Hypervirulent Klebsiella pneumoniae (hvKp) has emerged globally as a major public health concern, often associated with severe community-acquired and healthcare-associated human infections. Despite alerts from PAHO/WHO on convergent hvKp strains with multidrug resistance in Latin America, comprehensive data from Brazil, the region's largest country, remain lacking. We performed a retrospective and prospective large-scale surveillance of clinical, veterinary, and community isolates to identify hypervirulent and resistant K. pneumoniae. Among 1,008 isolates screened, one strain (ID_074_25) met hvKp criteria, displaying key virulence loci. Whole-genome sequencing confirmed its genomic features, including a novel sequence type and a novel cluster in NCBI Pathogen Detection tool. This study underscores the need for national surveillance and capacity-building in reference laboratories.

Background:After over a decade of minimal circulation, DENV-3 reemerged in Brazil in 2023, driven by the newly detected lineage 3III_B.3.2. Elucidating the patterns of DENV-3 spread and impact on public health, is critically important in the context of Brazil's hyperendemic dengue scenario. Here, we aimed to investigate the spatiotemporal dispersion of this new lineage and its epidemiological impact in Brazil. Methods:We generated 87 near-complete DENV-3 genomes, sampled in nine different Brazilian states, that were analysed with publicly available sequences. Phylogeographic reconstructions inferred introduction events and spatial dispersion of lineage 3III_B.3.2. In parallel, dengue cases notifications (2023-2025) were used to fit multiple logistic regression models assessing associations between DENV serotypes and severity, adjusting for demographic and spatiotemporal covariates. Findings:We detected at least 14 introductions of lineage 3III_B.3.2 into Brazil during 2023-2024, followed by diversification into six region-specific clades. Epidemiological analyses applied to the RT-qPCR dengue confirmed cases showed an adjusted odds ratios for severe dengue ranging from 1.24 to 1.71 for DENV-2 and from 1.47 to 1.94 for DENV-3, across different settings and using DENV-1 infection as the reference category. Sensitivity analysis to evaluate potential recent heterotypic infection among infants ≤2 years adjusted by confunders showed an association between DENV-2 and severe dengue, while DENV-3 estimates were not statistically significant. Interpretation:Our results reveal a dynamic pattern of multiple introductions and regionally structured spread of 3III_B.3.2, which may represent a general feature as a similar reconstructed history has also been observed for other DENV serotypes/lineages in Brazil. Although the association observed between DENV-2 and DENV-3 and dengue severity may be influenced by secondary infections, our findings underscore that the co-circulation of multiple serotypes contributes to more severe epidemic outcomes and emphasize the need for ongoing DENV genomic surveillance. Funding:DECIT, CGLAB, Fiocruz, CNPq, and FAPES.

IntroductionDiphtheria is a potentially fatal disease that still causes deaths mainly in unvaccinated children. Over the last decades, the incidence of this disease has reduced drastically in face to the increase in vaccination coverage. Diphtheria is mainly caused by toxigenic Corynebacterium diphtheriae, however, in more recent years, invasive infections due to nontoxigenic Corynebacterium diphtheriae have emerged. Given this epidemiological threat, the continued surveillance remains essential to guide prevention and control measures.MethodologyUsing whole genome sequencing, we characterized 299 Corynebacterium diphtheriae isolates, assessing their clinical origin, age distribution of patients, tox gene carriage, antimicrobial resistance markers, and phylogenetic relationships.ResultsThe tox gene was identified in 255 isolates (85.3%). Antimicrobial resistance genes aph(3’’)-Ib, aph(3’)-Ia, aph(6)Id, cmx, tet(33), tet(O), tet(W), and tet(Z) were detected in low (<10%) frequencies, but sul1 was found in 72 (24.1%) isolates. Phylogenetic analyses identified 11 main clades comprising 286 isolates, represented by 46 different sequence types (ST); the remaining 13 isolates were distributed in the other 12 ST. Twenty-one novel ST were described, comprising 51 isolates.DiscussionOur study represents the largest genomic survey of Corynebacterium diphtheriae in Latin America. These results enhance global understanding of diphtheria and reinforce the need for vigilance against reemergence in areas with suboptimal vaccination coverage.

