESULTS

We demonstrated that P4-9, a 13-amino acid peptide, induces a growth delay (i.e. post-antibiotic effect) of 1.3 h on a multidrug-resistant P. aeruginosa clinical isolate. Remarkably, when an independently P4-9-treated culture was allowed to grow in the absence of the peptide, cells remained sensitive to subinhibitory concentrations of antibiotics such as ceftazidime, fosfomycin and erythromycin for at least 2 h. We designated this persistent sensitization to antibiotics occurring in the absence of the sensitizing agent as Post-Antibiotic Effect associated Permeabilization (PAEP). Using atomic force microscopy, we showed that exposure to P4-9 induces profound alterations on the bacterial surface and that treated cells need at least 2 h of growth to repair those lesions. During PAEP, P. aeruginosa mutants overexpressing either the efflux pump MexAB-OprM system or the AmpC β-lactamase were rendered sensitive to antibiotics that are known substrates of those mechanisms of resistance. Finally, we showed for the first time that the descendants of bacteria surviving exposure to a membrane disturbing peptide retain a significant level of permeability to hydrophobic compounds, including propidium iodide, even after 20 h of growth in the absence of the peptide.

CONCLUSIONS

The phenomenon of long-term sensitization to antibiotics shown here may have important therapeutic implications for a combined peptide-antibiotic treatment because the peptide would not need to be present to exert its antibiotic enhancing activity as long as the target organism retains sensitization to the antibiotic.

Prevalence of Resistance to β-Lactam Antibiotics and bla Genes Among Commensal Haemophilus parainfluenzae Isolates from Respiratory Microbiota in Poland

(1) Background: Beta-lactams are the most frequently used antimicrobials, and are the first-line drugs in many infectious diseases, e.g., pneumonia, otitis media. Due to this fact, various bacteria have developed resistance to this group of drugs. (2) Methods: Eighty-seven Haemophilus parainfluenzae isolates were obtained from adults 18–70 years old in eastern Poland. The presence of 10 bla genes and 2 substitutions in ftsI reported as the most frequent in H. parainfluenzae were analyzed. (3) Results: Among 57 beta-lactam-resistant isolates, 63.2% encoded bla genes; bla_TEM-1 predominated (54.4%), followed by bla_OXA (19.3%), bla_DHA (12.3%), bla_SHV (10.5%), bla_GES (7.0%), bla_CMY (5.3%), bla_VEB (1.8%) and bla_ROB-1 (1.8%). Lys-526 was the most common substitution in ftsI gene. The resistance genotypes were as follows: gBLNAS (17.5%), low-gBLNAR I (1.8%), low-gBLNAR II (1.8%), gBLNAR II (15.8%), gBLPAS (15.8%), gBLPAR (19.3%), gBLPBS I (8.8%) and gBLPBS II (1.8%); (4) Conclusions: This has been the first study to report on the high diversity of bla genes in H. parainfluenzae isolates in Poland. High sensitivity and specificity of benzylpenicillin test, as well as PCR of bla genes were shown, indicating that these methods may be useful as tools for the rapid screening of beta-lactamase prevalence and resistance to beta-lactams among H. parainfluenzae isolated from respiratory microbiota.

Unexpected mechanisms of resistance in Dutch Pseudomonas aeruginosa isolates collected during 14 years of surveillance

Pseudomonas aeruginosa is one of the most important causes of infection in intensive care units (ICUs). It is intrinsically resistant to many antimicrobials and easily acquires additional resistance genes via horizontal gene transfer of mobile genetic elements. In this study, 1528 P. aeruginosa isolates obtained from a Dutch national surveillance programme between the years 1998-2011 were analysed for the presence of extended-spectrum β-lactamase (ESBL) genes (bla_CTX-M, bla_SHV, bla_TEM, bla_BEL, bla_PER, bla_VEB and bla_OXA-10) and metallo-β-lactamase (MBL) genes (bla_IMP, bla_VIM and bla_NDM). Of the ceftazidime-resistant isolates, 6.2% tested phenotypically positive for ESBL. Moreover, a Verona integron-encoded MBL (VIM) gene was found in 3.1% of isolates that were phenotypically resistant to imipenem and/or meropenem. Multilocus sequence typing (MLST) of ESBL-positive isolates indicated ST1216, ST111 and ST622, with all bla_VIM-positive isolates belonging to the ST111 clone. Although the prevalence of ESBL and MBL phenotypes in this Dutch national surveillance collection of >1500 ICU P. aeruginosa isolates was very low, all VIM-producing isolates belonged to the high risk-associated, international, clonal complex CC111, and most ESBL-producing isolates belonged to clonal complexes known for their successful spread, e.g. CC111 and CC235. These data indicate that high-risk clones of P. aeruginosa were present in the Netherlands between 1998-2011 and probably spread unnoticed throughout Dutch hospitals.

Epidemiological, Physiological, and Molecular Characteristics of a Brazilian Collection of Carbapenem-Resistant Acinetobacter baumannii and Pseudomonas aeruginosa

