Adaptive Laboratory Evolution of Probiotics toward Oxidative Stress Using a Microfluidic-Based Platform.

Adaptive laboratory evolution (ALE) can be used to make bacteria less susceptible to oxidative stress. An alternative to large batch scale ALE cultures is to use microfluidic platforms, which are often more economical and more efficient. Microfluidic ALE platforms have shown promise, but many have suffered from subpar cell passaging mechanisms and poor spatial definition. A new approach is presented using a microfluidic Evolution on a Chip (EVoc) design which progressively drives microbial cells from areas of lower H2O2 concentration to areas of higher concentration. Prolonged exposure, up to 72 h, revealed the survival of adaptive strains of Lacticaseibacillus rhamnosus GG, a beneficial probiotic often included in food products. After performing ALE on this microfluidic platform, the bacteria persisted under high H2O2 concentrations in repeated trials. After two progressive exposures, the ability of L. rhamnosus to grow in the presence of H2O2 increased from 1 mm H2O2 after a lag time of 31 h to 1 mm after 21 h, 2 mm after 28 h, and 3 mm after 42 h. The adaptive strains have different morphology, and gene expression compared to wild type, and genome sequencing revealed a potentially meaningful single nucleotide mutation in the protein omega-amidase.

Diffusion-Convection Hybrid Microfluidic Platform for Rapid Antibiotic Susceptibility Testing.

Conventional antibiotic susceptibility testing (AST) assays such as broth microdilution and Kirby-Bauer disk diffusion are time-consuming (e.g., 24-72 h) and labor-intensive. Here, we present a microfluidic platform to perform AST assays with a broad range of antibiotic concentrations and controls. A culture medium stream was serially enriched with antibiotics along the length of the platform via diffusion and flow-directing mass convection mechanisms, generating a concentration gradient captured in a series of microchamber duplicates. We observed an agreement between the simulated and experimental concentration gradients and applicability to a variety of different molecules by changing the loading time according to a simple linear equation. The AST assay in our platform is based on bacterial metabolism, indicated by resazurin fluorescence. The small reaction volume enabled a minimum inhibitory concentration (MIC) to be determined in 4-5 h. Proof-of-concept functionality testing, using human isolates and clinically important antibiotics from different classes, indicated a high rate of agreement (94%: MIC within ±1 two-fold dilution of the reference method) of on-chip MICs and conventional broth microdilution. Overall, our results showed that this microfluidic platform is capable of determining antibiotic susceptibility in a rapid and reliable manner.

Faster sperm selected by rheotaxis leads to superior early embryonic development in vitro.

To understand the impact of sperm speed as they swim against the flow on fertilization rates, we created conditions similar to the female reproductive tract (FRT) on a microfluidic platform for sperm selection. Selected sperm were evaluated based on early development of fertilized embryos. Bovine and human spermatozoa were selected at various fluid flow rates within the device. We found that the speed of bovine spermatozoa increases as the flow rate increases and that the amount of DNA fragmentation index is lowered by increasing the flow rate. Bovine spermatozoa selected by our platform at low (150 µL h-1, shear rate 3 s-1), medium (250 µL h-1, shear rate 5 s-1), and high flow rates (350 µL h-1, shear rate 7 s-1) were used for fertilization and compared to sperm sorted by centrifugation. The samples collected at the highest flow rate resulted in the formation of 23% more blastocysts compared to the control. While selecting for higher quality sperm by increasing the flow rate does result in lower sperm yield, quality improvement and yield may be balanced by better embryonic development.

A high-throughput integrated biofilm-on-a-chip platform for the investigation of combinatory physicochemical responses to chemical and fluid shear stress.