Carbapenemase-producing Enterobacterales (CPE) represent a major global health threat due to limited therapeutic options and high mortality. While isolates harboring a single carbapenemase are increasingly common, polymicrobial bloodstream infections involving multiple carbapenemase-producing species remain rare and pose substantial diagnostic and therapeutic challenges. We describe a case of polymicrobial bloodstream infection in a neutropenic patient with relapsed acute myeloid leukemia. Blood cultures yielded three distinct Enterobacterales species. Identification was performed by MALDI-TOF MS, antimicrobial susceptibility testing followed CLSI guidelines, and carbapenemase production was screened by immunochromatographic assay and PCR. Whole-genome sequencing was conducted for all isolates, with in silico multilocus sequence typing, resistome characterization, plasmid replicon analysis, and phylogenetic reconstruction. A literature review (2015–2025) was performed to contextualize this finding. Three carbapenem-resistant Enterobacterales were simultaneously isolated from blood cultures: Citrobacter freundii producing NDM-1, Klebsiella michiganensis producing IMP-16, and Enterobacter hormaechei producing KPC-2. One isolate harbored mcr-9 gene. The patient developed septic shock but was successfully treated with a targeted combination therapy of ceftazidime-avibactam plus aztreonam, supplemented with amikacin, alongside catheter removal and supportive care. Follow-up blood cultures were negative, and no secondary transmission was detected. We report a case of a polymicrobial bloodstream infection caused by three different carbapenemase-producing Enterobacterales species, each expressing a distinct carbapenemase. This case underscores the clinical value of rapid molecular diagnostics, highlights the need for strengthened surveillance and tailored antimicrobial strategies in high-risk patients facing extreme antimicrobial resistance scenarios.

Background:Invasive meningococcal disease (IMD) remains a major cause of mortality worldwide, yet its dynamics in the Brazilian Amazon are poorly understood. Following the COVID-19 pandemic, serogroup B IMD resurged in Brazil, raising concerns about changing transmission patterns in regions with limited healthcare access. Methods:We conducted an epidemiological and genomic investigation of an ongoing IMD outbreak in Pará State, Brazilian Amazon, between 2023 and 2025. Clinical, demographic, and outcome data were integrated with whole-genome sequencing of 69 isolates. Multivariate logistic regression identified independent predictors of mortality, and phylogenomic analyses characterized transmission dynamics and clonal expansion. Results:A total of 343 IMD cases were identified, of which 321 (93.6%) were caused by serogroup B, resulting 34 deaths (case-fatality rate, 10.6%). Incidence increased up to 5-fold compared with national rates and disproportionately affected young children and adults. Mortality was independently associated with meningococcemia (adjusted odds ratio, 84.52; 95% confidence interval, 5.70-1253.65; P = .001); however, this finding should be interpreted with caution due to the small number of meningococcemia cases. Genomic analysis identified a predominant ST-7983/cc60 lineage, accounting for 64 of 69 sequenced isolates (92.7%). This lineage displayed limited genetic diversity (median, 7 single nucleotide polymorphisms), consistent with sustained regional transmission across multiple municipalities. Conclusions:A highly clonal serogroup B meningococcal outbreak emerged in the Brazilian Amazon following the COVID-19 pandemic, with substantial mortality and rapid geographic spread. These findings highlight the importance of strengthened genomic surveillance and support targeted vaccination strategies to improve outbreak preparedness in underserved regions.

This study aimed to optimize a Fourier Transform Infrared (FT-IR) based protocol using the IR Biotyper® system for Leptospira strains and to provide the first spectral insights supporting its feasibility for serogroup and serovar differentiation. Reference Leptospira strains were cultured in Ellinghausen–McCullough–Johnson–Harris medium. A sample preparation workflow was optimized to accommodate liquid cultures, including chemical and thermal inactivation protocols to ensure biosafety. FT-IR spectra were acquired using the IR Biotyper® spectrometer and analyzed by Principal Component Analysis (PCA) in the 1300–800 cm⁻¹ spectral region. Whole Genome Sequencing (WGS) was used as the reference approach for taxonomic confirmation. Identification and serovar differentiation from genomic data were performed using the jSpecies, KmerFinder, and Pathogenwatch platforms. The sample preparation methods tested produced spectra suitable for analysis while ensuring biosafety. Spectral acquisition showed good reproducibility for most serovars across technical and biological replicates. Analysis of WGS performed using the jSpecies platform successfully differentiated the two major human-pathogenic serovars, Icterohaemorrhagiae and Copenhageni, whereas other bioinformatics tools showed limitations. PCA of FT-IR spectra generated by the IR Biotyper® demonstrated promising discriminatory potential among the serovars and serogroups evaluated, including closely related serovars such as Icterohaemorrhagiae and Copenhageni and serovars within the Australis and Sejroe serogroups. The IR Biotyper offers a rapid FT-IR approach for Leptospira typing. Under the experimental conditions evaluated, the method allowed differentiation of some serovars. Although preliminary, these findings suggest that FT-IR may represent a promising complementary tool for epidemiological surveillance of leptospirosis.

