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Antibiotic resistance has emerged as a global threat to public health, generating a growing interest in investigating the presence of antibiotic-resistant bacteria in environments influenced by anthropogenic activities. Wastewater treatment plants in hospital serve as significant reservoirs of antimicrobial-resistant bacteria, where a favorable environment is established, promoting the proliferation and transfer of resistance genes among different bacterial species. In our study, we isolated a total of 243 strains from 5 hospital wastewater sites in Mexico, belonging to 21 distinct Gram-negative bacterial species. The presence of ß-lactamase was detected in 46.9% (114/243) of the isolates, which belonging to the Enterobacteriaceae family. We identified a total of 169 ß-lactamase genes; blaTEM in 33.1%, blaCTX-M in 25.4%, blaKPC in 25.4%, blaNDM 8.8%, blaSHV in 5.3%, and blaOXA-48 in 1.1% distributed in 12 different bacteria species. Among the 114 of the isolates, 50.8% were found to harbor at least one carbapenemase and were discharged into the environment. The carbapenemase blaKPC was found in six Citrobacter spp. and E. coli, while blaNDM was detected in two distinct Enterobacter spp. and E. coli. Notably, blaNDM-1 was identified in a 110 Kb IncFII conjugative plasmid in E. cloacae, E. xiangfangensis, and E. coli within the same hospital wastewater. In conclusion, hospital wastewater showed the presence of Enterobacteriaceae carrying a high frequency of carbapenemase blaKPC and blaNDM. We propose that hospital wastewater serves as reservoirs for resistance mechanism within bacterial communities and creates an optimal environment for the exchange of this resistance mechanism among different bacterial strains. IMPORTANCE: The significance of this study lies in its findings regarding the prevalence and diversity of antibiotic-resistant bacteria and genes identified in hospital wastewater in Mexico. The research underscores the urgent need for enhanced surveillance and prevention strategies to tackle the escalating challenge of antibiotic resistance, particularly evident through the elevated frequencies of carbapenemase genes such as blaKPC and blaNDM within the Enterobacteriaceae family. Moreover, the identification of these resistance genes on conjugative plasmids highlights the potential for widespread transmission via horizontal gene transfer. Understanding the mechanisms of antibiotic resistance in hospital wastewater is crucial for developing targeted interventions aimed at reducing transmission, thereby safeguarding public health and preserving the efficacy of antimicrobial therapies.

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Infective endocarditis (IE) is a condition with low prevalence but high mortality rates within intensive care units. Microbiologically, most cases are attributed to Gram-positive cocci, while Gram-negative bacilli are less commonly involved. This case report describes a patient with IE caused by Citrobacter koseri (C. koseri) with secondary bacteremia due to blunt testicular trauma and epididymitis. We conducted a review of the literature to assess the clinical and associated risk factors of this underreported condition. Elderly and urinary tract infections could be associated with this entity. Cefazolin was used as the final targeted treatment. The use of precision medicine in IE is required for specific interventions.

Infection of the heart valve from testicular injury: a case study and review of medical literature Infective endocarditis (IE) is a serious but rare infection that can lead to death, especially in intensive care units. Typically, it's caused by certain types of bacteria, but our case study focuses on a patient whose IE was caused by a less common bacterium called Citrobacter koseri (C. koseri). This infection occurred after the patient experienced blunt trauma to the testicles, leading to a bloodstream infection. We looked at other similar cases in medical literature and found that older age and urinary tract infections might increase the risk of this type of IE. In this case, IE caused by this unusual bacteria was treated with cefazolin.

