Detection of Pseudomonas aeruginosa isolates of the international clonal complex 11 carrying the blaPER-1 extended-spectrum β-lactamase gene in Greece

Distribution of blaOXA-10, blaPER-1, and blaSHV genes in ESBL-producing Pseudomonas aeruginosa strains isolated from burn patients

Pseudomonas aeruginosa is resistant to a wide range of extended spectrum-lactamases (ESBLs) antibiotics because it produces several kinds of ESBLs. The goal of the current investigation was to identify the bacteria that produce extended spectrum -lactamases and the genes that encode three different ESBLs, such as blaOXA-10, blaPER-1 and blaSHV genes in Pseudomonas aeruginosa isolated from burn patients. In this investigation, 71 Pseudomonas aeruginosa isolates were isolated from burn wounds in Burn and Plastic Surgery Hospital, Duhok City between July 2021 to June 2022. For the purpose of finding the blaOXA-10, blaPER-1, and blaSHV ESBL expressing genes, Polymerase Chain Reaction (PCR) was used. Among 71 Pseudomonas aeruginosa isolates, 26.36% (29/71) were isolated from males and 38.18% (42/71) from females, and 76.06% (54/71) of the isolates were multidrug resistant. They exhibited higher resistance against Piperacillin with resistance rates of 98.59%. Among the ESBL-producing isolates tested, blaOXA-10 was found in 59.26% (32), blaPER-1 was found in 44.44% (24), and blaSHV was found in 11.11% (6). All isolates must undergo antimicrobial susceptibility testing because only a few numbers of the available antibiotics are effective for the treatment of this bacterium. This will prevent the development of resistance in burn units and aids in the management of the treatment plan.

Abundant diversity of accessory genetic elements and associated antimicrobial resistance genes in pseudomonas aeruginosa isolates from a single Chinese hospital

OBJECTIVES

Pseudomonas aeruginosa has intrinsic antibiotic resistance and the strong ability to acquire additional resistance genes. However, a limited number of investigations provide detailed modular structure dissection and evolutionary analysis of accessory genetic elements (AGEs) and associated resistance genes (ARGs) in P. aeruginosa isolates. The objective of this study is to reveal the prevalence and transmission characteristics of ARGs by epidemiological investigation and bioinformatics analysis of AGEs of P. aeruginosa isolates taken from a Chinese hospital.

METHODS

Draft-genome sequencing was conducted for P. aeruginosa clinical isolates (n = 48) collected from a single Chinese hospital between 2019 and 2021. The clones of P. aeruginosa isolates, type 3 secretion system (T3SS)-related virulotypes, and the resistance spectrum were identified using multilocus sequence typing (MLST), polymerase chain reaction (PCR), and antimicrobial susceptibility tests. In addition, 17 of the 48 isolates were fully sequenced. An extensive modular structure dissection and genetic comparison was applied to AGEs of the 17 sequenced P. aeruginosa isolates.

RESULTS

From the draft-genome sequencing, 13 STs were identified, showing high genetic diversity. BLAST search and PCR detection of T3SS genes (exoT, exoY, exoS, and exoU) revealed that the exoS+/exoU- virulotype dominated. At least 69 kinds of acquired ARGs, involved in resistance to 10 different categories of antimicrobials, were identified in the 48 P. aeruginosa isolates. Detailed genetic dissection and sequence comparisons were applied to 25 AGEs from the 17 isolates, together with five additional prototype AGEs from GenBank. These 30 AGEs were classified into five groups -- integrative and conjugative elements (ICEs), unit transposons, Inc_pPBL16 plasmids, Inc_p60512-IMP plasmids, and Inc_pPA7790 plasmids.

CONCLUSION

This study provides a broad-scale and deeper genomics understanding of P. aeruginosa isolates taken from a single Chinese hospital. The isolates collected are characterized by high genetic diversity, high virulence, and multiple drug resistance. The AGEs in P. aeruginosa chromosomes and plasmids, as important genetic platforms for the spread of ARGs, contribute to enhancing the adaptability of P. aeruginosa in hospital settings.

