Molecular evolution of metallo-beta-lactamase-producing Pseudomonas aeruginosa in a nosocomial setting of high-level endemicity

Clinically Relevant β-Lactam Resistance Genes in Wastewater Treatment Plants

Antimicrobial resistance (AMR) is one of the largest global concerns due to its influence in multiple areas, which is consistent with One Health's concept of close interconnections between people, animals, plants, and their shared environments. Antibiotic-resistant bacteria (ARB) and antibiotic-resistance genes (ARGs) circulate constantly in various niches, sediments, water sources, soil, and wastes of the animal and plant sectors, and is linked to human activities. Sewage of different origins gets to the wastewater treatment plants (WWTPs), where ARB and ARG removal efficiency is still insufficient, leading to their transmission to discharge points and further dissemination. Thus, WWTPs are believed to be reservoirs of ARGs and the source of spreading AMR. According to a World Health Organization report, the most critical pathogens for public health include Gram-negative bacteria resistant to third-generation cephalosporins and carbapenems (last-choice drugs), which represent β-lactams, the most widely used antibiotics. Therefore, this paper aimed to present the available research data for ARGs in WWTPs that confer resistance to β-lactam antibiotics, with a particular emphasis on clinically important life-threatening mechanisms of resistance, including extended-spectrum β-lactamases (ESBLs) and carbapenemases (KPC, NDM).

Interplay of OpdP Porin and Chromosomal Carbapenemases in the Determination of Carbapenem Resistance/Susceptibility in Pseudomonas aeruginosa

Carbapenem resistance in Pseudomonas aeruginosa strains responsible for chronic lung infections in cystic fibrosis (CF) patients is mainly due to loss of the OprD protein and, limited to meropenem and doripenem, to overexpression of efflux pumps. However, recent reports of isolates showing inconsistent genotype-phenotype combinations (e.g., susceptibility in the presence of resistance determinants and vice versa) suggest the involvement of additional factors whose role is not yet fully elucidated. Among them, the OpdP porin as an alternative route of entry for carbapenems other than OprD and the overexpression of two chromosomal carbapenemases, the Pseudomonas-derived cephalosporinase (PDC) and the PoxB oxacillinase, have recently been reconsidered and studied in specific model strains. Here, the contribution of these factors was investigated by comparing different phenotypic variants of three strains collected from the sputum of colonized CF patients. Carbapenem uptake through OpdP was investigated both at the functional level, by assessing the competition exerted by glycine-glutamate, the OpdP’s natural substrate, against imipenem uptake, and at the molecular level, by comparing the expression levels of opdP genes by quantitative real-time PCR (qRT-PCR). Moreover, overexpression of the chromosomal carbapenemases in some of the isolates was also investigated by qRT-PCR. The results showed that, even if OprD inactivation remains the most important determinant of carbapenem resistance in strains infecting the CF lung, the interplay of other determinants might have a nonnegligible impact on bacterial susceptibility, being able to modify the phenotype of part of the population and consequently complicating the choice of an appropriate therapy.

IMPORTANCE This study examines the interplay of multiple factors in determining a pattern of resistance or susceptibility to carbapenems in clinical isolates of Pseudomonas aeruginosa, focusing on the role of previously poorly understood determinants. In particular, the impact of carbapenem permeability through OprD and OpdP porins was analyzed, as well as the activity of the chromosomal carbapenemases AmpC and PoxB, going beyond the simple identification of resistance determinants encoded by each isolate. Indeed, analysis of the expression levels of these determinants provides a new approach to determine the contribution of each factor, both individually and in coexistence with the other factors. The study contributes to understanding some phenotype-genotype discordances closely related to the heteroresistance frequently detected in P. aeruginosa isolates responsible for pulmonary infections in cystic fibrosis patients, which complicates the choice of an appropriate patient-specific therapy.

