Novel Antibacterial and Biocompatible Nanostructured Gels Based on One-step Synthesis as a Potential Disinfectant for Endodontic Infection Control.

AIM: The objective of this study was to develop nanostructured gels as biocompatible intracanal disinfectants by one-step microwave radiation-assisted synthesis. METHODS: Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) were used as a support network, and polyethylene glycol (PEG) was used as a reducing agent. The gels were characterized by measuring the swelling ratio (SR) and rheological properties and by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The antibacterial effects of each gel were evaluated against the endodontic clinical strain Enterococcus faecalis. Then, the viability of the 21-day mature multispecies bacterial biofilm was assessed using confocal microscopy in an ex vivo model, where the biofilm was exposed to the mix of nanogels. The cell proliferation, viability, and morphology of human periodontal ligament (HPDL) cells were quantified using a real-time IncuCyte® S3 Live-Cell System. Viability was measured by confocal microscopy using an ex vivo model exposing a 21-day mature multispecies bacterial biofilm to the mix of nanogels. RESULTS: The antibacterial activity of the gels coincided with the superficial characterization and the solubility of the gel in the growth medium. Gels with higher viscosity (327.85-980.58 Pa s), higher dissolution (42-70%SR), and lower porosity (no porosity and 611.63 nm) showed excellent antibacterial activity against E. faecalis. Despite their physicochemical characteristics, CuNPs gels showed greater effectiveness against E. faecalis.These nanostructured gels with high PVA concentrations promote HPDL cells proliferation while still exerting antibacterial properties. Mix of nanogels showed an increase non-viable cells biomass from at of application. CONCLUSIONS: The use of biocompatible polymers influences the physicochemical, bactericidal, and cytotoxic response, making these materials potential disinfectant agents against resistant bacteria with good biocompatibility and improved HPDL cells proliferation.

Phenotypic and genotypic antimicrobial resistance in Escherichia coli strains isolated from household dogs in Chile.

Introduction: Antimicrobial resistance (AMR) is a major threat to animal and public health worldwide; consequently, several AMR surveillances programs have been implemented internationally in both human and veterinary medicine, including indicator bacteria such as Escherichia coli. However, companion animals are not typically included in these surveillance programs. Nevertheless, there have been reports of increasing levels of antimicrobial resistance in E. coli strains isolated from dogs worldwide. In Chile, there is limited information available on AMR in E. coli isolated from companion animals, which prevents the establishment of objective prevention and control measures. Methods: For this reason, the aim of this study was to characterize the phenotypic and genotypic AMR of E. coli strains isolated from healthy household dogs in Chile. For this purpose, a multi-stage sampling was carried out in the Metropolitan Region of Chile, obtaining samples from 600 healthy dogs. These samples were processed using traditional bacteriology and molecular techniques to isolate E. coli strains. We assessed the minimal inhibitory concentration of 17 antimicrobials and conducted a search of six antimicrobial resistance genes, as well as class 1 and 2 integrons, in the isolated strains. Results: Two-hundred and twenty-four strains of E. coli were recovered, and 96.9% (n = 217) showed resistance to at least one drug and only 3.1% (n = 7) were susceptible to all analyzed antimicrobials. Most strains were resistant to cefalexin (91.5%, n = 205, 1st-generation cephalosporin), followed by ampicillin (68.3%, n = 153) and cefpodoxime (31.3%, n = 70, 3rd-generation cephalosporin). Moreover, 24.1% (n = 54) tested positive for extended-spectrum-ß-lactamases and 34.4% (n = 77) were multidrug resistant. As for the AMR genes, the most detected was qnrB (28.1%, n = 63), followed by blaCTX-M (22.3%, n = 50), and blaTEM-1 (19.6%, n = 44). Additionally, 16.1% (n = 36) harbored class 1 integrons. Our study shows that E. coli strains isolated from healthy household dogs exhibit resistance to several relevant drugs and also antimicrobial resistance genes considered critical for human health. These results can be used as a starting point for the prevention and control of antimicrobial resistance from companion animals. This background should be considered when formulating future resistance surveillance programs or control plans in which companion animals must be included.

Molecular Characterization of the Convergent Carbapenem-Resistant and Hypervirulent Klebsiella pneumoniae Strain K1-ST23, Collected in Chile during the COVID-19 Pandemic.

