The emergence of 16S rRNA methyltransferase (16S-RMTases) poses a major therapeutic challenge, as they confer high-level resistance to all clinically relevant aminoglycosides. In Chile, data on these enzymes remain scarce. This study investigated the epidemiological distribution and genetic relatedness of Klebsiella pneumoniae strains carrying 16S-RMTase genes. Antibiotic susceptibility was assessed using the Kirby-Bauer method and complementary techniques. Gene detection was performed via conventional PCR, and genotyping via ERIC-PCR. Among 1,200 K. pneumoniae clinical strains collected between 1997 and 2023; 233 (19.4%) exhibited high-level resistance to both amikacin and gentamicin, suggesting 16S-RMTase gene carriage. All presumptive strains carried 16S-RMTase genes, with rmtG being the most prevalent (n = 174), followed by armA (n = 30), rmtC (n = 24), and rmtD (n = 5). Genotyping revealed 19 distinct clusters. The rmtG gene was widely distributed, whereas rmtC displayed regional clustering, particularly in Concepción, and was associated with broader resistance profiles, including resistance to carbapenems. In contrast, rmtG-positive strains retained partial susceptibility to these agents. Fisher's exact test revealed associations (p < 0.05) between specific 16S-RMTase genes and non-susceptibility antibiotic profiles. The spread of 16S-RMTase genes since 2007, from Iquique to Puerto Montt, highlights their growing clinical relevance. The recent rise of armA and rmtC suggests a shift in dominant resistance mechanisms.

Extensively drug-resistant (XDR) avian pathogenic Escherichia coli (APEC) poses a global threat to poultry and public health. In this study, we isolated an APEC strain, SDLYRA415, from broilers in Shandong, China, during an outbreak with ~20% mortality. To investigate the genomic characteristics, resistance mechanisms, and pathogenicity of SDLYRA415, drug susceptibility was tested by disk diffusion and minimum inhibitory concentration (MIC); whole-genome sequencing analyzed genomic features and resistance genes; conjugation assays evaluated resistance transfer; animal experiments (BALB/c mice, chicks) assessed pathogenicity. Drug susceptibility test results showed that SDLYRA415 was resistant to 32 antibiotics, showed intermediate resistance to polymyxin B and amikacin, and was only susceptible to tigecycline. Whole-genome sequencing showed SDLYRA415 had a 5.51 Mb genome, including one chromosome and four plasmids. Phylotyping, multilocus sequence typing (MLST), and serotyping classified SDLYRA415 as phylogroup A, ST48, and O6: H16. Plasmids 1, 2, and 4 belonged to IncHI2/IncHI2A/IncN, IncFIB(AP001918)/IncFIC(FII), and p0111 groups, respectively, while plasmid 3 was a novel type. A total of 78 antibiotic resistance genes (ARGs) were detected, including bla CTX-M-55, MCR-1, bla CTX-M-65, NDM-5, etc. Conjugation assays showed that SDLYRA415 transferred polymyxin B resistance to EC600 at 6.5 × 10-7efficiency, and EC600 recipient strains levels of resistance showed significant increases. Pathogenicity tests showed that SDLYRA415 caused 60% mortality in both BALB/c mice and chicks, demonstrating its potential to cause severe disease in mammalian models and underscoring its zoonotic threat. This study offers crucial insights into drug resistance and pathogenic patterns of XDR-APEC, aiding in the development of targeted strategies to prevent poultry colibacillosis and mitigate the public health risks of drug-resistant strains entering the human food chain.

Intraocular infections caused by Pseudomonas aeruginosa are difficult to treat due to bacterial biofilm-mediated antibiotic resistance. We used cationic polypeptide (XXYY) n to evaluate its effect and mechanism against Pseudomonas aeruginosa biofilm and its efficacy against Pseudomonas aeruginosa intraocular infection. Microbroth dilution showed that the MIC90 of (LLKK)3C against Pseudomonas aeruginosa was 32 μg/mL. After continuous passage for 10 generations, the stability of antibacterial activity of (LLKK)3C against Pseudomonas aeruginosa was better than that of amikacin. TEM, SEM and live/dead staining demonstrated that (LLKK)3C was able to destroy the integrity of bacterial and biofilm and exert antibacterial activity by interacting with phosphatidyl glycerol on the membrane to destroy the bacterial membrane. Electrophoretic gel and Alphafold3 demonstrated that (LLKK)3C binds to bacterial DNA through charge interactions. In the rabbit endophthalmitis model, the intraocular bacterial load decreased after intravitreal injection (LLKK)3C treatment (vs untreated, P < 0.05). Studies have shown that (LLKK)3C has synergistic antibacterial effects through the dual mechanism of targeting membrane destruction and DNA binding, which provides a new treatment strategy for biomembrane-associated intraocular infections.