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a common pathogen prevalent in Brazilian hospitals. Worldwide, dissemination of CRAB is associated with the Clonal Complex 2 (CC2); in South America, however, CC1, 15, 25, and 79 are the most prevalent clones. In July 2020, our reference laboratory received the first CC2 isolates from a COVID-19 hospital, and, in the following months, this clone was detected in 15 other Brazilian institutions. To understand the clonal structure of this emerging pathogen, we characterize 89 isolates by whole-genome sequencing and antimicrobial susceptibility testing. Disk diffusion revealed resistance to all beta-lactams, aminoglycosides, fluoroquinolones, folate pathway antagonists, and tetracyclines, but susceptibility to polymyxin B. Resistome analysis identified diverse antimicrobial resistance genes, including the blaOXA-23 associated with Tn2006, and armA in AbGRI3, conferring resistance to beta-lactams and aminoglycosides, respectively. Fine-scale phylogeny based on single nucleotide polymorphisms (SNPs) revealed that Brazilian CRAB CC2 isolates were closely related, presenting up to 755 SNPs in pairwise comparison. We did not observe hospital-specific subclones, indicating multiple introductions and/or inter-hospital dissemination. This study reports the rapid arrival and spread of CRAB CC2 isolates in multiple hospitals, likely driven by infection control deficiencies experienced during the COVID-19 pandemic.

Oropouche virus (OROV), historically endemic to the Amazon, had spread to nearly all Brazil states by 2024; Espírito Santo emerged as a transmission hotspot in the Atlantic Forest biome. We characterized the epidemiologic factors driving OROV spread in nonendemic southeast Brazil, analyzing environmental and agricultural conditions contributing to viral transmission. We tested samples from 29,080 suspected arbovirus-infected patients quantitative reverse transcription PCR for OROV and dengue, chikungunya, Zika, and Mayaro viruses. During March‒June 2024, the state had 339 confirmed OROV cases, demonstrating successful local transmission. Spatial analysis revealed that most cases clustered in municipalities with tropical climates and intensive cacao, robusta coffee, coconut, and pepper cultivation. Phylogenetic analysis identified the Espírito Santo OROV strains as part of the 2022-2024 Amazon lineage. The rapid spread of OROV outside the Amazon highlights its adaptive potential and public health threat, emphasizing the need for enhanced surveillance and targeted control measures.

Corynebacterium diphtheriae is the main etiological agent of diphtheria, a potentially fatal disease whose most severe signs and symptoms result from the action of an exotoxin, the diphtheria toxin (DT). Although non-toxigenic C. diphtheriae strains have been associated with several diseases, including cutaneous infections and endocarditis, they are not monitored in many countries, and their mechanisms of virulence and antimicrobial resistance remain underexplored. Therefore, this study aimed to provide a comprehensive characterization -through genomic, in vitro, and in vivo analyses - of a non-toxigenic C. diphtheriae strain (46855) isolated from a leg lesion, highlighting its pathogenic potential and resistance profile. The isolate was assigned to a novel sequence type (ST-925) and was found to be resistant to tetracycline and rifampin. Multiple antimicrobial resistance genes were predicted in the genome, such as tet(33), rbpA, and rpoB2, in addition to mutations in the rpoB gene. A diverse set of virulence-associated genes related to adhesion, iron uptake systems, gene regulation, and post-translational modification was also identified. The isolate was able to form biofilm in vitro and exhibited strong virulence in Galleria mellonella larvae and A549 human pneumocyte cells. Finally, the structural analysis of the rpoB gene, carried out for the first time in this study, linked the observed mutations to rifampin resistance in C. diphtheriae. In summary, the data revealed that C. diphtheriae 46855, although non-toxigenic, harbors multiple genes associated with antimicrobial resistance and virulence, emphasizing the need for greater surveillance and functional studies on non-toxigenic strains.