The aim of this study was to investigate the genomic features of a carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) isolate (K-2157) collected in Chile. Antibiotic susceptibility was determined using the disk diffusion and broth microdilution methods. Whole-genome sequencing (WGS) and hybrid assembly were performed, using data generated on the Illumina and Nanopore platforms. The mucoid phenotype was analyzed using both the string test and sedimentation profile. The genomic features of K-2157 (e.g., sequence type, K locus, and mobile genetic elements) were retrieved using different bioinformatic tools. Strain K-2157 exhibited resistance to carbapenems and was identified as a high-risk virulent clone belonging to capsular serotype K1 and sequence type 23 (ST23). Strikingly, K-2157 displayed a resistome composed of ß-lactam resistance genes (blaSHV-190, blaTEM-1, blaOXA-9, and blaKPC-2), the fosfomycin resistance gene fosA, and the fluoroquinolones resistance genes oqxA and oqxB. Moreover, several genes involved in siderophore biosynthesis (ybt, iro, and iuc), bacteriocins (clb), and capsule hyperproduction (plasmid-borne rmpA [prmpA] and prmpA2) were found, which is congruent with the positive string test displayed by K-2157. In addition, K-2157 harbored two plasmids: one of 113,644 bp (KPC+) and another of 230,602 bp, containing virulence genes, in addition to an integrative and conjugative element (ICE) embedded on its chromosome, revealing that the presence of these mobile genetic elements mediates the convergence between virulence and antibiotic resistance. Our report is the first genomic characterization of a hypervirulent and highly resistant K. pneumoniae isolate in Chile, which was collected during the coronavirus disease 2019 (COVID-19) pandemic. Due to their global dissemination and public health impact, genomic surveillance of the spread of convergent high-risk K1-ST23 K. pneumoniae clones should be highly prioritized. IMPORTANCE Klebsiella pneumoniae is a resistant pathogen involved primarily in hospital-acquired infections. This pathogen is characterized by its notorious resistance to last-line antibiotics, such as carbapenems. Moreover, hypervirulent K. pneumoniae (hvKp) isolates, first identified in Southeast Asia, have emerged globally and are able to cause infections in healthy people. Alarmingly, isolates displaying a convergence phenotype of carbapenem resistance and hypervirulence have been detected in several countries, representing a serious threat to public health. In this work, we analyzed the genomic characteristics of a carbapenem-resistant hvKp isolate recovered in 2022 from a patient with COVID-19 in Chile, representing the first analysis of this type in the country. Our results will provide a baseline for the study of these isolates in Chile, which will support the adoption of local measures aimed at controlling their dissemination.

Anthropogenic degradation alter surface soil biogeochemical pools and microbial communities in an Andean temperate forest.

Soil microbial communities regulate a myriad of critical biogeochemical functions in forest ecosystems. Anthropogenic disturbances in natural forests could drive major shifts in plant and microbial communities resulting in substantial biogeochemical alterations. We evaluated the effect of anthropogenic disturbances in the soils of Andean temperate forests with different levels of degradation: i) mature forest (MF), ii) secondary forest (SF), iii) degraded forest (DF), and iv) deforested site converted into a prairie (DP). We quantified total soil carbon, nitrogen and phosphorous (TC, TN, and TP), and available nutrient stocks. The soil microbial community structure (i.e., composition, diversity, and abundance) was assessed under each condition from amplicon sequence variants (ASVs) obtained via NGS-Illumina sequencing and subsequent microbiome analysis. There were no significant differences in TC, TN, and TP across the forested states (MF, SF, DF). The deforested site condition presented significantly higher soil TC, TN, and TP and the lowest C:N, C:P, and N:P ratios. The DP soil microbiome was significantly more diverse in bacteria (D' = 0.47 ± 0.04); and fungi (H' = 5.11 ± 0.33). The bacterial microbiome was dominated by Proteobacteria (45.35 ± 0.89 %), Acidobacteria (20.73 ± 1.48 %), Actinobacteria (12.59 ± 0.34 %), and Bacteroidetes (7.32 ± 0.36 %) phyla in all sites. The soil fungal community was dominated by the phyla Ascomycota (42.11 ± 0.95 %), Mortierellomycota (28.74 ± 2.25 %), Basidiomycota (24.61 ± 0.52), and Mucoromycota (2.06 ± 0.43 %). Yet, there were significant differences at the genus level across conditions. Forest to prairie conversion facilitated the introduction of exotic bacterial and fungal taxa associated with agricultural activities and livestock grazing (∼50 % of DP core microbiome composed of unique ASVs). For example, the ammonia-oxidizing bacteria community emerged as a dominant group in the DP soils, along with a reduction in the ectomycorrhizal fungi community. The surface soil microbial community was surprisingly resistant to forest degradation and did not show a clear succession along the degradation gradient, but it was strongly altered after deforestation.

Isolation of an Extensively Drug-Resistant Pseudomonas aeruginosa exoS+/O4 Strain Belonging to the "High-Risk" Clone ST654 and Coproducer of NDM-1 and the Novel VIM-80.