Carbapenem Resistance Determinants Acquired through Novel Chromosomal Integrations in Extensively Drug-Resistant Pseudomonas aeruginosa

Two novel bla_DIM-1- or bla_IMP-1-containing genomic islands (GIs) were discovered by whole-genome sequence analyses in four extensively drug-resistant (XDR) Pseudomonas aeruginosa isolates from inpatients at a tertiary hospital in Ghana. The strains were of sequence type 234 (ST234) and formed a phylogenetic clade together with ST111, which is recognized as a global high-risk clone. Their carbapenem resistance was encoded by two Tn402-type integrons, In1592 (bla_DIM-1) and In1595 (bla_IMP-1), both carrying complete tni mobilization modules. In1595 was bound by conserved 25-bp inverted repeats (IRs) flanked by 5-bp direct repeats (DRs) associated with target site duplication. The integrons were embedded in two GIs that contained cognate integrases and were distinguished by a lower GC content than the chromosomal average. PAGI-97A (52.659 bp; In1592), which encoded a P4-type site-specific integrase of the tyrosine recombinase family in its 3′ border, was integrated into tRNA-Pro(ggg) and bracketed by a 49-bp perfect DR created by 3′-end target duplication. GIs with the same structural features, but diverse genetic content, were identified in 41/226 completed P. aeruginosa genomes. PAGI-97B (22,636 bp; In1595), which encoded an XerC/D superfamily integrase in its 5′ border, was inserted into the small RNA (sRNA) PrrF1/PrrF2 locus. Specific insertions into this highly conserved locus involved in iron-dependent regulation, all leaving PrrF1 intact, were identified in an additional six phylogenetically unrelated P. aeruginosa genomes. Our molecular analyses unveiled a hospital-associated clonal dissemination of carbapenem-resistant ST234 P. aeruginosa in which the XDR phenotype resulted from novel insertions of two GIs into specific chromosomal sites.

Epidemiology of β-Lactamase-Producing Pathogens

β-Lactam antibiotics have been widely used as therapeutic agents for the past 70 years, resulting in emergence of an abundance of β-lactam-inactivating β-lactamases. Although penicillinases in Staphylococcus aureus challenged the initial uses of penicillin, β-lactamases are most important in Gram-negative bacteria, particularly in enteric and nonfermentative pathogens, where collectively they confer resistance to all β-lactam-containing antibiotics. Critical β-lactamases are those enzymes whose genes are encoded on mobile elements that are transferable among species. Major β-lactamase families include plasmid-mediated extended-spectrum β-lactamases (ESBLs), AmpC cephalosporinases, and carbapenemases now appearing globally, with geographic preferences for specific variants. CTX-M enzymes include the most common ESBLs that are prevalent in all areas of the world. In contrast, KPC serine carbapenemases are present more frequently in the Americas, the Mediterranean countries, and China, whereas NDM metallo-β-lactamases are more prevalent in the Indian subcontinent and Eastern Europe. As selective pressure from β-lactam use continues, multiple β-lactamases per organism are increasingly common, including pathogens carrying three different carbapenemase genes. These organisms may be spread throughout health care facilities as well as in the community, warranting close attention to increased infection control measures and stewardship of the β-lactam-containing drugs in an effort to control selection of even more deleterious pathogens.

First Italian outbreak of VIM-producing Serratia marcescens in an adult polyvalent intensive care unit, August-October 2018: A case report and literature review

BACKGROUND

Carbapenem-resistant Enterobacteriaceae has become a significant public health concern as hospital outbreaks are now being frequently reported and these organisms are becoming difficult to treat with the available antibiotics.

CASE SUMMARY

An outbreak of VIM-producing Serratia marcescens occurred over a period of 11 wk (August, 1 to October, 18) in patients admitted to the adult polyvalent intensive care unit of the University of Campania “Luigi Vanvitelli” located in Naples. Four episodes occurred in three patients (two patients infected, and one patient colonized). All the strains revealed the production of VIM.

CONCLUSION

After three decades of carbapenem antibiotics use, the emergence of carbapenem-resistance in Enterobacteriaceae has become a significant concern and a stricter control to preserve its clinical application is mandatory. This is, to our knowledge, the first outbreak of VIM-producing Serratia marcescens in Europe. Surveillance policies must be implemented to avoid future outbreaks.

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.

Spread of Vancomycin-Resistant Enterococcus faecium Isolates Despite Validated Infection Control Measures in an Italian Hospital: Antibiotic Resistance and Genotypic Characterization of the Endemic Strain

An alarming increase of vancomycin-resistant Enterococcus faecium (VREfm) isolates was detected in an Italian referral hospital subjected to policies of infection control validated by the Joint Commission International. Analysis of the population structure of 122 consecutive, nonreplicate VREfm isolates collected over an 18-month period identified a single major clone that spread around the whole hospital, rapidly establishing an endemic state. It belonged to sequence type (ST) 17 and showed a highly multidrug-resistant phenotype, being resistant to all antimicrobial classes for the carriage of several resistance determinants. Furthermore, some strains with decreased susceptibility to daptomycin were detected. Eighteen out of the 122 isolates did not group in the major clone. They showed a low spreading potential inside the hospital wards, even if most of them displayed a multidrug-resistant phenotype and belonged to a hospital-adapted lineage. Causes that led to the VREfm endemic state have not been fully elucidated. However, it is conceivable that the increase in systemic antibiotic consumption and the use of selective digestive tract decontamination, including vancomycin in critically ill patients during the period before 2014, may have played a role in the ST17 clone dissemination, but additional traits conferring high fitness in hospital environment cannot be excluded.