This study aimed to investigate the diversity of Acinetobacter spp. isolated from aquatic environments along the Brazilian coast, with a focus on environmental reservoirs of clinically relevant resistance genes. Twenty-three Acinetobacter isolates were recovered from marine animals, floating plastic, and surface water samples collected in two contrasting Brazilian regions: the heavily polluted Guanabara Bay (Rio de Janeiro) and the pristine Fernando de Noronha Archipelago (Pernambuco). Seven species were identified, with A. venetianus (n = 13) and A. johnsonii (n = 4) being the most frequent. Two A. johnsonii isolates carried the metallo-β-lactamase gene blaNDM-1, along with resistance to fluoroquinolones and carbapenems. Resistance to polymyxins and aminoglycosides was also observed in A. haemolyticus, A. baumannii, and A. modestus. ApaI-PFGE dendrogram and phylogenetic analyses based on single nucleotide position (SNPs) revealed high genetic diversity, and global comparisons placed the environmental isolates in lineages distinct from those commonly associated with healthcare-associated infections. This study highlights the diversity of Acinetobacter spp. in aquatic environments and their potential role as reservoirs of clinically important resistance genes, including blaNDM-1. By uncovering resistance mechanisms in environmental Acinetobacter strains, this work reinforces the relevance of environmental surveillance for One Health initiatives, particularly in regions with significant anthropogenic impact.

The accurate identification and characterization of Aeromonas species are essential to understand their ecological roles and potential health impacts. This study analyzed 90 Aeromonas isolates from various sources using whole genome sequencing (WGS) and matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). Species identification by WGS, based on Average Nucleotide Identity (ANI ≥96%), revealed inconsistencies in 12.2% of MALDI-TOF MS results, for species not represented in its database. Phylogenetic analyses using single nucleotide polymorphism (SNP) data were concordant in resolving species-level clusters and revealing intra-species diversity. This study reinforces the value of WGS and complementary genomic approaches as reliable tools for Aeromonas species identification, population structure analysis, and integrated One Health surveillance. The integration of genomic tools into routine diagnostics may enhance the capacity of laboratories, particularly in low and middle income countries to monitor emerging resistance and better understand the evolutionary and epidemiological dynamics of Aeromonas in clinical and environmental settings.

This study aimed to evaluate the antimicrobial susceptibility and clonal relatedness of Klebsiella pneumoniae isolates recovered from the milk of cows with mastitis in a large-scale study that clinical severity was scored. A total of 48 K. pneumoniae complex isolates were subjected to in vitro antimicrobial susceptibility tests (AST), PCR for carbapenemase-encoding genes, and molecular typing by pulsed-field gel electrophoresis (PFGE). Thirteen isolates, selected by PFGE type and AST results were subjected to whole-genome sequencing (WGS) for the identification of sequence types (STs) and the detection of antimicrobial resistance genes and virulence-encoding genes. A total of 39 different PFGE restriction profiles were identified. Thirteen different STs, including two novel STs, were identified among the 13 sequenced strains. The blaCTX-M-8, qnrE1, aadA2, cmlA4, dfrA15, sul1, tetA, and tetB genes were identified. Two isolates presented the yersiniabactin-encoding gene ybtAEPQSTUX. Klebsiella pneumoniae isolates from the milk of cows with mastitis clinically scored revealed high genetic diversity, according to both PFGE and MLST analysis, as well as harboring resistance genes commonly found in human clinical isolates.

AIMS:To evaluate the antimicrobial susceptibility and clonal relatedness of Klebsiella pneumoniae isolates recovered from diseased companion animals at a Teaching Veterinary Hospital in Brazil. METHODS AND RESULTS:A collection of 59 K. pneumoniae complex isolates originating from dogs and cats were subjected to antimicrobial susceptibility testing, multiple antimicrobial resistance (MAR) index determination, polymerase chain reaction for carbapenemase-encoding genes, and molecular typing by pulsed-field gel electrophoresis (PFGE). Nineteen isolates were subjected to whole-genome sequencing (WGS). MAR indices ranged from 0 to 0.73, 50 different PFGE restriction profiles were identified. No carbapenemase genes were detected. Seventeen different sequence types were identified among the 19 sequenced strains, and extended-spectrum β-lactamase genes were detected in five of them. CONCLUSIONS:Klebsiella pneumoniae isolates from companion animals revealed high genetic diversity, both in PFGE and multi-locus sequence typing analysis; conversely, they presented resistance genes commonly found in human clinical isolates.