High prevalence of blaVEB , blaGES and blaPER genes in beta-lactam resistant clinical isolates of Pseudomonas aeruginosa

The increased prevalence of β-lactamase is one of the main factors in resistance to β-lactams in Pseudomonas aeruginosa. This study aimed to investigate the prevalence of blaVEB , blaPER , and blaGES genes in β-lactam-resistant P. aeruginosa. We collected 100 non-duplicated clinical isolates of P. aeruginosa and identified them by standard tests. Using disk agar diffusion test, we detected the β-lactam-resistant isolates and extracted the DNAs of the isolates by alkaline lysis method. Then, the prevalence of blaVEB , blaPER and blaGES genes were detected by PCR method. The results were assessed by SPSS 21 software and Chi-square test. Out of 100 isolates, 43% were detected as resistant against at least one of the beta-lactams tested. Piperacillin-tazobactam was the most effective antibiotic, while 39% and 37% of the isolates were resistant to aztreonam and meropenem, respectively. A significant relationship was observed between the resistance to tested antibiotics and the presence of blaVEB , blaGES , and blaPER genes. Among 43 isolates that were resistant to at least one of the tested β-lactams, 93.02%, 83.72%, and 81.39% of them carried blaVEB , blaGES , and blaPER genes, respectively. According to this study and due to high prevalence of β-lactam resistance genes, it is better to check the level of antibiotic resistance and resistance genes for better management of patients with infection caused by this bacterium. Also, high prevalence of class A β-lactamases indicates the significant role of these enzymes in emerging resistance to beta-lactams.

Extended-spectrum β-lactamases: an update on their characteristics, epidemiology and detection

Extended-spectrum β-lactamase (ESBL)-producing Gram-negative pathogens are a major cause of resistance to expanded-spectrum β-lactam antibiotics. Since their discovery in the early 1980s, they have spread worldwide and an are now endemic in Enterobacterales isolated from both hospital-associated and community-acquired infections. As a result, they are a global public health concern. In the past, TEM- and SHV-type ESBLs were the predominant families of ESBLs. Today CTX-M-type enzymes are the most commonly found ESBL type with the CTX-M-15 variant dominating worldwide, followed in prevalence by CTX-M-14, and CTX-M-27 is emerging in certain parts of the world. The genes encoding ESBLs are often found on plasmids and harboured within transposons or insertion sequences, which has enabled their spread. In addition, the population of ESBL-producing Escherichia coli is dominated globally by a highly virulent and successful clone belonging to ST131. Today, there are many diagnostic tools available to the clinical microbiology laboratory and include both phenotypic and genotypic tests to detect β-lactamases. Unfortunately, when ESBLs are not identified in a timely manner, appropriate antimicrobial therapy is frequently delayed, resulting in poor clinical outcomes. Several analyses of clinical trials have shown mixed results with regards to whether a carbapenem must be used to treat serious infections caused by ESBLs or whether some of the older β-lactam-β-lactamase combinations such as piperacillin/tazobactam are appropriate. Some of the newer combinations such as ceftazidime/avibactam have demonstrated efficacy in patients. ESBL-producing Gram-negative pathogens will continue to be major contributor to antimicrobial resistance worldwide. It is essential that we remain vigilant about identifying them both in patient isolates and through surveillance studies.

Characterization of antibiotic resistance profiles in Pseudomonas aeruginosa isolates from burn patients

OBJECTIVE

To investigate the prevalence of multidrug-resistant (MDR) Pseudomonas aeruginosa (PA) producing extended-spectrum beta-lactamases (ESBLs) and metallo-beta-lactamases (MBLs) in burn patients in Algeria.

