Objective: To investigate fusidic acid resistance in Staphylococcus aureus (S.aureus) strains and to analyze their molecular characteristics. Methods: A total of 1 333 strains of S. aureus isolated in the First Affiliated Hospital of Wenzhou Medical University from October 2013 to March 2016 were collected. Fusidic acid resistance in these strains was detected by K-B method. Minimum inhibitory concentrations (MIC) of fusidic acid were measured by agar dilution method. Resistance genes of fusB, fusC and fusD and S. aureus A protein-coding gene (spa) were detected by PCR. Strains that did not carry fusB, fusC or fusD were detected for mutations in fusA by sequencing. Housekeeping genes were detected by PCR and analyzed by multilocus sequence typing (MLST). Results: Among the 1 333 strains of S. aureus, 52 were resistant to fusidic acid, accounting for 3.90%. From 2013 to 2016, fusidic acid-resistant strains accounted for 5.3% (7/132), 3.5% (20/571), 4.1% (21/510) and 3.3% (4/120), respectively. The MIC values of fusidic acid against S. aureus were 2, 4, 8, 64 and >64 μg/ml, which inhibited the growth of 26.9% (14/52), 34.6% (18/52), 13.5% (7/52), 1.9% (1/52) and 23.1% (12/52) of strains, respectively. MLST revealed that there were 13 sequence types (STs), among which ST630 was the predominant type accounting for 50% (26/52), followed by ST5 accounting for 17.3% (9/52). There were 19 spa types, among which t4549 (11/52), t2460 (8/52), t377 (8/52) were the predominant types. Nine strains carried drug resistance genes accounting for 17.3% (9/52), including seven fusB-positive and two fusD-positive strains. No fusc-positive strains were detected. Mutations in fusA gene were detected in 11 strains (21.2%, 11/52) and the MIC values against them were all >64 μg/ml. The predominant type of the strains with fusA gene mutations was ST5-t2460. Conclusion Fusidic acid shows a good and relatively stable in vitro antibacterial activity against S. aureus. The mechanism of high resistance to fusidic acid is closely related to fusA gene mutation.

Objective:To identify the core genes related to the disease severity of respiratory syncytial virus (RSV) bronchiolitis in children using RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA), aiming to provide reference for predicting the condition of RSV infection.Methods:Twenty-two patients admitted to the Second Affiliated Hospital of Wenzhou Medical University with RSV bronchiolitis from October 1, 2019 to February 29, 2020 were enrolled as the case group. They were divided into three groups based on the severity of the disease: mild group, moderate group and severe group. Twenty-two healthy children were selected as the control group. Total RNA was extracted from whole blood leukocytes and analyzed by RNA-seq to compare the differentially expressed genes (DEGs) between children with RSV bronchiolitis and healthy children. The gene co-expression modules related to disease severity and biological indicators for disease severity assessment were identified.Results:The median age of the 22 patients (19 males and 3 females) was 3 months. The median age of the 22 healthy children (14 males and 8 females) was 4 months. There was no significant difference in age or gender between the two groups. There were 8 cases in the mild group, 7 cases in the moderate group and 7 cases in the severe group. Through significance analysis, 416 DEGs were found in the mild group, 586 in the moderate group and 846 in the severe group. According to WGCNA analysis, 10 co-expression modules were found, among which brown module ( r=0.62, P<0.001) was significantly correlated with disease severity. The protein-protein interaction network of DEGs in brown module was constructed and the top 30 core genes were selected according to the connectivity of gene nodes, among which the genes with high correlation were RBX1 and PSMA7. The expression of RBX1 and PSMA7 genes was up-regulated in the severe group, but their expression in the mild and moderate groups was not significantly different from that in the control group. Conclusions:RBX1 and PSMA7 genes might be biological predictors of disease severity in RSV bronchiolitis.