Nonfermenting Gram-negative bacteria such as Pseudomonas aeruginosa and Acinetobacter baumannii are widespread in the environment and are increasingly associated with nosocomial infections, often associated with multidrug-resistance phenotypes. This study aimed to evaluate epidemiological, physiological, and molecular characteristics of carbapenem resistance in P. aeruginosa and A. baumannii. In total, 63 nonreplicated strains (44 A. baumannii and 19 P. aeruginosa) were isolated from hospitalized patients. Antimicrobial resistance patterns, biocide tolerance, oxidative stress, hemolytic activity, and biofilm formation were assessed. Genetic markers related to β-lactamase synthesis, efflux systems, and porin loss were screened by PCR. Epidemiological data of patients were analyzed. Advanced age, intensive care unit admission, invasive medical devices, treatment with fluoroquinolones or β-lactams/β-lactamase inhibitor combinations, and prolonged hospital stay were predisposing factors for infection. Colistin showed to be active in vitro against these bacteria. Carbapenem-resistant P. aeruginosa strains did not show hemolytic activity and were less tolerant to oxidative stress and biocides. However, increased ability of biofilm formation was observed, comparing to the carbapenem-susceptible isolates. Genetic markers related to oxacillinases synthesis (OXA-23 and OXA-143), oprD absence, and efflux pump (adeB) were detected in carbapenem-resistant A. baumannii. Screening for OXA-51-like gene was performed as confirmatory test for A. baumannii identification. In P. aeruginosa genes encoding efflux pumps (MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY-OprM) and SPM-1 were found; besides, oprD absence was also observed. Our results suggest that these organisms are well adapted to different environments and confirm the difficulty of therapeutic management of patients with infections associated with multidrug-resistant microorganisms, with direct impact on mortality and epidemiological control of these strains in health centers.

Distribution and Classification of Serine β-Lactamases in Brazilian Hospital Sewage and Other Environmental Metagenomes Deposited in Public Databases

β-lactam is the most used antibiotic class in the clinical area and it acts on blocking the bacteria cell wall synthesis, causing cell death. However, some bacteria have evolved resistance to these antibiotics mainly due the production of enzymes known as β-lactamases. Hospital sewage is an important source of dispersion of multidrug-resistant bacteria in rivers and oceans. In this work, we used next-generation DNA sequencing to explore the diversity and dissemination of serine β-lactamases in two hospital sewage from Rio de Janeiro, Brazil (South Zone, SZ and North Zone, NZ), presenting different profiles, and to compare them with public environmental data available. Also, we propose a Hidden-Markov-Model approach to screen potential serine β-lactamases genes (in public environments samples and generated hospital sewage data), exploring its evolutionary relationships. Due to the high variability in β-lactamases, we used a position-specific scoring matrix search method (RPS-BLAST) against conserved domain database profiles (CDD, Pfam, and COG) followed by visual inspection to detect conserved motifs, to increase the reliability of the results and remove possible false positives. We were able to identify novel β-lactamases from Brazilian hospital sewage and to estimate relative abundance of its types. The highest relative abundance found in SZ was the Class A (50%), while Class D is predominant in NZ (55%). CfxA (65%) and ACC (47%) types were the most abundant genes detected in SZ, while in NZ the most frequent were OXA-10 (32%), CfxA (28%), ACC (21%), CEPA (20%), and FOX (19%). Phylogenetic analysis revealed β-lactamases from Brazilian hospital sewage grouped in the same clade and close to sequences belonging to Firmicutes and Bacteroidetes groups, but distant from potential β-lactamases screened from public environmental data, that grouped closer to β-lactamases of Proteobacteria. Our results demonstrated that HMM-based approach identified homologs of serine β-lactamases, indicating the specificity and high sensitivity of this approach in large datasets, contributing for the identification and classification of a large number of homologous genes, comprising possible new ones. Phylogenetic analysis revealed the potential reservoir of β-lactam resistance genes in the environment, contributing to understanding the evolution and dissemination of these genes.

OXA β-lactamases

The OXA β-lactamases were among the earliest β-lactamases detected; however, these molecular class D β-lactamases were originally relatively rare and always plasmid mediated. They had a substrate profile limited to the penicillins, but some became able to confer resistance to cephalosporins. From the 1980s onwards, isolates of Acinetobacter baumannii that were resistant to the carbapenems emerged, manifested by plasmid-encoded β-lactamases (OXA-23, OXA-40, and OXA-58) categorized as OXA enzymes because of their sequence similarity to earlier OXA β-lactamases. It was soon found that every A. baumannii strain possessed a chromosomally encoded OXA β-lactamase (OXA-51-like), some of which could confer resistance to carbapenems when the genetic environment around the gene promoted its expression. Similarly, Acinetobacter species closely related to A. baumannii also possessed their own chromosomally encoded OXA β-lactamases; some could be transferred to A. baumannii, and they formed the basis of transferable carbapenem resistance in this species. In some cases, the carbapenem-resistant OXA β-lactamases (OXA-48) have migrated into the Enterobacteriaceae and are becoming a significant cause of carbapenem resistance. The emergence of OXA enzymes that can confer resistance to carbapenems, particularly in A. baumannii, has transformed these β-lactamases from a minor hindrance into a major problem set to demote the clinical efficacy of the carbapenems.

Detection of expanded-spectrum β-lactamases in Gram-negative bacteria in the 21st century

Emerging β-lactamase-producing-bacteria (ESBL, AmpC and carbapenemases) have become a serious problem in our community due to their startling spread worldwide and their ability to cause infections which are difficult to treat. Diagnosis of these β-lactamases is of clinical and epidemiological interest. Over the past 10 years, several methods have been developed aiming to rapidly detect these emerging enzymes, thus preventing their rapid spread. In this review, we describe the range of screening and detection methods (phenotypic, molecular and other) for detecting these β-lactamases but also whole genome sequencing as a tool for detecting the genes encoding these enzymes.

Molecular screening of carbapenemase-producing Gram-negative strains in Romanian intensive care units during a one year survey

This is the first study, to our knowledge, performed on a significant number of strains (79 carbapenem-resistant Enterobacteriaceae and 84 carbapenem-resistant non-fermenting Gram-negative rods, GNRs) isolated from tissue samples taken from patients in the intensive care units of two large hospitals in Bucharest, Romania, between 2011 and 2012. The results revealed a high prevalence and great diversity of carbapenemase genes (CRG), in both fermenting and non-fermenting Gram-negative carbapenem-resistant strains. The molecular screening of carbapenem-resistant GNRs revealed the presence of worldwide-distributed CRGs (i.e. blaOXA-48 and blaNDM-1 in Enterobacteriaceae and blaOXA-23, blaVIM-4, blaOXA-10-like, blaOXA-60-like, blaSPM-like and blaGES-like in non-fermenting GNRs), reflecting the rapid evolution and spread of carbapenemase producers, particularly in hospitals. Rapid identification of the colonized or infected patients is required, as are epidemiological investigations to establish the local or imported origin of the respective strains.