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Pericytes are located around blood vessels, in close contact with endothelial cells. We discovered that pericytes dampen pro-inflammatory endothelial cell responses. Endothelial cells co-cultured with pericytes had markedly reduced expression of adhesion molecules (PECAM-1 and ICAM-1) and proinflammatory cytokines (CCL-2 and IL-6) in response to bacterial stimuli (Brucella ovis, Listeria monocytogenes, or Escherichia coli lipopolysaccharide). Pericyte-depleted mice intraperitoneally inoculated with either B. ovis, a stealthy pathogen that does not trigger detectable inflammation, or Listeria monocytogenes, developed peritonitis. Further, during Citrobacter rodentium infection, pericyte-depleted mice developed severe intestinal inflammation, which was not evident in control mice. The anti-inflammatory effect of pericytes required connexin 43, as either chemical inhibition or silencing of connexin 43 abrogated pericyte-mediated suppression of endothelial inflammatory responses. Our results define a mechanism by which pericytes modulate inflammation during infection, which shifts our understanding of pericyte biology: from a structural cell to a pro-active player in modulating inflammation. IMPORTANCE: A previously unknown mechanism by which pericytes modulate inflammation was discovered. The absence of pericytes or blocking interaction between pericytes and endothelium through connexin 43 results in stronger inflammation, which shifts our understanding of pericyte biology, from a structural cell to a player in controlling inflammation.

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Citrobacter werkmanii is an emerging and opportunistic human pathogen found in developing countries and is a causative agent of wound, urinary tract, and blood infections. The present study conducted comparative genomic analyses of a C. werkmanii strain collection from diverse geographical locations and sources to identify the relevant virulence and antimicrobial resistance genes. Pangenome analyses divided the examined C. werkmanii strains into five distinct clades; the subsequent classification identified genes with functional roles in carbohydrate and general metabolism for the core genome and genes with a role in secretion, adherence, and the mobilome for the shell and cloud genomes. A maximum-likelihood phylogenetic tree with a heatmap, showing the virulence and antimicrobial genes' presence or absence, demonstrated the presence of genes with functional roles in secretion systems, adherence, enterobactin, and siderophore among the strains belonging to the different clades. C. werkmanii strains in clade V, predominantly from clinical sources, harbored genes implicated in type II and type Vb secretion systems as well as multidrug resistance to aminoglycoside, beta-lactamase, fluoroquinolone, phenicol, trimethoprim, macrolides, sulfonamide, and tetracycline. In summary, these comparative genomic analyses have demonstrated highly pathogenic and multidrug-resistant genetic profiles in C. werkmanii strains, indicating a virulence potential for this commensal and opportunistic human pathogen.

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Background: Citrobacter koseri, a Gram-negative organism, rarely causes an epidural spinal abscess. Case Description: A 50-year-old male presented with mild paraparesis attributed to an magnetic resonance (MR)-documented spinal epidural abscess (SEA) at the T10-level. Following surgical debridement, cultures grew C. koseri, a rare Gram-negative organism. The abscess was subsequently managed with a prolonged course of antibiotics resulting in complete symptom and MR-documented radiological resolution. Conclusion: A 50-year-old male presented with a T10 SEA attributed to a rare Gram-negative organism, C. koseri. The abscess was appropriately managed with surgical decompression/debridement, followed by prolonged antibiotic therapy.

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A Gram-stain-negative strain, designated BR102T, isolated from a soil sample in Brazil was characterized by a polyphasic approach. Comparative 16S rRNA gene sequences indicated that strain BR102T belonged to the genus Citrobacter. The recN- and whole-genome-based phylogeny, and multilocus sequence analysis based on concatenated partial fusA, leuS, pyrG and rpoB sequences strongly supported a clade encompassing strain BR102T and a strain from public database that was distinct from currently recognized species of the genus Citrobacter. Average nucleotide identity and digital DNA-DNA hybridization values between strain BR102T and the closest relative Citrobacter freundii ATCC 8090T were 91.8 and 48.8 %, respectively. The ability to metabolize different compounds further discriminated strain BR102T from other closely related species of the genus Citrobacter. The novel variants bla CMY-179 and qnrB97, which encoded a CMY-2-like ß-lactamase and a QnrB-type protein, respectively, were identified in strain BR102T. BR102T was resistant to ampicillin, amoxicillin/clavulanate and cefoxitin. The DNA G+C content of strain BR102T is 51.3 mol%. Based on these results, strain BR102T represents a novel species of the genus Citrobacter, for which the name Citrobacter meridianamericanus sp. nov. is proposed. The type strain is BR102T (=MUM 22.55T=IMI 507229T).

