Fitness trade-offs of multidrug efflux pumps in Escherichia coli K-12 in acid or base, and with aromatic phytochemicals

Multidrug efflux pumps are the frontline defense mechanisms of Gram-negative bacteria, yet little is known of their relative fitness trade-offs under gut conditions such as low pH and the presence of antimicrobial food molecules. Low pH contributes to the proton-motive force (PMF) that drives most efflux pumps. We show how the PMF-dependent pumps AcrAB-TolC, MdtEF-TolC, and EmrAB-TolC undergo selection at low pH and in the presence of membrane-permeant phytochemicals. Competition assays were performed by flow cytometry of co-cultured Escherichia coli K-12 strains possessing or lacking a given pump complex. All three pumps showed negative selection under conditions that deplete PMF (pH 5.5 with carbonyl cyanide 3-chlorophenylhydrazone or at pH 8.0). At pH 5.5, selection against AcrAB-TolC was increased by aromatic acids, alcohols, and related phytochemicals such as methyl salicylate. The degree of fitness cost for AcrA was correlated with the phytochemical's lipophilicity (logP). Methyl salicylate and salicylamide selected strongly against AcrA, without genetic induction of drug resistance regulons. MdtEF-TolC and EmrAB-TolC each had a fitness cost at pH 5.5, but salicylate or benzoate made the fitness contribution positive. Pump fitness effects were not explained by gene expression (measured by digital PCR). Between pH 5.5 and 8.0, acrA and emrA were upregulated in the log phase, whereas mdtE expression was upregulated in the transition-to-stationary phase and at pH 5.5 in the log phase. Methyl salicylate did not affect pump gene expression. Our results suggest that lipophilic non-acidic molecules select against a major efflux pump without inducing antibiotic resistance regulons.IMPORTANCEFor drugs that are administered orally, we need to understand how ingested phytochemicals modulate drug resistance in our gut microbiome. Bacteria maintain low-level resistance by proton-motive force (PMF)-driven pumps that efflux many different antibiotics and cell waste products. These pumps play a key role in bacterial defense by conferring resistance to antimicrobial agents at first exposure while providing time for a pathogen to evolve resistance to higher levels of the antibiotic exposed. Nevertheless, efflux pumps confer energetic costs due to gene expression and pump energy expense. The bacterial PMF includes the transmembrane pH difference (ΔpH), which may be depleted by permeant acids and membrane disruptors. Understanding the fitness costs of efflux pumps may enable us to develop resistance breakers, that is, molecules that work together with antibiotics to potentiate their effect. Non-acidic aromatic molecules have the advantage that they avoid the Mar-dependent induction of regulons conferring other forms of drug resistance. We show that different pumps have distinct selection criteria, and we identified non-acidic aromatic molecules as promising candidates for drug resistance breakers.

Depth-dependent intracortical myelin organization in the living human brain determined by in vivo ultra-high field magnetic resonance imaging

BACKGROUND

Intracortical myelin is a key determinant of neuronal synchrony and plasticity that underpin optimal brain function. Magnetic resonance imaging (MRI) facilitates the examination of intracortical myelin but presents with methodological challenges. Here we describe a whole-brain approach for the in vivo investigation of intracortical myelin in the human brain using ultra-high field MRI.

METHODS

Twenty-five healthy adults were imaged in a 7 Tesla MRI scanner using diffusion-weighted imaging and a T₁-weighted sequence optimized for intracortical myelin contrast. Using an automated pipeline, T₁ values were extracted at 20 depth-levels from each of 148 cortical regions. In each cortical region, T₁ values were used to infer myelin concentration and to construct a non-linearity index as a measure the spatial distribution of myelin across the cortical ribbon. The relationship of myelin concentration and the non-linearity index with other neuroanatomical properties were investigated. Five patients with multiple sclerosis were also assessed using the same protocol as positive controls.

RESULTS

Intracortical T₁ values decreased between the outer brain surface and the gray-white matter boundary following a slope that showed a slight leveling between 50% and 75% of cortical depth. Higher-order regions in the prefrontal, cingulate and insular cortices, displayed higher non-linearity indices than sensorimotor regions. Across all regions, there was a positive association between T₁ values and non-linearity indices (P < 10^-5). Both T₁ values (P < 10^-5) and non-linearity indices (P < 10^-15) were associated with cortical thickness. Higher myelin concentration but only in the deepest cortical levels was associated with increased subcortical fractional anisotropy (P = 0.05).

