TLA-1: a new plasmid-mediated extended-spectrum beta-lactamase from Escherichia coli

RATA: A novel class A carbapenemase with broad geographic distribution and potential for global spread

Carbapenem resistance's global proliferation poses a significant public health challenge. The primary resistance mechanism is carbapenemase production. In this study, we discovered a novel carbapenemase, RATA, located on the chromosome of Riemerella anatipestifer isolates. This enzyme shares ≤52 % amino acid sequence identity with other known β-lactamases. Antimicrobial susceptibility tests and kinetic assays demonstrated that RATA could hydrolyze not only penicillins and extended-spectrum cephalosporins but also monobactams, cephamycins, and carbapenems. Furthermore, its activity was readily inhibited by β-lactamase inhibitors. Bioinformatic analysis revealed 46 blaRATA-like genes encoding 27 variants in the NCBI database, involving 21 different species, including pathogens, host-associated bacteria, and environmental isolates. Notably, blaRATA-positive strains were globally distributed and primarily collected from marine environments. Concurrently, taxonomic analysis and GC content analysis indicated that blaRATA orthologue genes were predominantly located on the chromosomes of Flavobacteriaceae and shared a similar GC content as Flavobacteriaceae. Although no explicit mobile genetic elements were identified by genetic environment analysis, blaRATA-2 possessed the ability of horizontal transfer in R. anatipestifer via natural transformation. This work's data suggest that RATA is a new chromosome-encoded class A carbapenemase, and Flavobacteriaceae from marine environments could be the primary reservoir of the blaRATA gene.

Inter-phylum circulation of a beta-lactamase-encoding gene: a rare but observable event

Beta-lactamase-mediated degradation of beta-lactams is the most common mechanism of beta-lactam resistance in Gram-negative bacteria. Beta-lactamase-encoding genes can be transferred between closely related bacteria, but spontaneous inter-phylum transfers (between distantly related bacteria) have never been reported. Here, we describe an extended-spectrum beta-lactamase (ESBL)-encoding gene (blaMUN-1) shared between the Pseudomonadota and Bacteroidota phyla. An Escherichia coli strain was isolated from a patient in Münster (Germany). Its genome was sequenced. The ESBL-encoding gene (named blaMUN-1) was cloned, and the corresponding enzyme was characterized. The distribution of the gene among bacteria was investigated using the RefSeq Genomes database. The frequency and relative abundance of its closest homolog in the global microbial gene catalog (GMGC) were analyzed. The E. coli strain exhibited two distinct morphotypes. Each morphotype possessed two chromosomal copies of the blaMUN-1 gene, with one morphotype having two additional copies located on a phage-plasmid p0111. Each copy was located within a 7.6-kb genomic island associated with mobility. blaMUN-1 encoded for an extended-spectrum Ambler subclass A2 beta-lactamase with 43.0% amino acid identity to TLA-1. blaMUN-1 was found in species among the Bacteroidales order and in Sutterella wadsworthensis (Pseudomonadota). Its closest homolog in GMGC was detected frequently in human fecal samples. This is, to our knowledge, the first reported instance of inter-phylum transfer of an ESBL-encoding gene, between the Bacteroidota and Pseudomonadota phyla. Although the gene was frequently detected in the human gut, inter-phylum transfer was rare, indicating that inter-phylum barriers are effective in impeding the spread of ESBL-encoding genes, but not entirely impenetrable.

Horizontal transfer potential of antibiotic resistance genes in wastewater treatment plants unraveled by microfluidic-based mini-metagenomics

Wastewater treatment plants (WWTPs) are known to harbor antibiotic resistance genes (ARGs), which can potentially spread to the environment and human populations. However, the extent and mechanisms of ARG transfer in WWTPs are not well understood due to the high microbial diversity and limitations of molecular techniques. In this study, we used a microfluidic-based mini-metagenomics approach to investigate the transfer potential and mechanisms of ARGs in activated sludge from WWTPs. Our results show that while diverse ARGs are present in activated sludge, only a few highly similar ARGs are observed across different taxa, indicating limited transfer potential. We identified two ARGs, ermF and tla-1, which occur in a variety of bacterial taxa and may have high transfer potential facilitated by mobile genetic elements. Interestingly, genes that are highly similar to the sequences of these two ARGs, as identified in this study, display varying patterns of abundance across geographic regions. Genes similar to ermF found are widely found in Asia and the Americas, while genes resembling tla-1 are primarily detected in Asia. Genes similar to both genes are barely detected in European WWTPs. These findings shed light on the limited horizontal transfer potential of ARGs in WWTPs and highlight the importance of monitoring specific ARGs in different regions to mitigate the spread of antibiotic resistance.

Alteration of the gut microbiome and correlated metabolism in a rat model of long-term depression

Objective

This study aims to investigate the composition and function of the gut microbiome in long-term depression using an 8-week chronic unpredictable mild stress (CUMS) rat model.

Materials and methods

Animals were sacrificed after either 4 weeks or 8 weeks under CUMS to mimic long-term depression in humans. The gut microbiome was analyzed to identify potential depression-related gut microbes, and the fecal metabolome was analyzed to detect their functional metabolites. The correlations between altered gut microbes and metabolites in the long-term depression rats were explored. The crucial metabolic pathways related to long-term depression were uncovered through enrichment analysis based on these gut microbes and metabolites.

Results

The microbial composition of long-term depression (8-week CUMS) showed decreased species richness indices and different profiles compared with the control group and the 4-week CUMS group, characterized by disturbance of Alistipes indistinctus, Bacteroides ovatus, and Alistipes senegalensis at the species level. Additionally, long-term depression was associated with disturbances in fecal metabolomics. D-pinitol was the only increased metabolite in the 8-week CUMS group among the top 10 differential metabolites, while the top 3 decreased metabolites in the long-term depression rats included indoxyl sulfate, trimethylaminen-oxide, and 3 alpha,7 alpha-dihydroxy-12-oxocholanoic acid. The disordered fecal metabolomics in the long-term depression rats mainly involved the biosynthesis of pantothenate, CoA, valine, leucine and isoleucine.

Conclusion

Our findings suggest that the gut microbiome may participate in the long-term development of depression, and the mechanism may be related to the regulation of gut metabolism.