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The reference material (RM) is a technical requirement for the quality assurance of analytical results and proficiency tests or interlaboratory comparisons. Microbiological RMs are most available in the dehydrated form, mainly by freeze-drying, and maintaining bacterial survival after preparation is a challenge. Thus, obtaining the most resistant cells is essential. Considering that bacteria present cross-response to dehydration after being submitted to an array of stress conditions, this study aimed to evaluate the influence of growth conditions on enterobacteria for the production of mixed microbiological RMs by freeze-drying in skim milk powder. Salmonella enterica serovar Enteritidis, Cronobacter sakazakii, Escherichia coli, and Citrobacter freundii were grown in a minimal medium with 0.5 M NaCl and 0 to 5.0 mM of manganese sulfate (MnSO4) until stationary phase. Salmonella Enteritidis presented an increased resistance to dehydration in the presence of Mn, while C. sakazakii was the most resistant to freeze-drying and further storage for 90 days. Mixed microbiological RMs were produced by freeze-drying and containing Salmonella Enteritidis and coliforms in skim milk powder with 100 mM of trehalose and the Salmonella survival rate was 91.2 to 93.6%. The mixed RM was stable after 30 days at -20 °C, and Salmonella and coliforms were detected by different methods being, the Rambach Agar the best for the bacterial differentiation. The results showed that the culture conditions applied in this study resulted in bacterial cells being more resistant to dehydration, freeze-drying, and stabilization for the production of mixed microbiological RMs more stable and homogeneous.

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The occurrence of multidrug-resistant pathogens in the food chain causes health problems in humans, thus, research for novel antimicrobials to combat their growth is of interest. This study evaluates the antimicrobial potential of several combinations of peptide-protein extracts (PCs) consisting of peptide extracts from three native probiotic strains, Lactiplantibacillus plantarum UTNGt2, Lactococcus lactis UTNGt28, and L. plantarum UTNGt21A, alone or in combination with EDTA (ethylenediaminetetraacetic acid) against multidrug-resistant Staphylococcus aureus ATCC1026 and Citrobacter freundii UTNB3Sm1. Based on the antimicrobial assay, among the 19 tested PCs, two (PC11 and PC17) produced a greater zone of inhibition against both pathogens in vitro. Time-killing assays indicated the rapid death of S. aureus after exposure to PC11 and PC17, while C. freundii was rapidly inhibited by PC11 and PC1 (UTNGt2 only), suggesting that the inhibitory action is pathogen and dose-dependent of a particular molecule present in the extract. A marginal inhibitory effect was observed when the peptides were combined with EDTA. Transmission electron microscopy (TEM) revealed the structural membrane damage of both target strains upon interaction with individual peptide extracts. Different degrees of cell deformation, condensed cytoplasm, membrane blebbing, and ghost cell formation with visibly broken cell walls were observed in S. aureus. Likewise, the separation of the cytoplasmic membrane from the outer membrane, ghost cells, along with ovoid and deformed cells with undulated cell walls were observed for C. freundii. Furthermore, scanning electronic microscopy (SEM) analysis revealed different wrinkled and deformed cells covered by debris. A leakage of aromatic molecules was detected for both pathogens, indicating that PCs disrupted the cell wall integrity, inducing cell death. Given their inhibitory action and capacity to induce damage of the cytoplasmic membrane, the selected PCs may serve to slow bacterial growth in vitro; further research is required to prove their efficiency ex vitro to battle against food poisoning and subsequent human infection.

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Riboflavin is an essential, water-soluble vitamin (B2) and a component of basic cellular metabolism. The aim of the present study is to isolate and characterize riboflavin producing bacteria from different food sources. Ten different riboflavin enriched food sources were collected from Vellore district. Totally 72 bacterial strains were isolated and cultured on nutrient agar plates. Out of these, 43 strains were identified as riboflavin producers. Isolated bacterial strains HDS27, HDS07, HDS14, HDS18, HDS38 and HDS54 isolated from milk, mushroom, spinach, lamb kidney, beef liver and mackerel fish were found to be potent riboflavin producers. Based on morphological, biochemical and molecular characterization, the potent strains were identified as Lactobacillus plantarum (HDS27), Bacillus cereus (HDS07), Delftia tsuruhatensis (HDS14), Citrobacter freundii (HDS18), Enterobacter cloacae (HDS38) and Bacillus cereus (HDS54). The selected potent isolates HDS27 from milk and HDS07 from mushroom showed a maximum riboflavin production of 3.69 mg/L and 2.9mg/L respectively. The present study explores the riboflavin producing novel bacteria from different food sources. This is the first report that the Enterobacter cloacae isolated from beef liver, Delftia tsuruhatensis from spinach and Citrobacter freundii from lamb kidney has the ability to produce riboflavin. These potent strains could be a better starter for substituting the conventional bacteria for large scale production of riboflavin in industry.