CONCLUSIONS

We demonstrate the usefulness of an automatic, whole-brain method to perform depth-dependent examination of intracortical myelin organization. The extracted metrics, T₁ values and the non-linearity index, have characteristic patterns across cortical regions, and are associated with thickness and underlying white matter microstructure.

Reproducibility of myelin content-based human habenula segmentation at 3 Tesla

In vivo morphological study of the human habenula, a pair of small epithalamic nuclei adjacent to the dorsomedial thalamus, has recently gained significant interest for its role in reward and aversion processing. However, segmenting the habenula from in vivo magnetic resonance imaging (MRI) is challenging due to the habenula's small size and low anatomical contrast. Although manual and semi-automated habenula segmentation methods have been reported, the test-retest reproducibility of the segmented habenula volume and the consistency of the boundaries of habenula segmentation have not been investigated. In this study, we evaluated the intra- and inter-site reproducibility of in vivo human habenula segmentation from 3T MRI (0.7-0.8 mm isotropic resolution) using our previously proposed semi-automated myelin contrast-based method and its fully-automated version, as well as a previously published manual geometry-based method. The habenula segmentation using our semi-automated method showed consistent boundary definition (high Dice coefficient, low mean distance, and moderate Hausdorff distance) and reproducible volume measurement (low coefficient of variation). Furthermore, the habenula boundary in our semi-automated segmentation from 3T MRI agreed well with that in the manual segmentation from 7T MRI (0.5 mm isotropic resolution) of the same subjects. Overall, our proposed semi-automated habenula segmentation showed reliable and reproducible habenula localization, while its fully-automated version offers an efficient way for large sample analysis.

Molecular characterization and antimicrobial susceptibility profiles in Streptococcus agalactiae colonizing strains: association of erythromycin resistance with subtype III-1 genetic clone family

Knowledge of the epidemiology of Streptococcus agalactiae in Portugal is limited: therefore, the present study aimed to investigate the carriage rate of S. agalactiae among Portuguese women of reproductive age and the prevalence of antibiotic resistance, as well as to perform a molecular characterization of the clinical isolates. S. agalactiae was recovered from 6.2% of 4269 women during the period 2005–2007, with a predominance of capsular genotypes III (35%), V (33%), Ia (16%) and II (10%) in a sample of 100 isolates. To our knowledge, this is the first report of the S. agalactiae colonization rate in Portugal determined according to CDC guidelines. All isolates were susceptible to penicillin and vancomycin, whereas resistance to clindamycin and erythromycin was detected in 10% and 19% of isolates, respectively. Among the 19 erythromycin-resistant isolates, ten (53%) displayed the constitutive MLS(B) phenotype (conferring high-level resistance to macrolides), eight (42%) had the inducible MLS(B), and the M phenotype accounted for one isolate (5%). erm methylase genes were exclusively associated with MLS(B) phenotype isolates, whereas the M phenotype was a result of the presence of mefA. Multilocus sequence typing analysis of the genetic relatedness among isolates presenting resistance to erythromycin demonstrated a novel association between erythromycin resistance and the subtype III-1/ST-19 genetic clone family.

Sensitivity evaluation of the Gen-Probe AMP-CT assay by pooling urine samples for the screening of Chlamydia trachomatis urogenital infection

The sensitivity of two urine pool sizes versus individual testing, to detect Chlamydia trachomatis urogenital infection, was evaluated using the Gen-Probe AMP-CT assay. Thirty-three (33) known polymerase chain reaction (PCR) positive urine specimens were combined with 231 fresh first-catch urine (FCU) samples in 33 groups of four and 33 groups of eight, to make up 4X and 8X pooled samples, respectively. Gen-Probe AMP-CT assay was performed on pools as well as on individual samples at the same time. For the discrepant cases, the known positive samples were diluted 1:4 and 1:8 using the manufacturer's dilution buffer and were retested. Additional positive specimens found among fresh FCU samples were also tested by the Amplicor-PCR assay to confirm their positivity. The sensitivities of 8X pooling, 4X pooling and individual testing were 86.5%, 94.3% and 91.9%, respectively. The Gen-Probe AMP-CT assay applied to a 4X urine pooling model was highly sensitive and may be useful for a population based screening programme.

