Nosocomial spread of Pseudomonas aeruginosa producing the metallo-β-lactamase VIM-2 in a Spanish hospital: clinical and epidemiological implications

Detailed epidemiological analysis as a strategy for evaluating the actual behavior of tuberculosis in an apparently low-incidence region

Tuberculosis control in developing regions with apparent low incidence, like the low-income Mexican state of Michoacán, with mean annual incidence rates below 10/100,000 inhabitants, requires knowledge of the actual behavior of the disease. This can be determined using an epidemiological profile at sub-regional level, allowing disclosure of the clinical and social factors that may be hampering efforts to control tuberculosis. In this work, a detailed epidemiological profile was outlined using data of all new monthly cases registered in the National System of Epidemiological Surveillance Database for Michoacán municipalities from 2000 to 2012. Cases were grouped by gender and age, and sociodemographic data were obtained both from the National Institute of Statistics and Geography and from the United Nations Development Programme. Correlations were calculated by Chi-square, Mann-Whitney U, and Kruskal-Wallis H tests. We observed no statistically significant differences between notification rates for the years 2000, 2005 and 2010 (χ² = 0.222, p = 0.895). The percentage of cases is similar between all age groups older than 15, while some regions had low notification rates but high proportions of pediatric cases. Higher proportions of cases of extrapulmonary tuberculosis were observed in municipalities in northern Michoacán. No correlation was found between municipal Human Development Index values and municipal notification rates. Michoacán is undergoing an epidemiological transition with three regions having different epidemiological profiles and particular needs for effective prevention and containment of tuberculosis. Our work shows the importance of the spatial scale of epidemiological profiles for determining specific regional needs of surveillance and containment.

Italian nationwide survey on Pseudomonas aeruginosa from invasive infections: activity of ceftolozane/tazobactam and comparators, and molecular epidemiology of carbapenemase producers

Objectives

Pseudomonas aeruginosa is a major cause of severe healthcare-associated infections and often shows MDR phenotypes. Ceftolozane/tazobactam is a new cephalosporin/β-lactamase inhibitor combination with potent activity against P. aeruginosa. This survey was carried out to evaluate the susceptibility of P. aeruginosa, circulating in Italy, to ceftolozane/tazobactam and comparators and to investigate the molecular epidemiology of carbapenemase-producing strains.

Methods

Consecutive non-replicate P. aeruginosa clinical isolates (935) from bloodstream infections and lower respiratory tract infections were collected from 20 centres distributed across Italy from September 2013 to November 2014. Antimicrobial susceptibility testing was performed by broth microdilution and results were interpreted according to the EUCAST breakpoints. Isolates resistant to ceftolozane/tazobactam were investigated for carbapenemase genes by PCR, and for carbapenemase activity by spectrophotometric assay. WGS using an Illumina platform was performed on carbapenemase-producing isolates.

Results

Ceftolozane/tazobactam was the most active molecule, retaining activity against 90.9% of P. aeruginosa isolates, followed by amikacin (88.0% susceptibility) and colistin (84.7% susceptibility). Overall, 48 isolates (5.1%) were positive for carbapenemase genes, including blaVIM (n = 32), blaIMP (n = 12) and blaGES-5 (n = 4), while the remaining ceftolozane/tazobactam-resistant isolates tested negative for carbapenemase production. Carbapenemase producers belonged to 10 different STs, with ST175 (n = 12) and ST621 (n = 11) being the most common lineages. Genome analysis revealed different trajectories of spread for the different carbapenemase genes.

Conclusions

Ceftolozane/tazobactam exhibited potent in vitro activity against P. aeruginosa causing invasive infections in Italy. Carbapenemase production was the most common mechanism of resistance to ceftolozane/tazobactam.