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INTRODUCTION: Citrobacter spp. is an opportunistic bacteria that have been recognized as significant pathogens in patients with underlying diseases or immunocompromised status. The aim of this study was to identify extended-spectrum ß-lactamases in clinical isolates of Citrobacter spp. METHODS: This cross-sectional study was conducted at Hospital Central "Dr. Ignacio Morones Prieto" in San Luis Potosi, Mexico. Nineteen isolates of Citrobacter spp. were obtained from clinical specimens between April to December 2015. Four isolates were resistant to third-generation cephalosporins. The presence of genes encoding ESBL (bla CTX-M-15, bla TEM-1, bla VEB-1, bla SHV, and bla PER-1) was analyzed by PCR. For this purpose, plasmid DNA was extracted and horizontally transferred to recipient E. coli Top 10. RESULTS: bla CTX-M-15 and bla VEB-1 genes were detected in Citrobacter freundii and Citrobacter sedlakii, whereas bla PER-1 gene was identified in 1 isolate of Citrobacter freundii. In contrast, bla SHV gene was not detected in any isolate. One strain carried bla CTX-M-15, bla TEM-1, bla VEB-1, and bla PER-1 genes, most in a 275-kb plasmid. CONCLUSION: This study shows the presence of different types of ESBL in clinical isolates of Citrobacter freundii and Citrobacter sedlakii, which confer resistance to broad-spectrum ß-lactams. The plasmid identified in this study harboring ESBL genes could play an important role in the dissemination of antibiotic resistance.

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The main objective of this study was to characterize using whole-genome sequencing analysis, a new variant of the qnrB gene (qnrB89) carried by a fluoroquinolone-susceptible bacterium isolated from mucus of farmed Salmo salar fingerling in Chile. Citrobacter gillenii FP75 was identified by using biochemical tests and 16S ribosomal gene analysis. Nucleotide and amino acid sequences of the qnrB89 gene exhibited an identity to qnrB of 81.24% and 91.59%, respectively. The genetic environment of qnrB89 was characterized by the upstream location of a sequence encoding for a protein containing a heavy metal-binding domain and a gene encoding for a N-acetylmuramoyl-L-alanine amidase protein, whereas downstream to qnrB89 gene were detected the csp and cspG genes, encoding cold-shock proteins. The qnrB89 gene was located on a large chromosomal contig of the FP75 genome and was not associated with the 10-kb plasmid and class 1 integron harbored by the FP75 strain. This study reports for the first time the carriage of a qnrB gene by the C. gillenii species, and its detection in a bacterial strain isolated from farmed salmon in Chile.

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BACKGROUND: Studying the behavioral response of blood-sucking disease-vector insects to potentially repellent volatile compounds could shed light on the development of new control strategies. Volatiles released by human facial skin microbiota play different roles in the host-seeking behavior of triatomines. We assessed the repellency effect of such compounds of bacterial origin on Triatoma infestans and Rhodnius prolixus, two important vectors of Chagas disease in Latin America. METHODS: Using an exposure device, insects were presented to human odor alone (control) and in the presence of three individual test compounds (2-mercaptoethanol, dimethyl sulfide and 2-phenylethanol, the latter only tested in R. prolixus) and the gold-standard repellent NN-diethyl-3-methylbenzamide (DEET). We quantified the time the insects spent in the proximity of the host and determined if any of the compounds evaluated affected the behavior of the insects. RESULTS: We found volatiles that significantly reduced the time spent in the proximity of the host. These were 2-phenylethanol and 2-mercaptoethanol for R. prolixus, and dimethyl sulfide and 2-mercaptoethanol for T. infestans. Such an effect was also observed in both species when DEET was presented, although only at the higher doses tested. CONCLUSIONS: The new repellents modulated the behavior of two Chagas disease vectors belonging to two different triatomine tribes, and this was achieved using a dose up to three orders of magnitude lower than that needed to evoke the same effect with DEET. Future efforts in understanding the mechanism of action of repellent compounds such as 2-mercaptoethanol, as well as an assessment of their temporal and spatial repellent properties, could lead to the development of novel control strategies for these insect vectors, refractory to DEET.

