Background: Heteroresistance is a phenomenon that occurs in all bacteria and can cause treatment failure. Yet, the exact mechanisms responsible for heteroresistance still remain unknown. The following study investigated the mechanisms of imipenem-heteroresistance and -resistance in Pseudomonas aeruginosa clinical isolates from Wenzhou, China. Methods: Imipenem resistance was detected by the agar dilution method; heteroresistance was determined by population analysis profiles. Biofilm formation assay and modified carbapenem inactivation methods were also performed. Polymerase chain reaction (PCR) was conducted to detect oprD, and quantitative real-time PCR was used to determine expression levels of oprD, ampC and four efflux pump coding genes (mexB, mexD, mexE and mexY). Results: Six imipenem-heteroresistant and -resistant P. aeruginosa isolates were selected respectively. Deficient oprD was detected in all resistant isolates and two heteroresistant isolates. No strains produced carbapenemases. Expression levels of oprD were downregulated in heteroresistant isolates. Transcription levels of the mexE and mexY were significantly increased in all heterogeneous subpopulations compared with their respective native ones. Compared with the susceptible group, increased mean relative expression levels of mexE and mexY or the decreased mean relative expression levels of oprD were observed in the resistant group (P < 0.05), whereas transcription levels of the mexB and mexD remained unchanged. Conclusion: Down-regulation of oprD contributed to the resistance and heteroresistance of imipenem in our P. aeruginosa clinical isolates. In addition, the marginal up-regulation of efflux systems may indirectly affect imipenem resistance. Contrarily, defective oprD was less common in our experimental heteroresistant strains than resistant strains.

Contezolid is a novel oxazolidinone, which exhibits potent activity against gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and penicillin-resistant Streptococcus pneumoniae (PRSP). In this study, the in vitro activity of contezolid was compared with linezolid (LZD), tigecycline (TGC), teicoplanin (TEC), vancomycin (VA), daptomycin (DAP), and florfenicol (FFC) against MRSA and VRE strains isolated from China. Contezolid revealed considerable activity against MRSA and VRE isolates with MIC90 values of 0.5 and 1.0 μg/mL, respectively. For VRE strains with different resistance genotypes, including vanA- and vanM-type strains, contezolid did not exhibit significantly differential antibacterial activity. Furthermore, the antimicrobial activity of contezolid is similar to or slightly better than that of linezolid against MRSA and VRE strains. Subsequently, the activity of contezolid was tested against strains carrying linezolid resistance genes, including Staphylococcus capitis carrying cfr gene and Enterococcus faecalis carrying optrA gene. The results showed that contezolid exhibited similar antimicrobial efficacy to linezolid against strains with linezolid resistance genes. In general, contezolid may have potential benefits to treat the infections caused by MRSA and VRE pathogens.

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Method Endophytic Fungi were isolated from the stem, leaves and root of Angelica sinensis by the surface sterilization method and scoring method. the antimicrobial activity from isolated endophytic fungi were detected using filter paper method with Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae as indicator microorganisms. the partial isolates were identified based on morphological characteristics and classified according to ITS-rDNA sequences analysis. Result A total of 28 endophytic were isolated from the different tissues of the Angelica sinensis, antibiotic activity of the strain AS-R109 and AS-R203 against four indicator microorganisms were the highest, with inhibiting zones diameter of 18, 22, 25, 20 and20,22,19,23 mm respectively at concentration of 10mg/mL. With morphology and molecular biology identification, AS-R109 and AS-R203 was determined to belong to the genus for Alternaria sp. and Penicillium sp., respectively.

Objective To research antibacterial activity of Limonium aureum endophytic fungi. Methods The endophytic fungi of Limonium aureum root was isolated by general method. After incubation, fermentation broth and biomass were extracted by ethyl acetate, n-bothanol and ethanol. The bactefiostatic test was experimented with six different bacterium．The method used was filter paper slice tests. Results 21 endophytes were obtained. After bactefiostatic testing, there were 31 samples with antibaceterial activity against at least one test bacterium he MIC of extraction from E101 and E201 against test bacteria was 0.25mg/mL.