Presence of VIM-Positive Pseudomonas Species in Chickens and Their Surrounding Environment

Metallo-β-lactamase gene bla_VIM was identified on the chromosome of four Pseudomonas sp. isolates from a chicken farm, including one Pseudomonas aeruginosa isolate from a swallow (Yanornis martini), one Pseudomonas putida isolate from a fly, and two P. putida isolates from chickens. The four isolates shared two variants of bla_VIM-carrying genomic contexts that resemble the corresponding regions of clinical metallo-β-lactamase-producing Pseudomonas spp. Our study suggests that the surveillance of carbapenemase-producing bacteria in livestock and their surrounding environment is urgently needed.

Contamination of Hospital Water Supplies in Gilan, Iran, with Legionella pneumophila, Escherichia coli, and Pseudomonas aeruginosa

This study is designed to determine the contamination degree of hospital water supplies with Pseudomonas aeruginosa, Legionella pneumophila, and E. coli in Gilan, Iran. Samples were collected directly into sterile containers and concentrated by centrifuge. Half part of any sample transferred to yeast extract broth and the second part transferred to Trypticase Soy Broth and incubated for 3 days. DNA was extracted by using commercial kit. Four rounds of PCR were performed as follows: multiplex PCR for detecting Pseudomonas aeruginosa, Integron 1, and Metallo-β-lactamases gene; PCR for detecting Legionella pneumophila and mip gene separately; PCR for detecting E. coli; and another PCR for detecting whole bacterial presence. Contamination rates of cold, warm, and incubator water samples with P. aeruginosa, were 16.6%, 37.5%, and 6.8% consequently. Degrees of contamination with L. pneumophila were 3.3%, 9.3%, and 10.9% and with E. coli were zero, 6.2%, and zero. Total bacterial contamination of cold, warm, and incubator water samples was 93.3%, 84.4%, and 89.0% consequently. Metallo-β-lactamases gene was found in 20.0% of all samples. Contamination degree with P. aeruginosa was considerable and with L. pneumophila was moderate. Metallo-β-lactamases gene was found frequently indicating widespread multiple drug resistance bacteria. We suggest using new decontamination method based on nanotechnology.

Metallo-beta-Lactamase VIM-1, SPM-1, and IMP-1 Genes Among Clinical Pseudomonas aeruginosa Species Isolated in Zahedan, Iran

Background:

One of the major clinical problems regarding Pseudomonas aeruginosa is attributed to metallo-beta-lactamases (MBL). This group of enzymes is a subset of beta lactamases which belong to group B of Ambler classification and cause hydrolysis of carbapenems. Based on epidemiological studies conducted worldwide, it is proved that prevalence of genes coding MBLs in P. aeruginosa species are different in various geographic zones and even in various hospitals. Therefore, according to the clinical importance of organisms generating MBLs, it is necessary to identify and control these bacteria in hospitals for therapeutic purposes.

Objectives:

The current study aimed to investigate the Metallo-beta-Lactamase VIM-1, SPM-1, and IMP-1 genes among clinical P. aeruginosa species isolated in Zahedan, Iran.

Materials and Methods:

The current study investigated the presence of MBL through phenotypic and genotypic methods and also the pattern of antibiotic resistance in P. aeruginosa species isolated in hospitals. The Minimum Inhibitory Concentration (MIC) against imipeneme was measured for 191 P. aeruginosa species isolated from Zahedan hospitals after identification through biochemical methods and determination of the antibiotic resistance pattern. Strains with MIC > 4 µg/mL were studied by phenotypic and genotypic methods.

Results:

The rate of resistance against imipeneme was 5.7% and after carrying out the phenotypic experiments, nine species were identified as of MBL producer. Seven species were confirmed by Polymerase Chain Reaction (PCR) method. Gene VIM-1 was the predominant gene among the positive (antibiotic resistant) species.

Conclusions:

The study results showed that MBL genes were present in some of the species isolated from Zahedan hospitals. Regarding the importance of MBL producer bacteria in hospitals, quick identification and evaluation of these clinical species can be considered as an important and basic step for treatment and control of pseudomonad infections.