METHODS

Between April 2016 and October 2019, 47 non-redundant isolates of PA were collected from 47 burn patients admitted to the Department of Burns at the Military Hospital of Algiers in Algeria. Antibiotic susceptibility testing was performed by agar diffusion and the Phoenix automated method. Resistance genes were identified by PCR, and molecular typing of isolates was carried out by enterobacterial repetitive intergenic consensus (ERIC) sequences-polymerase chain reaction (PCR).

RESULTS

Among the 47 non-redundant MDR PA strains isolated, 59.57% were phenotypically ESBLs-positive, and 100% were phenotypically MBL-positive. The ESBL-positive isolates were subsequently screened for six groups of bla genes encoding ESBL-type enzymes, namely blaCTX-M2, blaPER, blaTEM, blaSHV, blaVEB, and blaGES. Out of the 28 ESBL-producing strains, 23 (82.14%) were blaCTX-M2 positive; 18 (38.29%) were blaPER positive, and 16 (34.04%) were blaTEM positive, while 5 (17.9%) were co-harboring blaCTX-M2, blaTEM, and blaPER genes. The blaSHV, blaVEB, and blaGES genes were not detected in any of the ESBL positive isolates. Since all isolates were MBL-positive, all 47 strains were screened for the blaNDM-1, blaIMP, blaVIM genes that produce MBLs; however, none of these genes were detected. Additional screening for the oprD gene demonstrated that 45 (95.74%) of the isolates were positive for this gene. Finally, ERIC PCR revealed 11 distinct PA clones among the blaCTX-M2 positive strains.

CONCLUSION

This is the first study to report the presence of CTX-M2-producing PA in the North Africa region and the first to detect blaCTX-M2-positive and blaPER-positive PA clinical isolates in Algeria, therefore demonstrating the spread of such MDR strains to this part of the world. Identification of bacterial genotypic alterations that confer antibiotic resistance is critical in determining the most effective antimicrobial strategies to be employed. Therefore, our findings could potentially facilitate clinical decision making regarding the antibiotics of choice for the treatment of burn patients that suffer from PA infections in Algeria.

Phenotypic and Genotypic Characterization of Acinetobacter spp. Panel Strains: A Cornerstone to Facilitate Antimicrobial Development

Acinetobacter spp. have emerged as significant pathogens causing nosocomial infections. Treatment of these pathogens has become a major challenge to clinicians worldwide, due to their increasing tendency to antibiotic resistance. To address this, much revenue and technology are currently being dedicated toward developing novel drugs and antibiotic combinations to combat antimicrobial resistance. To address this issue, we have constructed a panel of Acinetobacter spp. strains expressing different antimicrobial resistance determinants such as narrow spectrum β-lactamases, extended-spectrum β-lactamases, OXA-type-carbapenemase, metallo-beta-lactamase, and over-expressed AmpC β-lactamase. Bacterial strains exhibiting different resistance phenotypes were collected between 2008 and 2013 from Severance Hospital, Seoul. Antimicrobial susceptibility was determined according to the CLSI guidelines using agar dilution method. Selected strains were sequenced using Ion Torrent PGM system, annotated using RAST server and analyzed using Geneious pro 8.0. Genotypic determinants, such as acquired resistance genes, changes in the expression of efflux pumps, mutations, and porin alternations, contributing to the relevant expressed phenotype were characterized. Isolates expressing ESBL phenotype consisted of bla _PER-1 gene, the overproduction of intrinsic AmpC beta-lactamase associated with ISAba1 insertion, and carbapenem resistance associated with production of carbapenem-hydrolyzing Ambler class D β-lactamases, such as OXA-23, OXA-66, OXA-120, OXA-500, and metallo-β-lactamase, SIM-1. We have analyzed the relative expression of Ade efflux systems, and determined the sequences of their regulators to correlate with phenotypic resistance. Quinolone resistance-determining regions were analyzed to understand fluoroquinolone-resistance. Virulence factors responsible for pathogenesis were also identified. Due to several mutations, acquisition of multiple resistance genes and transposon insertion, phenotypic resistance decision scheme for for evaluating the resistance proved inaccurate, which highlights the urgent need for modification to this scheme. This complete illustration of mechanism contributing to specific resistance phenotypes can be used as a target for novel drug development. It can also be used as a reference strain in the clinical laboratory and for the evaluation of antibiotic efficacy for specific resistance mechanisms.

