Pervasive sign epistasis between conjugative plasmids and drug-resistance chromosomal mutations.

Multidrug-resistant bacteria arise mostly by the accumulation of plasmids and chromosomal mutations. Typically, these resistant determinants are costly to the bacterial cell. Yet, recently, it has been found that, in Escherichia coli bacterial cells, a mutation conferring resistance to an antibiotic can be advantageous to the bacterial cell if another antibiotic-resistance mutation is already present, a phenomenon called sign epistasis. Here we study the interaction between antibiotic-resistance chromosomal mutations and conjugative (i.e., self-transmissible) plasmids and find many cases of sign epistasis (40%)--including one of reciprocal sign epistasis where the strain carrying both resistance determinants is fitter than the two strains carrying only one of the determinants. This implies that the acquisition of an additional resistance plasmid or of a resistance mutation often increases the fitness of a bacterial strain already resistant to antibiotics. We further show that there is an overall antagonistic interaction between mutations and plasmids (52%). These results further complicate expectations of resistance reversal by interdiction of antibiotic use.

Rosette-forming glioneuronal tumor: pathology case report.

OBJECTIVE: Rosette-forming glioneuronal tumor is a newly described mixed glial and neuronal tumor. We describe two cases and review the literature to better characterize this entity. METHODS: Patients were surgically treated, and tumors were diagnosed by light microscopy and immunohistochemistry using the avidin-biotin complex method. PubMed was searched for previously reported cases. RESULTS: Patient 1 was a 38-year-old woman who presented with headaches and no neurological abnormality. Magnetic resonance imaging showed a solid mass in the fourth ventricle. Subtotal excision of the mass caused transient gait ataxia. Patient 2 was a 51-year-old woman with dizziness who fell and sustained head trauma. Magnetic resonance imaging revealed a right paramedian cerebellar cystic and nodular mass and a separate nodule in the vermis, which were excised gross totally with no morbidity. Microscopic examination showed neuroepithelial tumors composed of neurocytic cells focally forming well-defined rosettes that were immunopositive for neuronal markers and of elongated, glial fibrillary acidic protein-immunoreactive astrocytes. No histological anaplasia was present. Both patients were well 18 and 8 months after surgery, respectively. Eighteen rosette-forming glioneuronal tumors were identified with the literature search. CONCLUSION: These are tumors of young adulthood (range, 12-59 yr) usually in or close to the fourth ventricle. Histologically, they are low-grade, although multiple foci or local extension may prevent total excision and account for some recurrences. On imaging, they are cystic, solid, or both, with minimal perilesional edema or mass effect. They are composed of neurocytic and glial elements, probably arising from a common progenitor in the subependymal plate, and need to be differentiated from a variety of glioneuronal tumors.

[Clinical application of functional MR. Evaluation of motor functions and verbal fluency]. / Aplicação clínica da RM funcional. Avaliação de funções motoras e fluência verbal.

In this article we reviewed some examples of our experience in clinical applications of functional MRI (fMRI) in the motor and verbal fluency tasks evaluation. Seventeen patients with supratentorial cerebral pathology (5 arteriovenous malformations--AVMs, 2 meningiomas, 1 tuberculoma, 1 cortical tuberoma, 1 DNET, 2 cerebral metastases, 3 gliomas and 2 patients with mesial temporal sclerosis and medically intractable epilepsy--lateralization of language) and three healthy subjects were studied on a 1.5 T system (Signa GE) using a blood oxygen level-dependent (BOLD)--sensitive multi-slice EPI technique. Different paradigms for localization of the motor (hand/foot) and verbal fluency sensorimotor cortex were tested and selected for each pathology. In healthy subjects motor activation elicited BOLD signal changes in the sensorimotor cortex, permitting identification of primary motor and sensory cortical areas and focal activation of different cortical areas by a verbal fluency task. Twelve motor studies were performed and in 6 RMF results demonstrated the localization of motor hand areas near the lesion, and in nine studies of verbal fluency 6 activation were adjacent to the lesion. The studies were performed prior to neurosurgical procedures, contributed to therapeutical decisions and proved to be a valuable non invasive method of cortical mapping for preoperative planning.