Prevalence of Metallo-β-Lactamases in Acinetobacter Baumannii in Iran: A Review and Meta-Analysis

Acinetobacter baumannii (A. baumannii) is an important opportunistic pathogen that causes major public health concerns, especially in hospitalized patients due to acquisition of resistant genes. The aim of this study was to systematically review the published data on the prevalence and dispersion of metallo-β-lactamases (MBLs) genes in A. baumannii in different provinces of Iran and provide an overall prevalence rate using meta-analysis. All available national and international databanks from 2011 to 2017 were searched to find published studies. Quality of studies was assessed by STROBE. Due to the fact that a significant heterogeneity was observed, the random effects model was used to combine the results. Statistical analysis was performed by comprehensive meta-analysis (CMA) V2 software. Out of 78 articles, 28 were extracted based on certain inclusion and exclusion criteria. Most of the A. baumannii isolates were obtained from intensive care unit (ICU) ward of hospitals. Based on phenotypic and molecular detection tests, pooled prevalence of all MBLs was 58%, and blaVIM, blaIMP, and blaSPM-1 genes were estimated to be at 10.5, 6, and 5%, respectively. Based on the results, further attention should be given to report MBL genes in A. baumannii based on molecular detection rather than the phenotypic one. Furthermore, more effort should be focused on ICU sections in order to avoid the distribution of resistant genes.

Diverse Genetic Background of Multidrug-Resistant Pseudomonas aeruginosa from Mainland China, and Emergence of an Extensively Drug-Resistant ST292 Clone in Kunming

For a better understanding of the multidrug resistant Pseudomonas aeruginosa (MDR-PA) epidemiology in mainland China, a nationwide surveillance network of 27 tertiary hospitals was established. Non-duplicate MDR-PA isolates from 254 cases of nosocomial infections, were collected during the period August 2011 to July 2012. Minimum inhibitory concentrations (MICs) of nine antimicrobial agents were determined by broth micro-dilution method according to the CLSI guidelines [M7-A10]. Genotyping analysis was performed by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE). The presence of acquired carbapenemases was also determined by molecular approaches for 233 carbapenem-resistant isolates. Carbapenemase genes were detected in 19 (8.2%) isolates, with 13 of these isolates encoding IMP-type enzymes, five with VIM-2, and one with KPC-2. MLST analysis revealed significant genetic diversity among the MDR-PA isolates studied, and 91 STs (including 17 novel STs) were identified. However, a long-term outbreak of an emerging extensively drug-resistant (XDR) ST292/PFGE genotype A clone was detected in a hospital from Southwest China. This study has demonstrated that MDR-PA in mainland China have evolved from diverse genetic backgrounds. Evidence of clonal dissemination of the organism and nosocomial outbreaks in some regions, suggest a need to strengthen existing infection control measures.

Biological markers of Pseudomonas aeruginosa epidemic high-risk clones

A limited number of Pseudomonas aeruginosa genotypes (mainly ST-111, ST-175, and ST-235), known as high-risk clones, are responsible for epidemics of nosocomial infections by multidrug-resistant (MDR) or extensively drug-resistant (XDR) strains worldwide. We explored the potential biological parameters that may explain the success of these clones. A total of 20 isolates from each of 4 resistance groups (XDR, MDR, ModR [resistant to 1 or 2 classes], and MultiS [susceptible to all antipseudomonals]), recovered from a multicenter study of P. aeruginosa bloodstream infections performed in 10 Spanish hospitals, were analyzed. A further set of 20 XDR isolates belonging to epidemic high-risk clones (ST-175 [n = 6], ST-111 [n = 7], and ST-235 [n = 7]) recovered from different geographical locations was also studied. When unknown, genotypes were documented through multilocus sequence typing. The biological parameters evaluated included twitching, swimming, and swarming motility, biofilm formation, production of pyoverdine and pyocyanin, spontaneous mutant frequencies, and the in vitro competition index (CI) obtained with a flow cytometry assay. All 20 (100%) XDR, 8 (40%) MDR, and 1 (5%) ModR bloodstream isolate from the multicenter study belonged to high-risk clones. No significant differences were observed between clonally diverse ModR and MultiS isolates for any of the parameters. In contrast, MDR/XDR high-risk clones showed significantly increased biofilm formation and mutant frequencies but significantly reduced motility (twitching, swimming, and swarming), production of pyoverdine and pyocyanin, and fitness. The defined biological markers of high-risk clones, which resemble those resulting from adaptation to chronic infections, could be useful for the design of specific treatment and infection control strategies.