Cluster-distinguishing genotypic and phenotypic diversity of carbapenem-resistant Gram-negative bacteria in solid-organ transplantation patients: a comparative study

Purpose. Solid-organ transplant recipients may display high rates of colonization and/or infection by multidrug-resistant bacteria. We analysed and compared the phenotypic and genotypic diversity of carbapenem-resistant (CR) strains of Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter baumannii isolated from patients in the Solid Organ Transplantation department of our hospital.Methodology. Between March 2012 and August 2013, 56 CR strains from various biological fluids underwent antimicrobial susceptibility testing with VITEK 2, molecular analysis by PCR amplification and genotypic analysis with pulsed-field gel electrophoresis (PFGE). They were clustered according to antimicrobial drug susceptibility and genotypic profiles. Diversity analyses were performed by calculating Simpson's diversity index and applying computed rarefaction curves.Results/Key findings. Among K. pneumoniae, KP-producers predominated (57.1 %). VIM and OXA-23 carbapenemases prevailed among P. aeruginosa and A. baumannii (89.4 and 88.9 %, respectively). KPC-producing K. pneumoniae and OXA-23 A. baumannii were assigned in single PFGE pulsotypes. VIM-producing P. aeruginosa generated multiple pulsotypes. CR K. pneumoniae strains displayed phenotypic diversity in tigecycline, colistin (CS), amikacin (AMK), gentamicin (GEN) and co-trimoxazole (SXT) (16 clusters); P. aeruginosa displayed phenotypic diversity in cefepime (FEP), ceftazidime, aztreonam, piperacillin, piperacillin-tazobactam, AMK, GEN and CS (9 clusters); and A. baumannii displayed phenotypic diversity in AMK, GEN, SXT, FEP, tobramycin and rifampicin (8 clusters). The Simpson diversity indices for the interpretative phenotype and PFGE analysis were 0.89 and 0.6, respectively, for K. pneumoniae strains (P<0.001); 0.77 and 0.6 for P. aeruginosa (P=0.22); and 0.86 and 0.19 for A. baumannii (P=0.004).Conclusion. The presence of different antimicrobial susceptibility profiles does not preclude the possibility that two CR K. pneumoniae or A. baumannii isolates are clonally related.

Molecular Characterization and Phylogenetic Analysis of Pseudomonas aeruginosa Isolates Recovered from Greek Aquatic Habitats Implementing the Double-Locus Sequence Typing Scheme

The recently described double-locus sequence typing (DLST) scheme implemented to deeply characterize the genetic profiles of 52 resistant environmental Pseudomonas aeruginosa isolates deriving from aquatic habitats of Greece. DLST scheme was able not only to assign an already known allelic profile to the majority of the isolates but also to recognize two new ones (ms217-190, ms217-191) with high discriminatory power. A third locus (oprD) was also used for the molecular typing, which has been found to be fundamental for the phylogenetic analysis of environmental isolates given the resulted increased discrimination between the isolates. Additionally, the circulation of acquired resistant mechanisms in the aquatic habitats according to their genetic profiles was proved to be more extent. Hereby, we suggest that the combination of the DLST to oprD typing can discriminate phenotypically and genetically related environmental P. aeruginosa isolates providing reliable phylogenetic analysis at a local level.

Detection of ISAba1 in association with a novel allelic variant of the β-lactamase ADC-82 and class D β-lactamase genes mediating carbapenem resistance among the clinical isolates of MDR A. baumannii

PURPOSE

The objective of the present study is to investigate the diverse resistance determinants, their association with insertion sequence mobile elements and predilection of a particular clone for such associations in Acinetobacter baumannii.

