Tn5393d, a complex Tn5393 derivative carrying the PER-1 extended-spectrum beta-lactamase gene and other resistance determinants

On the use of antibiotics to control plant pathogenic bacteria: a genetic and genomic perspective

Despite growing attention, antibiotics (such as streptomycin, oxytetracycline or kasugamycin) are still used worldwide for the control of major bacterial plant diseases. This raises concerns on their potential, yet unknown impact on antibiotic and multidrug resistances and the spread of their genetic determinants among bacterial pathogens. Antibiotic resistance genes (ARGs) have been identified in plant pathogenic bacteria (PPB), with streptomycin resistance genes being the most commonly reported. Therefore, the contribution of mobile genetic elements (MGEs) to their spread among PPB, as well as their ability to transfer to other bacteria, need to be further explored. The only well-documented example of ARGs vector in PPB, Tn5393 and its highly similar variants (carrying streptomycin resistance genes), is concerning because of its presence outside PPB, in Salmonella enterica and Klebsiella pneumoniae, two major human pathogens. Although its structure among PPB is still relatively simple, in human- and animal-associated bacteria, Tn5393 has evolved into complex associations with other MGEs and ARGs. This review sheds light on ARGs and MGEs associated with PPB, but also investigates the potential role of antibiotic use in resistance selection in plant-associated bacteria.

Class 1 In-Tn5393c array contributed to antibiotic resistance of non-pathogenic Pseudoxanthomonas mexicana isolated from a wastewater bioreactor treating streptomycin

The emergence of antibiotic resistance in retort to environmental pollutants during wastewater treatment still remains elusive. Here, we first to investigate the emergence of antibiotic resistance in an environmental non-pathogenic bacterium, Pseudoxanthomonas mexicana isolated from a lab-scale bioreactor treating wastewater containing streptomycin. The molecular mechanism of antibiotic resistance development was evaluated in its genomic, transcriptional, and proteomic levels. The streptomycin resistant (SR) strain showed strong resistance to streptomycin (MIC > 600 μg/mL) as well to sulfamethoxazole, ampicillin, and kanamycin (≥250 μg/mL). A 13.4 kb class-1-integron array consisting of a new arrangement of gene cassette (IS6100-sul1-aadA2-catB3-aacA1-2-aadB-int1-IS256-int) linked with Tn5393c transposon was identified in the SR strain, which has only been reported in clinical pathogens so far. iTRAQ-LC-MS/MS proteomics revealed 22 up-regulated proteins in the SR strain growing under 100 mg L^-1 streptomycin, involving antibiotic resistance, toxin production, stress response, and ribosomal protein synthesis. At the mRNA level, elevated expressions of ARGs (strA, strB, and aadB) and 30S-ribosomal protein genes (rpsA and rpsU) were observed in the SR strain. The results highlighted the genomic plasticity and multifaceted regulatory mechanism employed by P. mexicana in adaptation to high-level streptomycin during biological wastewater treatment.

Complete genome analysis of the novel Alcaligenes faecalis phage vB_AfaP_QDWS595

A novel lytic phage named vB_AfaP_QDWS595 infecting Alcaligenes faecalis was isolated and characterized in this study. The genome of phage vB_AfaP_QDWS595 was sequenced and analyzed, and the result revealed that the phage contained 70,466 bp of double-stranded DNA with 41.12% GC content. There were 74 putative genes encoding proteins as well as 11 tRNAs predicted in the phage genome. Phenotype and phylogeny analysis indicated that this phage might be a new member of the family Schitoviridae.