Draft Genome Sequence of VIM-2-Producing Multidrug-Resistant Pseudomonas aeruginosa ST175, an Epidemic High-Risk Clone

The VIM-2-producing multidrug-resistant high-risk clone Pseudomonas aeruginosa sequence type (ST) 175 was isolated in the setting of a large outbreak in Hospital Universitario 12 de Octubre (Spain) from 2007 to 2010. This strain was resistant to all β-lactams, fluoroquinolones, and aminoglycosides, with the exception of amikacin, and has become an endemic clone in our institution.

VIM-2-producing multidrug-resistant Pseudomonas aeruginosa ST175 clone, Spain

This clone is a major public health problem because it limits antimicrobial drug therapy.

A total of 183 patients were colonized or infected with multidrug-resistant Pseudomonas aeruginosa isolates at a hospital in Spain during 2007–2010; prevalence increased over this period from 2.8% to 15.3%. To characterize these isolates, we performed molecular epidemiologic and drug resistance analysis. Genotyping showed that 104 (56.8%) isolates belonged to a single major clone (clone B), which was identified by multilocus sequence typing as sequence type (ST) 175. This clone was initially isolated from 5 patients in 2008, and then isolated from 23 patients in 2009 and 76 patients in 2010. PCR analysis of clone B isolates identified the bla_VIM-2 gene in all but 1 isolate, which harbored bla_IMP-22. ST175 isolates were susceptible to only amikacin (75%) and colistin (100%). Emergence of the ST175 clone represents a major health problem because it compromises therapy for treatment of P. aeruginosa nosocomial infections.

Spread of multidrug-resistant Pseudomonas aeruginosa clones in a university hospital

An outbreak of multidrug-resistant Pseudomonas aeruginosa (MDRPA) infections in a university hospital is described. Phenotypic and genotypic analysis of 240 isolates revealed that 152 patients, mainly in the intensive care unit (ICU), were colonized or infected with MDRPA, the majority with O11. All metallo-β-lactamase (MBL)-positive isolates carried the bla(VIM-2) or bla(VIM-1) gene. One or more type III secretion system toxin genes were detected in most isolates. Five dominant pulsed-field gel electrophoresis (PFGE) types were characterized, associated with ST235, ST111, ST253, ST309, and ST639.

Genetic markers of widespread extensively drug-resistant Pseudomonas aeruginosa high-risk clones

Recent reports have revealed the existence of widespread extensively drug-resistant (XDR) P. aeruginosa high-risk clones in health care settings, but there is still scarce information on their specific chromosomal (mutational) and acquired resistance mechanisms. Up to 20 (10.5%) of 190 bloodstream isolates collected from 10 Spanish hospitals met the XDR criteria. A representative number (15 per group) of isolates classified as multidrug-resistant (MDR) (22.6%), resistant to 1 to 2 classes (moderately resistant [modR]) (23.7%), or susceptible to all antibiotics (multiS) (43.2%) were investigated in parallel. Multilocus sequence typing (MLST) analysis revealed that all XDR isolates belonged to sequence type 175 (ST175) (n = 19) or ST111 (n = 1), both recognized as international high-risk clones. Clonal diversity was higher among the 15 MDR isolates (4 ST175, 2 ST111, and 8 additional STs) and especially high among the 15 modR (13 different STs) and multiS (14 STs) isolates. The XDR/MDR pattern in ST111 isolates correlated with the production of VIM-2, but none of the ST175 isolates produced acquired β-lactamases. In contrast, the analysis of resistance markers in 12 representative isolates (from 7 hospitals) of ST175 revealed that the XDR pattern was driven by the combination of AmpC hyperproduction, OprD inactivation (Q142X), 3 mutations conferring high-level fluoroquinolone resistance (GyrA T83I and D87N and ParC S87W), a G195E mutation in MexZ (involved in MexXY-OprM overexpression), and the production of a class 1 integron harboring the aadB gene (gentamicin and tobramycin resistance). Of particular interest, in nearly all the ST175 isolates, AmpC hyperproduction was driven by a novel AmpR-activating mutation (G154R), as demonstrated by complementation studies using an ampR mutant of PAO1. This work is the first to describe the specific resistance markers of widespread P. aeruginosa XDR high-risk clones producing invasive infections.