Antimicrobial Resistance Patterns and Clonal Distribution of E. coli, Enterobacter spp. and Acinetobacter spp. Strains Isolated from Two Hospital Wastewater Plants

The objective of this study was to determine the presence and persistence of antimicrobial-resistant enterobacteria and their clonal distribution in hospital wastewater. A descriptive cross-sectional study was carried out in wastewater from two Mexico City tertiary level hospitals. In February and March of 2020, eight wastewater samples were collected and 26 isolates of enterobacteria were recovered, 19 (73.1%) isolates were identified as E. coli, 5 (19.2%) as Acinetobacter spp. and 2 (7.7%) as Enterobacter spp. Antimicrobial susceptibility profiles were performed using the VITEK 2^® automated system and bacterial identification was performed by the Matrix-Assisted Laser Desorption/Ionization-Time of Flight mass spectrometry (MALDI-TOF MS^®). ESBL genes were detected by polymerase chain reaction (PCR) and clonal distributions of isolates were determined by pulsed-field gel electrophoresis (PFGE). E. coli susceptibility to different classes of antimicrobials was analyzed and resistance was mainly detected as ESBLs and fluoroquinolones. One E. coli strain was resistant to doripenem, ertapenem, imipenem and meropenem. The analysis by PCR showed the presence of specific β-lactamases resistance genes (bla_KPC, bla_CTX-M). The PFGE separated the E. coli isolates into 19 different patterns (A–R). PFGE results of Acinetobacter spp. showed the presence of a majority clone A. Surveillance of antimicrobial resistance through hospital wastewater is an important tool for early detection of clonal clusters of clinically important bacteria with potential for dissemination.

Resistance Detection and Transmission Risk Analysis of Pig-Derived Pathogenic Escherichia coli in East China

Objective: Antibiotics play an essential role in the treatment and prevention of diseases in pig farms. However, the irrational use of antibiotics leads to the emergence of multi-drug resistance of bacteria, which poses a critical threat to the efficacy of antibiotic treatments. Therefore, the study is designed to analyze the drug resistance of pathogenic Escherichia coli isolated from large-scale pig farms in East China, which provides a theoretical basis for precisely targeted clinical drugs in swine farms. Method: The pathogenic E. coli were isolated and identified from clinical samples of swine farms, and the drug resistance of pathogenic E. coli was detected by antimicrobial susceptibility test (AST) and minimum inhibitory concentration test (MIC). Moreover, the prevalence of plasmid-mediated β-lactam resistance genes was analyzed by PCR. Results: A total of 67 pathogenic E. coli were isolated from 152 samples collected from 20 large-scale pig farms in East China. All isolated pathogenic E. coli are associated with severe drug resistance. Moreover, 70% of isolated pathogenic E. coli is resistant to more than four antibiotics. Besides, there were 19 serotypes including O2, O4, O5, O6, O14, O26, O38, O42, O49, O57, O92, O93, O95, O101, O121, O131, O143, O158, and O161, of which the O4 and O92 serotype were the main serotypes in swine farms. The main extended-spectrum beta-lactamases (ESBLs)-encoding genes in East China were bla _CTX-M, bla _TEM, and bla _OXA by the detection of the ESBLs encoding genes of porcine pathogenic E. coli. The conjugation assays showed that a total of 30 transconjugants were obtained by conjugation, which indicated that drug resistance genes could be transmitted horizontally through conjugative plasmids. Conclusion: The isolated pathogenic E. coli were all multi-drug resistant, and especially O4 and O92 were the main serotypes. The β-lactam resistance genes were prevalent in large-scale pig farms in East China, which provided a theoretical basis for the prevention and control of pig-derived pathogenic E. coli in the future.

Extended Spectrum β-Lactamase (ESBL) Producing Escherichia coli in Pigs and Pork Meat in the European Union

The aim of this article is to review the fast and worldwide distribution of ESBL enzymes and to describe the role of the pork production chain as a reservoir and transmission route of ESBL-producing Escherichia coli and ESBLs in the European Union (EU). The use of β-lactam antibiotics in swine production and the prevalence of ESBL producing E. coli in fattening pigs and pork meat across Europe is analyzed. Overall, an increasing trend in the prevalence of presumptive ESBL producing E. coli in fattening pigs in the EU has been observed in the last decade, although with major differences among countries, linked to different approaches in the use of antimicrobials in pork production within the EU. Moreover, the various dissemination pathways of these bacteria along the pork production chain are described, along with factors at farm and slaughterhouse level influencing the risk of introducing or spreading ESBL producing bacteria throughout the food chain.

The crystal structure of ESBL TLA-1 in complex with clavulanic acid reveals a second acylation site

β-lactamases are the main molecules responsible for giving bacterial resistance against β-lactam antibiotics. The study of β-lactamases has allowed the development of antibiotics capable of inhibiting these enzymes. In this context, extended spectrum β-lactamase (ESBL) TLA-1 has spread in Escherichia coli and Enterobacter cloacae clinical isolates during the last 30 years in Mexico. In this research, the 3D structures of ESBL TLA-1 and TLA-1 S70G mutant, both ligand-free and in complex with clavulanic acid were determined by X-ray crystallography. Four clavulanic acid molecules were found in the structure of TLA-1, two of those were intermediaries of the acylation process and were localized covalently bound to two different amino acid residues, Ser70 and Ser237. The coordinates of TLA-1 in complex with clavulanic acid shows the existence of a second acylation site, additional to Ser70, which might be extendable to several members of the subclass A β-lactamases family. This is the first time that two serines involved in binding clavulanic acid has been reported and described to an atomic level.

Environmental superbugs: The case study of Pedobacter spp

The environment is one of the main reservoirs of antibiotic resistance genes (ARGs) but multidrug resistant (MDR) environmental isolates are barely characterised. As suggested by the name, Pedobacter species have been predominantly isolated from soils, but are also recovered from water (including drinking water), chilled food, fish, compost, sludge, glaciers and other extreme environments. The susceptibility phenotype of Pedobacter lusitanus NL19 (isolated from a deactivated uranium mine), its closely related species and the genus type strain were investigated. All strains are MDR bacteria, resistant to β-lactams, colistin, aminoglycosides and ciprofloxacin. Therefore, Pedobacter spp. are likely intrinsically resistant to β-lactams (including ertapenem) and to other three classes of antibiotics. 6%-8% of their total protein-encoding genes encode a diverse collection of putative ARGs, including β-lactamases. These enzymes are highly abundant in all the other Pedobacter strains with sequenced genomes, especially class C, class B3 and class A. LUS-1 and PLN-1 were further characterised in E. coli. LUS-1 is a class A β-lactamase and it conferred an increase in the MIC of cefotaxime, albeit very low. PLN-1 is a class B3 β-lactamase with carbapenemase activity, conferring resistance to ertapenem and a 66x and 16x increase in the MIC of imipenem and meropenem, respectively. PLN-1 also hydrolyses ampicillin, 1st and 3rd generation cephalosporins, and at a lower extent cephamycins and 4th generation cephalosporins. Therefore, Pedobacter spp. encode a large and diverse arsenal of resistance mechanisms that make them environmental superbugs.