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 a novel class 1 integron InSW39 and a novel transposon Tn5393k identified in an imipenem-nonsusceptible Salmonella Typhimurium strain in Sichuan, China

This study aimed to characterize molecular mechanism of 3 Salmonella enterica strains and novel mobile genetic elements identified in them. The strains, designated SW1, SW39, and SW109084, were obtained from diarrhea patients. The results of susceptibility testing showed SW39 was nonsusceptible to imipenem and cefotaxime. Whole genome sequencing was performed on Illumina HiSeq platform. Multilocus-sequence typing revealed SW1 belonged to ST2529 which was first confirmed in S. enterica, SW109084 was ST34 which was first reported in Enteritidis and SW39 was ST19. Resistome analysis showed SW1, SW109084, and SW39 carried 14, 19, and 17 antibiotic resistance genes. Seven transposons and 4 integrons were confirmed in these strains. Notably, a novel In6- and In7-like class 1 integron designated InSW39 and a novel transposon Tn5393k were identified in plasmid pSW39. The study of genomics and resistance in S. enterica plays a significant role in prevention and treatment of Salmonella infections.

Antibiotic Resistance Pattern and Frequency of PER-1, SHV-1 and AMPC Type B-Lactamase Genes in Pseudomonas aeruginosa Isolated from Clinical Samples

Background:

The existence of Extended Spectrum B-lactamase (ESBL) genes plays an important role in spreading B-lactam antibiotic resistance in the producing strains of these enzymes. The resistance of gram-negative bacteria, such as Pseudomonas aeruginosa, to different antimicrobial agents, especially B-lactams, has increasingly been reported.

Objective:

This study was conducted to determine the prevalence of TEM-1and VEB-1 beta-lactamases gene in P. aeruginosa isolates through Polymerase Chain Reaction (PCR) method.

Methods:

100 clinical isolates of P. aeruginosa were collected from different clinical samples. The antibiotic susceptibility was examined by the disc diffusion method. The presence of PER-1, SHV-1 and AMPC genes was detected by PCR method.

Results:

Out of the studied P. aeruginosa isolates, 7, 9 and 37 isolates were positive for PER-1, SHV-1 and AMPC B-lactamases resistance genes, respectively. Patients with urinary infection had the most resistant isolates. All isolates (100%) were sensitive to polymyxin B.

Conclusion:

Antibiotic resistance in isolates of Pseudomonas can be caused by B-lactamases resistance genes. Noticing the increasing rate of the ESBLs producing strains, using the appropriate treatment protocol based on the antibiogram pattern of the strains is highly recommended.

Aminoglycoside-modifying enzyme and 16S ribosomal RNA methyltransferase genes among a global collection of Gram-negative isolates

OBJECTIVES

The prevalence of genes encoding aminoglycoside-modifying enzymes (AMEs) and 16S rRNA methyltransferases among 200 Gram-negative clinical isolates resistant to different aminoglycosides and collected worldwide during 2013 was evaluated.

METHODS

Selected AMEs and 16S rRNA methyltransferase genes were screened by PCR/sequencing among 49 Acinetobacter spp., 52 Pseudomonas aeruginosa and 99 Enterobacterales.

RESULTS

In total 72 isolates carried aac(6')-lb variants (36.0% overall; 55.6% Enterobacterales): 30 aac(6')-Ib-cr, 21 aac(6')-Ib and 21 aac(6')-Ib-like displaying substitutions L119S (alone or in combination with V71A or R173K) or S100G. Ten aph(3')-VI variants were detected among 35 isolates (46.9% of Acinetobacter spp.). Nineteen isolates carried variants of aac(3)-I, with aac(3)-Ia (n=13, mostly Acinetobacter spp.) being the most prevalent. Other AME genes detected were ant(3″)-Ia (n=41), ant(2″)-Ia (n=24), aac(3)-IIe (n=23), aac(3)-IId (n=21), aac(6')-Im (n=13, mostly P. aeruginosa), aacA8 (n=3), aac(3)-IIf (n=1) and aac(3)-IVa (n=1). Among 42 isolates resistant to amikacin, gentamicin and tobramycin tested for 16S rRNA methyltransferase genes, 21 (50.0%) tested positive; armA was most common (n=14), but 4 isolates carried rmtB1, 2 rmtF1 and 1 new variant rmtB4. Over 60 gene combinations, consisting of one to four AMEs and 16S rRNA methyltransferases, were observed. Cloning genes not previously characterised revealed diverse aminoglycoside resistance patterns for some AMEs, but expected results for rmtB4.