Metallo-β-lactamases: a last frontier for β-lactams?

Metallo-β-lactamases are resistance determinants of increasing clinical relevance in Gram-negative bacteria. Because of their broad range, potent carbapenemase activity and resistance to inhibitors, these enzymes can confer resistance to almost all β-lactams. Since the 1990s, several metallo-β-lactamases encoded by mobile DNA have emerged in important Gram-negative pathogens (ie, in Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii). Some of these enzymes (eg, VIM-1 and NDM-1) have been involved in the recent crisis resulting from the international dissemination of carbapenem-resistant Klebsiella pneumoniae and other enterobacteria. Although substantial knowledge about the molecular biology and genetics of metallo-β-lactamases is available, epidemiological data are inconsistent and clinical experience is still lacking; therefore, several unsolved or debatable issues remain about the management of infections caused by producers of metallo-β-lactamase. The spread of metallo-β-lactamases presents a major challenge both for treatment of individual patients and for policies of infection control, exposing the substantial unpreparedness of public health structures in facing up to this emergency.

The laboratory diagnosis of Pseudomonas aeruginosa that produce metallo-β-lactamases in a Dutch tertiary care centre

BACKGROUND

The laboratory detection of Pseudomonas aeruginosa that produce metallo-β-lactamases (MBLs) is not well defined in regions with a low prevalence of these enzymes. We report a study that developed ethylenediaminetetraacetic acid (EDTA) disk screen tests using doripenem, imipenem and meropenem and investigated the prevalence of these enzymes among clinical isolates of imipenem-resistant P. aeruginosa in Rotterdam during 2008-2009.

METHODS

Using strains with well-characterized β-lactamases and the Clinical and Laboratory Standards Institute (CLSI) disk methodology similar to extended-spectrum β-lactamase (ESBL) detection, inhibition zone diameters were determined in tests with doripenem, imipenem, and meropenem, alone and in combination with 370 μg of EDTA. These tests were compared with the MBL E-test. A positive test was a ≥5 mm increase in zone diameter in the presence of EDTA.

RESULTS

The imipenem EDTA disk screen test showed a sensitivity of 100% and a specificity of 90% in 96 recent clinical isolates. Imipenem in combination with doripenem performed better than imipenem alone, meropenem, and the MBL E-test (sensitivity of 100%; specificity of 95%). The majority of clinical isolates were isolated from patient respiratory specimens. Of the 96 imipenem-resistant P. aeruginosa isolated, 35 (36%) were positive for bla(VIM) genes.

CONCLUSIONS

The EDTA imipenem/doripenem disk test showed accurate and reproducible results with excellent sensitivity and specificity. It is simple to perform and interpret and can be easily introduced into the workflow of a clinical laboratory to screen for MBLs in imipenem-resistant P. aeruginosa. Due to its high specificity the test is also suitable for regions with a low prevalence of these enzymes.

