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[Resumo] A resistencia antibiótica, con Acinetobacter baumannii e Enterobacter cloacae complex (ECC) como microorganismos clave, constitúe unha das principais causas de morbimortalidade a nivel mundial. O estudo destas poboacións resulta esencial para desenvolver estratexias que mitiguen o impacto das infeccións na saúde pública. Nesta Tese Doutoral analízanse dúas coleccións multicéntricas nacionais de cepas clínicas, unha de Acinetobacter spp. e outra de ECC, co propósito de determinar a súa epidemioloxía, patróns e mecanismos de resistencia antibiótica, así como de explorar a actividade de novas alternativas terapéuticas. Deste xeito, cefiderocol posicionouse como o antibiótico máis activo contra A. baumannii, seguido pola colistina, a pesar do descenso significativo na eficacia desta na última década. Sublíñase tamén a problemática relacionada co ST2, con numerosos illamentos XDR, e cunha representación destacada da OXA-23, que evidencia un cambio paradigmático na epidemioloxía de A. baumannii resistente a carbapenémicos en España. Esta resistencia, mediada na súa maioría por carbapenemasas de clase D, queda aplacada polo inhibidor LN-1-255, o cal restaura o potencial de antibióticos como imipenem ou sulbactam. Doutra banda, nesta Tese caracterízase por primeira vez a diseminación plasmídica da carbapenemasa OXA-24/40 entre illamentos de Acinetobacter no-baumannii pertencentes á colección, así como a súa propagación internacional. Finalmente, en referencia a ECC, demostrouse a asociación de VIM-1 coa redución da sensibilidade ao cefiderocol, abordando aspectos microbiolóxicos, bioquímicos e moleculares. Ademais, destácase a influencia de factores adicionais na restrición da actividade desta cefalosporina de última xeración en ECC., [Resumen] La resistencia antibiótica, con Acinetobacter baumannii y Enterobacter cloacae complex (ECC) como microorganismos clave, constituye una causa importante de morbimortalidad a nivel global. El estudio de estas poblaciones es esencial para desarrollar estrategias que mitiguen el impacto de sus infecciones en la salud pública. En la presente Tesis Doctoral se analizan dos colecciones multicéntricas nacionales de cepas clínicas, una de Acinetobacter spp. y otra de ECC, con el propósito de determinar su epidemiología, sus patrones y mecanismos de resistencia antibiótica, así como de explorar la actividad de nuevas alternativas terapéuticas. En este sentido, cefiderocol se posiciona como el antibiótico más activo contra A. baumannii, seguido de colistina, a pesar de la disminución significativa en la eficacia de esta en la última década. Se subraya asimismo la problemática relacionada con el ST2, con numerosos aislados XDR, y una representación destacada de OXA-23, que evidencia un cambio paradigmático en la epidemiología de A. baumannii resistente a carbapenémicos en España. Esta resistencia, mediada en su mayoría por carbapenemasas de clase D, queda aplacada por el inhibidor LN-1-255, que recupera el potencial de compuestos como imipenem o sulbactam. Por otro lado, en esta Tesis se caracteriza por primera vez la diseminación plasmídica de la carbapenemasa OXA-24/40 entre aislados de Acinetobacter no-baumannii pertenecientes a la colección, así como su propagación internacional. Finalmente, en referencia a ECC, se demuestra la asociación de VIM-1 con la reducción de la sensibilidad a cefiderocol, abordando aspectos microbiológicos, bioquímicos y moleculares. Además, se destaca la influencia de factores adicionales en la restricción de la actividad de esta cefalosporina de última generación en ECC., [Abstract] Antibiotic resistance, involving Acinetobacter baumannii and the Enterobacter cloacae complex (ECC) as pivotal microorganisms, significantly contributes to global morbimortality. Studying these populations is crucial for developing effective strategies to lessen the impact of the resulting infections on public health. In this Doctoral Thesis two multicentric national collections of clinical strains, one comprising Acinetobacter spp. and the other ECC isolates, are examined to discern their epidemiology, resistance patterns and mechanisms, and to ultimately explore the activity of new therapeutic alternatives. Cefiderocol emerges as the most potent antibiotic against A. baumannii, followed by colistin, despite its notable decrease in efficacy over the past decade. Attention is drawn to the issue of ST2, characterized by numerous XDR isolates and a notable representation of OXA-23, signaling a paradigm shift in carbapenem-resistant A. baumannii epidemiology in Spain. This resistance, largely mediated by class D carbapenemases, is mitigated by the LN-1-255 inhibitor, restoring the potential of compounds like imipenem or sulbactam. On another note, in this Thesis, plasmid-mediated dissemination of the carbapenemase OXA-24/40 among isolates of Acinetobacter non-baumannii belonging to the collection is characterized for the first time, highlighting its international spread. Concerning ECC, the association of VIM-1 with diminished susceptibility to cefiderocol is demonstrated, addressing microbiological, biochemical, and molecular factors. Furthermore, emphasis is placed on the influence of additional factors restricting the activity of this latest generation cephalosporin in ECC.