The aim of this study was to investigate the genomic features of an extensively drug-resistant (XDR) Pseudomonas aeruginosa isolate (P-469) emerging in Chile. Antibiotic susceptibility was determined by disk diffusion and "colistin agar" test. Whole-genome sequencing (WGS) was performed by the Illumina NextSeq 2000 platform, and epidemiologically and clinically relevant data (i.e., sequence-type, serotype, mobile genetic elements, virulome, resistome, plasmidome, prophages, and CRISPR-Cas systems) were retrieved using multiple bioinformatic tools. The P-469 strain displayed an XDR profile, remaining susceptible to colistin. Genomic analysis revealed that this isolate belonged to the "high-risk" clone ST654 (CC654), serotype O4, and genotype exoS+. Strikingly, two CRISPR-Cas systems, five intact prophages sequences, and a broad resistome that included blaNDM-1 and the novel blaVIM-80 carbapenemase genes were predicted. Our results revealed the genomic characteristics of P. aeruginosa belonging to the high-risk clone ST654/O4 coproducing NDM-1 and VIM-80 in Chile, supporting that genomic surveillance is necessary to track the emergence and spread of epidemiologically successful WHO's critical priority pathogens in order to prevent their rapid dissemination.

Novel Megaplasmid Driving NDM-1-Mediated Carbapenem Resistance in Klebsiella pneumoniae ST1588 in South America.

Carbapenem-resistant Enterobacterales (CRE) is a critical public health problem in South America, where the prevalence of NDM metallo-betalactamases has increased substantially in recent years. In this study, we used whole genome sequencing to characterize a multidrug-resistant (MDR) Klebsiella pneumoniae (UCO-361 strain) clinical isolate from a teaching hospital in Chile. Using long-read (Nanopore) and short-read (Illumina) sequence data, we identified a novel un-typeable megaplasmid (314,976 kb, pNDM-1_UCO-361) carrying the blaNDM-1 carbapenem resistance gene within a Tn3000 transposon. Strikingly, conjugal transfer of pNDM-1_UCO-361 plasmid only occurs at low temperatures with a high frequency of 4.3 × 10-6 transconjugants/receptors at 27 °C. UCO-361 belonged to the ST1588 clone, previously identified in Latin America, and harbored aminoglycoside, extended-spectrum ß-lactamases (ESBLs), carbapenem, and quinolone-resistance determinants. These findings suggest that blaNDM-1-bearing megaplasmids can be adapted to carriage by some K. pneumoniae lineages, whereas its conjugation at low temperatures could contribute to rapid dissemination at the human-environmental interface.

Phenotypic and Genotypic Characterization of Macrolide, Lincosamide and Streptogramin B Resistance among Clinical Methicillin-Resistant Staphylococcus aureus Isolates in Chile.

Macrolides, lincosamides, and type B streptogramins (MLSB) are important therapeutic options to treat methicillin-resistant Staphylococcus aureus (MRSA) infections; however, resistance to these antibiotics has been emerging. In Chile, data on the MLSB resistance phenotypes are scarce in both community-(CA) and hospital-acquired (HA) MRSA isolates. Antimicrobial susceptibility to MLSB was determined for sixty-eight non-repetitive isolates of each HA-(32) and CA-MRSA (36). Detection of SCCmec elements, ermA, ermB, ermC, and msrA genes was performed by PCR. The predominant clones were SCCmec I-ST5 (HA-MRSA) and type IVc-ST8 (CA-MRSA). Most of the HA-MRSA isolates (97%) showed resistance to clindamycin, erythromycin, azithromycin, and clarithromycin. Among CA-MRSA isolates, 28% were resistant to erythromycin, azithromycin, and 25% to clarithromycin. All isolates were susceptible to linezolid, vancomycin, daptomycin and trimethoprim/sulfamethoxazole, and over 97% to rifampicin. The ermA gene was amplified in 88% of HA-MRSA and 17% of CA-MRSA isolates (p < 0.001). The ermC gene was detected in 6% of HA-SARM and none of CA-SARM isolates, whereas the msrA gene was only amplified in 22% of CA-MRSA (p < 0.005). Our results demonstrate the prevalence of the cMLSB resistance phenotype in all HA-MRSA isolates in Chile, with the ermA being the predominant gene identified among these isolates.

Mec-Positive Staphylococcus Healthcare-Associated Infections Presenting High Transmission Risks for Antimicrobial-Resistant Strains in an Equine Hospital.

