Polymyxin-resistant Pseudomonas aeruginosa is a major threat to public health globally. We investigated the prevalence of polymyxin-resistant P. aeruginosa in a Chinese teaching hospital and determined the genetic and drug-resistant phenotypes of the resistant isolates. P. aeruginosa isolates identified by MALDI-TOF MS were collected across a 3-month period in Ruijin Hospital. Antimicrobial susceptibility was determined by a Vitek-2 Compact system with broth dilution used to determine polymyxin B (PMB) susceptibility. Polymyxin-resistant isolates were further characterized by molecular typing using PCR, multi-locus sequence typing (MLST) and whole-genome sequencing. Phylogenetic relationships were analyzed using single nucleotide polymorphism (SNP) from the whole-genome sequencing. Of 362 P. aeruginosa isolates collected, 8 (2.2%) isolates from separate patients across six wards were polymyxin-resistant (MIC range, PMB 4–16 μg/mL and colistin 4–≥16 μg/mL). Four patients received PMB treatments (intravenous, aerosolized and/or topical) and all patients survived to discharge. All polymyxin-resistant isolates were genetically related and were assigned to five different clades (Isolate 150 and Isolate 211 being the same ST823 type). Genetic variations V51I, Y345H, G68S and R155H in pmrB and L71R in pmrA were identified, which might confer polymyxin resistance in these isolates. Six of the polymyxin-resistant isolates showed reduced susceptibility to imipenem and meropenem (MIC range ≥ 16 μg/mL), while two of the eight isolates were resistant to ceftazidime. We revealed a low prevalence of polymyxin-resistant P. aeruginosa in a Chinese teaching hospital with most polymyxin-resistant isolates being multidrug-resistant. Therefore, effective infection control measures are urgently needed to prevent further spread of resistance to the last-line polymyxins.

Background: Aspergillus spp. infection in immunocompromised patients results in increasing morbidity and mortality. This study investigated clinical and microbiological characteristics of aspergillosis in a Chinese tertiary teaching hospital. Methods: A total of 114 patients with aspergillosis were included over a 5-year period at Ruijin Hospital. In sum, 114 Aspergillus strains were isolated and identified at species level using matrix-assisted laser desorption ionization time-of-flight mass spectrometry, confirmed by ITS gene region and β-tubulin (BenA) gene sequencing. Sensititre YeastOne was used in vitro to test susceptibility to antifungal drugs: amphotericin B, itraconazole, voriconazole, posaconazole, isavuconazole, micafungin, anidulafungin, and caspofungin. Results: The median age of the patients was 61 (19) years, men accounted for 53.5% (n=61) of the sample, about 64% were immunocompromised, and 36% had underlying diseases. Pulmonary diseases accounted for 27.2%. Aspergillus isolates were mainly isolated from sputum (n=42, 36.8%). Antifungal therapy was administered to 106 (93.0%) patients and voriconazole (n=76, 66.7%) was the most frequently used as empirical therapy. Aspergillus fumigatus (n=69, 60.5%) was the most common species. There was a 73.7% concordance between MALDI-TOF MS and molecular identification. All Aspergillus isolates showed good susceptibility to anidulafungin and caspofungin. Conclusion: Immunocompromised patients are an at-risk population for aspergillosis, and voriconazole was used as empirical therapy in Ruijin Hospital, China. A. fumigatus was the predominant Aspergillus species causing aspergillosis, and A. flavus — as non–A. fumigatus species are increasing — the second-leading cause of aspergillosis. Anidulafungin and caspofungin were the most active in vitro against the Aspergillus isolates tested. The MALDI-TOF MS method showed good accuracy for identification of common Aspergillus spp. In vitro antifungal-susceptibility testing is crucially important for decisions on effective therapy with aspergillosis.

Background: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a powerful technique for the identification of microorganisms. The technique normally requires a sample preparation procedure before instrumental analysis, which can be somewhat labor-intensive when numbers of samples are large. The direct smear method, in which samples are directly smeared on the sample plates and subsequently subjected to instrumental analyses, can save time and is less labor-intensive. However, the method has rarely been tested on filamentous fungi, although it has been successfully used in the identification of bacteria and yeasts. In the present study, we examined the method using clinically-collected filamentous fungi. Methods: Three hundred forty-eight isolates of filamentous fungi representing 9 species collected from body fluids of patients were analyzed on the VITEK MS version 3.0 system, a popular commercial MALDI-TOF MS system, using the direct smear method. For those misidentified or unidentified, the samples were retested. All fungal species were determined through DNA sequencing. Results: Among 334 isolates that were included in the database of the VITEK system, 286 (85.6%) samples were correctly identified. After retesting, the rate of correct identification increased to 91.0%. Aspergillus fumigatus exhibited a 95.2% rate of correct identification before retesting, whereas Aspergillus niger showed the rate at only 46.5% (58.1% even with retesting). Conclusions: The direct smear method could be used in the identification of filamentous fungi found in body fluids of patients by MALDI-TOF MS at good rates of correct identification. The method is simple and time-saving, and deserves further evaluation.

Acinetobacter junii , an emerging pathogen of the Acinetobacter genus, exhibits concerning environmental persistence and clinical virulence potential. Despite its growing significance in bloodstream infections (BSIs), the genetic determinants distinguishing pathogenic from environmental strains remain poorly characterized, limiting our understanding of its transmission dynamics and host adaptation mechanisms. We explored the diversity and population structure of A. junii using a comprehensive genome dataset, including four strains isolated from China, one of which (acj0210) was derived from BSIs. We analysed the pangenome of A. junii and characterized its virulence and antibiotic resistance profile. Bacterial genome-wide association studies (bGWAS) were performed to identify the virulence potential. The virulence potential for BSIs was further investigated through RNA-seq analysis under different conditions. Additionally, transmission dynamics of bla _NDM -carrying plasmids in carbapenem-resistant A. junii were inferred from plasmid network analysis. We identified seven lineages within A. junii , with BAPS1 as the dominant group. Discrepancies in accessory genes were observed between lineages, along with unique genes, particularly one novel capsular polysaccharide variant in acj0210. Using bGWAS, we uncovered key genetic differences, including transporter-encoding genes ( tauA , urtD ), regulatory mutations and exopolysaccharide-encoding genes that distinguish human and environmental strains. Transcriptomic analysis revealed potential virulence factors in BSIs, with distinct gene expression patterns between blood and immune cells, despite shared fatty acid metabolism profiles. As critical resistance determinants, bla _NDM genes may have been acquired from A. baumannii. A. junii has adapted to diverse geographical and ecological niches, particularly in BSIs, with lineage-specific virulence factors aligned with antibiotic resistance genes, especially those carried by bla _NDM harbouring plasmids.