Claudia Adriana Colín-Castro

Carbapenem resistance in Pseudomonas aeruginosa is a growing public health concern. Multiple mechanisms of antimicrobial resistance have been described. While surveillance often focuses on carbapenemase detection, non-carbapenemase mechanisms and their interplay with the genomic background remain underexplored. This study aimed to characterize how genomic background influences carbapenem resistance mechanisms and adaptive responses in carbapenem-resistant P. aeruginosa (CRPA). A total of 136 CRPA clinical isolates collected from 28 healthcare centres across Mexico were analysed through core genome phylogeny, sequence type (ST) assignment, resistome profiling, oprD variant analysis, bacterial growth kinetics under imipenem and meropenem exposure and qRT-PCR-based expression of oprD , mexA , mexC , mexE and mexY genes. Isolates clustered into PAO1 and PA14 phylogroups. ST309 was the most prevalent ST (29/136). Pseudomonas paraeruginosa lineage was also identified within these isolates. Phylogenetic clustering of antibiotic resistance genes was observed across phylogroups. In 36% (49/146) of the isolates, β -lactamases ( bla _VIM 16%, bla _GES 11% and bla _IMP 11%) were identified with carbapenemase activity previously reported. Potentially inactivating oprD variants were observed in 75% (102/136) of isolates, with nonsense and frameshift variants associated with resistance phenotypes. Isolates harbouring carbapenemase-encoding genes (CEGs) exhibited stable lag phases regardless of antibiotic exposure, whereas isolates lacking CEGs showed significantly prolonged lag phases. Overexpression of mexA, mexC and mexY genes was observed in 39% (7/18), 17% (3/18) and 39% (7/18) of isolates, respectively, under antibiotic-free condition, and increased under carbapenem exposure. mexA expression was significantly higher in PAO1 isolates (6/18) under antibiotic-free condition and in PA14 isolates under imipenem exposure (5/18). Carbapenem resistance in P. aeruginosa is shaped by both phylogenetic background and antibiotic-driven stress responses. This study provides an integrated analysis of resistance mechanisms – including gene expression and physiological adaptation – across major phylogenetic lineages in clinical isolates recovered in Mexico, underscoring the importance of considering non-carbapenemase resistance pathways in surveillance and treatment strategies.

Bloodstream infection is one of the most important and increasing complications in patients with severe burns. Most of the species affecting this population are Gram-negative bacilli that exhibit antimicrobial resistance. We conducted this study to determine the antimicrobial susceptibility profile and resistance mechanisms of these bacterial infections and their clinical associations on morbidity and mortality. We analyzed a retrospective cohort of burn patients. All patients included in this study had monobacterial blood stream infections during their hospital stay. We performed phenotypic and genotypic tests to determine the antimicrobial resistance mechanism and profile of each strain. Univariate and multivariate logistic regression analysis was performed between variables. We found 109 patients with monobacterial bacteremia. Pseudomonas spp. (50.7%), A. baumannii (46.4%), and Klebsiella spp. (13.8%) were the most common causative microorganisms. The Pseudomonas spp. isolates showed resistance to imipenem (81.5%), mainly by class A and class B carbapenemases. The A. baumannii isolates conferred resistance to imipenem (56.2%), mainly by class D carbapenemases. One quarter of Klebsiella spp. showed resistance to 3rd generation cephalosporins. We also observed that a total body surface area greater than 40% and three or more different types of invasive procedures might be related to increased mortality. Multidrug resistance is highly present. The extent of the burned area and a high number of different types of invasive procedures had an impact in decreasing survivorship in burn patients with bacteremia.