Physicochemical conditions play a key role in the development of biofilm removal strategies. This study presents an integrated, double-layer, high-throughput microfluidic chip for real-time screening of the combined effect of antibiotic concentration and fluid shear stress (FSS) on biofilms. Biofilms of Escherichia coli LF82 and Pseudomonas aeruginosa were tested against gentamicin and streptomycin to examine the time dependent effects of concentration and FSS on the integrity of the biofilm. A MatLab image analysis method was developed to measure the bacterial surface coverage and total fluorescent intensity of the biofilms before and after each treatment. The chip consists of two layers. The top layer contains the concentration gradient generator (CGG) capable of diluting the input drug linearly into four concentrations. The bottom layer contains four expanding FSS chambers imposing three different FSSs on cultured biofilms. As a result, 12 combinatorial states of concentration and FSS can be investigated on the biofilm simultaneously. Our proof-of-concept study revealed that the reduction of E. coli biofilms was directly dependent upon both antibacterial dose and shear intensity, whereas the P. aeruginosa biofilms were not impacted as significantly. This confirmed that the effectiveness of biofilm removal is dependent on bacterial species and the environment. Our experimental system could be used to investigate the physicochemical responses of other biofilms or to assess the effectiveness of biofilm removal methods.

Effects of Emulsifiers on an In vitro Model of Intestinal Epithelial Tight Junctions and the Transport of Food Allergens.

SCOPE: Certain food emulsifiers may interfere with gut barrier function in ways correlating to increased exposure to allergens. Understanding the consequences of interactions between these food ingredients and the intestinal epithelium is important for evaluating allergen dose exposure characteristics. METHODS AND RESULTS: This study challenged Caco-2 cell monolayers, an in vitro model of human intestinal epithelial tight junctions with synthetic polysorbate-80 or natural lecithin alone, or in combination with known allergens (egg proteins: ovalbumin, ovomucoid, and ovotransferrin; and a synthetic form of galactose-alpha-1,3-galactose [alpha-gal], an allergen of increasing concern). For most doses of individual emulsifiers and allergens, >90% cell viability and <15% cytotoxicity are observed; however, toxicity increased at a 0.5% concentration of emulsifiers. At low cytotoxic concentration (0.2%), only polysorbate-80 treatment reduced monolayer integrity (≈20%) with increased lucifer yellow passage. Dose-related differences in expression of tight junction-associated genes and occludin protein are observed with emulsifier treatments. The transport of all tested allergens across the cell monolayers, excluding ovotransferrin, nearly doubled in the presence of 0.2% polysorbate-80 compared to lecithin and untreated control. CONCLUSION: By modulating paracellular permeability, polysorbate-80 may enhance absorption of allergens in a size-dependent manner.

Antimicrobial Susceptibility Testing in a Rapid Single Test via an Egg-like Multivolume Microchamber-Based Microfluidic Platform.

Fast determination of antimicrobial agents' effectiveness (susceptibility/resistance pattern) is an essential diagnostic step for treating bacterial infections and stopping world-wide outbreaks. Here, we report an egg-like multivolume microchamber-based microfluidic (EL-MVM2) platform, which is used to produce a wide range of gradient-based antibiotic concentrations quickly (∼10 min). The EL-MVM2 platform works based upon testing a bacterial suspension in multivolume microchambers (microchamber sizes that range from a volume of 12.56 to 153.86 nL). Antibiotic molecules from a stock solution diffuse into the microchambers of various volumes at the same loading rate, leading to different concentrations among the microchambers. Therefore, we can quickly and easily produce a robust antibiotic gradient-based concentration profile. The EL-MVM2 platform's diffusion (loading) pattern was investigated for different antibiotic drugs using both computational fluid dynamics simulations and experimental approaches. With an easy-to-follow protocol for sample loading and operation, the EL-MVM2 platform was also found to be of high precision with respect to predicting the susceptibility/resistance outcome (>97%; surpassing the FDA-approval criterion for technology-based antimicrobial susceptibility testing instruments). These features indicate that the EL-MVM2 is an effective, time-saving, and precise alternative to conventional antibiotic susceptibility testing platforms currently being used in clinical diagnostics and point-of-care settings.

Biological small-molecule assays using gradient-based microfluidics.