CONCLUSIONS

Studies broadly evaluating these aminoglycoside resistance genes are needed. Using agents stable in the presence of these resistance genes might help overcome resistance.

Transposons: the agents of antibiotic resistance in bacteria

Transposons are a group of mobile genetic elements that are defined as a DNA sequence. Transposons can jump into different places of the genome; for this reason, they are called jumping genes. However, some transposons are always kept at the insertion site in the genome. Most transposons are inactivated and as a result, cannot move. Transposons are divided into two main groups: retrotransposons (class І) and DNA transposons (class ІІ). Retrotransposons are often found in eukaryotes. DNA transposons can be found in both eukaryotes and prokaryotes. The bacterial transposons belong to the DNA transposons and the Tn family, which are usually the carrier of additional genes for antibiotic resistance. Transposons can transfer from a plasmid to other plasmids or from a DNA chromosome to plasmid and vice versa that cause the transmission of antibiotic resistance genes in bacteria. The treatment of bacterial infectious diseases is difficult because of existing antibiotic resistance that part of this antibiotic resistance is caused by transposons. Bacterial infectious diseases are responsible for the increasing rise in world mortality rate. In this review, transposons and their roles have been studied in bacterial antibiotic resistance, in detail.

PER-8, a Novel Extended-Spectrum β-Lactamase PER Variant, from an Acinetobacter baumannii Clinical Isolate in Nepal

A novel PER-type extended-spectrum β-lactamase, PER-8, was identified in an Acinetobacter baumannii clinical isolate obtained in Nepal. The amino acid sequence of PER-8 has a substitution at position 39 (Gly to Glu) compared with that of PER-7. The k_cat/K_m ratio of PER-8 for aztreonam was lower than that of PER-7, while the k_cat/K_m ratio of PER-8 for imipenem was higher than that of PER-7. The genomic environment surrounding bla_PER-8 was intI1 bla_PSE-1qacEDI sulI ISCR1-bla_PER-8gts sulI orfX on a 100-kb plasmid.

Genome-based insights into the resistome and mobilome of multidrug-resistant Aeromonas sp. ARM81 isolated from wastewater

The draft genome of multidrug-resistant Aeromonas sp. ARM81 isolated from a wastewater treatment plant in Warsaw (Poland) was obtained. Sequence analysis revealed multiple genes conferring resistance to aminoglycosides, β-lactams or tetracycline. Three different β-lactamase genes were identified, including an extended-spectrum β-lactamase gene bla_PER-1. The antibiotic susceptibility was experimentally tested. Genome sequencing also allowed us to investigate the plasmidome and transposable mobilome of ARM81. Four plasmids, of which two carry phenotypic modules (i.e., genes encoding a zinc transporter ZitB and a putative glucosyltransferase), and 28 putative transposase genes were identified. The mobility of three insertion sequences (isoforms of previously identified elements ISAs12, ISKpn9 and ISAs26) was confirmed using trap plasmids.

Initial Assessment of the Molecular Epidemiology of blaNDM-1 in Colombia

We report complete genome sequences of four blaNDM-1-harboring Gram-negative multidrug-resistant (MDR) isolates from Colombia. The blaNDM-1 genes were located on 193-kb Inc FIA, 178-kb Inc A/C2, and 47-kb (unknown Inc type) plasmids. Multilocus sequence typing (MLST) revealed that these isolates belong to sequence type 10 (ST10) (Escherichia coli), ST392 (Klebsiella pneumoniae), and ST322 and ST464 (Acinetobacter baumannii and Acinetobacter nosocomialis, respectively). Our analysis identified that the Inc A/C2 plasmid in E. coli contained a novel complex transposon (Tn125 and Tn5393 with three copies of blaNDM-1) and a recombination "hot spot" for the acquisition of new resistance determinants.

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.