Molecular detection of metallo-β-lactamase gene blaVIM-1 in imipenem-resistant Pseudomonas aeruginosa strains isolated from hospitalized patients in the hospitals of Isfahan

BACKGROUND

Pseudomonas aeruginosa is an opportunistic human pathogen that causes serious problems, especially in people, who have immunodeficiency. In recent times, metallo-β-lactamase (MBLs) resistance in this bacterium has led to some difficulties in treating bacterial infections. The metallo-beta-lactamase family of genes, including blaVIM-1, is being reported with increasing frequency worldwide. The aim of this study is the detection of the metallo-β-lactamase gene blaVIM-1 in imipenem-resistant P. aeruginosa (IRPA) strains isolated from hospitalized patients.

MATERIALS AND METHODS

In this study, 106 P. aeruginosa samples were isolated from various nosocomial infections. The isolates were identified, tested for susceptibility to various antimicrobial agents by the Kirby-Bauer disk diffusion method, and all the imipenem-resistant isolates were screened for the presence of MBLs by using the combined disk (IMP-EDTA). The minimal inhibitory concentration (MIC) of imipenem was determined by E-test on the Mueller-Hinton agar. To detect the blaVIM-1 gene, the isolates were subjected to a polymerase chain reaction (PCR).

RESULTS

Of all the P. aeruginosa isolates, 62 (58.5%) were found to be imipenem-resistant P. aeruginosa (MIC ≥32 μg/ml). Twenty-six (42%) of the imipenem-resistant isolates were MBL positive. None of these isolates carried the blaVIM-1 gene using the PCR assay.

CONCLUSION

The results demonstrated the serious therapeutic threat of the MBL-producing P. aeruginosa populations. The rate of imipenem resistance due to MBL was increased dramatically. Early detection and infection-control practices are the best antimicrobial strategies for this organism. None of MBL-producing isolates in this study carry the blaVIM-1 gene; therefore, another gene in the MBL family should be investigated.

Green synthesis of Al2O3 nanoparticles and their bactericidal potential against clinical isolates of multi-drug resistant Pseudomonas aeruginosa

The high prevalence of extended-spectrum β-lactamases (76.3 %) and metallo-β-lactamases (7.3 %) amongst the bacteria Pseudomonas aeruginosa is a critical problem that has set forth an enormous therapeutic challenge. The suggested role of nanoparticles as next generation antibiotics, and inadequate information on antibacterial activity of aluminium oxide nanoparticles has led us to investigate the green synthesis of aluminium oxide nanoparticles (Al2O3 NPs) using leaf extracts of lemongrass and its antibacterial activity against extended-spectrum β-lactamases and metallo-β-lactamases clinical isolates of P. aeruginosa. The synthesized Al2O3-NPs were characterized by scanning electron microcopy, high resolution-transmission electron microscopy, atomic force microscopy, X-ray diffraction, Zeta potential, and differential light scattering techniques. The X-ray diffraction data revealed the average size of the spherical Al2O3-NPs as 34.5 nm. The hydrodynamic size in Milli Q water and Zeta potential were determined to be 254 nm and +52.2 mV, respectively. The minimal inhibitory concentration of Al2O3-NPs was found to be in the range of 1,600-3,200 µg/ml. Treatment at concentrations >2,000 µg/ml, resulted in complete growth inhibition of extended-spectrum β-lactamases and metallo-β-lactamases isolates. Scanning electron microcopy analysis revealed the clusters of nanoparticles attached to the bacterial cell surface, causing structural deformities in treated cells. High resolution-transmission electron microscopy analysis confirmed that nanoparticles crossed the cell membrane to become intracellular. The interaction of nanoparticles with the cell membrane eventually triggered the loss of membrane integrity, most likely due to intracellular oxidative stress. The data explicitly suggested that the synthesized Al2O3-NPs can be exploited as an effective bactericidal agent against extended-spectrum β-lactamases, non-extended-spectrum β-lactamases and metallo-β-lactamases strains of P. aeruginosa, regardless of their drug resistance patterns and mechanisms. The results elucidated the clinical significance of Al2O3-NPs in developing an effective antibacterial therapeutic regimen against the multi-drug resistant bacterial infections. The use of leaf extract of lemongrass for the synthesis of Al2O3-NPs appears to be cost effective, nontoxic, eco-friendly and its strong antibacterial activity against multi-drug resistant strains of P. aeruginosa offers compatibility for pharmaceutical and other biomedical applications.