Emergence of VIM-2 and IMP-15 carbapenemases and inactivation of oprD gene in carbapenem-resistant Pseudomonas aeruginosa clinical isolates from Lebanon

We report here the emergence of VIM-2 and IMP-15 carbapenemases in a series of clinical isolates of carbapenem-resistant Pseudomonas aeruginosa in Lebanon. We also describe the disruption of the oprD gene by either mutations or insertion sequence (IS) elements ISPa1328 and ISPre2 isoform. Our study reemphasizes a rapid dissemination of the VIM-2 carbapenemase-encoding gene in clinical isolates of P. aeruginosa in the Mediterranean basin.

Outbreak of PER-1 and diversity of β-lactamases among ceftazidime-resistant Pseudomonas aeruginosa clinical isolates

A growing number of β-lactamases have been reported in Pseudomonas aeruginosa clinical isolates. The aim of this study was to investigate the diversity of β-lactamases in the collection of 51 ceftazidime-resistant P. aeruginosa clinical isolates in four hospitals of southern China. Among these isolates, variable degrees of resistance to other β-lactam and non-β-lactam agents were observed. Pulsed-field gel electrophoresis (PFGE) revealed a high degree of clonality with five main genotypes. Of the 51 isolates tested, 35 (68.6 %) were identified as extended-spectrum β-lactamase (ESBL) producers, with 35 producing PER-1, 1 CTX-M-3, 7 CTX-M-15 and 1 CTX-M-14. Most (82.9 %, 29/35) PER-1-producing isolates were collected from two hospitals between January and April in 2008 and belonged to the same PFGE pattern (pattern B) with similar antibiogram and β-lactamase profiles, which suggested an outbreak of this clone at the time. The prevalence of CTX-M-type ESBL (17.6 %, 9/51) was unexpectedly high. One isolate was identified as producing VIM-2. Furthermore, we also reported an occurrence of a novel OXA-10 variant, OXA-246, in 14 P. aeruginosa isolates. In addition, AmpC overproduction was found to be the β-lactamase-mediated mechanism responsible for ceftazidime resistance in 6 isolates (11.8 %). Our results revealed an overall diversity of β-lactamases and outbreak of a PER-1-producing clone among ceftazidime-resistant P. aeruginosa in southern China.

First characterization of a Providencia stuartii clinical isolate from a Tunisian intensive care unit coproducing VEB-1-a, OXA-2, qnrA6 and aac(6')-Ib-cr determinants

A clinical Providencia stuartii isolate SM662 was recovered from a patient hospitalized in the intensive care unit at the Military hospital, Tunisia. This isolate was resistant to penicillins, cephalosporins, aminoglycosides and fluoroquinolones. A marked in vitro synergy between ceftazidime or cefotaxime and amoxicillin–clavulanic acid on Mueller-Hinton agar plates suggested the presence of an extended-spectrum-β-lactamase. In addition, an unusual synergy was found between cefepime or aztreonam, and cefoxitin or imipenem on a double disk synergy test suggesting a VEB-type extended-spectrum-β-lactamase. The characterization of β-lactamases and associated resistance genes was performed by isoelectric focusing, polymerase chain reaction and nucleotide sequencing. Two β-lactamases bands with pI values of 5.4 and 7.7, which were matched to TEM-1, VEB-1-a and OXA-2-like β-lactamases were detected. The bla_VEB-1-a gene was found to be associated with complex genetic structures, including Re elements. These β-lactamases were not transferred by electroporation or conjugation experiments to the transconjugants and electroporants. Hybridization methods showed that the extended-spectrum-β-lactamase encoding gene may have a chromosomal localization. The isolate SM662 produced the quinolone resistance determinants qnrA6 and aac(6′)-Ib-cr which were successfully transferred. The detection of an associated chromosomal quinolone resistance revealed the presence of a gyrA mutation at codon 83 (Ser83Ile). This is the first report of the linkage VEB-1-a/OXA-2-like in P. stuartii associated with the description of qnrA6 and aac(6′)-Ib-cr genes in this isolate.

Molecular investigation of carbapenem resistance among multidrug-resistant Pseudomonas aeruginosa isolated clinically in Thailand

Carbapenem resistant Pseudomonas aeruginosa were isolated among multidrug-resistant (CR-MDR) organisms from tertiary hospitals in Thailand. Decreased expression of oprD mRNA (93.65%) was predominant followed by increased expression of mexAB-oprM mRNA (92.06%) and mexXY mRNA (63.49%). Interestingly, 23 of 126 (18.25%) isolates were susceptible to imipenem with down-regulated oprD expression and non-up-regulated mexCD-oprJ mRNA expression. Metallo-β-lactamases production was clearly positive in 24 isolates (18.46%) and weakly positive in 12 isolates (9.23%). Among both of these sets of isolates, imp-1, imp-14 and vim-2 were identified. Hyperproduction of AmpC β-lactamase had the lowest prevalence rate (3.97%). It was concluded that CR-MDR P. aeruginosa clinical isolates in Thailand possess multifactorial resistance mechanisms.