ESBL-producing Escherichia coli and Its Rapid Rise among Healthy People

Since around the 2000s, Escherichia coli (E. coli) resistant to both oxyimino-cephalosporins and fluoroquinolones has remarkably increased worldwide in clinical settings. The kind of E. coli is also identified in patients suffering from community-onset infectious diseases such as urinary tract infections. Moreover, recoveries of multi-drug resistant E. coli from the feces of healthy people have been increasingly documented in recent years, although the actual state remains uncertain. These E. coli isolates usually produce extended-spectrum β-lactamase (ESBL), as well as acquisition of amino acid substitutions in the quinolone-resistance determining regions (QRDRs) of GyrA and/or ParC, together with plasmid-mediated quinolone resistance determinants such as Qnr, AAC(6')-Ib-cr, and QepA. The actual state of ESBL-producing E. coli in hospitalized patients has been carefully investigated in many countries, while that in healthy people still remains uncertain, although high fecal carriage rates of ESBL producers in healthy people have been reported especially in Asian and South American countries. The issues regarding the ESBL producers have become very complicated and chaotic due to rapid increase of both ESBL variants and plasmids mediating ESBL genes, together with the emergence of various "epidemic strains" or "international clones" of E. coli and Klebsiella pneumoniae harboring transferable-plasmids carrying multiple antimicrobial resistance genes. Thus, the current state of ESBL producers outside hospital settings was overviewed together with the relation among those recovered from livestock, foods, pets, environments and wildlife from the viewpoint of molecular epidemiology. This mini review may contribute to better understanding about ESBL producers among people who are not familiar with the antimicrobial resistance (AMR) threatening rising globally.

Structural Insights into the TLA-3 Extended-Spectrum β-Lactamase and Its Inhibition by Avibactam and OP0595

The development of effective inhibitors that block extended-spectrum β-lactamases (ESBLs) and restore the action of β-lactams represents an effective strategy against ESBL-producing Enterobacteriaceae We evaluated the inhibitory effects of the diazabicyclooctanes avibactam and OP0595 against TLA-3, an ESBL that we identified previously. Avibactam and OP0595 inhibited TLA-3 with apparent inhibitor constants (K_iapp) of 1.71 ± 0.10 and 1.49 ± 0.05 μM, respectively, and could restore susceptibility to cephalosporins in the TLA-3-producing Escherichia coli strain. The value of the second-order acylation rate constant (k₂/K, where k₂ is the acylation rate constant and K is the equilibrium constant) of avibactam [(3.25 ± 0.03) × 10³ M^-1 · s^-1] was closer to that of class C and D β-lactamases (k₂/K, <10⁴ M^-1 · s^-1) than that of class A β-lactamases (k₂/K, >10⁴ M^-1 · s^-1). In addition, we determined the structure of TLA-3 and that of TLA-3 complexed with avibactam or OP0595 at resolutions of 1.6, 1.6, and 2.0 Å, respectively. TLA-3 contains an inverted Ω loop and an extended loop between the β5 and β6 strands (insertion after Ser237), which appear only in PER-type class A β-lactamases. These structures might favor the accommodation of cephalosporins harboring bulky R1 side chains. TLA-3 presented a high catalytic efficiency (k_cat/K_m ) against cephalosporins, including cephalothin, cefuroxime, and cefotaxime. Avibactam and OP0595 bound covalently to TLA-3 via the Ser70 residue and made contacts with residues Ser130, Thr235, and Ser237, which are conserved in ESBLs. Additionally, the sulfate group of the inhibitors formed polar contacts with amino acid residues in a positively charged pocket of TLA-3. Our findings provide a structural template for designing improved diazabicyclooctane-based inhibitors that are effective against ESBL-producing Enterobacteriaceae.

A Structure-Based Classification of Class A β-Lactamases, a Broadly Diverse Family of Enzymes

For medical biologists, sequencing has become a commonplace technique to support diagnosis. Rapid changes in this field have led to the generation of large amounts of data, which are not always correctly listed in databases. This is particularly true for data concerning class A β-lactamases, a group of key antibiotic resistance enzymes produced by bacteria. Many genomes have been reported to contain putative β-lactamase genes, which can be compared with representative types. We analyzed several hundred amino acid sequences of class A β-lactamase enzymes for phylogenic relationships, the presence of specific residues, and cluster patterns. A clear distinction was first made between dd-peptidases and class A enzymes based on a small number of residues (S70, K73, P107, 130SDN132, G144, E166, 234K/R, 235T/S, and 236G [Ambler numbering]). Other residues clearly separated two main branches, which we named subclasses A1 and A2. Various clusters were identified on the major branch (subclass A1) on the basis of signature residues associated with catalytic properties (e.g., limited-spectrum β-lactamases, extended-spectrum β-lactamases, and carbapenemases). For subclass A2 enzymes (e.g., CfxA, CIA-1, CME-1, PER-1, and VEB-1), 43 conserved residues were characterized, and several significant insertions were detected. This diversity in the amino acid sequences of β-lactamases must be taken into account to ensure that new enzymes are accurately identified. However, with the exception of PER types, this diversity is poorly represented in existing X-ray crystallographic data.

Draft Genome Sequence of Strain ATCC 33958, Reported To Be Elizabethkingia miricola

We report the draft genome of Elizabethkingia strain ATCC 33958, which has been classified as Elizabethkingia miricola. Similar to other Elizabethkingia species, the ATCC 33958 draft genome contains numerous β-lactamase genes. ATCC 33958 also harbors a urease gene cluster which supports classification as E. miricola.

Multidrug-resistant phenotype and isolation of a novel SHV- beta-Lactamase variant in a clinical isolate of Enterobacter cloacae

Background

ESBL-producing bacteria are a clinical problem in the management of diseases caused by these pathogens. Worldwide, systemic infections with BL enzymes are evolving by mutations from classical bla genes in an intensified manner and they continue to be transferred across species.

Results

E.cloacae BF1417 isolate and its transconjugants gave positive results with the DDST, suggesting the presence of ESBL. Sequence analysis revealed a bla_SHV-ESBL-type gene that differs from the gene encoding SHV-1 by five point mutations resulting in three amino acid substitutions in the coding region: C123R, I282T and L286P. This novel SHV-type enzyme was designated SHV-128. The conjugation tests and plasmid characterization showed that the bla_SHV-128 is located on a conjugative plasmid IncFII type. Expression studies demonstrated that the above mutations participated in drug resistance, hydrolysis of extended spectrum β-lactam and the change of the isoelectric point of the protein.

Conclusion

These findings underscore the diversity by which antibiotic resistance can arise and the evolutionary potential of the clinically important ESBL enzymes. In addition, this study highlights the need for systematic surveillance of ESBL-mediated resistance as well as in clinical areas and communities.