(1) Background: Pseudomonas aeruginosa is a Gram-negative bacterium with several intrinsic and acquired antimicrobial resistance mechanisms. The spread of carbapenemase-encoding genes, an acquired mechanism, enables carbapenem resistance in clinical settings. Detection of the carbapenemase-producer strains is urgent. Therefore, we aimed to characterize carbapenemase production in the clinical strains of P. aeruginosa at a tertiary-care center. (2) Methods: We included clinical strains of P. aeruginosa (from August 2011 to December 2018) with resistance towards at least one carbapenem. Strains were isolated in a tertiary-care center in Mexico City. Antimicrobial susceptibility profiles were determined by broth microdilution. Screening for carbapenemase-encoding genes was performed in all strains. Phenotypic assays (CarbaNP and mCIM) were conducted. Additional modifications to mCIM were also tested. (3) Results: One-hundred seventy-one P. aeruginosa strains out of 192 included in this study were resistant towards at least one of the carbapenems tested. Forty-seven of these strains harbored a carbapenemase-encoding gene. VIM (59.6%) and GES (23.4%) were the most frequently found carbapenemases in our study, followed by IMP (14.9%). (4) Among the most frequent carbapenemase genes identified, metallo-ß-lactamases were the most prevalent, which impair new treatment options. Searching for carbapenemase genes should be performed in resistant isolates to stop transmission and guide antimicrobial treatment.

The identification of carbapenemase-producing Enterobacterales and Pseudomonas aeruginosa is important for treating and controlling hospital infections. The recommended methods for their identification require a long waiting time, technical training, and expertise. Lateral flow immunoassays such as NG-Test CARBA 5^® overcome these needs. We analyzed 84 clinical isolates of carbapenem-resistant Enterobacterales and P. aeruginosa from four different hospitals in a two-year period. Antimicrobial resistance patterns were confirmed with the broth dilution method. Evaluation of KPC, VIM, NDM, IMP, and OXA-48-like enzymes was performed and compared to NG-Test CARBA 5 and phenotypic assays. Enterobacterales represented 69% of isolates and P. aeruginosa represented 31%. Carbapenemase-producing strains were 51 (88%) of Enterobacterales and 23 (88.4%) of P. aeruginosa; 20 (34%) and 23 (88%) were Class B ß-lactamases, respectively. The NG-Test CARBA 5^® assay for Enterobacterales showed high sensitivity (98%), specificity (100%), and PPV (100%); however, it did not for P. aeruginosa. The Kappa concordance coefficient was 0.92 for Enterobacterales and 0.52 for P. aeruginosa. NG-Test CARBA 5^® is a fast and easy-to-use assay. In Enterobacterales, we found excellent agreement in our comparison with molecular tests. Despite the low agreement in P. aeruginosa, we suggest that this test could be used as a complementary tool.

The sterilization processes of nanoparticles (NP) by autoclaving and filtration are two of the most utilized methods in the pharmaceutical industry but are not always a viable option. For this reason, the search for alternative options such as UV and gamma radiation is of interest. In this work, we evaluated both types of sterilization on two types of NP in solid state widely employed in the literature for biomedical applications, poly-(ε-caprolactone) and poly(d,l-lactide-co-glycolide) acid NP stabilized with polyvinyl alcohol. Physicochemical properties and cell viability were studied pre- and post-sterilization. The efficiency of irradiation sterilization was performed by a test of sterility using 1 × 10⁸ CFU/mL of Escherichia coli, Staphylococcus aureus, and Candida albicans. Microbiological monitoring revealed that both methods were sufficient for sterilization. After the UV irradiation sterilization (100 µJ/cm²), no substantial changes were observed in the physicochemical properties of the NP or in the interaction or morphology of human glial cells, though 5 and 10 kGy of gamma irradiation showed slight changes of NP size as well as a decrease in cell viability (from 100 µg/mL of NP). At 5 kGy of radiation doses, the presence of trehalose as cryoprotectant reduces the cell damage with high concentrations of NP, but this did not occur at 10 kGy. Therefore, these methods could be highly effective and low-processing-time options for sterilizing NP for medical purposes. However, we suggest validating each NP system because these generally are of different polymer-composition systems.