Revealing the single-channel characteristics of OprD (OccAB1) porins from hospital strains of Acinetobacter baumannii

Nowadays, reports of antimicrobial resistance (AMR) against many antibiotics are increasing because of their misapplication. With this rise, there is a serious decrease in the discovery and development of new types of antibiotics amid an increase in multi-drug resistance. Unfermented Acinetobacter baumannii from gram-negative bacteria, which is one of the main causes of nosocomial infections and multi-drug resistance, has 4 main kinds of antibiotic resistance mechanism: inactivating antibiotics by enzymes, reduced numbers of porins and changing of their target or cellular functions due to mutations, and efflux pumps. In this study, characterization of the possible mutations in OprD (OccAB1) porins from hospital strains of A. baumannii were investigated using single channel electrophysiology and compared with the standard OprD isolated from wild type ATCC 19,606. For this aim, 5 A. baumannii bacteria samples were obtained from patients infected with A. baumannii, after which OprD porins were isolated from these A. baumannii strains. OprD porins were then inserted in an artificial lipid bilayer and the current-voltage curves were obtained using electrical recordings through a pair of Ag/AgCl electrodes. We observed that each porin has a characteristic conductance and single channel recording, which then leads to differences in channel diameter. Finally, the single channel data have been compared with the gene sequences of each porin. It was interesting to find out that each porin isolated has a unique porin diameter and decreased anion selectivity compared to the wild type.

Electrochemical-based ''antibiotsensor'' for the whole-cell detection of the vancomycin-susceptible bacteria

In this study, we aim to develop an antibiotic-based biosensor platform 'Antibiotsensor' for the specific detection of gram-positive bacteria using vancomycin modified Screen Printed Gold Electrodes (SPGEs). Through this pathway, vancomycin molecules were first functionalized with thiol groups and characterized with quadrupole time of flight (q-TOF) mass spectroscopy analysis. Immobilization of thiolated vancomycin molecules (HS-Van) onto SPGEs was carried out based on self-assembled monolayer (SAM) phenomenon. Electrochemical impedance spectroscopy (EIS) was employed to test the detection and showed a considerable change in impedance value upon the binding of HS-Van molecules onto the electrode surface. Atomic Force Microscopy analysis indicated that SPGE was successfully modified upon the treatment with HS-Van molecules based on the shift in surface roughness from 173 ± 2 nm to 301 ± 3 nm. Fourier Transform Infrared Spectroscopy (FTIR) spectroscopy proved the EIS and AFM results as well by showing characteristic peaks of immobilized HS-Van molecule. As a proof-of-concept, EIS-based susceptibility testing was performed using Escherichia coli, Staphylococcus aureus and Mycobacterium smegmatis bacteria to prove the specificity of obtained SPGE-Van. EIS data showed that the charge transfer resistance (R_ct) values changed from 1.08, 1.18 to 26.5, respectively, indicating that vancomycin susceptible S. aureus was successfully attached onto SPGE-Van surface strongly, while vancomycin resistance E. coli and M. smegmatis did not show any significant attachment properties. In addition, different concentration (10⁸-10 CFU/mL) of S. aureus was performed to investigate sensitivity of proposed sensor platform. Limit of detection and limit of quantitation was calculated as 10^1.58 and 10^4.81 CFU/mL, respectively. Scanning electron microscopy (SEM) analysis also confirmed that only S. aureus bacteria was attached to the surface in a dense monolayer distribution. We believe that the proposed approach is selective and sensitive towards the whole-cell detection of vancomycin-susceptible bacteria and can be modified for different purposes in the future.

Rapid fabrication of teflon apertures by controlled high voltage pulses for formation of free standing planar lipid bilayer membrane

Free standing artificial lipid bilayers are widely used in the study of biological pores. In these types of studies, the free standing planar lipid bilayer is formed over a micron-sized aperture consisting of either polymer such as Polytetrafluoroethylene (PTFE, Teflon) or glass. Teflon is chemically inert, has a low dielectric constant, and has a high electrical resistance which combined allow for obtaining low noise recordings. This study investigates the reproducible generation of micropores in the range of 50-100 microns in diameter in a Teflon film using a high energy discharge set-up. The discharger set-up consists of a microprocessor, a transformer, a voltage regulator, and is controlled by a computer. We compared two approaches for pore creation: single and multi-pulse methods. The results showed that the multi-pulse method produced narrower aperture size distributions and is more convenient for lipid bilayer formation, and thus would have a higher success rate than the single-pulse method. The bilayer stability experiments showed that the lipid bilayer lasts for more than 33 h. Finally, as a proof-of-concept, we show that the single and multi-channel electrophysiology experiments were successfully performed with the apertures created by using the mentioned discharger. In conclusion, the described discharger provides reproducible Teflon-pores in a cheap and easy-to-operate manner.

