Background: The emergence of carbapenem and colistin co-resistant Escherichia coli poses a huge challenge to infection control. The purpose of this study was to clarify the mechanism of the carbapenems and colistin co-resistance in E. coli strains. Methods: Antimicrobial susceptibility test was carried out by agar dilution methods and colistin resistance was confirmed by broth microdilution methods. Whole genome sequencing was carried out, and resistance genes, sequence types and virulence genes of carbapenems and colistin co-resistance E. coli isolates were analyzed. Results: The results showed that among the 176 carbapenem-resistant Enterobacteriaceae strains, 5 multidrug resistant E. coli strains exhibiting coresistance to carbapenem and colistin. The main mechanism of 5 E. coli strains in this study was generating carbapenem. Four E. coli strains were mcr-positive, while one mcr-negative strain had a new MgrB mutation. The blaNDM-5, blaCTX-M-65, blaOXA-10, blaTEM-1 and mcr-1.1 genes were simultaneously detected in E. coli 20IR1127 strain belonging to ST156 lineage. Other antimicrobial resistance genes encoding aminoglycosides-, sulfonamide-, chloramphenicol-, tetracyclines- and macrolides resistance were also detected. Conclusion: The main mechanisms of carbapenem and colistin resistance were encoded by bla_NDM and mcr1.1, meanwhile mgrB mutations also contribute to colistin resistance. To our knowledge, this study is the first to report of E. coli ST156 strain in which the bla_NDM-5, bla_CTX-M-65, bla_OXA-10, bla_TEM-1 and mcr1.1 genes coexist. In addition, there is also an E. coli ST457 strain, which carries bla_TEM-1, bla_NDM-9, bla_CTX-M-199 and is positive for mcr1.1 gene.

Salmonella serotyping is essential for epidemiological studies and clinical treatment guidance. However, traditional serological agglutination methods are time-consuming, technically complex, and difficult to adopt at scale. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is a rapid and cost-effective microbial identification technique, but it cannot be used to differentiate Salmonella serotypes. This study aims to integrate MALDI-TOF MS with machine learning algorithms to develop and validate a model for Salmonella serotype identification, improving efficiency and simplifying workflows. A total of 692 Salmonella isolates from Children’s Hospital, Zhejiang University School of Medicine (ZUCH) and Wanbei Coal-Electricity Group General Hospital (WCGH) were analyzed using MALDI-TOF MS, generating 2,048 spectra. The ZUCH data were randomly divided into training and internal validation sets. The WCGH data were used as an external validation set. Ten machine learning algorithms were evaluated for their ability to identify eight Salmonella serotypes (B, C1, C2/3, D, E, Not A-F, Salmonella Typhimurium, and Salmonella Enteritidis). From 192 initial features, 16 features were selected for the final model construction. XGBoost demonstrated the best discriminative ability (area under the receiver operating characteristic curve [AUC] = 0.9898, sensitivity = 0.88, and specificity = 0.98) for the training set. The streamlined XGBoost model achieved AUCs of 0.9662 and 0.9778 for the internal and external validation sets, respectively, accurately identifying Salmonella serotypes. To enhance usability, the model was deployed as a Streamlit-based application, facilitating interaction and broader application. MALDI-TOF MS combined with XGBoost provides a fast and accurate method for Salmonella serotype identification, offering an efficient solution for laboratory diagnostics and epidemiological studies. IMPORTANCE: Salmonella serotyping is vital for outbreak tracking and clinical guidance, but traditional methods are slow and laborious. This study combines matrix-assisted laser desorption ionization-time of flight mass spectrometry with machine learning (XGBoost) to enable rapid, accurate, and cost-effective serotyping. The streamlined model performed excellently in validation and was deployed as a user-friendly Streamlit app, enhancing usability. This innovation simplifies workflows, reduces diagnostic time, and supports scalable use in clinical and public health settings, improving outbreak response and epidemiological research.

Objective: This study aims to analyze the molecular epidemiology, resistance, and pathogenicity of Salmonella enterica subsp. diarizonae isolated from children.Methods: Whole genome sequencing was carried out, and molecular serotypes, sequence types, resistance genes, and virulence genes of S. enterica subsp. diarizonae isolates were analyzed. Antimicrobial susceptibility test was determined by commercialized microdilution method.Results: A total of three isolates of S. enterica subsp. diarizonae were isolated during 2015 to 2020. The molecular serotypes of the three strains were 61:c:z35, 61:l,v:1,5,7:[z57], and 65:k:z, respectively, and the sequence types were ST1845, ST233, and ST1263. All the three isolates were susceptible to ceftriaxone, ceftazidime, cefepime, amoxycillin/clavulanic acid, piperacillin/tazobactam, ertapenem, imipenem, levofloxacin, and trimethoprim/sulfamethoxazole. No other resistant gene was detected except aac(6’)-Iaa. There were no resistant plasmids detected in all the three isolates. A total of 76 genes were present in all isolates, containing 49 genes of Type III Secretion System (T3SS) mediated by SPI-1and SPI-2, 13 genes of adherence (type 1 fimbriae, Agf, and MisL-related genes), 11 genes of iron uptake (Yersiniabactin), two genes of magnesium uptake, and one gene of typhoid toxin(cdtB).Conclusion: The serotypes and sequence types of S. enterica subsp. diarizonae isolates were rarely reported in children; all the S. enterica subsp. diarizonae isolates were susceptible to detected antibiotics; T3SS, adherence, iron uptake, magnesium uptake, and typhoid toxin were responsible for pathogenicity of the S. enterica subsp. diarizonae isolates in children.

Staphylococcus argenteus is a novel species within the Staphylococcus aureus complex and can cause serious bloodstream infections (BSIs) in humans, which have been mainly reported in adults, especially the elderly. In this study, we analyzed the molecular characterization of a strain of S. argenteus (22WJ8192) isolated from the peripheral vein blood sample of a seven-month-old female infant in Eastern China. The 22WJ8192 belonged to sequence type (ST)2250 and harbored six antibiotic-resistance genes and 53 virulence genes and was resistant to penicillin. Additionally, we conducted a comparative analysis of the molecular characteristics of S. argenteus sourced from various origins within the dataset, predominantly from the National Center for Biotechnology Information Collection (NCBI) genome database. Antibiotic-resistance genes blaR1, blaI_of_Z, blaZ, fosB-Saur, tet(L), aph(3")-IIIa, mecA, and dfrG were more prevalent among the strains of human origin. Virulence genes lukF-PV, sak, sdrE, scn, sdrC, and sdrD were more prevalent among strains of human origin. The presence of antibiotic-resistance genes blaR1, blaI_of_Z, blaZ, fosB-Saur, and aph(3")-IIIa in strain 22WJ8192 was also more common among strains of human origin in the dataset. Conversely, the antibiotic-resistance genes tet(L), mecA, and dfrG, typically found in strains of human origin, were not detected in 22WJ8192. Additionally, virulence genes lukF-PV, sak, sdrE, scn, sdrC, and sdrD present in 22WJ8192 exhibited a higher prevalence among strains of human origin in the dataset. In conclusion, this study emphasizes the potential of S. argenteus ST2250 to induce severe bloodstream infections in infants, shedding light on the molecular characteristics of this strain.