New plasmid-mediated aminoglycoside 6'-N-acetyltransferase, AAC(6')-Ian, and ESBL, TLA-3, from a Serratia marcescens clinical isolate

OBJECTIVES

Enterobacteriaceae clinical isolates showing amikacin resistance (MIC 64 to >256 mg/L) in the absence of 16S rRNA methyltransferase (MTase) genes were found. The aim of this study was to clarify the molecular mechanisms underlying amikacin resistance in Enterobacteriaceae clinical isolates that do not produce 16S rRNA MTases.

METHODS

PCR was performed to detect already-known amikacin resistance determinants. Cloning experiments and sequence analyses were performed to characterize unknown amikacin resistance determinants. Transfer of amikacin resistance determinants was performed by conjugation and transformation. The complete nucleotide sequence of the plasmids was determined by next-generation sequencing technology. Amikacin resistance enzymes were purified with a column chromatography system. The enzymatic function of the purified protein was investigated by thin-layer chromatography (TLC) and HPLC.

RESULTS

Among the 14 isolates, 9 were found to carry already-known amikacin resistance determinants such as aac(6')-Ia and aac(6')-Ib. Genetic analyses revealed the presence of a new amikacin acetyltransferase gene, named aac(6')-Ian, located on a 169 829 bp transferable plasmid (p11663) of the Serratia marcescens strain NUBL-11663, one of the five strains negative for known aac(6') genes by PCR. Plasmid p11663 also carried a novel ESBL gene, named blaTLA-3. HPLC and TLC analyses demonstrated that AAC(6')-Ian catalysed the transfer of an acetyl group from acetyl coenzyme A onto an amine at the 6'-position of various aminoglycosides.

CONCLUSIONS

We identified aac(6')-Ian as a novel amikacin resistance determinant together with a new ESBL gene, blaTLA-3, on a transferable plasmid of a S. marcescens clinical isolate.

Outbreak of Nosocomial Sepsis and Pneumonia in a Newborn Intensive Care Unit by Multiresistant Extended-Spectrum β-Lactamase-ProducingKlebsiella pneumoniaeHigh Impact on Mortality

We describe a case-control study of a small outbreak of nosocomial sepsis and pneumonia with high mortality due to clonal dissemination of a multiresistantKlebsiella pneumoniaein the neonatal intensive care unit of a Mexican institution. Our study helped to change nosocomial infection control policy in this hospital.

Membrane interactions and biological activity of antimicrobial peptides from Australian scorpion

UyCT peptides are antimicrobial peptides isolated from the venom of the Australian scorpion. The activity of the UyCT peptides against Gram positive and Gram negative bacteria and red blood cells was determined. The membrane interactions of these peptides were evaluated by dye release (DR) of the fluorophore calcein from liposomes and isothermal titration calorimetry (ITC); and their secondary structure was determined by circular dichroism (CD). Three different lipid systems were used to mimic red blood cells, Escherichia coli and Staphylococcus aureus membranes. UyCT peptides exhibited broad spectrum antimicrobial activity with low MIC for S. aureus and multi-drug resistant Gram negative strains. Peptide combinations showed some synergy enhancing their potency but not hemolytic activity. The UyCT peptides adopted a helical structure in lipid environments and DR results confirmed that the mechanism of action is by disrupting the membrane. ITC data indicated that UyCT peptides preferred prokaryotic rather than eukaryotic membranes. The overall results suggest that UyCT peptides could be pharmaceutical leads for the treatment of Gram negative multiresistant bacterial infections, especially against Acinetobacter baumanni, and candidates for peptidomimetics to enhance their potency and minimize hemolysis. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.

Chromosome-encoded extended-spectrum class A β-lactamase MIN-1 from Minibacterium massiliensis

Minibacterium massiliensis strain CIP107820 is a recently discovered waterborne Gram-negative rod isolated from hospital water samples. It harbors a chromosomally located gene encoding an Ambler class A extended-spectrum β-lactamase termed MIN-1, sharing 56%, 54%, and 51% amino acid identities with β-lactamases LUT-1, KPC-2, and CTX-M-2, respectively. β-Lactamase MIN-1 hydrolyzes penicillins, narrow-spectrum cephalosporins, cefotaxime, and, less efficiently, cefepime, while ceftazidime and carbapenems are very poor substrates, and cephamycins and aztreonam are not hydrolyzed.

Characterization of CIA-1, an Ambler class A extended-spectrum β-lactamase from Chryseobacterium indologenes

An Ambler class A β-lactamase gene, bla(CIA-1), was cloned from the reference strain Chryseobacterium indologenes ATCC 29897 and expressed in Escherichia coli BL21. The bla(CIA-1) gene encodes a novel extended-spectrum β-lactamase (ESBL) that shared 68% and 60% identities with the CGA-1 and CME-1 β-lactamases, respectively. bla(CIA-1)-like genes were detected from clinical isolates. In addition to the metallo-β-lactamase IND of Ambler class B, C. indologenes has a class A ESBL gene, bla(CIA-1), located on the chromosome.

Antimicrobial, antioxidant, and antimutagenic activities of selected marine natural products and tobacco cembranoids

Multidrug resistance (MDR) in microorganisms is a cause of major concern for clinicians and pharmaceutical industries. Continuous development of new antimicrobial drugs with multiple targets and potentials is expected to efficiently combat MDR in these microorganisms. In a continued exploration of new antimicrobial drug leads, 11 marine natural products, semisynthetic, or related synthetic analogs (1-11) and two tobacco cembranoids (12 and 13) were screened for their antimicrobial, antioxidant, and antimutagenic activities. Eight compounds showed varying levels of both antibacterial and antifungal activities. Compounds such as 17-O-methyllatrunculin-A, verongiaquinol, (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol), and manzamine-A showed a broad spectrum of activity, inhibiting six of seven tested bacteria with zone of inhibition diameter from 9 to 30 mm. Four of these active compounds also showed antifungal activity. The findings of the in vitro time-kill assay of the most active compound, verongiaquinol, against Staphylococcus aureus indicated its subinhibitory effect at the level lower than the minimal inhibitory concentration (MIC) values (i.e., 2 and 4 µg/mL). At the MIC (8 µg/mL), bacterial cells were completely killed within 18 hours of incubation. DPPH free radical scavenging activity was demonstrated by five compounds in the range of 89.65-36.19% decolorization. Further, four compounds evaluated for their antimutagenic activity against the directly acting mutagens, methyl methanesulfonate and sodium azide, in Salmonella typhimurium strains, interestingly, showed no sign of mutagenicity. Verongiaquinol and manzamine A, in fact, reduced the mutagenicity by 50-75% at a dose of 5 µg/plate in different test strains. Our study seems to provide some novel antimicrobial leads with strong antioxidant potential and the associated ability of antimutagenicity.