[Abstract]: Background: As increasing antibiotic resistance in Acinetobacter baumannii poses a global healthcare challenge, understanding its evolution is crucial for effective control strategies. Aim: We aimed to evaluate the epidemiology, antimicrobial susceptibility and main resistance mechanisms of Acinetobacter spp. in Spain in 2020, and to explore temporal trends of A. baumannii. Methods: We collected 199 single-patient Acinetobacter spp. clinical isolates in 2020 from 18 Spanish tertiary hospitals. Minimum inhibitory concentrations (MICs) for nine antimicrobials were determined. Short-read sequencing was performed for all isolates, and targeted long-read sequencing for A. baumannii. Resistance mechanisms, phylogenetics and clonality were assessed. Findings on resistance rates and infection types were compared with data from 2000 and 2010. Results: Cefiderocol and colistin exhibited the highest activity against A. baumannii, although colistin susceptibility has significantly declined over 2 decades. A. non-baumannii strains were highly susceptible to most tested antibiotics. Of the A. baumannii isolates, 47.5% (56/118) were multidrug-resistant (MDR). Phylogeny and clonal relationship analysis of A. baumannii revealed five prevalent international clones, notably IC2 (ST2, n = 52; ST745, n = 4) and IC1 (ST1, n = 14), and some episodes of clonal dissemination. Genes blaOXA-23, blaOXA-58 and blaOXA-24/40 were identified in 49 (41.5%), eight (6.8%) and one (0.8%) A. baumannii isolates, respectively. ISAba1 was found upstream of the gene (a blaOXA-51-like) in 10 isolates. Conclusions: The emergence of OXA-23-producing ST1 and ST2, the predominant MDR lineages, shows a pivotal shift in carbapenem-resistant A. baumannii (CRAB) epidemiology in Spain. Coupled with increased colistin resistance, these changes underscore notable alterations in regional antimicrobial resistance dynamics.