Marine sediment bacteria harbor antibiotic resistance genes highly similar to those found in human pathogens

The ocean is a natural habitat for antibiotic-producing bacteria, and marine aquaculture introduces antibiotics into the ocean to treat infections and improve aquaculture production. Studies have shown that the ocean is an important reservoir of antibiotic resistance genes. However, there is a lack of understanding and knowledge about the clinical importance of the ocean resistome. We investigated the relationship between the ocean bacterial resistome and pathogenic resistome. We applied high-throughput sequencing and metagenomic analyses to explore the resistance genes in bacterial plasmids from marine sediments. Numerous putative resistance determinants were detected among the resistance genes in the sediment bacteria. We also found that several contigs shared high identity with transposons or plasmids from human pathogens, indicating that the sediment bacteria recently contributed or acquired resistance genes from pathogens. Marine sediment bacteria could play an important role in the global exchange of antibiotic resistance.

Evolution of an incompatibility group IncA/C plasmid harboring blaCMY-16 and qnrA6 genes and its transfer through three clones of Providencia stuartii during a two-year outbreak in a Tunisian burn unit

During a 2-year period in 2005 and 2006, 64 multidrug-resistant Providencia stuartii isolates, including 58 strains from 58 patients and 6 strains obtained from the same tracheal aspirator, were collected in a burn unit of a Tunisian hospital. They divided into four antibiotypes (ATB1 to ATB4) and three SmaI pulsotypes (PsA to PsC), including 49 strains belonging to clone PsA (48 of ATB1 and 1 of ATB4), 11 strains to clone PsB (7 of ATB2 and 4 of ATB3), and 4 strains to clone PsC (ATB3). All strains, except for the PsA/ATB4 isolate, were highly resistant to broad-spectrum cephalosporins due to the production of the plasmid-mediated CMY-16 β-lactamase. In addition, the 15 strains of ATB2 and ATB3 exhibited decreased quinolone susceptibility associated with QnrA6. Most strains (ATB1 and ATB3) were gentamicin resistant, related to an AAC(6')-Ib' enzyme. All these genes were located on a conjugative plasmid belonging to the incompatibility group IncA/C(2) of 195, 175, or 100 kb. Despite differences in size and in number of resistance determinants, they derived from the same plasmid, as demonstrated by similar profiles in plasmid restriction analysis and strictly homologous sequences of repAIncA/C(2), unusual antibiotic resistance genes (e.g., aphA-6), and their genetic environments. Further investigation suggested that deletions, acquisition of the ISCR1 insertion sequence, and integron cassette mobility accounted for these variations. Thus, this outbreak was due to both the spread of three clonal strains and the dissemination of a single IncA/C(2) plasmid which underwent a remarkable evolution during the epidemic period.

Emergence of resistance to carbapenems in Acinetobacter baumannii in Europe: clinical impact and therapeutic options

Despite having a reputation of low virulence, Acinetobacter baumannii is an emerging multidrug-resistant (MDR) pathogen responsible for community- and hospital-acquired infections that are difficult to control and treat. Interest in this pathogen emerged about one decade ago because of its natural MDR phenotype, its capability of acquiring new mechanisms of resistance and the existence of nosocomial outbreaks. Recent advances in molecular biology, including full genome sequencing of several A. baumannii isolates, has led to the discovery of the extraordinary plasticity of their genomes, which is linked to their great propensity to adapt to any environment, including hospitals. In this context, as well as the increasing antimicrobial resistance amongst A. baumannii isolates to the last-line antibiotics carbapenems and colistin, therapeutic options are very limited or absent in some cases of infections with pandrug-resistant bacteria. However, a large proportion of patients may be colonised by such MDR bacteria without any sign of infection, leading to a recurrent question for clinicians as to whether antibiotic treatment should be given and will be effective in the presence of resistance mechanisms. The worldwide emergence of A. baumannii strains resistant to colistin is worrying and the increasing use of colistin to treat infections caused by MDR bacteria will inevitably increase the recovery rate of colistin-resistant isolates in the future. Current knowledge about A. baumannii, including biological and epidemiological aspects as well as resistance to antibiotics and antibiotic therapy, are reviewed in this article, in addition to therapeutic recommendations.