Molecular characterization and antimicrobial susceptibility of extended-spectrum {beta}-lactamase-producing Enterobacteriaceae isolates at a tertiary-care centre in Monterrey, Mexico

Our objective was to analyse phenotypic and genetic data of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae, Enterobacter cloacae, Escherichia coli and Serratia marcescens that cause infections in our hospital. Over a 3 year period, 342 randomly selected clinical Enterobacteriaceae isolates were tested for ESBL production and evaluated for the presence of the β-lactamase genes bla(SHV), bla(TEM,) bla(CTX-M) and bla(TLA-1). The antibiotic susceptibilities of these isolates were also determined, and the clonality of the isolates was assessed by PFGE. Based on our analyses, 33/92 (35.9 %) K. pneumoniae, 31/87 (35.6 %) Enterobacter cloacae, 24/80 (30 %) E. coli and 17/83 (20.5 %) S. marcescens were identified as ESBL producers. The presence of TEM, SHV or CTX ESBL types was detected in 99/105 (94 %) of the isolates. TLA-1 was not detected in any of the 105 isolates. The dominant ESBL types were bla(SHV-5) (n=33), bla(SHV12) (n=31) and bla(CTX-M-15) (n=30). The predominant ESBL identified in E. coli and Enterobacter cloacae isolates was CTX-M-15, whereas in K. pneumoniae and S. marcescens the predominant types were SHV-12 and SHV-5, respectively. PFGE genotyping revealed two main genetic patterns in the K. pneumoniae isolates, types SHV-12 and TEM-1+SHV-5. An outbreak caused by Enterobacter cloacae SHV-5+CTX-M-15 was detected. In contrast, most ESBL-producing isolates of E. coli and S. marcescens did not have similar PFGE banding patterns and thus were not genetically similar. Enterobacteriaceae are a concern in our hospital, especially K. pneumoniae and Enterobacter cloacae. Our results confirm that the CTX-M-15 ESBL type has spread rapidly in the hospital, and thus requires careful monitoring.

Extended-spectrum β-lactamases in Gram Negative Bacteria

Extended-spectrum β-lactamases (ESBLs) are a group of plasmid-mediated, diverse, complex and rapidly evolving enzymes that are posing a major therapeutic challenge today in the treatment of hospitalized and community-based patients. Infections due to ESBL producers range from uncomplicated urinary tract infections to life-threatening sepsis. Derived from the older TEM is derived from Temoniera, a patient from whom the strain was first isolated in Greece. β-lactamases, these enzymes share the ability to hydrolyze third-generation cephalosporins and aztreonam and yet are inhibited by clavulanic acid. In addition, ESBL-producing organisms exhibit co-resistance to many other classes of antibiotics, resulting in limitation of therapeutic option. Because of inoculum effect and substrate specificity, their detection is also a major challenge. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in Klebsiella pneumoniae, K. oxytoca, Escherichia coli and Proteus mirabilis. In common to all ESBL-detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic-resistance mechanisms in the face of the introduction of new antimicrobial agents. Thus there is need for efficient infection-control practices for containment of outbreaks; and intervention strategies, e.g., antibiotic rotation to reduce further selection and spread of these increasingly resistant pathogens.

Association of the extended-spectrum beta-lactamase gene blaTLA-1 with a novel ISCR element, ISCR20

The bla(TLA-1) gene encoding an extended-spectrum beta-lactamase was identified in 11 enterobacterial isolates from Mexico City, Mexico. This gene was located on different plasmids and plasmid types with different sizes and incompatibility groups. It was associated with a novel insertion sequence, ISCR20, encoding a putative transposase that shared only 20% amino acid identity with the most closely related transposase of ISCR1. The ISCR20 element provided specific promoter sequences for expression of the bla(TLA-1) gene.

Characterization of CSP-1, a novel extended-spectrum beta-lactamase produced by a clinical isolate of Capnocytophaga sputigena

The Capnocytophaga sputigena isolate NOR, responsible for septicemia, was resistant to amoxicillin and narrow-spectrum cephalosporins. In a cloning experiment, a new gene, bla(CSP-1), was identified; this gene encodes a novel extended-spectrum beta-lactamase (ESBL) that shares only 52% and 49% identities with the CME-1 and VEB-1 beta-lactamases, respectively. The G+C content of this gene, its genetic environment, the absence of conjugation transfer, and its detection in two reference strains suggested that it was an intrinsic resistance gene located on the chromosome.

Prevalence and spread of extended-spectrum beta-lactamase-producing Enterobacteriaceae in Europe

Extended-spectrum beta-lactamases (ESBLs) represent a major threat among resistant bacterial isolates. The first types described were derivatives of the TEM-1, TEM-2 and SHV-1 enzymes during the 1980s in Europe, mainly in Klebsiella pneumoniae associated with nosocomial outbreaks. Nowadays, they are mostly found among Escherichia coli isolates in community-acquired infections, with an increasing occurrence of CTX-M enzymes. The prevalence of ESBLs in Europe is higher than in the USA but lower than in Asia and South America. However, important differences among European countries have been observed. Spread of mobile genetic elements, mainly epidemic plasmids, and the dispersion of specific clones have been responsible for the increase in ESBL-producing isolates, such as those with TEM-4, TEM-24, TEM-52, SHV-12, CTX-M-9, CTX-M-14, CTX-M-3, CTX-M-15 and CTX-M-32 enzymes.

Minor extended-spectrum beta-lactamases

Extended-spectrum beta-lactamases (ESBLs) are usually plasmid-mediated enzymes that confer resistance to a broad range of beta-lactams. Initially, resistance to third-generation cephalosporins in Gram-negative rods was mainly due to the dissemination of TEM- and SHV-type ESBLs, which are point mutants of the classic TEM and SHV enzymes with extended substrate specificity. During the last ten years, CTX-M-type ESBLs have become increasingly predominant, but less frequent class A beta-lactamases have also been described, including SFO, BES, BEL, TLA, GES, PER and VEB types. While several of these latter are rarely identified, or are very localised, others are becoming locally prevalent, or are increasingly isolated worldwide. In addition, mutations can extend the spectrum of some OXA-type beta-lactamases to include expanded-spectrum cephalosporins, and several of these enzymes are considered to be ESBLs.

