Crystal structure of the class A extended-spectrum ß-lactamase CTX-M-96 in complex with relebactam at 1.03 Angstrom resolution.

The use of ß-lactam/ß-lactamase inhibitors constitutes an important strategy to counteract ß-lactamases in multidrug-resistant (MDR) Gram-negative bacteria. Recent reports have described ceftazidime-/avibactam-resistant isolates producing CTX-M variants with different amino acid substitutions (e.g., P167S, L169Q, and S130G). Relebactam (REL) combined with imipenem has proved very effective against Enterobacterales producing ESBLs, serine-carbapenemases, and AmpCs. Herein, we evaluated the inhibitory efficacy of REL against CTX-M-96, a CTX-M-15-type variant. The CTX-M-96 structure was obtained in complex with REL at 1.03 Å resolution (PDB 8EHH). REL was covalently bound to the S70-Oγ atom upon cleavage of the C7-N6 bond. Compared with apo CTX-M-96, binding of REL forces a slight displacement of the deacylating water inwards the active site (0.81 Å), making the E166 and N170 side chains shift to create a proper hydrogen bonding network. Binding of REL also disturbs the hydrophobic patch formed by Y105, P107, and Y129, likely due to the piperidine ring of REL that creates clashes with these residues. Also, a remarkable change in the positioning of the N104 sidechain is also affected by the piperidine ring. Therefore, differences in the kinetic behavior of REL against class A ß-lactamases seem to rely, at least in part, on differences in the residues being involved in the association and stabilization of the inhibitor before hydrolysis. Our data provide the biochemical and structural basis for REL effectiveness against CTX-M-producing Gram-negative pathogens and essential details for further DBO design. Imipenem/REL remains an important choice for dealing with isolates co-producing CTX-M with other ß-lactamases.

Boronic Acid Transition State Inhibitors as Potent Inactivators of KPC and CTX-M ß-Lactamases: Biochemical and Structural Analyses.

Design of novel ß-lactamase inhibitors (BLIs) is one of the currently accepted strategies to combat the threat of cephalosporin and carbapenem resistance in Gram-negative bacteria. Boronic acid transition state inhibitors (BATSIs) are competitive, reversible BLIs that offer promise as novel therapeutic agents. In this study, the activities of two α-amido-ß-triazolylethaneboronic acid transition state inhibitors (S02030 and MB_076) targeting representative KPC (KPC-2) and CTX-M (CTX-M-96, a CTX-M-15-type extended-spectrum ß-lactamase [ESBL]) ß-lactamases were evaluated. The 50% inhibitory concentrations (IC50s) for both inhibitors were measured in the nanomolar range (2 to 135 nM). For S02030, the k2/K for CTX-M-96 (24,000 M-1 s-1) was twice the reported value for KPC-2 (12,000 M-1 s-1); for MB_076, the k2/K values ranged from 1,200 M-1 s-1 (KPC-2) to 3,900 M-1 s-1 (CTX-M-96). Crystal structures of KPC-2 with MB_076 (1.38-Å resolution) and S02030 and the in silico models of CTX-M-96 with these two BATSIs show that interaction in the CTX-M-96-S02030 and CTX-M-96-MB_076 complexes were overall equivalent to that observed for the crystallographic structure of KPC-2-S02030 and KPC-2-MB_076. The tetrahedral interaction surrounding the boron atom from S02030 and MB_076 creates a favorable hydrogen bonding network with S70, S130, N132, N170, and S237. However, the changes from W105 in KPC-2 to Y105 in CTX-M-96 and the missing residue R220 in CTX-M-96 alter the arrangement of the inhibitors in the active site of CTX-M-96, partially explaining the difference in kinetic parameters. The novel BATSI scaffolds studied here advance our understanding of structure-activity relationships (SARs) and illustrate the importance of new approaches to ß-lactamase inhibitor design.

Redefining the Origin and Evolution of Chromosomally Encoded blaCTX-M/KLU in the Context of a Revised Taxonomy of Genus Kluyvera.

Changes in Kluyvera taxonomy may clarify each species contribution for recruitment and dissemination of their relevant ß-lactamases. The CTX-M-2 subgroup is linked to Kluyvera ascorbata, KLUC to Kluyvera cryocrescens, and CTX-M-25 to Kluyvera georgiana. The CTX-M-8 subgroup can be linked to Kluyvera genomospecies 3 and CTX-M-9 to Kluyvera genomospecies 2. Kluyvera sichuanensis and Kluyvera genomospecies 1 harbor new subgroups. The CTX-M-1 subgroup has a direct counterpart in an isolate proposed as a new genomospecies 5.