Healthcare-associated infections caused by Staphylococcus, particularly Staphylococcus aureus, represent a high risk for human and animal health. Staphylococcus can be easily transmitted through direct contact with individual carriers or fomites, such as medical and non-medical equipment. The risk increases if S. aureus strains carry antibiotic resistance genes and show a phenotypic multidrug resistance behavior. The aim of the study was to identify and characterize methicillin resistant coagulase-positive staphylococci (MRSA) and coagulase-negative staphylococci (MRCoNS) in equine patients and environmental sources in an equine hospital to evaluate the genetic presence of multidrug resistance and to understand the dissemination risks within the hospital setting. We explored 978 samples for MRSA and MRCoNS using Oxacillin Screen Agar in an equine hospital for racehorses in Chile, which included monthly samples (n = 61-70) from equine patients (246) and hospital environments (732) in a one-year period. All isolates were PCR-assessed for the presence of methicillin resistance gene mecA and/or mecC. Additionally, we explored the epidemiological relatedness by Pulsed Field Gel Electrophoresis (PFGE) in MRSA isolates. Phenotypic antibiotic resistance was evaluated using the Kirby-Bauer disk diffusion method. We estimated the unadjusted and adjusted risk of acquiring drug-resistant Staphylococcus strains by employing logistic regression analyses. We identified 16 MRSA isolates and 36 MRCoNS isolates. For MRSA, we detected mecA and mecC in 100% and 87.5 % of the isolates, respectively. For MRCoNS, mecA was detected among 94% of the isolates and mecC among 86%. MRSA and MRCoNS were isolated from eight and 13 equine patients, respectively, either from colonized areas or compromised wounds. MRSA strains showed six different pulse types (i.e., A1-A3, B1-B2, C) isolated from different highly transited areas of the hospital, suggesting potential transmission risks for other patients and hospital staff. The risk of acquiring drug-resistant Staphylococcus species is considerably greater for patients from the surgery, equipment, and exterior areas posing higher transmission risks. Tackling antimicrobial resistance (AMR) using a One Health perspective should be advocated, including a wider control over antimicrobial consumption and reducing the exposure to AMR reservoirs in animals, to avoid cross-transmission of AMR Staphylococcus within equine hospitals.

Characterization and antimicrobial susceptibility of coagulase-positive Staphylococcus isolated in a veterinary teaching hospital in Chile.

There is limited information about the prevalence and antimicrobial susceptibility of coagulase-positive Staphylococcus (CoPS) strains in veterinary settings in Chile. The aim of this observational study was to identify and characterize CoPS strains from dogs, owners, veterinary professionals and surfaces in a veterinary teaching hospital at Universidad de Chile to determine the presence of methicillin-resistant strains and evaluate the genetic relationship among the strains. Veterinarians (n=24), surfaces (n=10), and healthy dogs (n=40) and their respective owners (n=40) were sampled for CoPS. Isolates were identified by PCR and antimicrobial susceptibility was assessed by the disk diffusion method and MIC. The presence of the mecA gene was evaluated by PCR, and the genetic relationship among the strains was established by PFGE. A total of 45 CoPS strains were obtained, eight from veterinary professionals, three from hospital surfaces, eight from owners and 26 from dogs. Nine of the strains were resistant to methicillin (20%), and all of them carried the mecA gene. A high percentage of the strains was resistant to clindamycin (33.3%). Additionally, the isolated CoPS showed high genetic diversity. This study suggests that veterinarians are in high risk of harboring methicillin-resistant CoPS (25% versus 2.5% from owners) and our results provide evidence that clindamycin could not be an empiric alternative for CoPS in the analyzed hospital. This is the first report of methicillin-resistant CoPS in veterinary settings in Chile, considering humans, pets and surfaces.

In vitro antibacterial activity of endodontic bioceramic materials against dual and multispecies aerobic-anaerobic biofilm models.

The aim of this in vitro study was to evaluate the antibacterial activity of calcium silicate repair cements and sealers against a dual-species planktonic aerobic model with different aging times and the ability to inhibit the formation of a mature 21-day-old multispecies anaerobic biofilm. The antibacterial activity of ProRoot MTA, MTA Angelus, Biodentine, BioRoot RCS and TotalFill BC sealer against a dual-species aerobic planktonic model, as well as measuring how materials were affected by aging, was evaluated using the Modified Direct Contact Test. Subsequently, the ability to inhibit the formation of a mature multispecies anaerobic biofilm was evaluated using scanning electron microscopy complemented with confocal laser scanning microscopy. Biodentine and BioRoot RCS had higher antibacterial action, and Biodentine was able to maintain its antibacterial action after a prolonged aging period in vitro. Calcium silicate repair cement MTA ProRoot and Biodentine had higher antibiofilm action.

Microbiota composition and susceptibility to florfenicol and oxytetracycline of bacterial isolates from mussels (Mytilus spp.) reared on different years and distance from salmon farms.