Performance of chromID ESBL, a chromogenic medium for detection of Enterobacteriaceae producing extended-spectrum beta-lactamases

The chromogenic agar medium chromID ESBL (bioMérieux) was compared with BLSE agar medium (AES) for selective isolation and presumptive identification of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae from clinical samples. A total of 765 samples (468 rectal swabs, 255 urine samples and 42 pulmonary aspirations) obtained from 547 patients was processed. All bacterial strains isolated on either medium were further characterized using biochemical tests, and ESBL producers were confirmed by synergy testing. Genetic characterization of ESBL genes was determined by PCR. A total of 33 ESBL-producing Enterobacteriaceae strains [Escherichia coli (n=16), Klebsiella pneumoniae (n=8), Enterobacter spp. (n=3), Citrobacter spp. (n=5) and Proteus mirabilis (n=1)] was recovered. The sensitivity after 24 h incubation was 88 % for chromID ESBL and 85 % for BLSE agar. At 48 h, the sensitivity of chromID ESBL increased to 94 % and was higher than that obtained with BLSE agar. The positive predictive value at 24 h for chromID ESBL was 38.7 % [95 % confidence interval (95 % CI) 28.3 -50.2 %)], which was significantly higher than that for BLSE agar [15.4 %, 95 % CI 10.1 -21.5 %]. On both media, false-positive results were mostly due to Pseudomonas aeruginosa and to Enterobacteriaceae overproducing chromosomal cephalosporinase (Enterobacter spp.) or a chromosomal penicillinase (Klebsiella oxytoca). This study showed that chromID ESBL, a ready-to-use chromogenic selective medium, is sensitive and specific for rapid, presumptive identification of ESBL-producing Enterobacteriaceae. Its chromogenic properties and its selectivity are particularly useful in specimens containing resident associated flora.

An epidemic of plasmids? Dissemination of extended-spectrum cephalosporinases among Salmonella and other Enterobacteriaceae

CTX-M- and AmpC-type beta-lactamases comprise the two most rapidly growing populations among the extended-spectrum cephalosporinases. The evolution and dissemination of resistance genes encoding these enzymes occur mostly through the transmission of plasmids. The high prevalence of clinical isolates of Enterobacteriaceae producing the plasmid-mediated extended-spectrum cephalosporinases resembles an epidemic of plasmids, and has generated serious therapeutic problems. This review describes the emergence and worldwide spread of various classes of plasmid-mediated extended-spectrum cephalosporinases in Salmonella and other Enterobacteriaceae, the transfer mechanism of the plasmids, detection methods, and therapeutic choices.

Antimicrobial resistance patterns of Shiga toxin-producing Escherichia coli O157:H7 and O157:H7- from different origins

Shiga toxin-producing Escherichia coli (STEC) serotypes including O157:H7 (n = 129) from dairy cows, cull dairy cow feces, cider, salami, human feces, ground beef, bulk tank milk, bovine feces, and lettuce; and O157:H7- (n = 24) isolated from bovine dairy and bovine feedlot cows were evaluated for antimicrobial resistance against 26 antimicrobials and the presence of antimicrobial resistance genes (tetA, tetB, tetC, tetD, tetE, tetG, floR, cmlA, strA, strB, sulI, sulII, and ampC). All E. coli exhibited resistance to five or more antimicrobial agents, and the majority of isolates carried one or more target antimicrobial resistance gene(s) in different combinations. The majority of E. coli showed resistance to ampicillin, aztreonam, cefaclor, cephalothin, cinoxacin, and nalidixic acid, and all isolates were susceptible to chloramphenicol and florfenicol. Many STEC O157:H7 and O157:H7-isolates were susceptible to amikacin, carbenicillin, ceftriaxone, cefuroxime, ciprofloxacin, fosfomycin, moxalactam, norfloxacin, streptomycin, tobramycin, trimethoprim, and tetracycline. The majority of STEC O157:H7 (79.8%) and O157:H7- (91.7%) carried one or more antimicrobial resistance gene(s) regardless of whether phenotypically resistant or susceptible. Four tetracycline resistant STEC O157:H7 isolates carried both tetA and tetC. Other tetracycline resistance genes (tetB, tetD, tetE, and tetG) were not detected in any of the isolates. Among nine streptomycin resistant STEC O157:H7 isolates, eight carried strA-strB along with aadA, whereas the other isolate carried aadA alone. However, the majority of tetracycline and streptomycin susceptible STEC isolates also carried tetA and aadA genes, respectively. Most ampicillin resistant E. coli of both serotypes carried ampC genes. Among sulfonamide resistance genes, sulII was detected only in STEC O157:H7 (4 of 80 sulfonamide-resistant isolates) and sulI was detected in O157:H7- (1 of 16 sulfonamide resistant isolates). The emergence and dissemination of multidrug resistance in STEC can serve as a reservoir for different antimicrobial resistance genes. Dissemination of antimicrobial resistance genes to commensal and pathogenic bacteria could occur through any one of the horizontal gene transfer mechanisms adopted by the bacteria.

Cefotaxime and ceftazidime-resistant Escherichia coli isolate producing TEM-15 beta-lactamase from a Tunisian hospital

A clinical isolate of Escherichia coli LBT04 was found to have a high-level resistance to broad-spectrum beta-lactams. Analysis of this strain by the disk diffusion test revealed synergies between clavulanic acid and ceftazidime, cefotaxime. Clavulanic acid decreased the MICs of ceftazidime, cefotaxime, and ceftriaxone, which suggested that LBT04 produced an extended-spectrum beta-lactamase. These resistances were carried by a 1080-bp chromosomal gene that encoded a beta-lactamase with a pI of 6.3. Cloning and sequencing experiments showed that this beta-lactamase revealed identity with the bla(TEM-1) gene encoding the TEM-1 beta-lactamase, except for a replacement of the Glu residue at position 104 by Lys, and of the Gly residue at position 238 by Ser. These two mutations were encountered in TEM-15 beta-lactamase, but this is the first description of this enzyme in the E. coli species in Tunisian hospitals.

In vitro efficacy of bioactive extracts of 15 medicinal plants against ESβL-producing multidrug-resistant enteric bacteria

Alcoholic crude extracts and some fractions from 15 traditionally used Indian medicinal plants were investigated for their ability to inhibit the growth of extended spectrum beta-lactamases (ESbetaL)-producing multidrug-resistant enteric bacteria. The test bacteria Eschrichia coli and Shigella were resistant to 16-23 antibiotics with intermediate or resistance to beta-lactams (minimum inhibitory concentration (MIC) value range 16-1024 microg/ml). The crude plant extracts demonstrated zone of inhibition in the range of 11-29 mm against one or more test bacteria. On the basis of promising activity, 12 plants were selected to determine their efficacy in terms of MIC, which ranged from 0.64 mg/ml to 10.24 mg/ml. The extracts of Acorus calamus, Hemidesmus indicus, Holarrhena antidysenterica and Plumbago zeylanica demonstrated relatively high activity as compared to other plant extracts and were fractionated into acetone, ethyl acetate and methanol. Acetone fraction in most of the cases exhibited higher potency (low MIC value) as compared to ethyl acetate and methanol fraction. However, in Plumbago zeylanica, ethyl acetate fraction was most active. Synergistic interactions among crude extracts were demonstrated in the 12 different combinations against ESbetaL-producing E. coli (ESbetaL-02). Certain combinations exhibited significant synergy with enlargement of combined inhibition zone size by 5 mm. Interaction of crude extracts with five antibiotics (Tetracycline, ciprofloxacin, nalidixic acid, chloramphenicol and streptomycin) demonstrated synergistic interaction with tetracycline and ciprofloxacin by 10 and 3 plant extracts respectively. Phytochemical analysis and thin layer chromatography (TLC) bioautography of crude extracts showed the presence of alkaloids, phenols and flavonoids as active phytoconstituents. Most active fractions of four plants were subjected to Infrared spectroscopy and the major groups of compounds were detected. The plant extracts were further tested for their in vitro haemolytic activity to sheep erythrocytes and demonstrated no haemolysis at recommended doses. Further activity-guided fractionation of active fractions is needed to isolate and characterize the active principle in order to establish the mode of action against the ESbetaL-producing multidrug-resistant enteric bacteria and the mechanism of synergy.