Increased frequency of integrons and β-lactamase-coding genes among extraintestinal Escherichia coli isolated with a 7-year interval

We analyzed the level of antimicrobial resistance, and the presence of integrons and β-lactamase-coding genes in 69 clinically relevant Escherichia coli strains originating from extraintestinal infections isolated in 1999–2001 and 2008–2010. Comparison of the two groups showed significant differences in drug resistance frequency, and the presence of integron and β-lactamase-coding genes. The frequency of resistance to all antimicrobials beside imipenem, streptomycin, piperacillin/tazobactam, and sulfamethoxazole increased significantly, especially towards aminoglycosides, β-lactams and fluoroquinolones. Similarly, we noticed an increase in the number of strains with integrons from 31.6 to 80.7 %. The presence of integrase genes was associated with elevated frequency of resistance to each antimicrobial tested besides imipenem, piperacillin/tazobactam and ceftazidime. The presence of integrons was also associated with multidrug resistance phenotype. The genetic content of integrons comprised genes determining resistance toward aminoglycosides, sulfonamides and trimethoprim. Moreover, we noticed a significant increase in the frequency of bla_CTX-M β-lactamases, with appearance of bla_CTX-M-15 variant and newer plasmid-encoded β-lactamases like CMY-15 and DHA. The emergence of strains resistant to several classes of antimicrobials and carrying integrons, ESBL and AmpC β-lactamase-coding genes may predict the spread of isolates with limited treatment options.

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?

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?

Differential selection of single-step AmpC or efflux mutants of Pseudomonas aeruginosa by using cefepime, ceftazidime, or ceftobiprole

Single-step Pseudomonas aeruginosa mutants, selected with ceftobiprole, ceftazidime, or cefepime, were generated at frequencies of 10(-6) to <10(-9) at two and four times the MIC. The chromosomal AmpC β-lactamase activity was increased in all ceftazidime-selected mutants. Mutants selected with cefepime either increased AmpC activity or upregulated expression of the mexXY efflux genes. Mutants selected with ceftobiprole did not overexpress AmpC; 90% of these produced elevated levels of mexXY RNA, indicating that increased efflux, not AmpC derepression, is the predominant response to ceftobiprole during first-step mutations in P. aeruginosa.

Prevalence characterization of extended-spectrum beta-lactamases among Escherichia coli isolates collected in Zhengzhou

OBJECTIVES

To determine the prevalence and the diversity of extended-spectrum beta-lactamases (ESBLs) among Escherichia coli isolates in Zhengzhou, China.

METHODS

Clinical isolates were collected and investigated from the first affiliated hospital of Zhengzhou University and its associated health-care facilities in Zhengzhou, China, during the period from January 2006 to June 2008. Antibiograms were performed on Mueller-Hinton agar plates with the disc-diffusion method and MICs were determined by the agar-dilution method. Total DNA was extracted with a Qiagen mini kit and screened by PCR.

RESULTS

Of 94 nonduplicate ESBL-positive isolates, TEM-type was encoded in 74 and 79% of the ESBL isolates. Fifty-six isolates were SHV type ESBLs. CTX-M-1, CTX-M-14, CTX-M-25, and CTX-M-38 types were encoded in 30, 54, 6, and 4, respectively. OXA-1-type beta-lactamases were encoded in six and OXA-20-type was encoded in two isolates.

CONCLUSIONS

We describe a complex ESBL epidemiology. The study revealed a high rate of ESBL-producing E. coli isolates. TEM and CTX-M enzymes dominated in ESBL-positive E. coli isolates in Zhengzhou, China.

Emergence of SHV-2a extended-spectrum beta-lactamases in clinical isolates of Pseudomonas aeruginosa in a university hospital in Tunisia

Extended-spectrum beta-lactamases (ESBLs) in Pseudomonas aeruginosa are increasingly reported worldwide. In our study, a total of 70 clinical isolates of multidrug-resistant P. aeruginosa were studied. Isoelectric focusing electrophoresis, PCR, and PCR product sequencing were designed to characterize the contained ESBLs. The Double Disk Synergy Test in Cloxacillin (250 microg/ml)-containing Mueller-Hinton agar plates with a 20 mm distance between disks was the most reliable ESBL-screening method. Seven out of 70 multidrug-resistant P. aeruginosa clinical isolates were positive for ESBL and have the bla(SHV-2a) ESBL gene. The bla(SHV-2a)-positive isolates were clonally related according to Enterobacterial Repetetive Intergenic Consensus-PCR (ERIC-PCR) results. The bla(SHV-2a) gene was found to be chromosomally located, and the flanking IS26 sequence in the immediate upstream region of the bla(SHV-2a) gene was detected in all SHV-2a-producing isolates. This is the first report of SHV-2a-producing P. aeruginosa isolates from Tunisia.

Hydrolysis of cefazolin by enzymes produced by Pseudomonas aeruginosa after exposure to ceftazidime in vitro

BACKGROUND/AIM

Sometimes resistance of Pseudomonas aeruginosa (Ps. aeruginosa) is developed during antibiotic treatment, in spite of the initial susceptibility in vitro. The aim of this study was to use an in vitro model for the study of the development of resistant strains of Ps. aeruginosa after a short exposure to ceftazidime, and to study the hydrolysing capacity of beta-lactamases produced by the resistant strains.

METHODS

Among 563 clinical strains of Ps. aeruginosa, 37 multisensitive strains were collected for the study. After being identified, strains with simultaneous sensitivity to 5 expanded spectrum cephalosporins were chosen. For each strain, the minimal inhibitory concentration (MIC) of the 5 expanded spectrum cephalosporins was determined, and the production of extended spectrum beta-lactamases (ESBL) was excluded by the double-disc synergy diffusion test. Strains non producing ESBL were cultivated in concentrations of ceftazidime equal to MICx2 and MICx4. After 24 hours of culture, the development of resistant strains was estimated and the cephalosporinase activity of the produced beta-lactamases was determined by their ability to hydrolyse cefazolin. Hydrolysis of cefazolin was studied by measuring the change of its absorbance on 272 nm using a Shimadzu 160A spectrophotometer. The hydrolyzing capacity of the enzymes was expressed as the percentage of the antibiotic, which was hydrolysed in 10 sec.