METHODOLOGY

Fifty-four consecutive isolates collected during 2011-2012 from a tertiary care hospital were subjected to susceptibility testing followed by PCR screening of commonly reported β-lactamases and 16S rRNA methyltransferase encoding genes. The integrity of resistance-nodulation-cell division efflux pump-related genes in their respective operons was also investigated.

RESULTS

β-Lactamase genes such as blaADC (100 %), blaOXA-23 (81 %), blaPER-1 (81 %), blaIMP-1 (31 %) and blaNDM-1 (15 %) were found to be present more frequently while blaVIM-2 and blaOXA-24 were not observed in our study population. ISAba1 was associated only with blaOXA-51-like like (30 %), blaOXA-23-like (55 %) and blaADC-like (33 %). armA was found in 87 % of isolates and ISAba1 linked with one novel variant of ADC, namely blaADC-82, which was identified to have 15 nucleotide differences with blaADC-79, and this finding is of much significance. In many isolates, efflux pump genes were not intact, resulting in severely altered effluxing functions. For the first time, we have identified ISAba1-mediated disruption of adeN among the isolates of ST 195B, which would have led to overexpression of AdeIJK efflux pump causing elevated resistance. Multilocus sequence typing revealed the predominance of CC 92B (IC-IIB) and CC 447B clonal complexes.

CONCLUSION

High incidence of IC-II clones, novel resistance determinants (ADC-82) and elevated resistance mediated by ISAba1 reported here will be of enormous importance while assessing the emergence of extremely resistant A. baumannii in India.

Genomic islands 1 and 2 play key roles in the evolution of extensively drug-resistant ST235 isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa are noscomially acquired, opportunistic pathogens that pose a major threat to the health of burns patients and the immunocompromised. We sequenced the genomes of P. aeruginosa isolates RNS_PA1, RNS_PA46 and RNS_PAE05, which displayed resistance to almost all frontline antibiotics, including gentamicin, piperacillin, timentin, meropenem, ceftazidime and colistin. We provide evidence that the isolates are representatives of P. aeruginosa sequence type (ST) 235 and carry Tn6162 and Tn6163 in genomic islands 1 (GI1) and 2 (GI2), respectively. GI1 disrupts the endA gene at precisely the same chromosomal location as in P. aeruginosa strain VR-143/97, of unknown ST, creating an identical CA direct repeat. The class 1 integron associated with Tn6163 in GI2 carries a bla_GES-5–aacA4–gcuE15–aphA15 cassette array conferring resistance to carbapenems and aminoglycosides. GI2 is flanked by a 12 nt direct repeat motif, abuts a tRNA-gly gene, and encodes proteins with putative roles in integration, conjugative transfer as well as integrative conjugative element-specific proteins. This suggests that GI2 may have evolved from a novel integrative conjugative element. Our data provide further support to the hypothesis that genomic islands play an important role in de novo evolution of multiple antibiotic resistance phenotypes in P. aeruginosa.

Molecular Epidemiology and Genetic Characteristics of Various blaPER Genes in Shanghai, China

We describe the genetic characteristics and possible transmission mechanism of blaPER in 25 clinical Gram-negative bacilli in Shanghai. blaPER, including blaPER-1, blaPER-3, and blaPER-4, was located chromosomally or in different plasmids. Tn1213 harboring blaPER-1 was first identified in two Proteus mirabilis isolates in China. The other blaPER variants were preceded by an ISCR1 element inside the complex class 1 integron associated with IS26, Tn21, Tn1696, and a miniature inverted-repeat transposable element.

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.