Este trabalho descreve a experiência do Instituto Adolfo Lutz (IAL) na implantação de ensaios de PCR em tempo real (qPCR) in house aplicados ao diagnóstico de meningites bacterianas (MB) causadas por Neisseria meningitidis (Nm), Streptococcus pneumoniae (Spn) e Haemophilus influenzae (Hi). São apresentadas estratégias para o aprimoramento dos ensaios de qPCR originalmente propostos, incluindo avaliação de diferentes alvos genéticos e incorporação de controle interno da qualidade pela detecção de gene constitutivo humano (RNase P) nas amostras biológicas processadas na rotina. Descreve os ensaios de qPCR estabelecidos para identificação dos principais genogrupos de Nm e dos seis genotipos de Hi, que geram informações capazes de contribuir para avaliação da efetividade das vacinas conjugadas presentes no Programa Nacional de Imunização. Mostra o repasse dos ensaios de qPCR para outros Laboratórios de Saúde Pública do país e a contribuição do uso desses ensaios na vigilância laboratorial das MB. Ademais, apresenta outras contribuições do IAL para o aprimoramento do diagnóstico laboratorial da doença, como a produção de controles genéticos que são distribuídos para os laboratórios públicos do país, avaliação do uso de cartões de papel de filtro no transporte de amostras clínicas entre laboratório local e de referência e avaliação de kits comerciais empregados no diagnóstico das MB. Por último, menciona as considerações finais do trabalho, com reflexões acerca do futuro do uso dos ensaios de qPCR no diagnóstico laboratorial das MB.

Public health faces daily challenges due to increasing reports of pathogenic microorganisms with new antimicrobial resistance. Klebsiella michiganensis, an emerging pathogen, poses difficulty in its identification using conventional techniques. This study presents the first documented case of NDM-1-producing K. michiganensis in Brazil, identified as the new ST418. Initially, the isolate from a tracheal secretion was misidentified as K. oxytoca. However, accurate identification was achieved through ANI analyses. Whole-genome sequencing was conducted to characterize the genetic context of the resistance genes, to identify virulence factors, and to construct a phylogenetic tree. The blaNDM-1 gene was found to be harbored on an IncFIB plasmid approximately 112 kb in length, which was transferable in conjugation assays. The detection of carbapenem resistance genes in this species highlights the importance of public health vigilance, as it may serve as a reservoir and disseminator of significant resistance genes.

BACKGROUND:Infections by carbapenem-resistant Pseudomonas aeruginosa (CRPA) have been associated with high morbidity and mortality among solid organ recipients. OBJECTIVES:To delineate the epidemiological and molecular characteristics of a recurrent outbreak of imipenem (IMP)-producing P. aeruginosa (CRPA) among kidney transplant (KT) recipient METHODS: We described a recurring CRPA outbreak in a KT ward, divided into two periods: before unit closure (Feb 2019-2020) and after reopening (Aug 2020-Dec 2023). Routine surveillance cultures (SCs) were performed using axillary-perineum-rectal swabs with immunochromatographic tests. A case-control study identified risk factors for CRPA acquisition. Pulsed-field gel electrophoresis and whole genome sequencing characterized the strains. RESULTS:After reopening, new cases arose from patients previously colonized, peaking 18 months later. A total of 67 KT recipients with CRPA-IMP-producing strains were identified. All except one sequenced strain belonged to the ST446 clone, differing by a maximum of 110 single nucleotide polymorphisms. Forty-five (67.2%) cases were identified through SC, with 45.7% showing intermittent SC positivity. Patients remained colonized for up to 623 days. Twenty-four (35.8%) patients had infections, with the most common site being the urinary tract. Identified risk factors included older age, deceased donor, re-transplantation, reoperation, carbapenem or quinolone use, lymphopenia, hospital stay >10 days, and the first 60 days post-KT. CONCLUSION:KT recipients can harbor CRPA for extended periods, and detecting CRPA-colonized patients is challenging. These characteristics highlight the patient as the major source and a critical point in outbreak control.