First outbreak of VIM-2 metallo-β-lactamase-producing Pseudomonas aeruginosa in The Netherlands: microbiology, epidemiology and clinical outcomes

This study was designed to investigate the prevalence and characteristics of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa in a tertiary care centre in The Netherlands, a country that is considered to have a low prevalence of antibiotic-resistant bacteria. Imipenem-resistant P. aeruginosa isolates cultured from clinical specimens during 2008-2009 were analysed phenotypically and molecularly by polymerase chain reaction (PCR) with sequencing. Genotyping was performed by multiple-locus variable-number tandem repeat (VNTR) analysis (MLVA). Clinical information was obtained by electronic chart review for all patients infected or colonised with an imipenem-resistant P. aeruginosa isolate that was included in the study. In total, 106 imipenem-resistant P. aeruginosa isolates were included. The bla(VIM-2) gene was detected in 35/106 isolates (33%) and was associated with integrons. Compared with non-MBL-producing imipenem-resistant P. aeruginosa, VIM-2 MBL-producing isolates showed higher rates of multidrug resistance. Patients with VIM-2 MBL-producing isolates were more likely to be admitted to the Intensive Care Unit (ICU) and had a higher risk of invasive infection, including development of bacteraemia. MLVA identified two separate VIM-2 MBL-producing clones, responsible for outbreaks in the ICU but also affecting 10 other departments. This is the first reported outbreak of VIM-2 MBL-producing P. aeruginosa in The Netherlands. Once introduced, VIM-2 MBL-producing P. aeruginosa cause significant infections and are easily spread within the hospital setting.

[Epidemic outbreak of Pseudomonas aeruginosa carbepenem-resistant producing metallo-beta-lactamase]

OBJECTIVE

To describe the nosocomial outbreak of multiresistant Pseudomonas aeruginosa producing metallo-beta-lactamase (MBL) in Cartagena (Murcia, Spain).

MATERIAL AND METHODS

In May 2009, six consecutive isolations of multiresistant Pseudomonas aeruginosa were detected. These were characterized by their profile of resistance to imipenem and cephalosporins and sensibility to aztreonam, this suggesting the production of carbapenemases. The isolations were screened for MBL and a PCR for the detection of the VIM gene was performed. Secondary, all of the isolations having the same characteristics in the year 2009 were analyzed retrospectively in order to establish the possibility of an endemic infection.

RESULTS

The molecular typing of the isolates revealed two clones in Pulsed Field Gel Electrophoresis (PFGE), the most frequent (Type 1) being represented by 4 isolates. All of them came from patients who were in the Intensive Care Unit. All (100%) of the isolates of the outbreak were considered to be multiresistant. PCR confirmed the presence of the VIM gene related with the production of MBL in 100% of the isolates corresponding to pulsotype 1.

CONCLUSIONS

We detected the existence of an outbreak of carbapenem-resistant Pseudomonas aeruginosa producing metallo-beta-lactamase. Am evident therapeutic problem as well as a problem of nosocomial infection was considered. The isolation means should be maximized and routine controls performed for the presence of MBL given its elevated prevalence in our setting.

Epidemiology and genetics of VIM-type metallo-β-lactamases in Gram-negative bacilli

Metallo-β-lactamases (MBLs) are a rapidly evolving group of β-lactamases, which hydrolyze most β-lactams including the carbapenems. Of the known MBLs, VIMs are one of the most common families, with 27 variants detected in at least 23 species of Gram-negative bacilli from more than 40 countries/regions. The amino acid similarities of VIM variants range from 72.9 to 99.6% with 1–72 different residues. Most of the bla VIMs are harbored by a class 1 integron, a genetic platform able to acquire and express gene cassettes. The integrons are usually embedded in transposons and, in turn, accommodated on plasmids, making them highly mobile. Integrons display considerable diversity, with at least 110 different structures associated with the gain and spread of the bla VIMs. In most instances, the bla VIMs co-exist with one or more other resistance genes. The processes for the identification of bacteria harboring bla VIMs are also discussed in this article.