Emergence of integron borne PER-1 mediated extended spectrum cephalosporin resistance among nosocomial isolates of Gram-negative bacilli

Background & objectives:

Pseudomonas extended resistant (PER) enzymes are rare type of extended-spectrum beta lactamases (ESBLs) that confer third generation cephalosporin resistance. These are often integron borne and laterally transmitted. The aim of the present study was to investigate the emergence of integron borne cephalosporin resistant PER-1 gene in diverse incompatibility (Inc) group plasmids among Gram-negative bacteria.

Methods:

A total of 613 consecutive, non-duplicate, Gram-negative bacteria of Enterobacteriaceae family and non-fermenting Gram-negative bacteria were isolated from different clinical specimens during a period of 18 months. For amplification and detection of bla_PER, multiplex PCR was done. For understanding the genetic environment of bla_PER-1, integrase gene PCR and cassette PCR (59 be) was performed. Gene transferability experiment was carried out and PCR based replicon typing was performed for incompatibility group typing of plasmids using 18 pairs of primers. An inhibitor based method was used for phenotypic detection of intrinsic resistance.

Results:

Multiplex PCR and sequencing confirmed that 45 isolates were harbouring bla_PER-1. Both class 1 and class 2 integrons were observed among them. Integrase and cassette PCR (59 be) PCR results confirmed that the resistant determinant was located within class 1 integron. Transformation and conjugation experiments revealed that PER-1 was laterally transferable and disseminated through diverse Inc plasmid type. Efflux pump mediated carbapenem resistance was observed in all isolates. All isolates belonged to heterogenous groups.

Interpretation & conclusions:

This study demonstrates the dissemination of cephalosporins resistant, integron borne bla_PER-1 in hospital setting in this part of the country and emphasizes on the rational use of third generation cephalosporins to slow down the expansion of this rare type of ESBL gene.

Antibiotic resistance profiles of Pseudomonas aeruginosa isolated from various Greek aquatic environments

A large number of antibiotic-resistant P. aeruginosa isolates are continuously discharged into natural water basins mainly through sewage. However, the environmental reservoirs of antibiotic resistance factors are poorly understood. In this study, the antibiotic resistance patterns of 245 isolates from various aquatic sites in Greece were analysed. Twenty-three isolates with resistance patterns cefotaxime-aztreonam-ceftazidime, cefotaxime-aztreonam-meropenem, cefotaxime-ceftazidime-meropenem, cefotaxime-ceftazidime-aztreonam-meropenem and cefotaxime-ceftazidime-cefepime-aztreonam-meropenem were screened phenotypically for the presence of extended spectrum β-lactamases (ESBLs), while 77 isolates with various resistant phenotypes were screened for the presence of class 1 and class 2 integrase genes. The aztreonam-resistant isolates and ESBL producers were the main resistant phenotypes in all habitats tested. In 13/77 isolates class 1 integron was detected, while all tested isolates were negative for the presence of the class 2 integrase gene. CTX-M group 9 β-lactamase was present in a small number of isolates (three isolates) highlighting the emergence of ESBL genes in aquatic environments. As a conclusion, it seems that Greek water bodies could serve as a potential reservoir of resistant P. aeruginosa isolates posing threats to human and animal health.