Epidemiology of VIM-1-imipenem resistant Pseudomonas aeruginosa in Iran: A systematic review and meta-analysis

BACKGROUND

Pseudomonas aeruginosa is an opportunistic human pathogen which causes serious problems, especially in people who have immunodeficiency. Metallo beta-lactamase (MBL) resistance in this bacterium has led some difficulties in treating bacterial infections. MBLs are being reported with increasing frequency worldwide. The aim of the present systematic review and meta-analysis was to collect data about the relative frequency (RF) of VIM-1-imipenem resistant P. aeruginosa (VIM-1-IRPA) in different regions of Iran and report an overall prevalence if possible.

MATERIALS AND METHODS

PubMed, ISI web of science, Scopus and Google Scholar were searched using following key terms: "P. aeruginosa," "imipenem," "VIM-1" and "Iran" were. Articles/abstracts, which used clinical specimens and had done polymerase chain reaction to detect the VIM-1 gene of MBL genes, were included in this review. STATA SE version 11.2 (StataCorp, College Station, TX, USA) was used for statistical analysis.

RESULTS

Out of 5457 results found, 10 articles were eligible to be included in our systematic review and meta-analysis. These studies were carried out in Tehran, Isfahan, Kurdistan, Ahvaz, Markazi and Northwest of Iran (Orumieh and Tabriz). Pooled estimation of 1972 P. aeruginosa samples showed that 13% (95% confidence interval = 10.5-16.5%]) of strains were VIM-1 positive. VIM-1-IRPA RF in different studies varied from 0% to 19.5% in Isfahan and Markazi provinces, respectively. We found a moderate heterogeneity (Chochran Q-test, P = 0.032, I-squared = 50.7%) of VIM-1-IRPA RF among studies.

CONCLUSION

According to the results of this study VIM-1-IRPA RF in Iran is in low-level Prevention strategies to reduce the prevalence rates of VIM-1 positive strains in Iran are needed.

Nosocomial infections with metallo-beta-lactamase-producing Pseudomonas aeruginosa: molecular epidemiology, risk factors, clinical features and outcomes

BACKGROUND

Metallo-β-lactamases (MBLs) have emerged as one of the most important bacterial resistance mechanisms because of their ability to hydrolyse virtually all β-lactam agents. MBL-producing Pseudomonas aeruginosa (MBL-PA) are an important cause of nosocomial infections, particularly in intensive care units (ICUs), where they are associated with serious infections and present a significant clinical risk.

AIM

To assess the molecular epidemiology, risk factors and outcomes of nosocomial infections caused by MBL-PA in a teaching hospital in Southern Brazil.

METHODS

From January 2001 to December 2008, 142 carbapenem-resistant P. aeruginosa strains were isolated from distinct clinical samples from hospitalized patients. These isolates were screened for MBLs, and underwent polymerase chain reaction, sequencing and pulsed-field gel electrophoresis (PFGE). Patients infected with carbapenem-resistant MBL-PA were considered as cases, and patients infected with non-MBL-PA were considered as controls.

FINDINGS

Eighty-four of 142 patients with positive carbapenem-resistant P. aeruginosa cultures met the criteria of the Centers for Disease Control and Prevention for infection. Fifty-eight patients were infected with MBL-PA (69%) and 26 patients were infected with non-MBL-PA (31%). Multi-variate analysis revealed that ICU stay [P = 0.003, odds ratio (OR) 4.01, 95% confidence interval (CI) 1.15-14.01] and urinary tract infection (P = 0.001, OR 9.67, 95% CI 1.72-54.48) were important risk factors for MBL-PA infection. Patients infected with MBL-PA showed faster onset of infection (P = 0.002) and faster progression to death (P = 0.04).

CONCLUSIONS

These results showed the severity of MBL-PA infections, and demonstrated the urgent need for strategies to improve infection control measures to prevent an increase in these nosocomial infections.

The complete nucleotide sequence of the carbapenem resistance-conferring conjugative plasmid pLD209 from a Pseudomonas putida clinical strain reveals a chimeric design formed by modules derived from both environmental and clinical bacteria

The complete sequence of the carbapenem-resistance-conferring conjugative plasmid pLD209 from a Pseudomonas putida clinical strain is presented. pLD209 is formed by 3 well-defined regions: an adaptability module encompassing a Tn402-like class 1 integron of clinical origin containing blaVIM-2 and aacA4 gene cassettes, partitioning and transfer modules, and a replication module derived from plasmids of environmental bacteria. pLD209 is thus a mosaic of modules originating in both the clinical and environmental (nonclinical) microbiota.