Chilean aquaculture mainly produces salmonids and molluscs. Salmonid production has been questioned by its excessive use of antimicrobials. This study aimed to investigate the bacterial microbiota composition of Mytilus spp. cultivated near salmonid farms and to determine the minimum inhibitory concentration (MIC) to florfenicol and oxytetracycline of its culturable bacteria. Seven Mytilus farming sites classified according to their proximity to salmon farms as close (CSF) or distant (DSF) were sampled in two years. We analyzed Mytilus microbiota composition through culture-independent methods, and isolated culturable bacteria, and identified those isolates with MIC values ≥ 64 µg mL-1 to florfenicol or oxytetracycline. Results revealed that the alpha diversity was affected by sampling year but not by Mytilus farming site location or its interaction. Nevertheless, in 2018, we observed a significant negative correlation between the alpha diversity of Mytilus microbiota in each farm sites and the tonnes of florfenicol reported for each phytosanitary management area. We detected significant differences in beta diversity and relative abundance of specific bacterial taxa in Mytilus microbiota depending on the proximity to salmon farms and years. A higher proportion of isolates with MIC values ≥ 64 µg mL-1 to both antibiotics was detected in 2019 compared to 2018, but not significant differences were detected according to Mytilus farming site location. However, in 2019, isolates from CSF sites showed higher MIC values for both antibiotics than those from DSF. Bacterial genera corresponding to isolates with MIC values ≥ 64 µg mL-1 represented a low proportion of Mytilus microbiota identified with the culture-independent approach, reflecting the need to implement new methodologies in the study of antimicrobial resistance. These results suggest that the proximity to salmonid farms and sampling year influence the Mytilus microbiota and MIC values of their bacterial isolates; however, other environmental variables should be considered in further studies.

Antimicrobial Effect of Leukocyte- and Platelet-Rich Fibrin Against Aggregatibacter actinomycetemcomitans Mono-Multiserotypes Model

ABSTRACT: Leukocyte- and platelet-rich fibrin is a widely used platelet concentrate for periodontal surgery procedures. Many benefits are described regarding its use, such as antimicrobial properties. The objective of this study was to evaluate the antimicrobial effects of the different zones of this platelet concentrated against the most prevalent serotypes of Aggregatibacter actinomycetemcomitans in an in vitro mono-multiserotype model. Three patients who were treated at a School of Dentistry in the city where the researchers reside, were included. Modified direct contact method tests and results were analyzed using multivariate logistic regression analysis. In the modified direct contact method test, a decrease in bacterial count was found at time 1, but at time 2, the count increased for all serotypes and zones of L-PRF. It can be noted that the areas with more cellular content in leukocytes and platelet-rich fibrin are the areas with the most antimicrobial powe r. This platelet concentrate would have better results with serotype c. At time point 2, it is likely to act as a growth promoter of A. actinomycetemcomitans.

RESUMEN: La Fibrina rica en Leucocitos y Plaquetas es un concentrado plaquetario ampliamente utilizado en procedimientos quirúrgicos periodontales. Muchos beneficios se describen con respecto a su uso, tales como propiedades antimicrobianas. El objetivo de este estudio fue evaluar los efectos antimicrobianos de las diferentes zonas de este concentrado plaquetario frente a los serotipos más prevalentes de Aggregatibacter actinomycetemcomitans en un modelo mono-multi serotipo in vitro. Se incluyeron tres pacientes que fueron tratados en la Facultad de Odontología de la ciudad donde residen los investigadores. Se utilizó para su análisis una prueba de contacto directo modificado. En la prueba de contacto directo modificado, se encontró una disminución en el recuento bacteriano en el tiempo 1, pero en el tiempo 2, el recuento aumentó para todos los serotipos y zonas de L-PRF. Se puede observar que las áreas con mayor contenido celular en la Fibrina rica en Leucocitos y Plaquetas son las áreas con mayor poder antimicrobiano. Este concentrado de plaquetas tendría mejores resultados con el serotipo c. En el tiempo 2, es probable que actúe como un promotor del crecimiento de A. actinomycetemcomitans.

Diversity and Host Relationships of the Mycoparasite Sepedonium (Hypocreales, Ascomycota) in Temperate Central Chile.

We present the first major survey of regional diversity, distribution and host-association of Sepedonium. Whereas the rather scarce worldwide records of this mycoparasitic fungus suggested no specific distribution pattern of most species before, we provide new evidence of endemic and specific host-parasite guilds of Sepedonium in Southern South America, including the description of a new species. The corresponding inventory was performed in temperate central Chile. The regional landscape, a mosaic of exotic timber plantations and remnants of native Nothofagus forests, facilitates a unique combination of endemic and adventitious Boletales hosts. During a two-year survey, 35 Sepedonium strains were isolated and cultured from infected basidiomata of allochthonous Chalciporus piperatus, Paxillus involutus, Rhizopogon spp. and Suillus spp., as well as from the native Boletus loyita, B. loyo, B. putidus and Gastroboletus valdivianus. Taxonomic diagnosis included morphology of conidia and conidiophores, sequences of ITS, RPB2 and EF1 molecular markers and characteristics of in vitro cultures. Phylogenetic reconstructions were performed using Bayesian methods. Four Sepedonium species could be identified and characterized, viz.: S. ampullosporum, S. chrysospermum, S. laevigatum and the newly described species S. loyorum. The most frequent species on introduced Boletales was S. ampullosporum, followed by S. chrysospermum and S. laevigatum. S. loyorum sp. nov. was found exclusively on native boletacean hosts, separated from its closest relative S. chalcipori by micromorphological and molecular attributes. Species descriptions and identification keys are provided. Ecological and biogeographical aspects of endemic and allochthonous symbiotic units consisting of mycoparasite, ectomycorrhizal fungal host and respective mycorrhizal tree are discussed.