Impacts of anthropogenic activity on the ecology of class 1 integrons and integron-associated genes in the environment

The impact of human activity on the selection for antibiotic resistance in the environment is largely unknown, although considerable amounts of antibiotics are introduced through domestic wastewater and farm animal waste. Selection for resistance may occur by exposure to antibiotic residues or by co-selection for mobile genetic elements (MGEs) which carry genes of varying activity. Class 1 integrons are genetic elements that carry antibiotic and quaternary ammonium compound (QAC) resistance genes that confer resistance to detergents and biocides. This study aimed to investigate the prevalence and diversity of class 1 integron and integron-associated QAC resistance genes in bacteria associated with industrial waste, sewage sludge and pig slurry. We show that prevalence of class 1 integrons is higher in bacteria exposed to detergents and/or antibiotic residues, specifically in sewage sludge and pig slurry compared with agricultural soils to which these waste products are amended. We also show that QAC resistance genes are more prevalent in the presence of detergents. Studies of class 1 integron prevalence in sewage sludge amended soil showed measurable differences compared with controls. Insertion sequence elements were discovered in integrons from QAC contaminated sediment, acting as powerful promoters likely to upregulate cassette gene expression. On the basis of this data, >1 × 10(19) bacteria carrying class 1 integrons enter the United Kingdom environment by disposal of sewage sludge each year.

Embedded elements in the IncPβ plasmids R772 and R906 can be mobilized and can serve as a source of diverse and novel elements

IncP plasmids are important contributors to bacterial adaptation. Their phenotypic diversity is due largely to accessory regions located in one or two specific parts of the plasmid. The accessory regions are themselves diverse, as judged from sequenced plasmids mostly isolated from non-clinical sources. To further understand the diversity, evolutionary history and functional attributes of the accessory regions, we compared R906 and R772, focusing on the oriV–trfA accessory region. These IncPβ plasmids were from porcine and clinical sources, respectively. We found that the accessory regions formed potentially mobile elements, Tn510 (from R906) and Tn511 (from R772), that differed internally but had identical borders. Both elements appeared to have evolved from a TnAO22-like mer transposon that had inserted into an ancestral IncPβ plasmid and then accrued additional transposable elements and genes from various proteobacteria. Structural comparisons suggested that Tn510 (and a descendent in pB10), Tn511 and the mer element in pJP4 represent three lineages that evolved from the same widely dispersed IncPβ carrier. Functional studies on Tn511 revealed that its mer module is inactive due to a merT mutation, and that its aphAI region is prone to deletion. More significantly, we showed that by providing a suitable transposase gene in trans, the defective Tn510 and Tn511 could transpose intact or in part, and could also generate new elements (stable cointegrates and novel transposons). The ingredients for assisted transposition events similar to those observed here occur in natural microcosms, providing non-self-mobile elements with avenues for dispersal to new replicons and for structural diversification. This work provides an experimental demonstration of how the complex embedded elements uncovered in IncP plasmids and in other plasmid families may have been generated.

PER-7, an extended-spectrum beta-lactamase with increased activity toward broad-spectrum cephalosporins in Acinetobacter baumannii

Acinetobacter baumannii isolate AP2 was recovered from a bronchial lavage sample of a patient hospitalized in Paris, France. A. baumannii AP2 was resistant to all β-lactams, including carbapenems, and expressed the extended-spectrum β-lactamase (ESBL) PER-7, which differs from PER-1 by 4 amino acid substitutions. Compared to PER-1, PER-7 possessed higher-level hydrolytic activities against cephalosporins and aztreonam. The blaPER-7 gene was chromosomally located and associated with a mosaic class 1 integron structure. Additionally, isolate AP2 expressed the carbapenem-hydrolyzing oxacillinase OXA-23 and the 16S RNA methylase ArmA, conferring high-level resistance to aminoglycosides.