[Abstract] Carbapenem resistance is increasing among Gram-negative bacteria, including the genus Acinetobacter. This study aimed to characterize, for the first time, the development of carbapenem resistance in clinical isolates of Acinetobacter junii and Acinetobacter nosocomialis conferred by the acquisition of a plasmid-borne blaOXA-24/40 gene and also to characterize the dissemination of this gene between species of Acinetobacter. Carbapenem-resistant A. nosocomialis HUAV-AN66 and A. junii HUAV-AJ77 strains were isolated in the Arnau de Vilanova Hospital (Spain). The genomes were sequenced, and in silico analysis were performed to characterize the genetic environment and the OXA-24/40 transmission mechanism. Antibiotic MICs were determined, and horizontal transfer assays were conducted to evaluate interspecies transmission of OXA-24/40. Carbapenems MICs obtained were ≥64 mg/L for HUAV-AN66 and HUAV-AJ77. Genome analysis revealed the presence in both strains of a new plasmid, designated pHUAV/OXA-24/40, harboring the carbapenem-resistance gene blaOXA-24/40 and flanked by sequences XerC/XerD. pHUAV/OXA-24/40 was successfully transferred from A. nosocomialis and A. junii to a carbapenem-susceptible A. baumannii strain, thus conferring carbapenem resistance. A second plasmid (pHUAV/AMG-R) was identified in both clinical isolates for the successful horizontal transfer of pHUAV/OXA-24/40. blaOXA-24/40-carrying plasmids of the GR12 group and showing high identity with pHUAV/OXA-24/40 were identified in at least 8 Acinetobacter species. In conclusion the carbapenemase OXA-24/40 is described for the first time in A. nosocomialis and A. junii. In both isolates the blaOXA-24/40 gene was located in the GR12 pHUAV/OXA-24/40 plasmid. GR12 plasmids are implicated in the dissemination and spread of carbapenem resistance among Acinetobacter species. IMPORTANCE Acinetobacter baumannii is one of the most relevant pathogens in terms of antibiotic resistance. The main resistance mech

[Resumen] La aparición y propagación de resistencias frente a los agentes antimicrobianos se ha visto acelerada en los últimos años, provocando una crisis sanitaria a nivel mundial y poniendo de manifiesto la necesidad urgente de desarrollar nuevos fármacos más efectivos. Una de las tendencias actuales para enfrentarse a las bacterias patógenas multirresistentes se basa en el uso de estrategias tipo “caballo de Troya”, que emplean portadores moleculares reconocidos por receptores específicos para facilitar la penetración en las células y limitar, en algunos casos, la aparición de resistencias. En el presente trabajo se llevó a cabo la evaluación biológica de un conjugado sideróforo-antibiótico con el que se pretende aprovechar el mecanismo de captación de hierro mediado por sideróforos para promover la absorción activa de un antibiótico. Para su construcción, el vector de entrada seleccionado fue un análogo de las amonabactinas, un sideróforo de la bacteria patógena Aeromonas salmonicida subsp. salmonicida, y como antibiótico se empleó ampicilina. Se determinó la concentración mínima inhibitoria tanto del conjugado sideróforo-antibiótico como del fragmento espaciador-ampcilina (sin vector de entrada), y se compararon con la ampicilina libre. Los resultados parecen indicar la presencia de un mecanismo mediado por el análogo de las amonabactinas que facilita la entrada del conjugado mejorando su actividad respecto a la esperada para su peso molecular. Además, se inhibe el crecimiento bacteriano con el fragmento espaciador-ampicilina, lo que demuestra que el espaciador no impide la unión de la ampicilina a su diana celular., [Abstract] The emergence and spread of resistance to antimicrobial agents has accelerated in recent years, causing a global health crisis and highlighting the urgent need to develop new more effective drugs. One of the current trends in dealing with multidrug-resistant pathogenic bacteria is based on the use of “Trojan horse” strategies, which employ molecular carriers recognized by specific receptors to facilitate cell penetration and limit, in some cases, the emergence of resistance. In the present work, the biological evaluation of a siderophore-antibiotic conjugate was carried out to exploit the iron uptake mechanism mediated by siderophores to promote the active absorption of an antibiotic. For its construction, the selected input vector was an analog of amonabactins, siderophores from the pathogenic bacterium Aeromonas salmonicida subsp. salmonicida, and ampicillin was used as the antibiotic. The minimum inhibitory concentration of both the siderophore-antibiotic conjugate and the linker-ampillin fragment (without input vector) were determined and compared to that of free ampicillin. The results seem to indicate the presence of a mechanism mediated by the amonabactin analog that facilitates the entry of the conjugate, improving its activity with respect to that expected for its molecular weight. In addition, bacterial growth is inhibited by the linker-ampicillin fragment, demonstrating that the linker does not prevent the binding of ampicillin to its cell target.