Studying the potency of small-molecules on eukaryotic and prokaryotic cells using conventional biological settings requires time-consuming procedures and large volumes of expensive small-molecules. Microfluidics could significantly expedite these assays by enabling operation in high-throughput and (semi)automated modes. Here, we introduce a microfluidics platform based on multi-volume microchamber arrays that can produce a wide range of small-molecule concentrations with a desired gradient-based profile for rapid and precise biological testing within a single device with minimal hands-on time. The concept behind this device is based on introducing the same amount of a small-molecule into microchambers of different volumes to spontaneously generate a gradient concentration profile via diffusion. This design enables to obtain an unprecedented concentration range (e.g., three orders of magnitude) that can be easily adjusted, allowing us to pinpoint the precise effect of small-molecules on pre-loaded prokaryotic and eukaryotic cells. We also propose a comprehensive relationship for determining the loading time (the only required parameter for implementing this platform) in order to study the effects of any small-molecule on a biological species in a desired test. We demonstrate the versatility of this microfluidics platform by conducting two small-molecule assays-antimicrobial resistance and sugar-phosphate toxicity for both eukaryotic and prokaryotic biological systems.

Gradient-Based Microfluidic Platform for One Single Rapid Antimicrobial Susceptibility Testing.

Antimicrobial resistance is a growing problem, necessitating rapid antimicrobial susceptibility testing (AST) to enable effective in-clinic diagnostic testing and treatment. Conventional AST using broth microdilution or the Kirby-Bauer disk diffusion are time-consuming (e.g., 24-72 h), labor-intensive, and costly and consume reagents. Here, we propose a novel gradient-based microchamber microfluidic (GM2) platform to perform AST assay for a wide range of antibiotic concentrations plus zero (positive control) and maximum (negative control) concentrations all in a single test. Antibiotic lateral diffusion within enriched to depleted (Cmax and zero, respectively) cocurrent flowing fluids, moving alongside a micron-sized main channel, is led to form an antibiotic concentration profile in microchambers, connected to the depleted side of the main channel. We examined the tunability of the GM2 platform, in terms of producing a wide range of antibiotic concentrations in a gradient mode between two consecutive microchambers with changing either the loading fluids' flow rates or their initial concentrations. We also tested the GM2 platform for profiling bacteria associated with human Crohn's disease and bovine mastitis. Time to result for performing a complete AST assay was ∼ 3-4 h in the GM2 platform. Lastly, the GM2 platform tracked the bacterial growth independent of an antibiotic mechanism of action or bacterial species in a robust and easy-to-implement fashion.

Enhanced quantitation of egg allergen in foods using incurred standards and antibodies against processed egg in a model ELISA.

Underestimation of egg allergen from processed foods prompted the evaluation of critical Enzyme-Linked Immunosorbent Assay (ELISA) parameters: (1) extraction of egg proteins from a processed matrix; (2) use of anti-heat processed egg antibodies (Abs) on detectability of modified proteins, and (3) utilization of incurred material as standards. The relative affinity of two combinations of raw (R), boiled (B) and fried (F) Abs to unprocessed/processed egg proteins with or without matrix was determined from antibody (Ab) binding curves. In ELISAs using RBF-Abs and BF-Abs, denaturing buffer, and incurred standards, the Limit of Detection (LOD) and Limit of Quantitation (LOQ) were 0.47 and 0.25; and 1.58 and 0.85, respectively, and the linear range was 0-24 µg g-1 egg protein. The recoveries of egg protein from cookies, cereal bar, and muffin (incurred levels 4.8-48 µg g-1) with the developed ELISAs were in an acceptable range (50-130%). These ELISAs consistently detected more declared/undeclared egg proteins in market samples compared to assays using PBS for extraction. Overall, better assay performance was observed using BF-Abs. An ELISA combining anti-processed egg Abs, denaturing buffer, and incurred standards promises improved quantitation of egg proteins in processed foods.