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The biocatalyzed synthesis of purine nucleosides and their analogs is a case widely studied due to the high pharmaceutical interest of these compounds, providing the whole-cell biocatalysts, a useful tool for this purpose. Vidarabine and fludarabine are commercial examples of expensive bioactive nucleosides that can be prepared using a microbial transglycosylation approach. Citrobacter koseri whole-cells immobilized on agarose beads proved to be an interesting option to transform this biotransformation in a preparative process. The entrapment matrix provided a useful and resistant multipurpose biocatalyst regarding its stability, mechanical strength, microbial viability and reuse. Immobilized biocatalyst retained the initial activity for up to 1 year storage and after 10 years, the biocatalyst did not show cell leaking and still exhibited residual activity. In addition, the biocatalyst could be reused in batch 68 times keeping up to 50% of the initial biocatalytic activity and for at least 124 h in a continuous process.

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Background: Studying the behavioral response of blood-sucking disease-vector insects to potentially repellent volatile compounds could shed light on the development of new control strategies. Volatiles released by human facial skin microbiota play diferent roles in the host-seeking behavior of triatomines. We assessed the repellency efect of such compounds of bacterial origin on Triatoma infestans and Rhodnius prolixus, two important vectors of Chagas disease in Latin America. Methods: Using an exposure device, insects were presented to human odor alone (control) and in the presence of three individual test compounds (2-mercaptoethanol, dimethyl sulfde and 2-phenylethanol, the latter only tested in R. prolixus) and the gold-standard repellent NN-diethyl-3-methylbenzamide (DEET). We quantifed the time the insects spent in the proximity of the host and determined if any of the compounds evaluated afected the behavior of the insects. Results: We found volatiles that signifcantly reduced the time spent in the proximity of the host. These were 2-phenylethanol and 2-mercaptoethanol for R. prolixus, and dimethyl sulfde and 2-mercaptoethanol for T. infestans. Such an efect was also observed in both species when DEET was presented, although only at the higher doses tested. Conclusions: The new repellents modulated the behavior of two Chagas disease vectors belonging to two diferent triatomine tribes, and this was achieved using a dose up to three orders of magnitude lower than that needed to evoke the same efect with DEET. Future eforts in understanding the mechanism of action of repellent compounds such as 2-mercaptoethanol, as well as an assessment of their temporal and spatial repellent properties, could lead to the development of novel control strategies for these insect vectors, refractory to DEET.

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Enterohemorrhagic (EHEC) and enteropathogenic Escherichia coli (EPEC) are human intestinal pathogens of clinical importance and their mechanism of pathogenicity is widely studied. However, both EHEC and EPEC poorly infect mice, whereas they do not develop important characteristics of the disease, hindering studies about mechanisms of virulence in vivo. Citrobacter rodentium exhibits high similarity of its genes with these human pathogens, including the island of pathogenicity Locus of Enterocyte Effacement (LEE). Therefore, C. rodentium becomes an alternative in vivo model for microorganisms that harbor LEE. The QseC directly regulates LEE as well as virulence mechanisms on these pathogens. Here, we report a novel surface motility in C. rodentium QseC-mediated in this non-flagellated bacterium. Moreover, we show norepinephrine and ethanolamine act as environmental signals in this movement. Hence, this study clarifies a novel role of the sensor QseC in completely unreported motility process of C. rodentium.