RESULTS

A total of 60% and 50% of strains developed resistant strains after exposure to ceftazidime in concentration MICx2 and MICx4, respectively. The hydrolyzing capacity of the original strains was 15-36% while the hydrolyzing capacity of the resistant strains was 10-73%. Totally 64% of the resistant strains expressed higher hydrolyzing capacity than the original strains.

CONCLUSION

Regardless of the susceptibility test results, Ps. aeruginosa presented a high tendency to develop resistant strains after a short exposure to ceftazidime in vitro. In most cases the resistant strains expressed higher cephalosporinase activity than the original strains, suggesting derepression of chromosomal beta-lactamases. Our model offers a simple, inexpensive and rapid method for detecting resistance of Ps. aeruginosa developed due to derepression of beta-lactamases, and for discriminating resistant strains with derepressed beta-lactamases from strains that developed other mechanisms of resistance.

[Dissemination of IMP-1 and OXA type beta-lactamase in carbapenem-resistant Acinetobacter baumannii]

BACKGROUND

Acinetobacter baumannii is an aerobic, gram-negative, glucose-nonfermenting bacterium, which has emerged as a serious opportunistic pathogen. In recent years, the increasing instance of carbapenem-resistant A. baumannii producing metallo-beta-lactamases (MBLs) or OXAtype beta-lactamases is causing a serious clinical problem. In this study, we investigated the prevalence of Ambler class A, B, and D beta-lactamases and their extended-spectrum derivatives in carbapenem-resistant A. baumannii isolates.

METHODS

A total of 31 consecutive, non-duplicate, carbapenem-resistant A. baumannii were isolated from three university hospitals in the Chungcheong province of Korea. The modified Hodge and inhibitor-potentiated disk diffusion tests were conducted for the screening of carbapenemase and MBL production, respectively. PCR and DNA sequencing were performed for the detection of beta-lactamase genes. We also employed the enterobacterial repetitive intergenic consensus (ERIC)-PCR method for the epidemiologic study.

RESULTS

Twenty-three of 31 isolates harbored bla(OXA-2)(51.6%), bla(OXA-23)(22.6%), bla(IMP-1)(48.4%),and bla(VIM-2)(3.2%). All of the OXA-2-producing strains also evidenced MBLs. The strains that harbored bla(OXA-23)were isolated only in hospital C, and only in a limited fashion. The ERIC-PCR pattern of the five OXA-23 strains indicated that the isolates were closely related in terms of clonality. The six strains producing IMP-1 isolated from hospital A were confirmed to be identical strains.

CONCLUSIONS

A. baumannii strains harboring IMP-1 or OXA-type beta-lactamases are currently widely distributed throughout the Chungcheong province of Korea. The most notable finding in this study was that a bla(OXA-2)-producing A. baumannii harboring MBL, which has not been previously reported, can also lead to outbreaks.

Imported PER-1 producing Pseudomonas aeruginosa, PER-1 producing Acinetobacter baumanii and VIM-2-producing Pseudomonas aeruginosa strains in Hungary

Introduction

Pseudomonas aeruginosa and Acinetobacter baumanii are important nosocomial pathogens with wide intrinsic resistance. However, due to the dissemination of the acquired resistance mechanisms, such as extended-spectrum beta-lactamase (ESBL) and metallo beta-lactamase (MBL) production, multidrug resistant strains have been isolated more often.

Case presentation

We report a case of a Hungarian tourist, who was initially hospitalized in Egypt and later transferred to Hungary. On the day of admission PER-1-producing P. aeruginosa, PER-1 producing A. baumannii, SHV-5-producing Klebsiella pneumoniae and VIM-2-producing P. aeruginosa isolates were subcultured from the patient's samples in Hungary. Comparing the pulsed-field gel electrophoresis (PFGE) patterns of the P. aeruginosa strains from the patient to the P. aeruginosa strains occurring in this hospital, we can state that the PER-1-producing P. aeruginosa and VIM-2-producing P. aeruginosa had external origin.

Conclusion

This is the first report of PER-1-producing P. aeruginosa,and PER-1-producing A. baumanii strains in Hungary. This case highlights the importance of spreading of the beta-lactamase-mediated resistance mechanisms between countries and continents, showing the importance of careful screening and the isolation of patients arriving from a different country.

Beta-lactam and aminoglycoside resistance rates and mechanisms among Pseudomonas aeruginosa in French general practice (community and private healthcare centres)

OBJECTIVES

The aim of this study was to assess antibiotic resistance rates and mechanisms of beta-lactam and aminoglycoside resistance among isolates of Pseudomonas aeruginosa isolated in the extra-hospital setting (community and private healthcare centres).

PATIENTS AND METHODS

During a 4 month period, 226 non-repetitive strains of P. aeruginosa were collected from patients residing in private healthcare centres (73.5%) or at home (26.5%). Resistance rates were evaluated by MIC determination, and beta-lactam and aminoglycoside resistance was analysed by phenotypic tests, PCR amplification, cloning and sequencing.

RESULTS

Among the ticarcillin-resistant strains (38.1%), 33.7% overexpressed their chromosomal cephalosporinase, 27.9% produced acquired penicillinases (21 PSE-1, 2 OXA-21 and 1 TEM-2), 4.7% produced extended-spectrum beta-lactamases (ESBLs) (3 TEM-21 and 1 SHV-2a) and 45.3% possessed a non-enzymatic resistance (NER). Thus, 88.4% had a single mechanism of resistance, whereas 11.6% cumulated several mechanisms. No carbapenemases were detected among the 6.6% imipenem-resistant strains. With regard to aminoglycosides, 23.0% of the strains exhibited an acquired resistance to gentamicin (GEN), tobramycin (TOB), amikacin (AMK) or netilmicin (NET). Enzymatic resistance was more frequent (71.2%) than NER (34.6%). Various aminoglycoside modifying enzymes were associated with overlapping phenotypes: 36.5% strains produced AAC(6')-I with either a serine (GEN-TOB-NET) or a leucine (TOB-NET-AMK) at position 119, or both variants (GEN-TOB-NET-AMK); 21.2% expressed ANT(2'')-I (GEN-TOB), 7.7% AAC(3)-II (GEN-TOB-NET), 5.8% AAC(3)-I (GEN) and 1.9% AAC(6')-II (GEN-TOB-NET-AMK) or AACA7 (TOB-NET-AMK).