Structural and Biochemical Characterization of the Novel CTX-M-151 Extended-Spectrum ß-Lactamase and Its Inhibition by Avibactam.

The diazabicyclooctane (DBO) inhibitor avibactam (AVI) reversibly inactivates most serine ß-lactamases, including the CTX-M ß-lactamases. Currently, more than 230 unique CTX-M members distributed in five clusters with less than 5% amino acid sequence divergence within each group have been described. Recently, a variant named CTX-M-151 was isolated from a Salmonella enterica subsp. enterica serovar Choleraesuis strain in Japan. This variant possesses a low degree of amino acid identity with the other CTX-Ms (63.2% to 69.7% with respect to the mature proteins), and thus it may represent a new subgroup within the family. CTX-M-151 hydrolyzes ceftriaxone better than ceftazidime (kcat/Km values 6,000-fold higher), as observed with CTX-Ms. CTX-M-151 is well inhibited by mechanism-based inhibitors like clavulanic acid (inactivation rate [kinact]/inhibition constant [Ki ] = 0.15 µM-1 · s-1). For AVI, the apparent inhibition constant (Kiapp), 0.4 µM, was comparable to that of KPC-2; the acylation rate (k2/K) (37,000 M-1 · s-1) was lower than that for CTX-M-15, while the deacylation rate (koff) (0.0015 s-1) was 2- to 14-fold higher than those of other class A ß-lactamases. The structure of the CTX-M-151/AVI complex (1.32 Å) reveals that AVI adopts a chair conformation with hydrogen bonds between the AVI carbamate and Ser70 and Ser237 at the oxyanion hole. Upon acylation, the side chain of Lys73 points toward Ser130, which is associated with the protonation of Glu166, supporting the role of Lys73 in the proton relay pathway and Glu166 as the general base in deacylation. To our knowledge, this is the first chromosomally encoded CTX-M in Salmonella Choleraesuis that shows similar hydrolytic preference toward cefotaxime (CTX) and ceftriaxone (CRO) to that toward ceftazidime (CAZ).

Proposing Kluyvera georgiana as the Origin of the Plasmid-Mediated Resistance Gene fosA4.

A putative fosA gene in Kluyvera georgiana 14751 showed 99% nucleotide identity with plasmid-encoded fosA4 Due to a single-nucleotide insertion translating to a truncated protein, K. georgiana 14751 fosA does not confer fosfomycin resistance. However, analysis of another genome deposit (Kluyvera ascorbata WCH1410) that could be recategorized as K. georgiana after phylogenetic analysis revealed a fosA gene 100% identical to the plasmid-borne fosA4 gene. We suggest that Kluyvera georgiana represents the most probable origin of fosA4.

Defining Substrate Specificity in the CTX-M Family: the Role of Asp240 in Ceftazidime Hydrolysis.

The natural diversification of CTX-M ß-lactamases led to the emergence of Asp240Gly variants in the clinic that confer reduced susceptibility to ceftazidime (CAZ). In this study, we compared the impact of this substitution on CAZ and ceftazidime-avibactam (CZA) MICs against isogenic Escherichia coli strains with different porin deficiencies. Our results show a noticeable increase in CAZ resistance in clones expressing Asp240Gly-harboring CTX-M when combined with OmpF porin deficiency. Kinetic analysis revealed that the kcat/Km for CAZ was 5- to 15-fold higher for all Asp240Gly variants but remained 200- to 725-fold lower than that for cefotaxime (CTX). In vitro selection of CAZ-resistant clones yielded nonsusceptible CTX-M producers (MIC of >16 µg/ml) only after overnight incubation; the addition of avibactam (AVI) decreased MICs to a susceptible range against these variants. In contrast, the use of CZA as a selective agent did not yield resistant clones. AVI inactivated both CTX-M-12 and CTX-M-96, with an apparent inhibition constant comparable to that of SHV-2 and 1,000-fold greater than that of PER-2 and CMY-2, and k2/K for CTX-M-12 was 24- and 35-fold higher than that for CTX-M-96 and CTX-M-15, respectively. Molecular modeling suggests that AVI interacts similarly with CTX-M-96 and CTX-M-15. We conclude that the impact of Asp240Gly in resistance may arise when other mechanisms are also present (i.e., OmpF deficiency). Additionally, CAZ selection could favor the emergence of CAZ-resistant subpopulations. These results define the role of Asp240 and the impact of the -Gly substitution and allow us to hypothesize that the use of CZA is an effective preventive strategy to delay the development of resistance in this family of extended-spectrum ß-lactamases.