Carbapenem-hydrolyzing GES-type extended-spectrum beta-lactamase in Acinetobacter baumannii

Acinetobacter baumannii isolate AP was recovered from a bronchial lavage of a patient hospitalized in Paris, France. A. baumannii AP was resistant to all β-lactams, including carbapenems, and produced the extended-spectrum β-lactamase (ESBL) GES-14, which differs from GES-1 by two substitutions, Gly170Ser and Gly243Ala. Cloning of the bla(GES-14) gene followed by its expression in Escherichia coli showed that GES-14 compromised significantly the efficacy of all β-lactams, including cephalosporins, aztreonam, and carbapenems. The carbapenemase activity of purified GES-14 was confirmed by kinetic studies. The bla(GES-14) gene was located into a class 1 integron structure and located onto a ca. 95-kb self-transferable plasmid. This study identified a very broad-spectrum β-lactamase in A. baumannii.

Metagenomic analysis of apple orchard soil reveals antibiotic resistance genes encoding predicted bifunctional proteins

To gain insight into the diversity and origins of antibiotic resistance genes, we identified resistance genes in the soil in an apple orchard using functional metagenomics, which involves inserting large fragments of foreign DNA into Escherichia coli and assaying the resulting clones for expressed functions. Among 13 antibiotic-resistant clones, we found two genes that encode bifunctional proteins. One predicted bifunctional protein confers resistance to ceftazidime and contains a natural fusion between a predicted transcriptional regulator and a beta-lactamase. Sequence analysis of the entire metagenomic clone encoding the predicted bifunctional beta-lactamase revealed a gene potentially involved in chloramphenicol resistance as well as a predicted transposase. A second clone that encodes a predicted bifunctional protein confers resistance to kanamycin and contains an aminoglycoside acetyltransferase domain fused to a second acetyltransferase domain that, based on nucleotide sequence, was predicted not to be involved in antibiotic resistance. This is the first report of a transcriptional regulator fused to a beta-lactamase and of an aminoglycoside acetyltransferase fused to an acetyltransferase not involved in antibiotic resistance.

Molecular epidemiology of metallo-beta-lactamase-producing Pseudomonas aeruginosa isolates from Norway and Sweden shows import of international clones and local clonal expansion

Scandinavia is considered a region with a low prevalence of antimicrobial resistance. However, the number of multidrug-resistant (MDR) Gram-negative bacteria is increasing, including metallo-beta-lactamase (MBL)-producing Pseudomonas aeruginosa. In this study MBL-producing P. aeruginosa isolates identified in Norway (n = 4) and Sweden (n = 9) from 1999 to 2007 were characterized. Two international clonal complexes (CC), CC111 (n = 8) and CC235 (n = 2), previously associated with MBL-producing isolates, were dominant. CC111 isolates (ST111/229; serotype O12; bla(VIM-2)) included clonally related isolates identified in Skåne County, Sweden (n = 6), and two isolates associated with importation from Greece and Denmark. In all CC111 isolates, bla(VIM-2) was located in integron In59.2 or In59 variants. The two CC235 isolates (ST235/ST230; serotype O11; bla(VIM-4)) were imported from Greece and Cyprus, were possibly clonally related, and carried bla(VIM-4) in two different integron structures. Three isolates imported from Ghana (ST233; serotype O6; bla(VIM-2)), Tunisia (ST654; serotype O11; bla(VIM-2)), and Thailand (ST260; serotype O6; bla(IMP-14)) were clonally unrelated. ST233 was part of a new CC (CC233) that included other MBL-producing isolates, while ST654 could also be part of a new CC associated with MBL producers. In the isolates imported from Ghana and Tunisia, bla(VIM-2) was part of unusual integron structures lacking the 3' conserved segment and associated with transposons. The bla(VIM) gene was found to be located on the chromosome in all isolates. Known risk factors for acquisition of MBL were reported for all patients except one. The findings suggest that both import of successful international clones and local clonal expansion contribute to the emergence of MBL-producing P. aeruginosa in Scandinavia.