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Citrobacter freundii, en ocasiones puede actuar como patógeno oportunista, se presenta un caso de este microorganismo aislado como agente etiológico de infección del tracto urinario, en un paciente con enfermedad pulmonar obstructiva crónica. El aislado fue multirresistente, mostrando resistencia a gentamicina, amikacina, trimetoprim sulfametoxazole, ciprofloxacino, ceftriaxona, ceftazidima, cefepime, imipenem, meropenem y doripenem y, susceptibilidad a tigeciclina y colistina, el estudio molecular demostró la presencia del gen blaKPC.

Citrobacter freundii, sometimes it can act as opportunistic pathogen, a case of this isolated microorganism is presented as an etiological agent of urinary tract infection, in a patient with chronic obstructive pulmonary disease. The isolate was multiresistant to gentamicin, amikacin, trimetoprim sulfamethoxazole, ciprofloxacin, ceftriaxone, ceftazidime, cefepime, imipenem, meropenem and doripenem and it was susceptible to tigecycline and colistin, the molecular analysis showed the presence of the blaKPC gene.

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A multidrug resistant isolate, identified as Citrobacter amalonaticus using MALDI-TOF MS and confirmed by genomic analysis, was recovered from a pediatric patient in a hospital from Buenos Aires, Argentina. By whole-genome sequencing a total of 16 resistance genes were detected, including blaNDM-1 and mcr-1.5. To the best of our knowledge this is the first description of these two genes together in a clinical isolate of the Citrobacter genus.

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Introducción: La emergencia de enterobacterias productoras de carbapenemasas en el ámbito hospitalario representa un verdadero problema de salud pública mundial. Las carbapenemasas son enzimas que producen resistencia a los antibióticos carbapenémicos, teniendo un directo impacto en la disponibilidad de alternativas terapéuticas. En Argentina, a partir de 2013 han emergido carbapenemasas tipo-NDM (Nueva Delhi Metalo-ß-lactamasa, MßL), que constituyen una resistencia emergente a nivel global. Objetivo: Reportar el primer aislamiento clínico de enterobacteria portadora de NDM en nuestra institución. Materiales y métodos: El aislamiento estudiado fue recuperado de una muestra ósea de un paciente adulto. La identificación bacteriana y los ensayos de susceptibilidad antibiótica se realizaron mediante metodología manual y sistema automatizado Vitek 2C (Biomérieux). La detección y caracterización de carbapenemasas se efectuó por ensayos fenotípicos y moleculares. Resultados: Los ensayos revelaron que el aislamiento, tipificado como Citrobacter freundii, es productor de carbapenemasa tipo NDM. Resultó sensible a aztreonam, colistina y fosfomicina. No se detectó fenotípicamente la presencia de beta lactamasas de espectro extendido. Discusión: Se reporta el primer aislamiento de enterobacteria productor de MßL tipo-NDM en nuestro nosocomio, siendo multirresistente, con escasas alternativas terapéuticas. Dado que la presencia de este tipo de aislamiento es considerado de alto riesgo, se requiere un monitoreo activo de este mecanismo de resistencia y la instauración de medidas de control adecuadas para hacer frente a la amenaza que suponen

Introduction: the emergence of carbapenemase-producing Enterobaceriaceae in the hospital environment represents a major challenge for health care worldwide. Carbapene-mases are carbapenem-hydrolysing enzymes that confer resistance to these "last-line" antibiotics having a direct im-pact on the limited treatment options available. In Argentina, carbapenemases NDM-like (New DelhiMetallo-ß-lactamase, MßL) have emerged in 2013. This resistance has increased in frequency and it has disseminated around the world at unprecedented levels.Objective:report the first isolation of a NDM-producing En-terobacteriaceae in our hospital.Materials and methods: the isolate analysed in this study was recovered from a bone biopsy belonging to an adult patient. The bacterial identification and antimicrobial sus-ceptibility testings were performed using conventional methods and the automated system Vitek 2C (Biomérieux). Phenotypic and molecular techniques were carried out for the detection and characterization of carbapenemases.Results: it was confirmed that the isolate, identified as Citro-bacter freundii, produces the NDM enzyme. It showed sensi-bility to aztreonam, colistin and fosfomicyn. Extended-spec-trum beta-lactamases were not detected.Discussion: in this study we report the first isolation of NDM-like MßL in our institution, a multirresistant pathogen associ-ated with a lack of effective antimicrobial treatment options. Given the high risk of these infections, an active search of mechanisms of resistance is mandatory. In addition, the establishment of accurate control measures is a must to attempt to overcome this formidable threat