Structural and Kinetic Insights into the "Ceftazidimase" Behavior of the Extended-Spectrum ß-Lactamase CTX-M-96.

Diversification of the CTX-M ß-lactamases led to the emergence of variants responsible for decreased susceptibility to ceftazidime, like the Asp240Gly-harboring "ceftazidimases". We solved the crystallographic structure of the Asp240Gly variant CTX-M-96 at 1.2 Å and evaluated the role of Asp240 in the activity toward oxyimino-cephalosporins through simulated models and kinetics. There seem to be subtle changes in the conformation of the active site cavity of CTX-M-96, compared to enzyme variants harboring the Asp240, and these small rearrangements could be due to localized shifts in the environment of the ß3 strand. According to the crystallographic evidence, CTX-M-96 presents a "compact" active site, which in spite of its reduced cavity seems to allow the proper interaction with oxyimino-cephalosporins, as suggested by simulated models. The term "ceftazidimases" that is currently applied for the Asp240Gly-harboring CTX-M variants should be used carefully. Structural differences between CTX-M harboring the Asp240Gly mutation (and also probably others like those at Pro167) do not seem to be conclusive to determine the "ceftazidimase" behavior observed in vivo, which is in turn partially supported by the mild improvement in the catalytic efficiency toward ceftazidime by CTX-M-96 and similar enzymes, compared to "parental" Asp240-harboring variants. In addition, it is observed that alterations in OmpF expression could act synergistically with CTX-M-96 for yielding clinical resistance toward ceftazidime. We therefore propose that the observed resistance in vivo is due to the sum of synergic mechanisms, and the term "cefotaximases associated with ceftazidime resistance" could be conveniently used to describe CTX-M harboring the Asp240Gly substitution.

Characterisation of KLUA-9, a beta-lactamase from extended-spectrum cephalosporin-susceptible Kluyvera ascorbata, and genetic organisation of bla(KLUA-9).

This study characterised the genetic environment of the chromosomally encoded bla(KLUA-9) gene from a clinical Kluyvera ascorbata isolate and performed a kinetic characterisation of KLUA-9. Purified KLUA-9 showed the highest catalytic efficacies towards benzylpenicillin, ampicillin, piperacillin, first-generation cephalosporins, cefuroxime and cefoperazone; like other 'cefotaximases', it showed a much higher rate of hydrolysis of cefotaxime than ceftazidime, whilst dicloxacillin, cefoxitin and imipenem behaved as poor substrates. A 9kb insert from K. ascorbata was cloned (Escherichia coli KK68C1) and sequenced. bla(KLUA-9) and its 266bp upstream flanking region (almost identical to the integron-associated bla(CTX-M-2)) are preceded by an aspat variant, a ypdABC-like operon and two open reading frames with unknown functions. Unlike ISCR1-associated bla(CTX-M-2) genes, we failed to detect the putative orf513 recombination sites. Instead, we were able to localise the 5bp target sites for insertion of ISEcp1B, suggesting that this element could be responsible for future (or still undetected) mobilisation of bla(KLUA-9) to more efficiently transferred elements.

Crystal structure and kinetic analysis of the class B3 di-zinc metallo-ß-lactamase LRA-12 from an Alaskan soil metagenome.

We analyzed the kinetic properties of the metagenomic class B3 ß-lactamase LRA-12, and determined its crystallographic structure in order to compare it with prevalent metallo-ß-lactamases (MBLs) associated with clinical pathogens. We showed that LRA-12 confers extended-spectrum resistance on E. coli when expressed from recombinant clones, and the MIC values for carbapenems were similar to those observed in enterobacteria expressing plasmid-borne MBLs such as VIM, IMP or NDM. This was in agreement with the strong carbapenemase activity displayed by LRA-12, similar to GOB ß-lactamases. Among the chelating agents evaluated, dipicolinic acid inhibited the enzyme more strongly than EDTA, which required pre-incubation with the enzyme to achieve measurable inhibition. Structurally, LRA-12 contains the conserved main structural features of di-zinc class B ß-lactamases, and presents unique structural signatures that differentiate this enzyme from others within the family: (i) two loops (α3-ß7 and ß11-α5) that could influence antibiotic entrance and remodeling of the active site cavity; (ii) a voluminous catalytic cavity probably responsible for the high hydrolytic efficiency of the enzyme; (iii) the absence of disulfide bridges; (iv) a unique Gln116 at metal-binding site 1; (v) a methionine residue at position 221that replaces Cys/Ser found in other B3 ß-lactamases in a predominantly hydrophobic environment, likely playing a role in protein stability. The structure of LRA-12 indicates that MBLs exist in wild microbial populations in extreme environments, or environments with low anthropic impact, and under the appropriate antibiotic selective pressure could be captured and disseminated to pathogens.