TLA-2, a novel Ambler class A expanded-spectrum beta-lactamase

Beta-lactamase TLA-2 is encoded by a 47-kb plasmid isolated from an unidentified bacterial strain from a wastewater treatment plant. TLA-2 is an Ambler class A beta-lactamase that shares 52% amino acid identity with CGA-1 from Chryseobacterium gleum and 51% with TLA-1 from Escherichia coli. The enzyme hydrolyzes mostly cephalosporins.

CTX-M-2 and a new CTX-M-39 enzyme are the major extended-spectrum beta-lactamases in multiple Escherichia coli clones isolated in Tel Aviv, Israel

The rate of occurrence of the extended-spectrum beta-lactamase (ESBL)-producing phenotype among Escherichia coli isolates in Tel Aviv is 12% (22). The aim of this study was to understand the molecular epidemiology of E. coli ESBL producers and to identify the ESBL genes carried by them. We studied 20 single-patient ESBL-producing E. coli clinical isolates. They comprised 11 distinct nonrelated pulsed-field gel electrophoresis (PFGE) genotypes: six isolates belonged to the same PFGE clone, four other clones included two isolates each, and six unrelated clones included only one isolate. All isolates produced various beta-lactamases with pIs ranging from 5.2 to 8.2, varying within similar PFGE clones. The most prevalent ESBL gene was bla(CTX-M); 16 isolates carried bla(CTX-M-2) and three carried a new ESBL gene designated bla(CTX-M-39). Three strains carried bla(SHV) (two bla(SHV-12) and one bla(SHV-5)), and two strains carried inhibitor-resistant ESBL genes, bla(TEM-33) and bla(TEM-30); 18 strains carried bla(TEM-1) and eight strains carried bla(OXA-2). Plasmid mapping and Southern blot analysis with a CTX-M-2 probe demonstrated that bla(CTX-M-2) is plasmid borne. The wide dissemination of ESBLs among E. coli isolates in our institution is partly related to clonal spread, but more notably to various plasmid-associated ESBL genes, occurring in multiple clones, wherein the CTX-M gene family appears almost uniformly. We report here a new CTX-M gene, designated bla(CTX-M-39), which revealed 99% homology with bla(CTX-M-26), with a substitution of arginine for glutamine at position 225.

Extended-spectrum beta-lactamases: a clinical update

Extended-spectrum beta-lactamases (ESBLs) are a rapidly evolving group of beta-lactamases which share the ability to hydrolyze third-generation cephalosporins and aztreonam yet are inhibited by clavulanic acid. Typically, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these beta-lactamases. This extends the spectrum of beta-lactam antibiotics susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have recently been described. The presence of ESBLs carries tremendous clinical significance. The ESBLs are frequently plasmid encoded. Plasmids responsible for ESBL production frequently carry genes encoding resistance to other drug classes (for example, aminoglycosides). Therefore, antibiotic options in the treatment of ESBL-producing organisms are extremely limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have recently been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. There is substantial debate as to the optimal method to prevent this occurrence. It has been proposed that cephalosporin breakpoints for the Enterobacteriaceae should be altered so that the need for ESBL detection would be obviated. At present, however, organizations such as the Clinical and Laboratory Standards Institute (formerly the National Committee for Clinical Laboratory Standards) provide guidelines for the detection of ESBLs in klebsiellae and Escherichia coli. In common to all ESBL detection methods is the general principle that the activity of extended-spectrum cephalosporins against ESBL-producing organisms will be enhanced by the presence of clavulanic acid. ESBLs represent an impressive example of the ability of gram-negative bacteria to develop new antibiotic resistance mechanisms in the face of the introduction of new antimicrobial agents.

Antibiotic multiresistance plasmid pRSB101 isolated from a wastewater treatment plant is related to plasmids residing in phytopathogenic bacteria and carries eight different resistance determinants including a multidrug transport system

Ten different antibiotic resistance plasmids conferring high-level erythromycin resistance were isolated from an activated sludge bacterial community of a wastewater treatment plant by applying a transformation-based approach. One of these plasmids, designated pRSB101, mediates resistance to tetracycline, erythromycin, roxythromycin, sulfonamides, cephalosporins, spectinomycin, streptomycin, trimethoprim, nalidixic acid and low concentrations of norfloxacin. Plasmid pRSB101 was completely sequenced and annotated. Its size is 47 829 bp. Conserved synteny exists between the pRSB101 replication/partition (rep/par) module and the pXAC33-replicon from the phytopathogen Xanthomonas axonopodis pv. citri. The second pRSB101 backbone module encodes a three-Mob-protein type mobilization (mob) system with homology to that of IncQ-like plasmids. Plasmid pRSB101 is mobilizable with the help of the IncP-1alpha plasmid RP4 providing transfer functions in trans. A 20 kb resistance region on pRSB101 is located within an integron-containing Tn402-like transposon. The variable region of the class 1 integron carries the genes dhfr1 for a dihydrofolate reductase, aadA2 for a spectinomycin/streptomycin adenylyltransferase and bla(TLA-2) for a so far unknown Ambler class A extended spectrum beta-lactamase. The integron-specific 3'-segment (qacEDelta1-sul1-orf5Delta) is connected to a macrolide resistance operon consisting of the genes mph(A) (macrolide 2'-phosphotransferase I), mrx (hydrophobic protein of unknown function) and mphR(A) (regulatory protein). Finally, a putative mobile element with the tetracycline resistance genes tetA (tetracycline efflux pump) and tetR was identified upstream of the Tn402-specific transposase gene tniA. The second 'genetic load' region on pRSB101 harbours four distinct mobile genetic elements, another integron belonging to a new class and footprints of two more transposable elements. A tripartite multidrug (MDR) transporter consisting of an ATP-binding-cassette (ABC)-type ATPase and permease, and an efflux membrane fusion protein (MFP) of the RND-family is encoded between the replication/partition and the mobilization module. Homologues of the macrolide resistance genes mph(A), mrx and mphR(A) were detected on eight other erythromycin resistance-plasmids isolated from activated sludge bacteria. Plasmid pRSB101-like repA amplicons were also obtained from plasmid-DNA preparations of the final effluents of the wastewater treatment plant indicating that pRSB101-like plasmids are released with the final effluents into the environment.