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Abstract Introduction: This paper presents the first case of empyema necessitatis secondary to infection with Citrobacter freundii (according to the databases consulted), and one of the few reports of this pathology in Colombia. Case presentation: This is the case of a 26-year-old patient from a rural area, with a history of severe cognitive deficit, who was taken to the emergency department due to a clinical picture of 15 days of evolution consisting of neurological deterioration associated with asthenia, adynamia, fever and cough with purulent expectoration. On admission, a chest x-ray was taken, finding pneumonia of the middle lobe with associated pleural effusion, for which empirical antibiotic management was initiated. The patient presented clinical deterioration and appearance of right pectoral mass, so a computed tomography of the thorax was performed, revealing empyema necessitatis. Close drainage and culture of the collection were made, with negative mycobacteria culture and positive report for C. freundii. The patient received specific antibiotic treatment for 8 weeks, with complete improvement of his clinical condition. Conclusion: Besides being the first case of empyema necessitatis by C. freundii that has been reported, this case is important because of the low amount of reports on this pathology in Colombia, considering that its main cause is tuberculosis, which is endemic in the country.

Resumen Introducción. Según lo encontrado en las bases de datos consultadas, el presente es el primer caso de empiema necessitatis secundario a Citrobacter freundii. Además, constituye uno de los pocos reportes de esta patología en Colombia. Presentación del caso. Se trata de un paciente de 26 años procedente de área rural, con antecedente de déficit cognitivo severo, quien fue llevado al servicio de urgencias por cuadro clínico de 15 días de evolución consistente en deterioro neurológico asociado a astenia, adinamia, fiebre y tos con expectoración purulenta. Al ingreso se tomó radiografía de tórax, encontrando neumonía del lóbulo medio con derrame pleural asociado, por lo que se inició cubrimiento antibiótico empírico. El paciente presentó deterioro clínico y aparición de masa pectoral derecha, por lo que se realizó tomografía computarizada de tórax, evidenciando empiema necessitatis. Luego, se hizo drenaje de la colección, con cultivo negativo para micobacterias y aislamiento de C. freundii. Se dio tratamiento guiado por antibiograma durante ocho semanas, con posterior recuperación completa del cuadro clínico. Conclusión. Además de ser el primer caso de empiema necessitatis por C. freundii, este es importante por la escasa cantidad de reportes en Colombia, considerando que su principal causa es la tuberculosis, la cual es endémica en el país.

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Citrobacter rodentium is a specific murine enteropathogen which causes diarrheal disease characterized by colonic hyperplasia and intestinal inflammation. Recruitment of neutrophils and macrophages constitute a key step to control the infection. Since modulation of the activity of professional phagocytic cells could contribute to improve host´s defences against C. rodentium, we investigated the effect of Lactobacillus delbrueckii subsp. lactis (strain CIDCA 133) on the interaction between murine macrophages (RAW 264.7) and C. rodentium. Phagocytosis, surface molecules and inducible nitric oxide synthase (iNOs) expression were determined by flow cytometry. Reactive oxygen species (ROS) were assessed by fluorescence microscopy. The presence of lactobacilli increased phagocytosis of C. rodentium whereas C. rodentium had no effect on lactobacilli internalization. Survival of internalized C. rodentium diminished when strain CIDCA 133 was present. CD-86, MHCII, iNOs expression and nitrite production were increased when C. rodentium and lactobacilli were present even though strain CIDCA 133 alone had no effect. Strain CIDCA 133 led to a strong induction of ROS activity which was not modified by C. rodentium. Lactobacillus delbrueckii subsp. lactis (strain CIDCA 133) is able to increase the activation of murine macrophages infected with C. rodentium. The sole presence of lactobacilli is enough to modify some stimulation markers (e.g. ROS induction) whereas other markers require the presence of both bacteria; thus, indicating a synergistic effect.

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