Electrofermentation increases concentration of poly γ-glutamic acid in Bacillus subtilis biofilms.

Fluctuations in redox conditions in bioprocesses can alter the end-products, reduce their concentration, and lengthen the process time. Electrofermentation enables rapid metabolic modulation of biosynthesis and allows control of redox imbalances in biofilm-based fermentation processes. In this study, electrofermentation is used to boost the production of the bacterial biopolymer poly-γ-glutamic acid (γ-PGA) from Bacillus subtilis ATCC 6051. When compared to control experiments (3.3 ± 0.99 g L-1 ), the application of an electrode potential E = 0.4 V versus Ag/AgCl results in a more than two-fold increase in the production of γ-PGA (9.13 ± 1.4 g L-1 ). Using an engineered B. subtilis strain, in which γ-PGA production is driven by isopropyl ß-d-1-thiogalactopyranoside, electrofermentation improves polymer concentrations from 15.4 ± 1.5 to 23.1 ± 1.6 versus g L-1 . These results confirm that electrofermentation conditions can be adopted to increase the concentration of γ-PGA and perhaps other extracellular biopolymers in industrial strains.

Biochemical and electrochemical characterization of biofilms formed on everolimus-eluting coronary stents.

Drug-eluting stents (DES) are mostly used in percutaneous coronary intervention, which is the main treatment for coronary artery occlusion. This procedure aims to restore the natural lumen, while minimizing the risk of restenosis. However, stent insertion increases the risk for infections, due to contamination of the device or insertion hub with normal skin flora. While coronary stent infection is a rare complication, it can be fatal. Currently, there is little information on biofilm formation on everolimus-eluting stents. Although everolimus is not designed as an antimicrobial agent, its antimicrobial activity should be investigated. In this study, biofilm formation on everolimus-eluting and bare metal stents (BMS) is characterized through biochemical and electrochemical methods. DES and BMS are inoculated with Pseudomonas aeruginosa and Staphylococcus epidermidis, both independently and in co-culture. Biofilms formed on DES were 49.6 %, 12.9 % and 47.5 % higher than on BMS for P. aeruginosa, S. epidermidis and their co-culture, respectively. Further, the charge output for DES was 18.9 % and 59.7 % higher than BMS for P. aeruginosa and its co-culture with S. epidermidis, respectively. This observation is most likely due to higher surface roughness of DES, which favors biofilm formation. This work shows that bioelectrochemical methods can be used for rapid detection of biofilms on drug-eluting and bare metal stents, which may find application in quality assessment of stents and in characterization of stents removed after polymicrobial infections.

Biofilm Detection by a Fiber-Tip Ball Resonator Optical Fiber Sensor.

Bacterial biofilms are one of the most important challenges that modern medicine faces due to the difficulties of diagnosis, antibiotic resistance, and protective mechanisms against aggressive environments. For these reasons, methods that ensure the inexpensive and rapid or real-time detection of biofilm formation on medical devices are needed. This study examines the possibilities of using optical- and fiber-based biosensors to detect and analyze early bacterial biofilms. In this study, the biofilm-forming model organism Pseudomonas aeruginosa was inoculated on the surface of the optical sensor and allowed to attach for 2 h. The biosensors were made by a fiber-tip ball resonator, fabricated through a CO2 laser splicer on a single-mode fiber, forming a weak reflective spectrum. An optical backscatter reflectometer was used to measure the refractive index detected by the sensors during different growth periods. The early biofilm concentration was determined by crystal violet (CV) binding assay; however, such a concentration was lower than the detection limit of this assay. This work presents a new approach of biofilm sensing in the early attachment stage with a low limit of detection up to 10-4 RIU (refractive index units) or 35 ± 20 × 103 CFU/mL (colony formed units).

Assessment of physiological and electrochemical effects of a repurposed zinc dithiocarbamate complex on Acinetobacter baumannii biofilms.

Acinetobacter baumannii is an infectious agent of global proportion and concern, partly due to its proficiency in development of antibiotic resistance phenotypes and biofilm formation. Dithiocarbamates (DTC) have been identified as possible alternatives to the current antimicrobials. We report here the evaluation of several DTC-metal complexes against A. baumannii planktonic cells and biofilms. Among the DTC-metal complexes and DTCs tested, ZnL1 (N-methyl-1-phenyldithiocarbamato-S,S' Zn(II)), originally designed as an antitumor agent, is effective against biofilm forming A. baumannii. A MIC value of 12.5 µM, comparable to that of Gentamicin (5 µM) was measured for planktonic cells in tryptic soy broth. Spectroscopy, microscopy and biochemical analyses reveal cell membrane degradation and leakage after treatment with ZnL1. Bioelectrochemical analyses show that ZnL1 reduces biofilm formation and decreases extracellular respiration of pre-formed biofilms, as corroborated by microscopic analyses. Due to the affinity of Zn to cells and the metal chelating nature of L1 ligand, we hypothesize ZnL1 could alter metalloprotein functions in the membranes of A. baumannii cells, leading to altered redox balance. Results indicate that the DTC-Zn metal complex is an effective antimicrobial agent against early A. baumannii biofilms under laboratory conditions.