CONCLUSIONS

Antibiotic resistance rates in P. aeruginosa were globally similar in general practice as in French hospitals. This first analysis of resistance mechanisms showed an unexpectedly high frequency of ESBLs and an unusual distribution of aminoglycoside modifying enzymes.

Resistance mechanisms of multiresistant Pseudomonas aeruginosa strains from Germany and correlation with hypermutation

In this study, we analyzed the mechanisms of multiresistance for 22 clinical multiresistant and clonally different Pseudomonas aeruginosa strains from Germany. Twelve and 10 strains originated from cystic fibrosis (CF) and non-CF patients, respectively. Overproduction of the efflux systems MexAB-OprM, MexCD-OprJ, MexEF-OprN, and MexXY-OprM was studied. Furthermore, loss of OprD, alterations in type II topoisomerases, AmpC overproduction, and the presence of 25 acquired resistance determinants were investigated. The presence of a hypermutation phenotype was also taken into account. Besides modifications in GyrA (91%), the most frequent mechanisms of resistance were MexXY-OprM overproduction (82%), OprD loss (82%), and AmpC overproduction (73%). Clear differences between strains from CF and non-CF patients were found: numerous genes coding for aminoglycoside-modifying enzymes and located, partially in combination with beta-lactamase genes, in class 1 integrons were found only in strains from non-CF patients. Furthermore, multiple modifications in type II topoisomerases conferring high quinolone resistance levels and overexpression of MexAB-OprM were exclusively detected in multiresistant strains from non-CF patients. Correlations of the detected phenotypes and resistance mechanisms revealed a great impact of efflux pump overproduction on multiresistance in P. aeruginosa. Confirming previous studies, we found that additional, unknown chromosomally mediated resistance mechanisms remain to be determined. In our study, 11 out of 12 strains and 3 out of 10 strains from CF patients and non-CF patients, respectively, were hypermutable. This extremely high proportion of mutator strains should be taken into consideration for the treatment of multiresistant P. aeruginosa.

Nosocomial outbreak of OXA-18-producing Pseudomonas aeruginosa in Tunisia

Following systematic screening for ceftazidime-resistant (CAZ-R) Pseudomonas aeruginosa, 24 isolates producing extended-spectrum beta-lactamase (ESBL) were recovered during a 24-month period at the National Bone Marrow Transplant Centre of Tunisia. These isolates were from seven immunocompromised patients and from environmental swabs. ESBLs inhibited by clavulanic acid were detected by double-disk diffusion tests. Isoelectric focusing revealed that these isolates produced two to four beta-lactamases with pIs of 5.5, 6.1, 6.4, 7.6 or 8.2, and PCR detected the presence of bla(OXA-18), bla(SHV) and bla(TEM) genes in 24, 21 and two isolates, respectively. Pulsed-field gel electrophoresis defined two dominant genotypic groups: group A (16 isolates) and group B (four isolates). Sequencing of PCR products from representative isolates identified the bla(OXA-18) gene and revealed nucleotide sequences belonging to the bla(SHV-1) and bla(TEM-1) genes. Isolates producing OXA-18 belonged to genomic group A and were isolated from four immunocompromised patients in the haematology and graft units, and from two wash-basins in the graft unit. No immunocompromised patient harboured the clonal epidemic strain upon admission. This is the first report of the OXA-18-type ESBL in P. aeruginosa in Tunisia, and the first description of an outbreak caused by an OXA-18-producing strain of P. aeruginosa.

Outbreak of Pseudomonas aeruginosa infections with PER-1 extended-spectrum beta-lactamase in Warsaw, Poland: further evidence for an international clonal complex

Forty-one Pseudomonas aeruginosa isolates with extended-spectrum beta-lactamases (ESBLs) from a hospital in Warsaw, Poland, were analyzed. Thirty-seven isolates from several wards were collected over 9 months in 2003 and 2004. The isolates were recovered from patients with multiple types of infections, mostly respiratory tract and postoperative wound infections. All 41 isolates produced the PER-1 ESBL, originally observed in Turkey but recently also identified in several countries in Europe and the Far East. The bla(PER-1) gene resided within the Tn1213 composite transposon, which was chromosomally located. Pulsed-field gel electrophoresis and multilocus sequence typing (MLST) revealed the presence of three separate clones among the isolates. Two of these, corresponding to sequence types (STs) ST244 and ST235, were responsible for parallel outbreaks. Apart from PER-1, all the isolates produced OXA-2 oxacillinase. ST235 isolates additionally expressed a novel enzyme, OXA-74, differing by one amino acid from the OXA-17 ESBL identified originally in PER-1- and OXA-2-positive P. aeruginosa isolates from Ankara, Turkey, in 1992. These earlier Ankara isolates with PER-1, OXA-2, and OXA-17 were also classified into ST235, which is a single-locus variant of two other STs, ST227 and ST230. ST227, ST230, and ST235 all correspond to the recently described clonal complex BG11, which seems to be internationally distributed, having spread in Turkey, Greece, Italy, Hungary, Poland, Sweden, and much of Russia. It is associated with various beta-lactamases, including PER-1 and VIM metalloenzymes. This work further demonstrates the value of MLST of P. aeruginosa.