Orbital nocardiosis is an uncommon pyogranulomatous infection rarely reported in immunocompetent individuals. Trauma is a major predisposing factor. We describe three cases of orbital nocardiosis highlighting the clinical features, microbiological profile, and histopathological characteristics. This retrospective case series included patients with histopathological and microbiological confirmed orbital nocardiosis diagnosed between January 2016 and December 2025 across the L V Prasad Eye Institute network in India. Cases were identified through electronic medical records, and data on demographics, clinical features, imaging, and treatment were collected. Three immunocompetent patients (2 males, 1 female; age 34-58 years) presented with chronic orbital inflammation following remote trauma. Clinical findings included preseptal abscesses, diffuse orbital masses, discharging sinuses, bony erosions, and intracranial extension (in one case). Imaging showed ill-defined soft tissue lesions involving the lacrimal gland, paranasal sinuses, or orbital roof. Nocardia nova was confirmed by sequencing in one patient, and two patients had co-infection with Staphylococcus aureus. Treatment included surgical debridement, intravenous amikacin, and oral trimethoprim - sulfamethoxazole. Two patients achieved complete resolution, and one patient was lost to follow up. Orbital nocardiosis can occur in immunocompetent patients, particularly after trauma. Early suspicion, tissue diagnosis, and prolonged antimicrobial therapy are essential to improve outcomes.

The sustainable expansion of striped catfish (P. hypophthalmus) aquaculture in Egypt is constrained by environmental stressors, recurrent bacterial infections, and rising antimicrobial resistance. This study offers the first integrated assessment of water quality parameters, pathogen identity and virulence, antimicrobial resistance (AMR) patterns, and the immunoprotective potential of dietary S. platensis under Egyptian farming conditions. Field assessments from naturally infected farms revealed chronic hypoxia (mean DO 3.66 mg L[-1]) and persistent thermal stress (32.6 °C), both significantly outside recommended ranges, while nitrite levels approached the known toxicity threshold. Two major bacterial pathogens-Aeromonas hydrophila and Streptococcus agalactiae-were isolated with comparable prevalences across liver, kidney, and spleen tissues. Molecular characterization (16S rRNA sequencing; GenBank PX371951 and PX371952) confirmed their identity. Probit challenge assays demonstrated markedly higher virulence for A. hydrophila (LD50 = 1.05 × 10[5] CFU fish[-1]) compared with S. agalactiae (LD50 = 1.06 × 10[6] CFU fish[-1]). Both species exhibited multidrug resistance, notably universal resistance to penicillin (A. hydrophila) and high resistance to ampicillin, tetracycline, and amikacin (S. agalactiae), underscoring the limitations of empirical antibiotic use. A 4-week feeding trial demonstrated that dietary S. platensis (5 g kg[-1]) significantly enhanced innate immunity, reduced stress (lower cortisol) and oxidative damage (lower malondialdehyde), and improved antioxidant enzyme activities (SOD, catalase). Spirulina supplementation reduced mortality by 22.6% after A. hydrophila challenge and by 79.2% after S. agalactiae challenge, demonstrating substantial immunomodulatory and protective benefits. Overall, this work highlights critical environmental stressors and AMR challenges in Egyptian catfish farming and identifies Spirulina platensis as a practical, eco-friendly immunostimulant that can reduce disease burden in striped catfish aquaculture. Overall, this work highlights critical environmental stressors and AMR challenges in Egyptian catfish farming and identifies Spirulina platensis as a practical, eco-friendly immunostimulant that can reduce disease burden in striped catfish aquaculture, suggesting promising avenues for improving disease resilience in health management strategies.