A new dynamic in vitro model for evaluating antimicrobial activity against bacterial biofilms on central venous catheters.

Central venous catheters (CVCs) are widely used for intravenous medication administration. However, biofilm formation along the catheter surface is the main most important cause of catheter-related bloodstream infections. Nowadays, several antimicrobial-coated catheters are available to prevent biofilm development. In this study, we introduced a new dynamic in vitro model to evaluate the antimicrobial activity against bacterial biofilms on CVCs. Rifampicin-minocycline-coated catheters and control catheters without antimicrobial component were assembled into the model to test the antimicrobial activity on external surface and internal surface. After 1 h irrigation of Staphylococcus epidermidis or Staphylococcus aureus preculture and 23 h irrigation of Trypticase Soy Broth, the viable adherent organism was collected and counted. The enumeration results showed that the number of bacteria attached to antibacterial catheter was significantly less than that of the control catheter, both on external surface (P < 0.05) and internal surface (P < 0.05). The results were further confirmed by the scanning electron microscopy. In conclusion, the dynamic in vitro model can be applied to evaluate the antimicrobial activity against bacterial biofilms grown on the external and internal surfaces of CVCs used in clinical practice.IMPORTANCEFor the first time, a new dynamic in vitro model was constructed to evaluate the antimicrobial activity against bacterial biofilms on central venous catheters (CVCs) on both external surface and internal surface. This model could be applied to evaluate the antimicrobial activity against bacterial biofilms not only on CVCs but also other types of catheters.

Application of ß-glucuronidase (GusA) as an effective reporter for extremely acidophilic Acidithiobacillus ferrooxidans.

Acidithiobacillus ferrooxidans is a model organism for investigating metal sulfide bioleaching. The regulatory mechanism of gene expression by metabolizing various substrates is critical for understanding its role in bioleaching processes. However, no reporter has been successfully employed to study gene expression in A. ferrooxidans to date. In this study, a sensitive and robust reporter system based on ß-glucuronidase (GusA) was described for feasible application in A. ferrooxidans. A set of vectors, which contained the transcriptional and translational fusions of gusA, were constructed and employed to analyze promoter activity and efficiency of translation initiation in A. ferrooxidans. Ptac and P2811 were screened out from ten tested promoters and could be used as strong promoters for gene overexpression in A. ferrooxidans. Among the four translational fusions of gusA with different start codons, ATG was most active, followed by TTG and GTG, while CTG showed the least activity. The transcriptional inhibition effect of an IclR-like transcription factor was also observed on its own encoding gene AFE_1668 as well as its neighboring AFE_1667. In addition, the specific chromogenic reaction of GusA could be detected and visualized by colonies of A. ferrooxidans containing gusA expression plasmids. Generally, the established GusA reporter system would be applied not only for quantitative analysis of promoter strength and its transcriptional regulation but also for qualitative colony screening in A. ferrooxidans in the future.