Isolation of Ciprofloxacin and Ceftazidime-Resistant Enterobacterales From Vegetables and River Water Is Strongly Associated With the Season and the Sample Type.

The dissemination of antibiotic-resistant bacteria (ARB) from water used for crop irrigation to vegetables is poorly studied. During a year, five farmer markets in a city in Central Chile were visited, and 478 vegetable samples (parsleys, corianders, celeries, lettuces, chards, and beets) were collected. Simultaneously, 32 water samples were collected from two rivers which are used to irrigate the vegetables produced in the area. Resistant Enterobacterales were isolated and identified. Colistin resistance gene mcr-1 and extended spectrum ß-lactamases (ESBL) were molecularly detected. The association of environmental factors was evaluated, with the outcomes being the presence of Enterobacterales resistant to four antibiotic families and the presence of multidrug resistance (MDR) phenotypes. Parsley, coriander, and celery showed the highest prevalence of resistant Enterobacterales (41.9% for ciprofloxacin and 18.5% for ceftazidime). A total of 155 isolates were obtained, including Escherichia coli (n=109), Citrobacter sp. (n=20), Enterobacter cloacae complex (n=8), Klebsiella pneumoniae (n=8), and Klebsiella aerogenes (n=1). Resistance to ampicillin (63.2%) and ciprofloxacin (74.2%) was most frequently found; 34.5% of the isolates showed resistance to third-generation cephalosporins, and the MDR phenotype represented 51.6% of the isolates. In two E. coli isolates (1.29%), the gene mcr-1 was found and ESBL genes were found in 23/62 isolates (37%), with bla CTX-M being the most frequently found in 20 isolates (32%). Resistant Enterobacterales isolated during the rainy season were less likely to be MDR as compared to the dry season. Understanding environmental associations represent the first step toward an improved understanding of the public health impact of ARB in vegetables and water.

Antibacterial Activity of Zinc Oxide Nanoparticles in Self- Curing Acrylic Resin Against Streptococcus mutans

ABSTRACT: Antibacterial activity of zinc oxide nanoparticles in self-curing acrylic resin against Streptococcus mutans. The main objective of this study was to investigate whether nanoparticles of zinc oxide (ZnO) in self-curing acrylic resin, hav e antimicrobial properties against Streptococcus mutans, one of the microorganisms involved in the development of caries. Self- cured acrylic resin samples were prepared by incorporating ZnO nanoparticles at different concentrations based on the minimum inhibitory concentration (MIC) for Streptococcus mutans ATCC 25175. Antibacterial activity against a biofilm was evaluated in samples that were aged in artificial saliva for different times using spectral confocal laser microscopy and scanning electron microscopy. Kruskal-Wallis test using IBM SPSS Statistics version 23.0 software (SPSS Inc. ®, Chicago, IL, United States) were used, establishing the value of p <0.05 for statistical significance. The volume of the total biomass that formed in the samples aged for one day was significantly lower than the volume of the total biomass that was formed in those aged for additional days (p <0.001). Electron microscopy analysis revealed high porosity surfaces in all samples. Bacterial clusters wer e located next to large pores and irregular surfaces, while smooth surfaces had defined and linear organization cocci or simple chains. Considering the limitations of this study, the results suggest that the antibacterial activity of ZnO nanoparticles add ed to self-curing acrylic (ALIKE) is effective, mainly in fresh 1-day samples, independent of their concentration, and in samples with 16 MIC aged for 14 days, indicating it does not lose its antibacterial activity despite setting for more days. In addition, the ZnO nanoparticles added to ALIKE have the ability to inhibit the formation of biofilms, although they do not minimize the number of viable bacteria.