Activity of a new antipseudomonal cephalosporin, CXA-101 (FR264205), against carbapenem-resistant and multidrug-resistant Pseudomonas aeruginosa clinical strains

The activity of the new cephalosporin CXA-101 (CXA), previously designated FR264205, was evaluated against a collection of 236 carbapenem-resistant P. aeruginosa isolates, including 165 different clonal types, from a Spanish multicenter (127-hospital) study. The MICs of CXA were compared to the susceptibility results for antipseudomonal penicillins, cephalosporins, carbapenems, aminoglycosides, and fluoroquinolones. The MIC of CXA in combination with tazobactam (4 and 8 microg/ml) was determined for strains with high CXA MICs. The presence of acquired beta-lactamases was investigated by isoelectric focusing and PCR amplification followed by sequencing. Additional beta-lactamase genes were identified by cloning and sequencing. The CXA MIC50/MIC90 for the complete collection of carbapenem-resistant P. aeruginosa isolates was 1/4 microg/ml, with 95.3% of the isolates showing an MIC of <or=8 microg/ml. Cross-resistance with any of the antibiotics tested was not observed; the MIC50/MIC90 of CXA-101 was still 1/4 when multidrug-resistant (MDR) strains (42% of all tested isolates) or AmpC-hyperproducing clones (53%) were analyzed. Almost all (10/11) of the strains showing a CXA MIC of >8 microg/ml produced a horizontally acquired beta-lactamase, including the metallo-beta-lactamase (MBL) VIM-2 (one strain), the extended-spectrum beta-lactamase (ESBL) PER-1 (one strain), several extended-spectrum OXA enzymes (OXA-101 [one strain], OXA-17 [two strains], and a newly described OXA-2 derivative [W159R] designated OXA-144 [four strains]), and a new BEL variant (BEL-3) ESBL (one strain), as identified by cloning and sequencing. Synergy with tazobactam in these 11 strains was limited, although 8 microg/ml reduced the mean CXA MIC by 2-fold. CXA is highly active against carbapenem-resistant P. aeruginosa isolates, including MDR strains. Resistance was restricted to still-uncommon strains producing an acquired MBL or ESBL.

Dispersal of carbapenemase blaVIM-1 gene associated with different Tn402 variants, mercury transposons, and conjugative plasmids in Enterobacteriaceae and Pseudomonas aeruginosa

The emergence of bla(VIM-1) within four different genetic platforms from distinct Enterobacteriaceae and Pseudomonas aeruginosa isolates in an area with a low prevalence of metallo-beta-lactamase producers is reported. Forty-three VIM-1-producing isolates (including 19 Enterobacter cloacae, 2 Escherichia coli, and 2 P. aeruginosa isolates, 18 Klebsiella pneumoniae isolate, and 2 Klebsiella oxytoca isolate) recovered from 2005 to 2007 and corresponding to 15 pulsed-field gel electrophoresis types were studied. The Enterobacteriaceae isolates corresponded to a hospital outbreak, and the P. aeruginosa isolates were sporadically recovered. The genetic context of the integrons carrying bla(VIM-1) (arbitrarily designated types A, B, C, and D) was characterized by PCR mapping based on known Tn402 and mercury transposons and further sequencing. Among Enterobacteriaceae isolates, bla(VIM-1) was part of integrons located either in an In2-Tn402 element linked to Tn21 (type A; In110-bla(VIM-1)-aacA4-aadA1) or in a Tn402 transposon lacking the whole tni module [type B; In113-bla(VIM-1)-aacA4-dhfrII (also called dfrB1)-aadA1-catB2] and the transposon was associated with an IncHI2 or IncI1 plasmid, respectively. Among P. aeruginosa isolates, bla(VIM-1) was part of a new gene cassette array located in a defective Tn402 transposon carrying either tniBDelta3 and tniA (type C; bla(VIM-1)-aadA1) or tniC and DeltatniQ (type D; bla(VIM-1)-aadB), and both Tn402 variants were associated with conjugative plasmids of 30 kb. The dissemination of bla(VIM-1) was associated with different genetic structures and bacterial hosts, depicting a complex emergence and evolutionary network scenario in our facility, Ramón y Cajal University Hospital, Madrid, Spain. Knowledge of the complex epidemiology of bla(VIM-1) is necessary to control this emerging threat.