Development of resistance in wild-type and hypermutable Pseudomonas aeruginosa strains exposed to clinical pharmacokinetic profiles of meropenem and ceftazidime simulated in vitro

In this study we investigated the interplay of antibiotic pharmacokinetic profiles and the development of mutation-mediated resistance in wild-type and hypermutable Pseudomonas aeruginosa strains. We used in vitro models simulating profiles of the commonly used therapeutic drugs meropenem and ceftazidime, two agents with high levels of antipseudomonal activity said to have different potentials for stimulating resistance development. During ceftazidime treatment of the wild-type strain (PAO1), fully resistant mutants overproducing AmpC were selected rapidly and they completely replaced wild-type cells in the population. During treatment with meropenem, mutants of PAO1 were not selected as rapidly and showed only intermediate resistance due to the loss of OprD. These mutants also replaced the parent strain in the population. During the treatment of the mutator P. aeruginosa strain with meropenem, the slowly selected mutants did not accumulate several resistance mechanisms but only lost OprD and did not completely replace the parent strain in the population. Our results indicate that the commonly used dosing regimens for meropenem and ceftazidime cannot avoid the selection of mutants of wild-type and hypermutable P. aeruginosa strains. For the treatment outcome, including the prevention of resistance development, it would be beneficial for the antibiotic concentration to remain above the mutant prevention concentration for a longer period of time than it does in present regimens.

Stability of FR264205 against AmpC beta-lactamase of Pseudomonas aeruginosa

FR264205 is a novel parenteral 3'-aminopyrazolium cephalosporin. Here, we compared the stability of FR264205 against AmpC beta-lactamase of Pseudomonas aeruginosa with that of ceftazidime. The effect of ampD inactivation, which causes a moderate degree of hyperinducible AmpC expression, on the minimum inhibitory concentration (MIC) of FR264205 was eight-fold less than that on the MIC of ceftazidime. Hydrolysis efficiency (k(cat)/K(m)) towards FR264205 was substantially lower than that towards ceftazidime owing to a 20-fold-higher K(m) value. These results indicate that FR264205 is more stable against AmpC beta-lactamase than ceftazidime because of its low affinity.

Problematic clinical isolates of Pseudomonas aeruginosa from the university hospitals in Sofia, Bulgaria: current status of antimicrobial resistance and prevailing resistance mechanisms

A total of 203 clinical isolates of Pseudomonas aeruginosa was collected during 2001–2006 from five university hospitals in Sofia, Bulgaria, to assess the current levels of antimicrobial susceptibility and to evaluate resistance mechanisms to antipseudomonal antimicrobial agents. The antibiotic resistance rates against the following antimicrobials were: carbenicillin 93.1 %, azlocillin 91.6 %, piperacillin 86.2 %, piperacillin/tazobactam 56.8 %, ceftazidime 45.8 %, cefepime 48.9 %, cefpirome 58.2 %, aztreonam 49.8 %, imipenem 42.3 %, meropenem 45.5 %, amikacin 59.1 %, gentamicin 79.7 %, tobramycin 89.6 %, netilmicin 69.6 % and ciprofloxacin 80.3 %. A total of 101 of the studied P. aeruginosa isolates (49.8 %) were multidrug resistant. Structural genes encoding class A and class D β-lactamases showed the following frequencies: bla VEB-1 33.1 %, bla PSE-1 22.5 %, bla PER-1 0 %, bla OXA-groupI 41.3 % and bla OXA-groupII 8.8 %. IMP- and VIM-type carbapenemases were not detected. In conclusion, the studied clinical strains of P. aeruginosa were problematic nosocomial pathogens. VEB-1 extended-spectrum β-lactamases appear to have a significant presence among clinical P. aeruginosa isolates from Sofia. Carbapenem resistance was related to non-enzymic mechanisms such as a deficiency of OprD proteins and active efflux.

Prevalence of AmpC over-expression in bloodstream isolates of Pseudomonas aeruginosa

This study examined the contribution of AmpC over-expression to beta-lactam resistance in clinical isolates of Pseudomonas aeruginosa obtained from a hospital in Houston, TX, USA. Seventy-six non-repeat bloodstream isolates obtained during 2003 were screened for ceftazidime resistance in the presence and absence of clavulanic acid 4 mg/L. AmpC was identified by isoelectric focusing (with and without cloxacillin inhibition); stable derepression was ascertained phenotypically by a spectrophotometric assay (with and without preceding induction by imipenem) using nitrocefin as the substrate, and was confirmed subsequently by quantitative RT-PCR of the ampC gene. The clonal relatedness of the AmpC-over-expressing isolates was assessed by pulsed-field gel electrophoresis. In addition, the ampC and ampR gene sequences were determined by PCR and sequencing. For comparison, two standard wild-type strains (PAO1 and ATCC 27853) and three multidrug-susceptible isolates were used as controls. AmpC over-expression was confirmed in 14 ceftazidime-resistant isolates (overall prevalence rate, 18.4%), belonging to seven distinct clones. The most prevalent point mutations in ampC were G27D, V205L and G391A. Point mutations in ampR were also detected in eight ceftazidime-resistant isolates. AmpC over-expression appears to be a significant mechanism of beta-lactam resistance in P. aeruginosa. Understanding the prevalence and mechanisms of beta-lactam resistance in P. aeruginosa may guide the choice of empirical therapy for nosocomial infections in hospitals.

SCO-1, a novel plasmid-mediated class A beta-lactamase with carbenicillinase characteristics from Escherichia coli

A novel class A beta-lactamase (SCO-1) encoded by an 80-kb self-transferable plasmid from Escherichia coli is described. The interaction of SCO-1 with beta-lactams was similar to that of the CARB-type enzymes. Also, SCO-1 exhibited a 51% amino acid sequence identity with the RTG subgroup of chromosomal carbenicillinases (RTG-1, CARB-5, and CARB-8).