On‐chip label‐free impedance‐based detection of antibiotic permeation

Biosensors are analytical tools used for the analysis of biomaterial samples and provide an understanding about the biocomposition, structure, and function of biomolecules and/or biomechanisms by converting the biological response into an electrical and/or optical signal. In particular, with the rise in antibiotic resistance amongst pathogenic bacteria, the study of antibiotic activity and transport across cell membranes in the field of biosensors has been gaining widespread importance. Herein, for the rapid and label‐free detection of antibiotic permeation across a membrane, a microelectrode integrated microfluidic device is presented. The integrated chip consists of polydimethylsiloxane based microfluidic channels bonded onto microelectrodes on‐glass and enables us to recognize the antibiotic permeation across a membrane into the model membranes based on electrical impedance measurement, while also allowing optical monitoring. Impedance testing is label free and therefore allows the detection of both fluorescent and non‐fluorescent antibiotics. As a model membrane, Giant Unilamellar Vesicles (GUVs) are used and impedance measurements were performed by a precision inductance, capacitance, and resistance metre. The measured signal recorded from the device was used to determine the change in concentration inside and outside of the GUVs. We have found that permeation of antibiotic molecules can be easily monitored over time using the proposed integrated device. The results also show a clear difference between bilayer permeation that occurs through the lipidic bilayer and porin‐mediated permeation through the porin channels inserted in the lipid bilayer.

Towards understanding single-channel characteristics of OccK8 purified from Pseudomonas aeruginosa

Antibiotic resistance in Gram-negative bacteria causes serious health issues worldwide. Bacteria employ several resistance mechanisms to cope with antimicrobials. One of their strategies is to reduce the permeability of antibiotics either through general diffusion porins or substrate-specific channels. In this study, one of the substrate-specific channels from Pseudomonas aeruginosa, OccK8 (also known as OprE), was investigated using single-channel electrophysiology. The study also includes the investigation of permeability properties of several amino acids with different charged groups (i.e. arginine, glycine and glutamic acid) through OccK8. We observed four different conformations of the same OccK8 channel when inserted in lipid bilayers. This is in contrast to previous studies where heterologous expressed OccK8 in E. coli showed only one conformation. We hypothesized that the difference in our study was due to the expression and purification of the native channel from P. aeruginosa. The single-channel uptake characteristics of the porin showed that negatively charged glutamic acid preferentially interacted with the channel while the positively charged arginine molecule showed infrequent interaction with OccK8. The neutral amino acid glycine did not show any interaction at the physiological conditions.

Investigation of the Effect of Channel Structure and Flow Rate on On-Chip Bacterial Lysis

Successful lysis of cells/microorganisms is a key step in the sample preparation in fields like molecular biology, bioengineering, and biomedical engineering. This study therefore aims to investigate the lysis of bacteria on-chip and its dependence on both microfluidic channel structure and flow rate. Effects of temperature on lysis on-chip were also investigated. To perform these investigations, three different microfluidic chips were designed and produced (straight, zigzag and circular configurations), while the length of the channels were kept constant. As an exemplary case, Mycobacterium smegmatis was chosen to represent the acid-fast bacteria. Bacterial suspensions of 1.5 McFarland were injected into the chips at various flow rates (0.6- [Formula: see text]/min) either at room temperature or 50° C. In order to understand the on-chip lysis performance fully, off-chip experiments were carried out at durations which are equal to those bacteria spent in the channel from inlet to the outlet at different flow rates. We also performed COMSOL multiphysics program simulations to evaluate further the effect of the applied parameters. As a result, we found that the structure and the flow rate do not affect lysis over all in all investigated channel types, however on-chip experiments at room temperature produced more effective lysis compared to the on-chip and the off-chip samples performed at higher temperatures. Interestingly on-chip experiments at higher tempratures do not result in effective lysis.