RESUMEN: El objetivo principal de este estudio fue investigar si nanopartículas de óxido de zinc (ZnO), incorporadas a acrílico acrilico de autocurado, tienen propiedades antimicrobianas contra Streptococcus mutans, uno de los microorganismos implicados en el desarrollo de caries. Se prepararon muestras de resina acrílica autopolimerizada mediante la incorporación de nanopartículas de ZnO a diferentes concentraciones basadas en la concentración mínima inhibitoria (MIC) para Streptococcus mutans ATCC 25175. Se evaluó la actividad antibacteriana contra una biopelícula en muestras envejecidas en saliva artificial para diferentes tiempos utilizando espectros microscopía láser confocal y microscopía electrónica de barrido. Se utilizó la prueba de Kruskal-Wallis utilizando el software IBM SPSS Statistics versión 23.0 (SPSS Inc. ®, Chicago, IL, Estados Unidos), estableciendo el valor de p <0,05 para la significancia estadística. El volumen de la biomasa total que se formó en las muestras envejecidas durante un día fue significativamente menor que el volumen de la biomasa total que se formó en las envejecidas durante días adicionales (p <0,001). El análisis de microscopía electrónica reveló superficies de alta porosidad en todas las muestras. Los cúmulos bacterianos se ubicaron junto a poros grandes y superficies irregulares, mientras que las superficies lisas tenían cocos o cadenas simples de organización lineal y definida. Considerando las limitaciones de este estudio, los resultados sugieren que la actividad antibacteriana de las nanopartículas de ZnO agregadas al acrílico autopolimerizable (ALIKE) es efectiva, principalmente en muestras frescas de 1 día, independientemente de su concentración, y en muestras con 16 MIC envejecidas para 14 días, lo que indica que no pierde su actividad antibacteriana a pesar de estar fraguada durante más días. Además, las nanopartículas de ZnO añadidas a ALIKE tienen la capacidad de inhibir la formación de biopelículas, aunque no minimizan el número de bacterias viables.

Antimicrobial resistance in wildlife and in the built environment in a wildlife rehabilitation center.

Injured and orphaned wildlife are often brought to Wildlife Rehabilitation Centers (WRC) to be cared for by professionals to ultimately be released back to their natural habitats. In these centers, animals may spend months and frequently receive prolonged antibiotic therapy. Therefore, WRC may play a role in the emergence and dissemination of antimicrobial resistance (AMR). The goal of this study was to investigate the presence and antibiotic resistance profiles of Gram-negative bacteria with reduced susceptibility to cephalosporins in both the wildlife admitted to a WRC and in the WRC built environment in Chile. A cross-sectional study was conducted sampling animals undergoing rehabilitation (n = 64) and the WRC environment (n = 160). Isolated bacterial species were identified with MALDI-TOF, and antimicrobial susceptibility determined using the disk diffusion method. Enterobacteriaceae and Pseudomonadaceae were the dominant bacterial families among the environmental (n = 78) and animal (n = 31) isolates. For Enterobacteriaceae, isolates of the most abundant species (E. coli) were classified into 20 antibiotic resistance profiles, with eight of those isolates being resistant to more than nine antibiotics, including imipenem. Isolates of the Pseudomonadaceae family identified 11 isolates with resistance to antibiotics such as carbapenems and quinolones. Even though a cluster analysis based on antibiotic resistance patterns did not show a clear overlap between environmental and animal isolates, it is important to highlight the identification of isolates resistant to carbapenems, which is very relevant from a public health perspective. Further, numerous antibiotic resistance profiles were observed in different bacterial species, indicating not only environmental contamination with a wide diversity of bacteria, but also a wide diversity of resistant bacteria in animals at the WRC. The approach taken by sampling animals and their hospital environment can be useful in understanding AMR dynamics in wildlife rehabilitation settings, as well as the potential dissemination of AMR into the natural environment.

Selective digestive decontamination with oral colistin plus gentamicin for persistent bacteraemia caused by non-carbapenemase-producing carbapenem-resistant Klebsiella pneumoniae in a neutropenic patient.

BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CRKp) have become an increasing public health problem worldwide. While most CRKp around the world harbour a carbapenemase enzyme, the clinical relevance of non-carbapenemase-producing CRKp (non-CP-CRKp) is increasingly recognized. Selective digestive decontamination (SDD) has been proven successful as a decolonization strategy for patients colonized with Gram-negatives in the ICU. However, it is not regularly used to treat invasive infections. OBJECTIVES: To report the use of SDD as a useful strategy for managing recalcitrant CRKp bloodstream infections. PATIENTS AND METHODS: We present a neutropenic patient with a recalcitrant bloodstream infection with non-CP-CRKp treated with SDD. Besides, genomic analyses of five isolates of non-CP-CRKp was performed. RESULTS: After 11 days of SDD treatment with oral colistin and gentamicin, bacteraemia was successfully eradicated. Genomic analysis indicates a fully carbapenem-resistant phenotype evolved in vivo and suggests that the mechanism of carbapenem resistance in our strains relates to gene amplification of narrow-spectrum ß-lactamases. CONCLUSIONS: Our report highlights that SDD might be a useful strategy to manage CRKp bloodstream infections, when intestinal translocation is the likely source of the bacteraemia. In addition, the development of a resistant phenotype during therapy is worrisome as therapies directed against these organisms are likely to favour the amplification process.