The increasing threat of Pseudomonas aeruginosa high-risk clones

The increasing prevalence of chronic and hospital-acquired infections produced by multidrug-resistant (MDR) or extensively drug-resistant (XDR) Pseudomonas aeruginosa strains is associated with significant morbidity and mortality. This growing threat results from the extraordinary capacity of this pathogen for developing resistance through chromosomal mutations and from the increasing prevalence of transferable resistance determinants, particularly those encoding carbapenemases or extended-spectrum β-lactamases (ESBLs). P. aeruginosa has a nonclonal epidemic population structure, composed of a limited number of widespread clones which are selected from a background of a large quantity of rare and unrelated genotypes that are recombining at high frequency. Indeed, recent concerning reports have provided evidence of the existence of MDR/XDR global clones, denominated high-risk clones, disseminated in hospitals worldwide; ST235, ST111, and ST175 are likely those more widespread. Noteworthy, the vast majority of infections by MDR, and specially XDR, strains are produced by these and few other clones worldwide. Moreover, the association of high-risk clones, particularly ST235, with transferable resistance is overwhelming; nearly 100 different horizontally-acquired resistance elements and up to 39 different acquired β-lactamases have been reported so far among ST235 isolates. Likewise, MDR internationally-disseminated epidemic strains, such as the Liverpool Epidemic Strain (LES, ST146), have been noted as well among cystic fibrosis patients. Here we review the population structure, epidemiology, antimicrobial resistance mechanisms and virulence of the P. aeruginosa high-risk clones. The phenotypic and genetic factors potentially driving the success of high-risk clones, the aspects related to their detection in the clinical microbiology laboratory and the implications for infection control and public health are also discussed.

Emerging broad-spectrum resistance in Pseudomonas aeruginosa and Acinetobacter baumannii: Mechanisms and epidemiology

Multidrug resistance is quite common among non-fermenting Gram-negative rods, in particular among clinically relevant species including Pseudomonas aeruginosa and Acinetobacter baumannii. These bacterial species, which are mainly nosocomial pathogens, possess a diversity of resistance mechanisms that may lead to multidrug or even pandrug resistance. Extended-spectrum β-lactamases (ESBLs) conferring resistance to broad-spectrum cephalosporins, carbapenemases conferring resistance to carbapenems, and 16S rRNA methylases conferring resistance to all clinically relevant aminoglycosides are the most important causes of concern. Concomitant resistance to fluoroquinolones, polymyxins (colistin) and tigecycline may lead to pandrug resistance. The most important mechanisms of resistance in P. aeruginosa and A. baumannii and their most recent dissemination worldwide are detailed here.

Detection of Pseudomonas aeruginosa isolates carrying the blaOXA-142 extended-spectrum β-lactamase gene in Taiwan

BACKGROUND/PURPOSE

The emergence of extended-spectrum β-lactamase (ESBL) OXA-142 gene (bla_OXA-142) in Pseudomonas aeruginosa has been reported in Bulgaria and other European countries, but rarely in Asia.

METHODS

From January 2009 to December 2012, 90 P. aeruginosa isolates with reduced susceptibility or resistance to ceftazidime (minimum inhibitory concentration ≥ 8 mg/L) were screened for ESBL and other broad-spectrum β-lactamase genes by polymerase chain reaction and sequencing. Clonal relationship of the isolates was determined by pulsed-field gel electrophoresis.

RESULTS

Three isolates were positive for ESBL production, exhibited resistance to ceftazidime, and carried the bla_OXA-142 gene. The bla_OXA-142 gene was integrated into class 1 integron. Using Southern blot analysis, bla_OXA-142-containing integron was found to be located on a plasmid in all three isolates. Eleven strains of P. aeruginosa carrying bla_OXA-17 gene were found. The oprD mutation was found in all the 21 ESBL strains of P. aeruginosa.

CONCLUSIONS

This study confirmed the presence of bla_OXA-142-positive P. aeruginosa isolates in Taiwan.

Spread of extended-spectrum β-lactamase genes of blaOXA-10, blaPER-1 and blaCTX-M in Pseudomonas aeruginosa strains isolated from burn patients

BACKGROUND

Pseudomonas aeruginosa is resistant to many antibiotics due to production of different classes of extended spectrum β-lactamases (ESBLs). Prevalence of ESBLs among P. aeruginosa has been increased in recent years, demonstrate a serious health problem especially in burn units worldwide.

OBJECTIVE

Present study was designed to determine the ESBL producing strains and identify the genes encoding three different ESBLs of bla PER-1, bla OXA-10 and bla CTX-M genes in P. aeruginosa isolates from burn patients.