In vitro and in vivo activities of a new cephalosporin, FR264205, against Pseudomonas aeruginosa

FR264205 is a novel parenteral 3'-aminopyrazolium cephalosporin. This study evaluated the in vitro and in vivo activities of FR264205 against Pseudomonas aeruginosa. The MIC of FR264205 at which 90% of 193 clinical isolates of P. aeruginosa were inhibited was 1 microg/ml, 8- to 16-fold lower than those of ceftazidime (CAZ), imipenem (IPM), and ciprofloxacin (CIP). FR264205 also exhibited this level of activity against CAZ-, IPM-, and CIP-resistant P. aeruginosa. The reduction in the susceptibility of FR264205 by AmpC beta-lactamase was lower than that of CAZ, indicating a relatively high stability of FR264205 against AmpC beta-lactamase, the main resistance mechanism for cephalosporins. Neither expression of efflux pumps nor deficiency of OprD decreased the activity of FR264205. No spontaneous resistance mutants were selected in the presence of FR264205, and the reduction in susceptibility to FR264205 was lower than that to CAZ, IPM, and CIP after serial passage, suggesting that FR264205 has a low propensity for selecting resistance. In murine pulmonary, urinary tract, and burn wound models of infection caused by P. aeruginosa, the efficacy of FR264205 was superior or comparable to those of CAZ and IPM. These results indicate that FR264205 should have good potential as an antibacterial agent for P. aeruginosa.

Frequency and predictors of colonization of the respiratory tract by VIM-2-producing Pseudomonas aeruginosa in patients of a newly established intensive care unit

The aim of this study was to examine the frequency and predictors of colonization of the respiratory tract by metallo-beta-lactamase (MBL)-producing Gram-negative bacteria in patients admitted to a newly established intensive care unit (ICU) of a tertiary care hospital. Specimens of tracheobronchial aspirates for microbiological studies were obtained every day for the first 3 days of the ICU stay and subsequently every third day for the rest of the ICU stay. PCR analysis and nucleotide sequencing were performed to identify bacteria that had MBL genes. Thirty-five patients (20 male, 15 female) were hospitalized during the initial 3 month period of functioning of the ICU. Colonization of the lower respiratory tract by Gram-negative bacteria was found in 29 of 35 patients (83 %) during the first 6-20 days (median 13 days) following admission to the ICU (13 patients with Acinetobacter baumannii, ten with Pseudomonas aeruginosa, three with Enterobacter aerogenes, two with Klebsiella pneumoniae and one with Stenotrophomonas maltophilia). Six of 29 patients (21 %) colonized with Gram-negative bacteria had bla(VIM-2)-positive P. aeruginosa isolates; one of these patients developed clinical infection due to this micro-organism. Previous use of carbapenems (P=0.01) or other beta-lactams (P=0.03), as well as a stay in the ICU of >20 days (P<0.001), were associated with colonization with bla(VIM-2)-producing P. aeruginosa. In conclusion, colonization by Gram-negative bacteria of the respiratory tract of patients in this newly established ICU was common (83 %). Use of beta-lactams, including carbapenems, was associated with subsequent colonization of the respiratory tract with MBL-positive P. aeruginosa.

Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa

Acinetobacter species and Pseudomonas aeruginosa are noted for their intrinsic resistance to antibiotics and for their ability to acquire genes encoding resistance determinants. Foremost among the mechanisms of resistance in both of these pathogens is the production of beta -lactamases and aminoglycoside-modifying enzymes. Additionally, diminished expression of outer membrane proteins, mutations in topoisomerases, and up-regulation of efflux pumps play an important part in antibiotic resistance. Unfortunately, the accumulation of multiple mechanisms of resistance leads to the development of multiply resistant or even "panresistant" strains.

Analysing diversity among beta-lactamase encoding genes in aquatic environments

The most common mechanism of resistance to beta-lactam antibiotics is the production of beta-lactamases. These enzymes are encoded by genes that evolve rapidly, thus constituting a group characterized by high levels of molecular diversity. Most of the genetic determinants of resistance to beta-lactam antibiotics characterized until now were obtained from clinical isolates. This study was designed in order to exploit the presence of beta-lactamase gene sequences in an aquatic environment, and to get information on the distinctive features of those sequences when compared to others available on databases. DNA sequences potentially encoding proteins of three different families of clinically relevant beta-lactamases were assessed: TEM, IMP and OXA-2 derivatives. The presence of bla sequences in DNA extracted from water samples from the lagoon Ria de Aveiro was checked by PCR and hybridization. Sequences representing the three families of beta-lactamases studied were detected. The molecular diversity of the amplicons was assessed by cloning and sequence analysis, and denaturing gradient gel electrophoresis (PCR-DGGE) separation. Most of the retrieved sequences (particularly sequences representing bla(TEM)and bla(OXA-2)) were identical or very similar to beta-lactamase gene sequences previously characterized from clinical isolates. Phylogenetic analysis suggests that this aquatic ecosystem is a reservoir of molecular diverse putative bla sequences. The patterns of molecular diversity found within the beta-lactamase gene families studied do not correspond to those reported in studies focussing on clinical isolates.

Cephalosporinase over-expression resulting from insertion of ISAba1 in Acinetobacter baumannii

ISAba1-like sequences were identified immediately upstream of the bla(ampC) gene in ceftazidime-resistant Acinetobacter baumannii isolates, but were absent in ceftazidime-susceptible A. baumannii isolates. AmpC over-expression resulted from insertion of ISAba1-like sequences upstream of bla(ampC). ISAba1 provided strong promoter sequences, and it was demonstrated that the change in the ribosome binding site sequence resulting from insertion of ISAba1 did not influence expression of the bla(ampC) gene. Sequence analysis revealed that AmpC sequences of A. baumannii isolates were almost identical and that ISAba1 elements had a high percentage of identity.