On-Chip Isoniazid Exposure of Mycobacterium smegmatis Penicillin-Binding Protein (PBP) Mutant Using Time-Lapse Fluorescent Microscopy.

Meltem Elitas

doi:10.3390/mi9110561

Abstract

Antibiotic resistance has been one of the biggest threats to global health. Despite the available prevention and control strategies and efforts in developing new antibiotics, the need remains for effective approaches against antibiotic resistance. Efficient strategies to cope with antimicrobial resistance require a quantitative and deeper understanding of microbial behavior, which can be obtained using different techniques to provide the missing pieces of the current antibiotic-resistance puzzle. Microfluidic-microscopy techniques are among the most promising methods that contribute modernization of traditional assays in microbiology. They provide monitoring and manipulation of cells at micro-scale volumes. Here, we combined population-level, culture-based assays with single-cell resolution, microfluidic-microscopy systems to investigate isoniazid response of Mycobacterium smegmatis penicillin-binding protein (PBP) mutant. This mutant exhibited normal growth in plain medium and sensitivity to stress responses when treated with thermal stress (45 °C), detergent stress (0.1% sodium dodecyl sulfate), acid stress (pH 4.5), and nutrient starvation (1XPBS). The impact of msm0031 transposon insertion on drug-mediated killing was determined for isoniazid (INH, 50 µg/mL), rifampicin (RIF, 200 µg/mL), ethionamide (ETH, 200 µg/mL), and ethambutol (EMB, 5 µg/mL). The PBP mutant demonstrated remarkable isoniazid-killing phenotype in batch culture. Therefore, we hypothesized that single-cell analysis will show increased lysis kinetics and fewer intact cells after drug treatment. However, the single-cell analysis data showed that upon isoniazid exposure, the percentage of the intact PBP mutant cells was 24%, while the percentage of the intact wild-type cells was 4.6%. The PBP mutant cells exhibited decreased cell-lysis profile. Therefore, the traditional culture-based assays were not sufficient to provide insights about the subpopulation of viable but non-culture cells. Consequently, we need more adequate tools to be able to comprehend and fight the antibiotic resistance of bacteria.

Highlights

Antibiotic resistance remains one of the biggest threats to global health in spite of being an old fight for humankind
In contrast to statically culturing cells in flasks, bacteria are cultured in microchannels, fed by a continuous medium flow where the antibiotic can be added into the medium, and the antibiotic response of the cells can be dynamically observed at single-cell resolution [10]
Pioneering work by Dr Austin and his co-workers has combined theoretical and experimental methods to unearth the cryptic complexity of bacterial evolution in studying the antibiotic response of the cells in dynamic, spatially heterogeneous microenvironments [17,18,19]

Summary

Introduction

Antibiotic resistance remains one of the biggest threats to global health in spite of being an old fight for humankind. In contrast to statically culturing cells in flasks, bacteria are cultured in microchannels, fed by a continuous medium flow where the antibiotic can be added into the medium, and the antibiotic response of the cells can be dynamically observed at single-cell resolution [10]. These technologies have great potential for observing and quantifying the microenvironmental conditions that shape the survival strategies of bacteria, such as biofilms. Single-cell level and culture-based assays are complementary pieces of the current state-of-the-art

Objectives

Methods

Results