Polymer-mediated colloidal stability: on the transition between adsorption and depletion.

Addition of polymers to a colloidal dispersion modulates the interactions between the colloids. We briefly review the effects of positive and negative adsorption (also termed depletion). The effective colloid-polymer interactions sensitively affect the colloidal phase behavior. We present a theoretical framework to predict the phase behavior of colloid-polymer mixtures for varying affinities between colloid and polymer, leading to either positive or negative adsorption of polymer segments. For certain conditions, polymers are neither depleted nor adsorbed: the polymer concentration is essentially constant up to the colloidal surface, a condition which we term neutral adsorption. Near this condition, the calculated phase diagrams reveal a stable-unstable-restabilisation transition with increasing polymer concentration. Similar effects have been reported experimentally, for instance as a function of temperature [Feng et al., Nat. Mat., 2015, 14, 61-65], which may modulate the effective polymer-colloid affinity. Understanding how to achieve neutral adsorption opens up the possibility of preparing highly dense, yet stable, colloid-polymer mixtures.

Prevalence of antimicrobial drug resistant bacteria carried by in- and outpatients attending a secondary care hospital in Zambia.

OBJECTIVE: Antimicrobial resistance is an increasing global health problem. Very little data on resistance patterns of pathogenic bacteria in low-income countries exist. The aim of this study was to measure the prevalence of antimicrobial drug resistant bacteria carried by in- and outpatients in the resource constraint setting of a secondary care hospital in Zambia. Nasal and rectal samples from 50 in- and 50 outpatients were collected. Patients were randomly selected and informed consent was obtained. Nasal samples were tested for the presence of methicillin-resistant Staphylococcus aureus (MRSA), and rectal samples for Gram-negative rods (family of Enterobacteriaceae) non-susceptible to gentamicin, ciprofloxacin and ceftriaxone. Additionally, E-tests were performed on ceftriaxone-resistant Enterobacteriaceae to detect extended-spectrum ß-lactamases (ESBLs). RESULTS: 14% of inpatients carried S. aureus, and 18% of outpatients. No MRSA was found. 90% of inpatients and 48% of outpatients carried one or more Enterobacteriaceae strains (75% Escherichia coli and Klebsiella pneumonia) resistant to gentamicin, ciprofloxacin and/or ceftriaxone (p < 0.001). Among inpatients gentamicin resistance was most prevalent (in 78%), whereas among outpatients ciprofloxacin resistance prevailed (in 38%). All ceftriaxone-resistant Enterobacteriaceae were ESBL-positive; these were present in 52% of inpatients versus 12% of outpatients (p < 0.001). We conclude it is feasible to perform basic microbiological procedures in the hospital laboratory in a low-income country and generate data on antimicrobial susceptibility. The high prevalence of antimicrobial drug resistant Enterobacteriaceae carried by in- and outpatients is worrisome. In order to slow down antimicrobial resistance, surveillance data on local susceptibility patterns of bacteria are a prerequisite to generate guidelines for antimicrobial therapy, to guide in individual patient treatment and to support implementation of infection control measures in a hospital.

Assessing the Firing Properties of the Electrically Stimulated Auditory Nerve Using a Convolution Model.

The electrically evoked compound action potential (eCAP) is a routinely performed measure of the auditory nerve in cochlear implant users. Using a convolution model of the eCAP, additional information about the neural firing properties can be obtained, which may provide relevant information about the health of the auditory nerve. In this study, guinea pigs with various degrees of nerve degeneration were used to directly relate firing properties to nerve histology. The same convolution model was applied on human eCAPs to examine similarities and ultimately to examine its clinical applicability. For most eCAPs, the estimated nerve firing probability was bimodal and could be parameterised by two Gaussian distributions with an average latency difference of 0.4 ms. The ratio of the scaling factors of the late and early component increased with neural degeneration in the guinea pig. This ratio decreased with stimulation intensity in humans. The latency of the early component decreased with neural degeneration in the guinea pig. Indirectly, this was observed in humans as well, assuming that the cochlear base exhibits more neural degeneration than the apex. Differences between guinea pigs and humans were observed, among other parameters, in the width of the early component: very robust in guinea pig, and dependent on stimulation intensity and cochlear region in humans. We conclude that the deconvolution of the eCAP is a valuable addition to existing analyses, in particular as it reveals two separate firing components in the auditory nerve.