Large dissemination of VIM-2-metallo-{beta}-lactamase-producing pseudomonas aeruginosa strains causing health care-associated community-onset infections

During a 3-year period (May 2005 to April 2008), a series of 45 outpatients presented with community-onset urinary tract infections due to carbapenem-resistant Pseudomonas aeruginosa isolates. Forty of them had a history of previous hospitalization or exposure to healthcare facilities, while the remaining five had not been previously admitted to our healthcare facilities or elsewhere within the preceding 12 months. In 18 outpatients, the carbapenem-resistant organisms caused recurrent community-onset urinary tract infections, while in three outpatients the organisms were also implicated in bacteremic episodes. All 45 single-patient P. aeruginosa isolates harbored the bla(VIM-2) metallo-beta-lactamase (MBL) gene in a common class 1 integron structure. They belonged to one predominant pulsed-field gel electrophoresis type and three sporadically detected types; two of the sporadic clonal types were identified among outpatients without previous exposure to healthcare facilities, while the predominant clonal type was also identified to cause infections in hospitalized patients. This is the first study documenting that MBL-producing P. aeruginosa isolates cause community-onset infections that are related or not with exposure to healthcare facilities. Community-onset infections in our patients most likely resulted from the nosocomial acquisition of MBL producers, followed by a prolonged digestive carriage. The high rate of recurrent infections in the community underlies the difficulty of constraining infections caused by such microorganisms in the extrahospital setting.

Pseudomonas aeruginosa - a phenomenon of bacterial resistance

Pseudomonas aeruginosa is one of the leading nosocomial pathogens worldwide. Nosocomial infections caused by this organism are often hard to treat because of both the intrinsic resistance of the species (it has constitutive expression of AmpC beta-lactamase and efflux pumps, combined with a low permeability of the outer membrane), and its remarkable ability to acquire further resistance mechanisms to multiple groups of antimicrobial agents, including beta-lactams, aminoglycosides and fluoroquinolones. P. aeruginosa represents a phenomenon of bacterial resistance, since practically all known mechanisms of antimicrobial resistance can be seen in it: derepression of chromosomal AmpC cephalosporinase; production of plasmid or integron-mediated beta-lactamases from different molecular classes (carbenicillinases and extended-spectrum beta-lactamases belonging to class A, class D oxacillinases and class B carbapenem-hydrolysing enzymes); diminished outer membrane permeability (loss of OprD proteins); overexpression of active efflux systems with wide substrate profiles; synthesis of aminoglycoside-modifying enzymes (phosphoryltransferases, acetyltransferases and adenylyltransferases); and structural alterations of topoisomerases II and IV determining quinolone resistance. Worryingly, these mechanisms are often present simultaneously, thereby conferring multiresistant phenotypes. This review describes the known resistance mechanisms in P. aeruginosa to the most frequently administrated antipseudomonal antibiotics: beta-lactams, aminoglycosides and fluoroquinolones.

Metallo-beta-lactamase-producing Pseudomonas aeruginosa isolated from a large tertiary centre in Kenya

This study was designed to characterize the beta-lactamase content of carbapenem-resistant Pseudomonas aeruginosa isolates recovered during 2006 and 2007 in a large tertiary-care centre in Nairobi, Kenya. Molecular characterization was done using PCR and sequencing, and typing was performed using pulsed-field gel electrophoresis (PFGE). In total, 416 P. aeruginosa isolates were obtained during that period, of which 57 (13.7%) were resistant to carbapenems. All carbapenem-resistant isolates tested positive for metallo-beta-lactamase (MBL) production. All MBL isolates produced VIM-2 with two types of integron structures. PFGE identified three clonally related groups of VIM-2-producing P. aeruginosa, including a pan-resistant clone that was responsible for nosocomial outbreaks during 2006 and 2007 in the intensive-care unit. These findings suggest that continuous molecular surveillance needs to be performed to monitor the spread within the hospital of this pan-resistant strain. This study is the first report of VIM-2-producing P. aeruginosa from the African continent.