Complete sequence of pOZ176, a 500-kilobase IncP-2 plasmid encoding IMP-9-mediated carbapenem resistance, from outbreak isolate Pseudomonas aeruginosa 96

Pseudomonas aeruginosa 96 (PA96) was isolated during a multicenter surveillance study in Guangzhou, China, in 2000. Whole-genome sequencing of this outbreak strain facilitated analysis of its IncP-2 carbapenem-resistant plasmid, pOZ176. The plasmid had a length of 500,839 bp and an average percent G+C content of 57%. Of the 618 predicted open reading frames, 65% encode hypothetical proteins. The pOZ176 backbone is not closely related to any plasmids thus far sequenced, but some similarity to pQBR103 of Pseudomonas fluorescens SBW25 was observed. Two multiresistant class 1 integrons and several insertion sequences were identified. The blaIMP-9-carrying integron contained aacA4 → bla(IMP-9) → aacA4, flanked upstream by Tn21 tnpMRA and downstream by a complete tni operon of Tn402 and a mer module, named Tn6016. The second integron carried aacA4 → catB8a → bla(OXA-10) and was flanked by Tn1403-like tnpRA and a sul1-type 3' conserved sequence (3'-CS), named Tn6217. Other features include three resistance genes similar to those of Tn5, a tellurite resistance operon, and two pil operons. The replication and maintenance systems exhibit similarity to a genomic island of Ralstonia solanacearum GM1000. Codon usage analysis suggests the recent acquisition of bla(IMP-9). The origins of the integrons on pOZ176 indicated separate horizontal gene transfer events driven by antibiotic selection. The novel mosaic structure of pOZ176 suggests that it is derived from environmental bacteria.

Detection and characterization of VIM-31, a new variant of VIM-2 with Tyr224His and His252Arg mutations, in a clinical isolate of Enterobacter cloacae

We report the first description of the metallo-β-lactamase VIM-31, a new variant of VIM-2 with Tyr224His and His252Arg mutations, in Enterobacter cloacae 11236, which was isolated from blood specimens of a patient with colonic adenocarcinoma in Belgium. bla(VIM-31) was found on a class 1 integron located on a self-transferable but not typeable 42-kb plasmid. Compared to values published elsewhere for VIM-2, the purified VIM-31 enzyme showed weaker catalytic efficiency against all the tested beta-lactam agents (except for ertapenem), resulting from lower k(cat) (except for ertapenem) and higher K(m) values for VIM-31.

Analysis of integrons and associated gene cassettes of metallo-β-lactamase-positive Pseudomonas aeruginosa in Malaysia

In this study, 90 non-replicate imipenem-resistant Pseudomonas aeruginosa (IRPA) Malaysian isolates collected between October 2005 and March 2008 were subjected to a screening test for detection of the integron and the gene cassette. Class 1 integrons were detected in 54 IRPA clinical isolates, whilst three isolates contained class 2 integrons. Analysis of the gene cassettes associated with the class 1 integrons showed the detection of accC1 in isolates carrying bla(IMP-7) and aacA7 in isolates carrying bla(VIM-2). aadA6 was detected in two isolates carrying bla(IMP-4). Using random amplification of polymorphic DNA analysis, 14 PCR fingerprint patterns were generated from the 32 isolates carrying metallo-β-lactamase (MBL) genes (35.5 %), whilst 20 patterns were generated from the 58 non-MBL gene isolates (64.4 %). Based on the differences in the fingerprinting patterns, two clusters (A and B) were identified among the MBL-producing isolates. Cluster A comprised 18 isolates (56 %) carrying the bla(VIM) gene, whereas cluster B comprised 14 (44 %) isolates carrying the bla(IMP) gene. The non-MBL isolates were divided into clusters C and D. Cluster C comprised 22 non-MBL isolates harbouring class 1 integrons, whilst cluster D consisted of three isolates carrying class 2 integrons. These findings suggest that the class 1 integron is widespread among P. aeruginosa isolated in Malaysia and that characterization of cassette arrays of integrons will be a useful epidemiological tool to study the evolution of multidrug resistance and the dissemination of antibiotic resistance genes.