Although diphtheria is a vaccine-preventable disease, numerous cases are still reported around the world, as well as outbreaks in countries, including European ones. Species of the Corynebacterium diphtheriae complex are potentially toxigenic and, therefore, must be considered given the possible consequences, such as the circulation of clones and transmission of antimicrobial resistance and virulence genes. Recently, Corynebacterium rouxii was characterized and included among the valid species of the complex. Therefore, two cases of C. rouxii infection arising from infections in domestic animals are presented here. We provide molecular characterization, phylogenetic analyses, genome sequencing, and CRISPR-Cas analyses to contribute to a better understanding of the molecular bases, pathogenesis, and epidemiological monitoring of this species, which is still little studied. We confirmed its taxonomic position with genome sequencing and in silico analysis and identified the ST-918 for both strains. The clinical isolates were sensitive resistance to benzylpenicillin and rifampin. Antimicrobial resistance genes, including tetB, rpoB2, and rbpA genes, were predicted. The bla and ampC genes were not found. Several virulence factors were also detected, including adhesion, iron uptake systems, gene regulation (dtxR), and post-translational modification (MdbA). Finally, one prophage and the Type I-E CRISPR-Cas system were identified.

Cases of diphtheria, even in immunized individuals, are still reported in several parts of the world, including in Brazil. New outbreaks occur in Europe and other continents. In this context, studies on Corynebacterium diphtheriae infections are highly relevant, both for a better understanding of the pathogenesis of the disease and for controlling the circulation of clones and antimicrobial resistance genes. Here we present a case of cutaneous infection by multidrug-resistant Corynebacterium diphtheriae and provide its whole-genome sequencing. Genomic analysis revealed resistance genes, including tet(W), sul1, cmx, rpoB2, rbpA and mutation in rpoB. We performed phylogenetic analyzes and used the BRIG to compare the predicted resistance genes with those found in genomes from other significant isolates, including those associated with some outbreaks. Virulence factors such as spaD, srtBC, spaH, srtDE, surface-anchored pilus proteins (sapD), nonfimbrial adhesins (DIP0733, DIP1281, and DIP1621), embC and mptC (putatively involved in CdiLAM), sigA, dtxR and MdbA (putatively involved) in post-translational modification, were detected. We identified the CRISPR-Cas system in our isolate, which was classified as Type II-U based on the database and contains 15 spacers. This system functions as an adaptive immune mechanism. The strain was attributed to a new sequence type ST-928, and phylogenetic analysis confirmed that it was related to ST-634 of C. diphtheriae strains isolated in French Guiana and Brazil. In addition, since infections are not always reported, studies with the sequence data might be a way to complement and inform C. diphtheriae surveillance.

Until 2015, polymyxin resistance was primarily attributed to chromosomal mutations. However, with the first report of mobile colistin resistance (mcr-1) in commensal Escherichia coli from food animals in China, the landscape has changed. To evaluate the presence of polymyxin resistance in Salmonella spp., a drop screening test for colistin and polymyxin B was carried out on 1156 isolates of non-human origin (animals, food, and the environment), received in Brazil, between 2016 and 2021. Subsequently, 210 isolates with resistant results in the drop test were subjected to the gold-standard test (broth microdilution) for both colistin and polymyxin B. Whole-genome sequencing (WGS) of 102 resistant isolates was performed for a comprehensive analysis of associated genes. Surprisingly, none of the isolates resistant to colistin in the drop test harbored any of the mcr variants (mcr-1 to mcr-10). WGS identified that the most common mutations were found in pmrA (n= 22; T89S) and pmrB (n = 24; M15T, G73S, V74I, I83A, A111V). Other resistance determinants were also detected, such as the aac(6')-Iaa gene in 72 isolates, while others carried beta-lactamase genes (bla(TEM-1) bla(CTX-M-2), bla(CMY-2)). Additionally, genes associated with fluoroquinolone resistance (qnrB19, qnrS1, oqxA/B) were detected in 11 isolates. Colistin and polymyxin B resistance were identified among Salmonella from non-human sources, but not associated with the mcr genes. Furthermore, the already-described mutations associated with polymyxin resistance were detected in only a small number of isolates, underscoring the need to explore and characterize unknown genes that contribute to resistance.