Interplay between environmental yielding and dynamic forcing modulates bacterial growth

Many bacterial habitats-ranging from gels and tissues in the body to cell-secreted exopolysaccharides in biofilms-are rheologically complex, undergo dynamic external forcing, and have unevenly distributed nutrients. How do these features jointly influence how the resident cells grow and proliferate? Here, we address this question by studying the growth of Escherichia coli dispersed in granular hydrogel matrices with defined and highly tunable structural and rheological properties, under different amounts of external forcing imposed by mechanical shaking, and in both aerobic and anaerobic conditions. Our experiments establish a general principle: that the balance between the yield stress of the environment that the cells inhabit, σy, and the external stress imposed on the environment, σ, modulates bacterial growth by altering transport of essential nutrients to the cells. In particular, when σy<σ, the environment is easily fluidized and mixed over large scales, providing nutrients to the cells and sustaining complete cellular growth. By contrast, when σy>σ, the elasticity of the environment suppresses large-scale fluid mixing, limiting nutrient availability and arresting cellular growth. Our work thus reveals a new mechanism, beyond effects that change cellular behavior via local forcing, by which the rheology of the environment may modulate microbial physiology in diverse natural and industrial settings.

3D Printing Bacteria to Study Motility and Growth in Complex 3D Porous Media

Bacteria are ubiquitous in complex three-dimensional (3D) porous environments, such as biological tissues and gels, and subsurface soils and sediments. However, the majority of previous work has focused on studies of cells in bulk liquids or at flat surfaces, which do not fully recapitulate the complexity of many natural bacterial habitats. Here, this gap in knowledge is addressed by describing the development of a method to 3D-print dense colonies of bacteria into jammed granular hydrogel matrices. These matrices have tunable pore sizes and mechanical properties; they physically confine the cells, thus supporting them in 3D. They are optically transparent, allowing for direct visualization of bacterial spreading through their surroundings using imaging. As a proof of this principle, here, the capability of this protocol is demonstrated by 3D printing and imaging non-motile and motile Vibro cholerae, as well as non-motile Escherichia coli, in jammed granular hydrogel matrices with varying interstitial pore sizes.

Causes of polymyxin treatment failure and new derivatives to fill the gap

Polymyxins are a class of antibiotics that were discovered in 1947 from programs searching for compounds effective in the treatment of Gram-negative infections. Produced by the Gram-positive bacterium Paenibacillus polymyxa and composed of a cyclic peptide chain with a peptide-fatty acyl tail, polymyxins exert bactericidal effects through membrane disruption. Currently, polymyxin B and colistin (polymyxin E) have been developed for clinical use, where they are reserved as "last-line" therapies for multidrug-resistant (MDR) infections. Unfortunately, the incidences of strains resistant to polymyxins have been increasing globally, and polymyxin heteroresistance has been gaining appreciation as an important clinical challenge. These phenomena, along with bacterial tolerance to this antibiotic class, constitute important contributors to polymyxin treatment failure. Here, we review polymyxins and their mechanism of action, summarize the current understanding of how polymyxin treatment fails, and discuss how the next generation of polymyxins holds promise to invigorate this antibiotic class.

A double-blind randomized controlled trial and economic evaluation of transurethral resection vs contact laser vaporization for benign prostatic enlargement: a 3-year follow-up

OBJECTIVE

To evaluate the effect of contact laser prostate surgery in the treatment of benign prostatic hyperplasia.

PATIENTS AND METHODS

A prospective double-blind randomized controlled trial of transurethral resection of the prostate (TURP) and contact laser prostatectomy was conducted, with an economic evaluation of both procedures. The primary outcome measure was the change in the American Urologic Association symptom score, with secondary outcome measures being the peak urinary flow rate, treatment-related complications, re-operation rate and health service costs.

RESULTS

The perioperative blood loss and transfusion requirements were statistically significantly lower for laser prostatectomy than for TURP. There was no clinically significant difference between TURP and contact laser prostatectomy in the mean change in symptom scores and flow rates. There were distinct perioperative advantages in favour of the contact laser treatment, but some disadvantages in terms of re-catheterization and re-operation rates.

CONCLUSIONS

Contact laser prostatectomy is a valid treatment for benign prostatic hypertrophy. The performance of contact laser prostatectomy as day-case surgery would have cost advantages to the National Health Service.

The Oxford Laser Prostate Trial: economic issues surrounding contact laser prostatectomy

OBJECTIVE

To compare the economic implications of transurethral resection of the prostate (TURP) and contact-laser vaporization of the prostate (with the SLT system) using data obtained from a randomized controlled trial.

METHODS

All aspects of management before, during and after surgery on 102 patients, followed up for 3 months, were costed and analysed. Based on the data from the trial, the mean costs were calculated. A sensitivity analysis was then performed to examine the effect of changes in some of the relevant variables. The mean difference in cost between laser treatment and TURP was plotted against the cost of laser consumables, assuming a 5% re-operation rate for both operations at 5 years and a 5% discount rate. A range of laser re-operation rates was compared with the mean difference in costs, assuming a hospital stay of one night and two district-nurse visits. Other assumptions on discounts and re-operation rates, based on collected data, were also tested.

RESULTS

TURP will remain more economical until the cost of laser consumables is reduced to 20% of the current list price, or a hospital stay of one night is introduced.

CONCLUSIONS

The costs of contact-laser vaporization of the prostate are likely to exceed the costs of TURP unless laser treatment is accompanied by a more active approach to post-operative management, including a hospital stay of one night and, if necessary, the removal of the patient's catheter at home by a district nurse.