Metallo-β-lactamase expression confers an advantage to Pseudomonas aeruginosa isolates compared with other β-lactam resistance mechanisms, favoring the prevalence of metallo-β-lactamase producers in a clinical environment

The Pseudomonas aeruginosa isolate TS-832035 was responsible for an outbreak that occurred in an Italian hospital between 1999 and 2002. It exhibited a high-level resistance to carbapenems due to the contemporary presence of two independent mechanisms: the production of a carbapenemase, coded by a bla(VIM-1) determinant carried by the chromosomal class 1 integron In70.2 (containing also the aacA4, aphA15, and aadA1 genes in its cassette array), and the lack of the OprD porin. We compared TS-832035 with a strictly related isolate, TS-103, whose resistance to carbapenems was due to the lack of the OprD porin only, as it did not carry In70.2. We evaluated their growth kinetics, in both separate cultures and competition assays, under permissive conditions. These experiments highlighted a significant in vitro fitness cost associated with the integron. On the contrary, none of the resistance determinants other than the bla(VIM-1) seemed to confer a real selective advantage to its host. Comparison of these results with the in vivo behavior, showing that the In70.2-carrying isolates largely prevailed over the In70.2-lacking ones, besides the detection of similar integrons in other Italian clinical isolates, evidenced the need to investigate accurately the causes of their large distribution, as possible soft spots could exist in the ability of their hosts to adapt to the hospital settings.

First survey of metallo-beta-lactamases in clinical isolates of Pseudomonas aeruginosa in a German university hospital

A total of 489 clinical isolates of Pseudomonas aeruginosa was investigated for metallo-beta-lactamase (MBL) production. Molecular analysis detected a blaVIM-1 gene in the chromosome of one isolate and a blaVIM-2 gene carried on the plasmid in seven isolates. Moreover, we showed that an initial screening by combined susceptibility testing of imipenem and ceftazidime followed by a confirmatory EDTA combination disk test represents a valid alternative to the molecular investigation of MBL genes, making MBL detection possible in routine diagnostic laboratories.

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.

Molecular epidemiology of outbreak-related pseudomonas aeruginosa strains carrying the novel variant blaVIM-17 metallo-beta-lactamase gene

A study was designed to investigate the molecular epidemiological characteristics of multidrug-resistant outbreak-related Pseudomonas aeruginosa isolates collected in a university hospital in northern Greece. Of 29 nonreplicate P. aeruginosa isolates resistant to carbapenems and ceftazidime, 14 were positive for metallo-beta-lactamase production. PCR analyses with primers specific for bla(VIM) and bla(IMP) revealed that 13 isolates carried a novel bla(VIM-2) gene variant, designated bla(VIM-17), and only 1 isolate carried bla(VIM-2), a gene predominant among P. aeruginosa strains in Greek hospitals. Pulsed-field gel electrophoresis of XbaI-digested genomic DNAs showed a close genetic relationship for 12 of 13 bla(VIM-17)-carrying outbreak-related isolates, which were of the O11 serotype; the clonally unrelated isolate carrying bla(VIM-17) was of the O12 serotype. PCR mapping strategies for the detection of class 1 integrons and sequencing approaches revealed the presence of integrons containing one bla(VIM) cassette flanked by two aacA29 cassettes. These integrons were similar but not identical to In59 (GenBank accession number AF263519) initially described in France. All isolates carrying bla(VIM-17), regardless of their genetic profile, had an identical integron, named In59.3, indicating that although the hospital outbreak was mainly due to clonal dissemination, the horizontal transmission of the bla(VIM-17)-containing integron among P. aeruginosa isolates should also have occurred. An outbreak-related isolate and a control strain, both of which carried the bla(VIM-2) gene but which were clonally distinct, had an identical integron, named In59.2, which differed only at the level of the bla(VIM) gene from In59.3 integrons, suggesting a common ancestry. The spread of the bla(VIM-17)-containing integron in clonally unrelated P. aeruginosa isolates without any evidence of plasmid carriage is probably associated with a transposon.

Nosocomial colonization due to imipenem-resistant Pseudomonas aeruginosa epidemiologically linked to breast milk feeding in a neonatal intensive care unit

AIM

We describe a one-year investigation of colonization by imipenemresistant, metallo-beta-lactamase (MBL) producing Pseudomonas aeruginosa in a neonatal intensive care unit (NICU) of the University Hospital of Palermo, Italy.