Rosai-Dorfman disease presenting with isolated bilateral orbital masses: report of two cases

Rosai-Dorfman disease (sinus histiocytosis with massive lymphadenopathy) is a rare benign idiopathic proliferative disease of phagocytic histiocytes. Approximately 80% of patients present with painless massive cervical lymphadenopathy. Isolated extranodal involvement is relatively uncommon. Two cases of Rosai-Dorfman disease are reported: one with isolated bilateral orbital involvement and one with marked cervical lymphadenopathy and multiple dural-based and intraventricular masses.

Patterns of local-regional recurrence following parotid-sparing conformal and segmental intensity-modulated radiotherapy for head and neck cancer

PURPOSE

To analyze the patterns of local-regional recurrence in patients with head and neck cancer treated with parotid-sparing conformal and segmental intensity-modulated radiotherapy (IMRT).

METHODS AND MATERIALS

Fifty-eight patients with head and neck cancer were treated with bilateral neck radiation (RT) using conformal or segmental IMRT techniques, while sparing a substantial portion of one parotid gland. The targets for CT-based RT planning included the gross tumor volume (GTV) (primary tumor and lymph node metastases) and the clinical target volume (CTV) (postoperative tumor bed, expansions of the GTVs and lymph node groups at risk of subclinical disease). Lymph node targets at risk of subclinical disease included the bilateral jugulodigastric and lower jugular lymph nodes, bilateral retropharyngeal lymph nodes at risk, and high jugular nodes at the base of skull in the side of the neck at highest risk (containing clinical neck metastases and/or ipsilateral to the primary tumor). The CTVs were expanded by 5 mm to yield planning target volumes (PTVs). Planning goals included coverage of all PTVs (with a minimum of 95% of the prescribed dose) and sparing of a substantial portion of the parotid gland in the side of the neck at less risk. The median RT doses to the gross tumor, the operative bed, and the subclinical disease PTVs were 70.4 Gy, 61.2 Gy, and 50.4 Gy respectively. All recurrences were defined on CT scans obtained at the time of recurrence, transferred to the pretreatment CT dataset used for RT planning, and analyzed using dose-volume histograms. The recurrences were classified as 1) "in-field," in which 95% or more of the recurrence volume (V(recur)) was within the 95% isodose; 2) "marginal," in which 20% to 95% of V(recur) was within the 95% isodose; or 3) "outside," in which less than 20% of V(recur) was within the 95% isodose.

RESULTS

With a median follow-up of 27 months (range 6 to 60 months), 10 regional recurrences, 5 local recurrences (including one noninvasive recurrence) and 1 stomal recurrence were seen in 12 patients, for a 2-year actuarial local-regional control rate of 79% (95% confidence interval 68-90%). Ten patients (80%) relapsed in-field (in areas of previous gross tumor in nine patients), and two patients developed marginal recurrences in the side of the neck at highest risk (one in the high retropharyngeal nodes/base of skull and one in the submandibular nodes). Four regional recurrences extended superior to the jugulodigastric node, in the high jugular and retropharyngeal nodes near the base of skull of the side of the neck at highest risk. Three of these were in-field, in areas that had received the dose intended for subclinical disease. No recurrences were seen in the nodes superior to the jugulodigastric nodes in the side of the neck at less risk, where RT was partially spared.

CONCLUSIONS

The majority of local-regional recurrences after conformal and segmental IMRT were "in-field," in areas judged to be at high risk at the time of RT planning, including the GTV, the operative bed, and the first echelon nodes. These findings motivate studies of dose escalation to the highest risk regions.

Serum immunoglobulin E levels in relation to adenoid surgery

The adenoid tissue is an immunecompetent lymphoid organ, which has the capacity of reacting against numerous antigens. We have studied the influence that the elimination of the said tissue would have on the total IgE serum levels in 33 patients of an average age of 5 and criteria of adenoidectomy and in whom these levels were measured before and after surgery. We have not noticed any statistically significant differences in the IgE values after adenoidectomy with respect to those prior to surgery, which were normal. Adenoidectomy, like other authors have observed after tonsillectomy, does not alter the IgE serum values.