METHODS

In total 185 clinical isolates of P. aeruginosa were collected from infectious wounds of hospitalized burn patients. Antimicrobial susceptibility testing and phenotypic detection of ESBL were performed by disk diffusion method and Double disk Synergy Test (DDST). Polymerase Chain Reaction (PCR) was done for detection of bla OXA-10, bla PER-1 and bla CTX-M ESBL encoding genes.

RESULTS

In total, 176 (95.13%) isolates were multidrug resistant. The DDST demonstrated 96 (51.9%) isolates as putative ESBL producers with 100% or highly resistance to ofloxacin, cephalexin, aztreonam (97.57%) and ceftriaxone (91.6%). By PCR amplification, bla PER-1, bla OXA-10 and bla CTX-M genes were detected in 52 (54.16%), 66 (68.75%) and 1 (1.04%) isolates of ESBL producers respectively. Forty-three isolates (44.79%) were simultaneously positive for both bla OXA-10 and bla PER-1 related genes.

CONCLUSION

The rate of ESBL producing P. aeruginosa was notable in present study. Since there are only limited effective antibiotics against the bacterium, therefore all isolates must be investigated by antimicrobial susceptibility testing, which limits resistance development in burn units and helps the management of treatment strategy.

The complex genetic context of blaPER-1 flanked by miniature inverted-repeat transposable elements in Acinetobacter johnsonii

On a large plasmid of Acinetobacter johnsonii strain XBB1 from hospital sewage, bla_PER-1 and ISCR1 were found in a complex Tn402-like integron carrying an arr3-aacA4 cassette array. The integron was truncated by the same 439-bp miniature inverted-repeat transposable element (MITE) at both ends. bla_PER-1 and its complex surroundings might have been mobilized by the MITEst into an orf of unknown function, evidenced by the presence of the characteristic 5-bp direct target repeats. The same 439-bp MITEs have also been found flanking class 1 integrons carrying metallo-β-lactamases genes bla_IMP-1, bla_IMP-5 and bla_VIM-2 before but without ISCR1. Although the cassette arrays are different, integrons have always been truncated by the 439-bp MITEs at the exact same locations. The results suggested that MITEs might be able to mobilize class 1 integrons via transposition or homologous recombination and therefore represent a possible common mechanism for mobilizing antimicrobial resistance determinants.

FIM-1, a new acquired metallo-β-lactamase from a Pseudomonas aeruginosa clinical isolate from Italy

Acquired metallo-β-lactamases (MBLs) are resistance determinants of increasing clinical importance in Gram-negative bacterial pathogens, which confer a broad-spectrum β-lactam resistance, including carbapenems. Several such enzymes have been described since the 1990s. In the present study, a novel acquired MBL, named FIM-1, was identified and characterized. The bla(FIM-1) gene was cloned from a multidrug-resistant Pseudomonas aeruginosa clinical isolate (FI-14/157) cultured from a patient with a vascular graft infection in Florence, Italy. The isolate belonged in the sequence type 235 epidemic clonal lineage. The FIM-1 enzyme is a member of subclass B1 and, among acquired MBLs, exhibited the highest similarity (ca. 40% amino acid identity) with NDM-type enzymes. In P. aeruginosa FI-14/157, the bla(FIM-1) gene was apparently inserted into the chromosome and associated with ISCR19-like elements that were likely involved in the capture and mobilization of this MBL gene. Transfer experiments of the bla(FIM-1) gene to an Escherichia coli strain or another P. aeruginosa strain by conjugation or electrotransformation were not successful. The FIM-1 protein was produced in E. coli and purified by two chromatography steps. Analysis of the kinetic parameters, carried out with the purified enzyme, revealed that FIM-1 has a broad substrate specificity, with a preference for penicillins (except the 6α-methoxy derivative temocillin) and carbapenems. Aztreonam was not hydrolyzed. Detection of this novel type of acquired MBL in a P. aeruginosa clinical isolate underscores the increasing diversity of such enzymes that can be encountered in the clinical setting.