METHODS

A prospective epidemiological investigation was conducted in the period 2003 January to 2004 January. Rectal swabs were collected twice a week from all neonates throughout their NICU stay. MBL production by imipenem-resistant strains of P aeruginosa was detected by phenotypic and molecular methods. Pulsed field gel electrophoresis (PFGE) was carried out on all isolates of P aeruginosa. The association between risk factors and colonization by imipenem-resistant, imipenem-susceptible P aeruginosa isolates and other multidrug-resistant Gram negative (MDRGN) organisms was analyzed for variables present at admission and during the NICU stay. Data analysis was carried out by the Cox proportional hazards regression model.

RESULTS

Twentytwo of 210 neonates were colonized with imipenem-resistant, MBL-producing P aeruginosa isolates and 14 by imipenem-susceptible P aeruginosa isolates. A single pulsotype, named A, was shared by all imipenem-resistant isolates. Colonization by P aeruginosa of pulsotype A was positively correlated with breast milk feeding and administration of ampicillin-sulbactam, and inversely correlated with exclusive feeding by formula. In the Cox proportional hazards regression model, birthweight of more than 2500 g and breast milk feeding were independently associated with an increased risk of colonization by MBL producing P aeruginosa.

CONCLUSION

The results strongly support an association between colonization by a well-defined imipenem-resistant, MBL producing P aeruginosa strain and breast milk feeding. Such a study may highlight the need for implementation of strategies to prevent expressed breast milk from becoming a vehicle of health care-associated infections.

Relative strengths of the class 1 integron promoter hybrid 2 and the combinations of strong and hybrid 1 with an active p2 promoter

The relative strengths of the uncommon promoters hybrid 2, hybrid 1 with an active P2 promoter (hybrid 1+P2), and strong+P2, which drive transcription of resistance genes in class 1 integrons, were evaluated using bla(GES-1) as a reporter gene cassette. Hybrid 2 was stronger than hybrid 1. Coupling P2 with the strong promoter and with hybrid 1 caused a measurable increase in GES-1 expression.

First countrywide survey of acquired metallo-beta-lactamases in gram-negative pathogens in Italy

Metallo-beta-lactamases (MBLs) can confer resistance to most beta-lactams, including carbapenems. Their emergence in gram-negative pathogens is a matter of major concern. Italy was the first European country to report the presence of acquired MBLs in gram-negative pathogens and is one of the countries where MBL producers have been detected repeatedly. Here, we present the results of the first Italian nationwide survey of acquired MBLs in gram-negative pathogens. Of 14,812 consecutive nonreplicate clinical isolates (12,245 Enterobacteriaceae isolates and 2,567 gram-negative nonfermenters) screened for reduced carbapenem susceptibility during a 4-month period (September to December 2004), 30 isolates (28 Pseudomonas aeruginosa isolates, 1 Pseudomonas putida isolate, and 1 Enterobacter cloacae isolate) carried acquired MBL determinants. MBL producers were detected in 10 of 12 cities, with a predominance of VIM-type enzymes over IMP-type enzymes (4:1). Although having an overall low prevalence (1.3%) and significant geographical differences, MBL-producing P. aeruginosa strains appeared to be widespread in Italy, with a notable diversity of clones, enzymes, and integrons carrying MBL gene cassettes.

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.

Detection of metallo-β-lactamase–producing Pseudomonas aeruginosa strains isolated from burn patients in Ahwaz, Iran

The antimicrobial activities of 6 common antimicrobial agents including carbapenems were tested against 100 clinical Pseudomonas aeruginosa isolates using a disk diffusion method. All imipenem (IPM)-resistant isolates were screened for metallo-beta-lactamase (MBL) production by Etest assay and were subsequently subjected to polymerase chain reaction (PCR) analysis with the bla(IMP) and bla(VIM) genes. Of 41 IPM-nonsusceptible isolates detected, 8 (19.51%) appeared to produce MBL, as determined by Etest. Using PCR assay, these isolates were positive for bla(VIM) genes, whereas none were positive for bla(IMP) genes.

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.

Metallo-beta-lactamases as emerging resistance determinants in Gram-negative pathogens: open issues

The rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of particular concern worldwide and primarily in Europe, one of first continents where the emergence of acquired MBLs has been reported and possibly the geographical area where the increasing diversity of these enzymes and the number of bacterial species affected are most impressive. This spread has not been paralleled by accuracy/standardisation of detection methods, completeness of epidemiological knowledge or a clear understanding of what MBL production entails in terms of clinical impact, hospital infection control and antimicrobial chemotherapy. A number of European experts in the field met to review the current knowledge on this phenomenon, to point out open issues and to reinforce and relate to one another the existing activities set forth by research institutes, scientific societies and European Union-driven networks.