Complete Sequence of p07-406, a 24,179-base-pair plasmid harboring the blaVIM-7 metallo-beta-lactamase gene in a Pseudomonas aeruginosa isolate from the United States

An outbreak involving a Pseudomonas aeruginosa strain that was resistant to all tested antimicrobials except polymyxin B occurred in a hospital in Houston, TX. Previous studies on this strain showed that it possesses a novel mobile metallo-beta-lactamase (MBL) gene, designated bla(VIM-7), located on a plasmid (p07-406). Here, we report the complete sequence, annotation, and functional characterization of this plasmid. p07-406 is 24,179 bp in length, and 29 open reading frames were identified related to known or putatively recognized proteins. Analysis of this plasmid showed it to be comprised of four distinct regions: (i) a region of 5,200 bp having a Tn501-like mercuric resistance (mer) transposon upstream of the replication region; (ii) a Tn3-like transposon carrying a truncated integron with a bla(VIM-7) gene and an insertion sequence inserted at the other end of this transposon; (iii) a region of four genes, upstream of the Tn3-like transposon, possessing very high similarity to plasmid pXcB from Xanthomonas campestris pv. citri commonly associated with plants; (iv) a backbone sequence similar to the backbone structure of the IncP group plasmid Rms149, pB10, and R751. This is the first plasmid to be sequenced carrying an MBL gene and highlights the amelioration of DNA segments from disparate origins, most noticeably from plant pathogens.

Molecular epidemiology of PER-1 extended spectrum beta-lactamase among gram-negative bacteria isolated at a tertiary care hospital

The bla(PER-1) presence was sought by PCR in 289 ceftazidime resistant Gram-negative bacteria isolated at Dokuz Eylul University Hospital (Turkey) between 1998 and 2003. PER-1 production rates were 32.3, 33.9, 14.9 and 37.9% in the 1998-2000 period, 2001, 2002 and 2003, respectively. bla(PER-1) was detected in 46.2 and 35.9% of ceftazidime-resistant Pseudomonas aeruginosa and Acinetobacter baumannii isolates, respectively. ERIC-PCR results revealed that dissemination of two endemic clones for both P. aeruginosa (X and Y) and A. baumannii (A and B) was responsible for the high prevalence. Results of the conjugation tests and plasmid curing experiments suggested that bla(PER-1) was located on the chromosome in the representative strains. It was also shown for the first time that bla(PER-1) in a clinical isolate was associated with class-1 integron which could facilitate dissemination of bla(PER-1) among bacteria.

The influence of green fluorescent protein incorporation on bacterial physiology: a note of caution

AIMS

To investigate the effect of green flourescent protein (GFP) incorporation on bacterial physiology.

METHODS AND RESULTS

Comparisons were made between four different isogenic pairings of non-GFP-containing parents and their GFP-containing transformants with respect to growth rate and antimicrobial susceptibility. For the latter, sensitivities to 12 different antibiotics were measured initially by disc-diffusion assay, and then subsequently by generation of dose-dependent survival curves for 1 h exposure to different concentrations of tetracycline, ciprofloxacin and cetrimide USP. Whilst no significant difference in growth rate was observed, GFP-containing strains were uniformly and significantly more sensitive to all antimicrobial agents tested, excluding the beta-lactams, than their respective non-GFP-containing counterparts.

CONCLUSIONS

GFP incorporation has a significant effect on bacterial physiology and can modulate antimicrobial susceptibility.

SIGNIFICANCE AND IMPACT OF THE STUDY

Transformation with GFP can affect the physiology of bacterial cells. This may therefore affect the quality and accuracy of data generated depending on the application for which GFP is used.

A comparison of antibiotic resistance integrons in cattle from separate beef meat production systems at slaughter

AIMS

To compare antibiotic resistance integrons in cattle from three separate grass-fed, grain-fed and certified organic cattle production systems at slaughter.