Detection of blaCTX-M-type genes in complex class 1 integrons carried by Enterobacteriaceae isolated from retail chicken meat in Brazil.

CTX-M-type extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae have been increasingly identified in humans and animals, and their potential transmission by contaminated food has been highlighted. In this study, we report for the first time the isolation of multidrug-resistant (MDR) Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis strains harboring blaCTXM-2 or blaCTXM-8 gene variants in chicken meat sold in markets in southeast Brazil. In this regard, the genetic environment of the blaCTX-M-2 gene is composed of a complex class 1 integron and an ISCR1-associated sequence with dfr and/or aadA gene cassettes located within the variable region. In summary, chicken meat may be a reservoir of MDR Enterobacteriaceae harboring blaCTX-M-type genes, which is a public health concern.

La preparación del docente para el desarrollo de la cultura analcohólica / The non-alcoholic culture: a challenge in the teaching overcoming

Fundamento: La cultura analcohólica en la educación de jóvenes y adultos se debe proyectar desde un enfoque interdisciplinario. Objetivo: Proponer procedimientos teórico-metodológicos, actitudinales y de actuación pedagógica para el tratamiento del contenido de la cultura analcohólica con enfoque interdisciplinario. Metodología: Se seleccionó una muestra de 21 docentes de la educación de jóvenes y adultos y se emplearon métodos del nivel teórico, empírico y estadísticos y/o procedimientos matemáticos. Resultados: Se logró la apropiación activa y creadora de los docentes para el tratamiento del contenido de la cultura analcohólica con enfoque interdisciplinario, lo cual propicia el desarrollo de su autoperfeccionamiento constante, su autonomía y autodeterminación, en estrecha relación con los procesos de socialización, compromiso y responsabilidad social a favor del desarrollo de estilos de vida saludables como parte de la cultura general integral. Se obtuvieron resultados satisfactorios ya que los docentes se apropiaron de conocimientos y actitudes, evidenciado en su actuación pedagógica y en el establecimiento de relaciones interdisciplinarias entre las asignaturas del currículo para contribuir al desarrollo de estilos de vida saludables Conclusiones: El promover una cultura analcohólica constituye una alternativa para desde una concepción interdisciplinar el docente pueda emprender tan importante tarea, como portador de la política del estado y promotor de salud.

Background: The non-alcoholic culture in the adults and youngsters education must be projected from an interdisciplinary approach. Objective: To propose theoretical-methodological, attitudinal procedures in the pedagogical performances for the treatment of contents of the non-alcoholic culture with an interdisciplinary approach. Methodology: A sample of 21 professors of the education of youngsters and adults and different methods from the theoretical, empirical and statistical and/or mathematical levels were. Results: The active and creative appropriation of professors was obtained in the treatment of non-alcoholic culture with an interdisciplinary approach which propitiates the development of the constant self-improvement, its autonomy and self-determination in close relation with the processes of socialization, commitment and social responsibility in favor of the development of healthy life styles as part of the general comprehensive culture. Good results were obtained for the professors grabbed the knowledge and attitudes evident in the pedagogical performance and in the establishment of interdisciplinary relations among the subjects of the curriculum to contribute to the development of healthy life styles. Conclusion: The advance of a non-alcoholic culture constitutes an alternative from an interdisciplinary trend for professors to learn about this important task as a carrier of this state policy and health promoter.

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).

Chromosome-encoded CTX-M-3 from Kluyvera ascorbata: a possible origin of plasmid-borne CTX-M-1-derived cefotaximases.

A gene identical to plasmid-borne bla(CTX-M-3) is present in the chromosome of one Kluyvera ascorbata strain. It is associated with a structure including an inverted repeat right and an open reading frame 477-like gene probably involved in the mobilization of bla(CTX-M-3). Two other K. ascorbata strains rendered the previously described bla(KLUA-9) gene.