Characterization of Pasteurella multocida strains isolated from human infections.

Isolates of Pasteurella multocida recovered from infected humans (n = 15) were characterized by traditional and molecular microbiological methods and were compared with cat-derived strains (n = 5). The most prevalent subspecies among strains from human infections was P. multocida subsp. septica (80%), and nearly all isolates showed a similar combination of virulence-associated genes. MLST analysis classified the 20 P. multocida strains into 16 different sequence types, and we assigned 11 new sequence types (ST), however, only one of those (ST 334) was shared by two human and one cat isolates. P. multocida subsp. septica strains formed a distinct phylogenetic group within the species. The strains showed resistance to erythromycin, clindamycin and sulfamethoxazole, and with two exceptions, resistance to tilmicosin was also detected. Each strain was susceptible to ampicillin, streptomycin, gentamycin, tetracycline, doxycycline, cefazolin, cefpodoxime, chloramphenicol, florfenicol and enrofloxacin. Common characteristics (virulence profile and antibiotic sensitivity pattern) shared by strains isolated from humans and cats support the view that domestic cats may serve as a potential reservoir for P. multocida.

Long-lasting dephosphorylation of connexin 43 in acute seizures is regulated by NMDA receptors in the rat cerebral cortex.

Gap junctions consisting of connexin 43 subunits provide intercellular communication between astrocytes, contributing to their function of maintaining the central nervous system (CNS) microenvironment. Magnetic resonance imaging (MRI) studies demonstrate prolonged astrocyte swelling related to seizures, while in vitro studies show the disruption of intercellular coupling and the cytotoxic swelling of astrocytes in seizure-equivalent environments. We examined the relation between astrocyte swelling and connexin 43 regulation using an in vivo seizure model. Generalised tonic-clonic convulsions were induced in adult rats using intraperitoneally (i.p.)-administered 4-aminopyridine (4-AP). The expression of connexin 43 mRNA and protein at 1, 3 and 24 h after seizure induction was measured. Astrocytic swelling was assessed at the same time points using transmission electron microscopy. mRNA and protein levels remained unaltered at all time periods. However, a significant (≈50%) reduction was found in the amount of phosphorylated (P1, P2) to unphosphorylated (NP) forms of connexin 43 at 3 h. The amount increased thereafter, but was still significantly lower than in the controls at 24 h post-seizure. Simultaneously, marked astrocytic swelling was measured in the neocortex. Pre-treatment with N-methyl-D-aspartate (NMDA) receptor antagonist dizocilpine maleate (MK-801) resulted in the amelioration of seizure symptoms and the prevention of connexin 43 dephosphorylation, as well as significantly reduced astrocytic swelling. Dephosphorylation of connexin 43 was shown to reduce astrocytic gap junction (GJ) permeability. Our results therefore suggest that, during acute seizures, a prolonged inhibition of intercellular coupling develops in the astrocyte network. This accounts for the long-lasting astrocyte swelling observed, and potentially impairs buffering function. The results also imply that this uncoupling is regulated through neuronal and/or glial NMDA-type glutamate receptors.

Structural and functional MRI following 4-aminopyridine-induced seizures: a comparative imaging and anatomical study.

Structural and functional MRI was used in conjunction with computerized electron microscopy morphometry to study changes 2 h, 24 h and 3 days after 4-aminopyridine-induced seizures lasting 2 h in rats. T2 (relaxation time) values showed changes throughout the cerebral cortex, hippocampus, amygdala and medial thalamus, with a different temporal progression, showing a complete recovery only after 3 days. Two hours after seizures, the apparent diffusion coefficient was decreased throughout the brain compared to control animals, and a further decrease was evident 24 h after seizures. This was followed by a complete recovery at 3 days post-seizures. Functional MRI was performed using regional cerebral blood volume (rCBV) maps. The rCBV was increased shortly after convulsions (2 h) in all structures investigated, with a significant return to baseline values in the parietal cortex and hippocampus, but not in the medial thalamic nuclei, 24 h after seizure onset. No rCBV alterations were detected 3 days after seizures. Electron microscopy of tissue samples of parietal neocortex and hippocampus revealed prominent astrocytic swelling 2 h post-convulsions which decreased thereafter gradually. In conclusion, this experiment reports for the first time structural and functional brain alterations, lasting several hours, in 4-aminopyridine-treated rats after seizure onset. MRI approach combined with histological and ultrastructural analysis provided a clarification of the mechanisms involved in the brain acute response to ictal activity.