METHODS AND RESULTS

In this study 198 samples from three separate cattle production systems were tested by PCR for the presence of class 1 and class 2 integrons. Integron-containing bacteria were readily isolated from pen faeces and hide samples regardless of production system. Lower numbers of integron-containing bacteria were isolated from the remaining sample types. Ninety-one class 1 and 34 class 2 integron-containing bacteria were isolated. Characterization of the integrons demonstrated a high degree of similarity across the three production systems with aadA1 and aadA2 routinely present. Integrons harbouring the cassette array cmlA5-bla(OXA-10)-aadA1 and the putative insertion sequence IS1066 were isolated from organic and grass-fed cattle and have not been described previously.

CONCLUSIONS

Integrons carrying antibiotic resistance genes were common in cattle from differing production systems at slaughter and the likelihood of presence appears unrelated to the production system.

SIGNIFICANCE AND IMPACT OF THE STUDY

Similar integron arrays are present in different cattle production systems suggesting that their presence may be independent of production practices. This is the first report of two novel integron structures present in Aeromonas.

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

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

Biochemical characterization of PER-2 and genetic environment of blaPER-2

PER-2 was the first detected and the second most prevalent extended-spectrum beta-lactamase in clinical pathogens isolated in Argentina and was also reported only in other South American countries. Citrobacter freundii 33587 was isolated in 1999 in Buenos Aires and was resistant to all tested beta-lactams except cephamycins and carbapenems. The strain produced both plasmid-borne TEM-1 and PER-2 (pI 5.4), which could be transferred by conjugation. By PCR screening, thermal asymmetric interlaced PCR, and DNA sequencing, we detected an ISPa12/IS1387a insertion sequence upstream of bla(PER-2), previously reported as also being associated with bla(PER-1). The presence of similar structures upstream of bla(PER-1) and bla(PER-2) suggests a common origin and mobilization. Compared to bla(PER-1) genes, an additional putative promoter for bla(PER-2) was found. PER-2 kinetic analysis showed its high hydrolysis efficiencies toward both CTX and CAZ (k(cat)/K(m), 0.76 and 0.43 microM(-1).s(-1), respectively).

Erythromycin resistance-conferring plasmid pRSB105, isolated from a sewage treatment plant, harbors a new macrolide resistance determinant, an integron-containing Tn402-like element, and a large region of unknown function

The erythromycin resistance plasmid pRSB105 was previously isolated from an activated sludge bacterial community of a municipal wastewater treatment plant. Compilation of the complete pRSB105 nucleotide sequence revealed that the plasmid is 57,137 bp in size and has a mean G+C content of 56.66 mol%. The pRSB105 backbone is composed of two different replication and/or partitioning modules and a functional mobilization region encoding the mobilization genes mobCDE and mobBA. The first replicon (Rep1) is nearly identical to the corresponding replication module of the multiresistance plasmid pRSB101 isolated from an unknown activated sludge bacterium. Accordingly, pRSB101 and pRSB105 are sister plasmids belonging to a new plasmid family. The second replicon (Rep2) of pRSB105 was classified as a member of the IncP-6 group. While Rep1 confers replication ability only in gamma-proteobacteria, Rep2 extents the host range of the plasmid since it is also functional in the beta-proteobacterium Ralstonia eutropha. Plasmid pRSB105 harbors the macrolide resistance genes mel and mph, encoding, respectively, a predicted ABC-type efflux permease and a macrolide-2'-phosphotransferase. Erythromycin resistance is mainly attributed to mel, whereas mph contributes to erythromycin resistance to a lesser extent. The second resistance region, represented by an integron-containing Tn402-like element, includes a beta-lactam (oxa10) and a trimethoprim (dfrB2) resistance gene cassette. In addition to antibiotic resistance modules, pRSB105 encodes a functional restriction/modification system and two nonresistance regions of unknown function. The presence of different mobile genetic elements that flank resistance and nonresistance modules on pRSB105 indicates that these elements were involved in acquisition of accessory plasmid modules. Comparative genomics of pRSB105 and related plasmids elucidated that pRSB105 evolved by integration of distinct modules from different plasmid sources, including Pseudomonas aeruginosa plasmids, and thus represents a mosaic plasmid.