New Quinone Antibiotics against Methicillin-Resistant S. aureus.

There is an urgent need for the development of new antibiotics. Here, we describe the inhibitory activity of new quinone compounds against methicillin-resistant Staphylococcus aureus (ATCC® 43300), methicillin-sensitive S. aureus (ATCC® 29213), and two clinical isolates from Chile (ISP-213 and ISP-214). We observed 99.9% reduction in viability within 2 h of exposure without the cultures exhibiting any post-antibiotic effect, which was twice the kinetics to that observed with vancomycin. These clinical isolates did not acquire resistance to these quinone derivatives during the course of our study. We found that these compounds protected larvae of the greater wax moth, sp. Galleria mellonella, from infection by these MRSA clinical strains as effectively as vancomycin. These quinone derivatives are potential drug candidates worth further development.

Molecular characterization and antibacterial activity of oral antibiotics and copper nanoparticles against endodontic pathogens commonly related to health care-associated infections.

OBJECTIVE: To carry out molecular characterization and determine the antibacterial activity of oral antibiotics and copper nanoparticles (Cu-NPs) against endodontic strains isolated from persistent infections. MATERIALS AND METHODS: Root canal samples from 24 teeth in different patients with persistent endodontic infections were obtained. The isolated strains were identified by biochemical tests and 16S rDNA sequencing. Genotyping was achieved by molecular methods. The antibacterial activity of antibiotics and copper nanostructures was determined by using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. Furthermore, a time-kill kinetics assay was evaluated. Nonparametric tests (Kruskal-Wallis ANOVA) were performed (p value <0.05). RESULTS: Twenty-one isolated strains were identified. Six isolates of Enterococcus faecalis were grouped into two clusters of three isolates each, two of which were clones. All were clarithromycin-resistant and erythromycin. Eight Pseudomonas putida presented two clusters, two Pseudomonas spp. were not clonal, and all were resistant to the tested antibiotics except tetracycline. Two of five strains of Cutibacterium acnes were clonal, and all were resistant only to metronidazole. The lowest MIC and MBC values were obtained with Cu-NPs. Time-kill kinetics using Cu-NPs showed a significant decrease in all tested species within 4 h and reached 100% in 2 h for C. acnes. CONCLUSION: In this study, in relation to health care-associated infections, endodontic strains of each species isolated at least in one patient were polyclonal. In Pseudomonas spp., at least one clone was shared between patients. E. faecalis and C. acnes strains were susceptible to low Cu-NP concentrations, while Pseudomonas spp. strains were resistant. CLINICAL RELEVANCE: Assessing and keeping track of the susceptibility of clinical strains to antimicrobial compounds is important for the clinical outcome. Based on our results, Cu-NPs could be an alternative for endodontic treatment, in order to avoid selection of resistant strains.

[Carbapenemases produced by Carbapenem-resistant Pseudomonas aeruginosa isolated from hospitals in Chile]. / Carbapenemasas en aislamientos de Pseudomonas aeruginosa resistentes a carbapenémicos aisladas en hospitales de Chile.

BACKGROUND: Carbapenem resistance mediated by carbapenemases in Pseudomonas aeruginosa is an important mechanism; however, loss of porin OprD remains as the most frequent. AIM: To determine the proportion of P. aeruginosa isolates, resistant to imipenem and/or meropenem, producing carbapenemases, the type of enzyme produced and the genetic relationship between the isolates. METHODS: One hundred and thirteen resistant to at least one carbapenem isolates, obtained in 12 hospitals and 9 cities in Chile were studied. Additionally, susceptibility to ceftazidime, amikacin, gentamicin, piperacillin/tazobactam, ciprofloxacin and colistin was determined. Carba NP was performed and in the positive isolates carbapenemase genes were detected by PCR. The isolates were typified by restriction with SpeI and PFGE. RESULTS: Not all isolates produce carbapenemases, and only in 61/113 of them (54%) the blaKPC (32) or blaVIM (29) was amplified. In none of the isolates was found the coharboring of both genes. The pulsotypes indicated no clonal dissemination of the isolates, evidencing an important genetic diversity. CONCLUSIONS: P. aeruginosa isolates producing carbapenemases, obtained in Chilean hospitals carry blaKPC and blaVIM genes and, mostly, are polyclonal. These results emphasize the importance of carrying out epidemiological studies with a greater number of isolates to allow a better understanding of the epidemiology of carbapenemase-producing P. aeruginosa in Chile.