The prevalence of bacterial resistance in clinical, food, water and some environmental samples in Southwest Nigeria

The resistance pattern and mechanisms of bacterial isolates obtained from clinical origin, soil, industrial effluent, orange juice products and drinking water were studied using commonly used antibiotics. The microbial load of the water samples, industrial effluent and orange juice products were 1.0 x 10(1)-2.25 x 10(6), 2.15 x 10(5), and 3.5 x 10(4)-2.15 x 10(5) cfu mL(-1), respectively. The faecal coliform test revealed that only two out of twenty orange juice products had MPN of 2 and 20, the MPN of water ranged from 1-> or = 1800, while the effluent had MPN of > or = 1800. The bacterial isolates that were isolated include E. coli, S. aureus, P. vulgaris, S. marcescens, S. pyogenes, B. cereus, B. subtilis, Micrococcus sp., Klebsiella sp., P. aeruginosa, and Enterobacter sp. Also, clinical and soil isolates of P. aeruginosa were used in the study. Among the eight antibiotics tested for resistance on five strains of each bacterium, seven different resistance patterns were observed among the bacterial isolates obtained from water, effluent and orange juice products. Among the clinical and soil isolates of P. aeruginosa, four multiple-drug resistance patterns were obtained. Thirty strains of E. coli and S. aureus were tested for beta-lactamase production and fourteen strains, seven each of E. coli and S. aureus that had high Minimum Inhibitory Concentration values (MIC) for both Amoxycillin and Cloxacillin were positive.

Characteristics, epidemiology and clinical importance of emerging strains of Gram-negative bacilli producing extended-spectrum beta-lactamases

Beta-lactam antimicrobial agents represent the most common treatment for bacterial infections and continue to be the leading cause of resistance to beta-lactam antibiotics among Gram-negative bacteria worldwide. The persistent exposure of bacterial strains to a multitude of beta-lactams has induced dynamic and continuous production and mutation of beta-lactamases in these bacteria, expanding their activity even against the newly developed beta-lactam antibiotics. These enzymes are known as extended-spectrum beta-lactamases (ESBLs). The majority of ESBLs are derived from the widespread broad-spectrum beta-lactamases TEM-1 and SHV-1. There are also new families of ESBLs, including the CTX-M and OXA-type enzymes as well as novel unrelated beta-lactamases. In recent years, there has been an increased incidence and prevalence of ESBLs. ESBLs are mainly found in strains of Escherichia coli and Klebsiella pneumoniae but have also been reported in other Enterobacteriaceae strains and Pseudomonas aeruginosa. Infections with ESBL-producing bacterial strains are encountered singly or in outbreaks, especially in critical care units in hospitals, resulting in increasing cost of treatment and prolonged hospital stays. Not only may nursing home patients be an important reservoir of ESBL-containing multiple antibiotic-resistant organisms, but ambulatory patients with chronic conditions may also harbor ESBL-producing organisms.

Nosocomial bacteremia and urinary tract infections caused by extended-spectrum beta -lactamase-producing Klebsiella pneumoniae with plasmids carrying both SHV-5 and TLA-1 genes

We describe the prevalence and molecular characteristics of extended-spectrum beta -lactamase (ESBL)-producing Klebsiella pneumoniae causing nosocomial bacteremia and urinary tract infections in a Mexican general hospital. We analyzed 82 episodes of bacteremia (approximately 60% of episodes) and urinary tract infection (approximately 40% of episodes) due to K. pneumoniae during a 23-month surveillance period. The neonatal intensive care unit accounted for 49% of all episodes. All strains were imipenem susceptible; 62.2% of the strains were resistant to ceftazidime, cefotaxime, and aztreonam; 69.5% were resistant to amikacin; 58.5% were resistant to gentamicin; and 7.3% were resistant to ciprofloxacin. All strains were associated with 28 pulsed-field gel electrophoresis patterns, and dissemination of 2 ceftazidime-resistant clones produced 44% of the cases. The ESBL phenotype in these clones was transferred by identical or highly related megaplasmids. The ESBL activity corresponded to SHV-5 and TLA-1. Cross-transmission of 2 ceftazidime-resistant clones and the horizontal spread of identical or highly related megaplasmids explain the high prevalence of ESBL phenotype in these infections.

Clonal and horizontal dissemination of Klebsiella pneumoniae expressing SHV-5 extended-spectrum beta-lactamase in a Mexican pediatric hospital

One hundred eighty-four clinical isolates of Klebsiella pneumoniae were recovered from August 1996 to October 1997 at the Pediatric Hospital of the Instituto Mexicano del Seguro Social in Mexico City, Mexico. Most of the isolates were collected from the neonatal intensive care unit and infant wards, which are located on the same floor of the hospital. Isolates were genotypically compared by pulsed-field gel electrophoresis with XbaI restriction of chromosomal DNA. Of 184 clinical isolates, 91 belonged to cluster A and comprised three subtypes (A1, A2, and A3), while 93 isolates, comprising two minor clones, B (10 isolates) and C (7 isolates), and 76 unique patterns, were considered unrelated isolates (URI). Susceptibility patterns were indistinguishable in both groups. Fifty extended-spectrum beta-lactamase-producing isolates, including 34 from clone A and 16 from URI, were examined for further studies. Molecular and genetic analysis showed that 47 of 50 clinical isolates expressed the SHV-5 beta-lactamase. This enzyme, in combination with TEM-1, was encoded in a >or=170-kb conjugative plasmid. Results indicate that dissemination of this resistance was due to clonal and horizontal spread.

Molecular and biochemical characterization of Ambler class A extended-spectrum beta-lactamase CGA-1 from Chryseobacterium gleum

Antibiotic susceptibility testing by disk diffusion of a Chryseobacterium gleum isolate, strain CIP 103039, showed a typical synergy image between clavulanic acid and expanded-spectrum cephalosporins. Shotgun cloning gave a recombinant plasmid in Escherichia coli that produced a beta-lactamase, CGA-1, with a pI value of 8.9 that conferred resistance to most penicillins (except ureidopenicillins) and narrow-spectrum cephalosporins and an intermediate susceptibility to expanded-spectrum cephalosporins and aztreonam. The CGA-1 amino acid sequence shared only 60% amino acid identity with CME-1 and CME-2 from Chryseobacterium meningosepticum, the most closely related beta-lactamases. CGA-1 was very likely chromosome encoded. It is a novel member of the PER subgroup of Ambler class A beta-lactamases (Bush functional group 2be).