Nanofluidic Immobilization and Growth Detection of Escherichia coli in a Chip for Antibiotic Susceptibility Testing.

Infections with antimicrobial resistant bacteria are a rising threat for global healthcare as more and more antibiotics lose their effectiveness against bacterial pathogens. To guarantee the long-term effectiveness of broad-spectrum antibiotics, they may only be prescribed when inevitably required. In order to make a reliable assessment of which antibiotics are effective, rapid point-of-care tests are needed. This can be achieved with fast phenotypic microfluidic tests, which can cope with low bacterial concentrations and work label-free. Here, we present a novel optofluidic chip with a cross-flow immobilization principle using a regular array of nanogaps to concentrate bacteria and detect their growth label-free under the influence of antibiotics. The interferometric measuring principle enabled the detection of the growth of Escherichia coli in under 4 h with a sample volume of 187.2 µL and a doubling time of 79 min. In proof-of-concept experiments, we could show that the method can distinguish between bacterial growth and its inhibition by antibiotics. The results indicate that the nanofluidic chip approach provides a very promising concept for future rapid and label-free antimicrobial susceptibility tests.

Cross-Flow Filtration of Escherichia coli at a Nanofluidic Gap for Fast Immobilization and Antibiotic Susceptibility Testing.

Infections with antimicrobial-resistant (AMR) bacteria are globally on the rise. In the future, multi-resistant infections will become one of the major problems in global health care. In order to enable reserve antibiotics to retain their effect as long as possible, broad-spectrum antibiotics must be used sparingly. This can be achieved by a rapid microfluidic phenotypic antibiotic susceptibility test, which provides the information needed for a targeted antibiotic therapy in less time than conventional tests. Such microfluidic tests must cope with a low bacteria concentration. On-chip filtering of the samples to accumulate bacteria can shorten the test time. By means of fluorescence microscopy, we examined a novel nanogap filtration principle to hold back Escherichia coli and to perform cultivation experiments with and without antibiotics present. Microfluidic chips based on the nanogap flow principle showed to be useful for the concentration and cultivation of E. coli. With a concentration of 106 cells/mL, a specific growth rate of 0.013 min-1 and a doubling time of 53 min were achieved. In the presence of an antibiotic, no growth was observed. The results prove that this principle can, in future, be used in fast and marker-free antimicrobial susceptibility testing (AST).

Use of the international caries detection and assessment system two-digit coding method by predoctoral dental students at Philipps University of Marburg, Germany.

When the International Caries Detection and Assessment System (ICDAS-II) was introduced, a two-number coding system that identifies restorations/sealants with the first digit and scores the caries lesions with a second digit was suggested. The aim of this study was, first, to assess the intra- and interexaminer reproducibility of this method applied by predoctoral dental students and, second, to evaluate the influence of an additional theoretical training session on the reproducibility values. Twenty-four third-year dental students at Philipps University of Marburg, Germany, were trained in a theoretical session by an experienced examiner. The students were randomly divided into two groups to examine extracted teeth. The assessments were repeated after three weeks. Prior to the second examinations, one group received an additional theoretical training session. For the restoration code, mean kappa values for intra- and interexaminer reproducibility were between 0.28 and 0.82. For the caries code, mean kappa values for intra- and interexaminer reproducibility were between 0.34 and 0.72. The mean kappa values of the two groups did not differ significantly, either on the first digit or on the caries code (p>0.05).