[Abstract] The discovery of new antibiotics that are effective against Acinetobacter baumannii and Enterobacteralesis a research priority. Several essential oils (EOs) have displayed some antimicrobial activity and could potentially act as antibiotic adjuvants. Research in this area aims to develop new therapeutic alternatives to treat infections caused by these pathogens. MICs of different EOs were determined against A. baumannii and Klebsiella pneumoniae. Combined disk diffusion tests and checkerboard assays were used to study the synergy between the EOs and antibiotics. The fractional inhibitory concentration index (FICindex) was calculated in order to categorize the interaction. Time-kill assays were also performed. The EOs that displayed the highest levels of antimicrobial activity were clove (Syzygium aromaticum L.) and thyme (Thymus zygis L.). Combined disk diffusion tests and checkerboard assays revealed synergy between these EOs and colistin. Addition of either clove or thyme EO decreased the MIC of colistin by 8- to 64-fold and 8- to 128-fold in the colistin-resistant A. baumannii and K. pneumoniae strains, respectively (FICindex ≤ 0.5, synergy). MICs were also reduced in the colistin-susceptible strains. Time-kill assays also indicated the strong activity of the combined therapy. In summary, the use of clove or thyme EO in combination with colistin could improve the efficacy of the antibiotic and significantly reduce the concentrations needed to inhibit growth of A. baumannii and K. pneumoniae.

[Abstract] A total of 51 sponges (Porifera) and 13 ascidians (Chordata) were collected on the coast of the Yucatan Peninsula (Mexico) and extracted with organic solvents. The resulting extracts were screened for antibacterial activity against four multidrug-resistant (MDR) bacterial pathogens: the Gram-negative Acinetobacter baumannii, Klebsiella pneumoniae, and Pseudomonas aeruginosa and the Gram-positive Staphylococcus aureus. The minimum inhibitory concentrations (MICs) of the organic extracts of each marine organism were determined using a broth microdilution assay. Extracts of eight of the species, in particular the Agelas citrina and Haliclona (Rhizoniera) curacaoensis, displayed activity against some of the pathogens tested. Some of the extracts showed similar MIC values to known antibiotics such as penicillins and aminoglycosides. This study is the first to carry out antimicrobial screening of extracts of marine sponges and ascidians collected from the Yucatan Peninsula. Bioassay-guided fractionation of the active extracts from the sponges Amphimedon compressa and A. citrina displayed, as a preliminary result, that an inseparable mixture of halitoxins and amphitoxins and (-)-agelasine B, respectively, are the major compounds responsible for their corresponding antibacterial activities. This is the first report of the antimicrobial activity of halitoxins and amphitoxins against major multidrug-resistant human pathogens. The promising antibacterial activities detected in this study indicate the coast of Yucatan Peninsula as a potential source of a great variety of marine organisms worthy of further research.

[Abstract] The pyrrole-imidazoles, a group of alkaloids commonly found in marine sponges belonging to the genus Agelas, display a wide range of biological activities. Herein, we report the first chemical study of the secondary metabolites of the sponge A. dilatata from the coastal area of the Yucatan Peninsula (Mexico). In this study, we isolated eight known alkaloids from an organic extract of the sponge. We used NMR and MS analysis and comparison with existing databases to characterize the alkaloids: ageliferin (1), bromoageliferin (2), dibromoageliferin (3), sceptrin (4), nakamuric acid (5), 4-bromo-1H-pyrrole-2-carboxylic acid (6), 4,5-dibromopyrrole-2-carboxylic acid (7) and 3,7-dimethylisoguanine (8). We also evaluated, for the first time, the activity of these alkaloids against the most problematic multidrug-resistant (MDR) pathogens, i.e., the Gram-negative bacteria Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Bromoageliferin (2) displayed significant activity against P. aeruginosa. Comparison of the antibacterial activity of ageliferins 1–3 (of similar structure) against P. aeruginosa revealed some relationship between structure and activity. Furthermore, in in vitro assays, 2 inhibited growth and biofilm production in clinical strains of P. aeruginosa. Moreover, 2 increased the survival time in an in vivo Galleria mellonella model of infection. The findings confirm bromoageliferin (2) as a potential lead for designing new antibacterial drugs.