Characterization of the new metallo-beta-lactamase VIM-13 and its integron-borne gene from a Pseudomonas aeruginosa clinical isolate in Spain

During a survey conducted to evaluate the incidence of class B carbapenemase (metallo-beta-lactamase [MBL])-producing Pseudomonas aeruginosa strains from hospitals in Majorca, Spain, five clinical isolates showed a positive Etest MBL screening test result. In one of them, strain PA-SL2, the presence of a new bla(VIM) derivative (bla(VIM-13)) was detected by PCR amplification with bla(VIM-1)-specific primers followed by sequencing. The bla(VIM-13)-producing isolate showed resistance to all beta-lactams (except aztreonam), gentamicin, tobramycin, and ciprofloxacin. VIM-13 exhibited 93% and 88% amino acid sequence identities with VIM-1 and VIM-2, respectively. bla(VIM-13) was cloned in parallel with bla(VIM-1), and the resistance profile conferred was analyzed both in Escherichia coli and in P. aeruginosa backgrounds. Compared to VIM-1, VIM-13 conferred slightly higher levels of resistance to piperacillin and lower levels of resistance to ceftazidime and cefepime. VIM-13 and VIM-1 were purified in parallel as well, and their kinetic parameters were compared. The k(cat)/K(m) ratios for the antibiotics mentioned above were in good agreement with the MIC data. Furthermore, EDTA inhibited the activity of VIM-13 approximately 25 times less than it inhibited the activity of VIM-1. VIM-13 was harbored in a class 1 integron, along with a new variant (Ala108Thr) of the aminoglycoside-modifying enzyme encoding gene aacA4, which confers resistance to gentamicin and tobramycin. Finally, the VIM-13 integron was apparently located in the chromosome, since transformation and conjugation experiments consistently yielded negative results and the bla(VIM-13) probe hybridized only with the genomic DNA.

Molecular epidemiology and mechanisms of carbapenem resistance in Pseudomonas aeruginosa isolates from Spanish hospitals

All (236) Pseudomonas aeruginosa isolates resistant to imipenem and/or meropenem collected during a multicenter (127-hospital) study in Spain were analyzed. Carbapenem-resistant isolates were found to be more frequently resistant to all beta-lactams and non-beta-lactam antibiotics than carbapenem-susceptible isolates (P < 0.001), and up to 46% of the carbapenem-resistant isolates met the criteria used to define multidrug resistance (MDR). Pulsed-field gel electrophoresis revealed remarkable clonal diversity (165 different clones were identified), and with few exceptions, the levels of intra- and interhospital dissemination of clones were found to be low. Carbapenem resistance was driven mainly by the mutational inactivation of OprD, accompanied or not by the hyperexpression of AmpC or MexAB-OprM. Class B carbapenemases (metallo-beta-lactamases [MBLs]) were detected in a single isolate, although interestingly, this isolate belonged to one of the few epidemic clones documented. The MBL-encoding gene (bla(VIM-2)), along with the aminoglycoside resistance determinants, was transferred to strain PAO1 by electroporation, demonstrating its plasmid location. The class 1 integron harboring bla(VIM-2) was characterized as well, and two interesting features were revealed: intI1 was found to be disrupted by a 1.1-kb insertion sequence, and a previously undescribed aminoglycoside acetyltransferase-encoding gene [designated aac(6')-32] preceded bla(VIM-2). AAC(6')-32 showed 80% identity to AAC(6')-Ib' and the recently described AAC(6')-31, and when aac(6')-32 was cloned into Escherichia coli, it conferred resistance to tobramycin and reduced susceptibility to gentamicin and amikacin. Despite the currently low prevalence of epidemic clones with MDR, active surveillance is needed to detect and prevent the dissemination of these clones, particularly those producing integron- and plasmid-encoded MBLs, given their additional capacity for the intra- and interspecies spread of MDR.