[Cervical spondylotic myelopathy: motor and somatosensory evoked potentials, clinical and radiological correlation]. / Myélopathie cervicarthrosique: intérêt des explorations électrophysiologiques et corrélations avec les données radiologiques.

Somatosensory and motor evoked potentials (EPs) have been recorded in 38 patients with cervical spondylosis, documented by MRI. All were symptomatic, 23 presented with myelopathy. Somatosensory evoked potentials were abnormal in 66p.cent as well as motor evoked potentials. The N13 potential, generated by the posterior dorsal horn of the cervical spinal cord, was abnormal in 63p.cent of patients and was the only disorder detected in 12p.cent. Together, somatosensory and motor evoked potentials were abnormal in 82p.cent of patients. There was no correlation between EPs findings and radiological data. Similary, MRI and clinical data were agreeing in only 50p.cent of patients. When a spondylotic myelopathy is suspected, SEPs proved more sensitive to detect somatosensory dysfunctionning than clinical testing and radiological data were discordant with clinical status in 50p.cent of cases. In order to obtain a high sensitivity, both somatosensory and motor evoked potentials should be recorded on all limbs with a special attention to segmental cervical and cervico-medullary responses. EPs data help to identify patients with cervical cord dysfunction and thus contribute to the therapeutic decision for surgery.

Assessment of Three Methods for Detection and Quantification of Nitrite-Oxidizing Bacteria and Nitrobacter in Freshwater Sediments (MPN-PCR, MPN-Griess, Immunofluorescence).

> Abstract Nitrification in freshwater, a key process in the nitrogen cycle, is now well known to take place predominantly on suspended particles and in sediment. Nitrobacter is the most commonly isolated nitrite oxidizing bacteria from water environments. Three methods for counting nitrite oxidizing communities (especially Nitrobacter) in sediment were investigated: MPN-Griess, fluorescent antibodies (immunofluorescence), and a more recent molecular method coupling specific DNA amplification by PCR and statistical MPN quantification. After preliminary adjustments of the MPN-PCR technique, the detection level and the yield of each method were determined by inoculating a sediment with a pure Nitrobacter culture. The best recovery yield was obtained with the immunofluorescence technique (21.3%) and the lowest detection level was reached with the MPN-Griess method (10(3) Nitrobacter/g dry weight sediment). The MPN-PCR method resulted in the lowest recovery yields and needs further adaptation to become a reliable and precise tool for investigations of nitrifying bacteria in sediment.

[Auditory perception disorders due to bilateral cortical lesions. An electrophysiology study]. / Troubles perceptifs auditifs par lésion corticale bilatérale. Etude électrophysiologique.

A 78-year-old right handed man with a past history of atrial fibrillation developed in November 1994, a slight right hemiparesis with aphasia which cleared over one month. Head CT scan showed a left middle cerebral artery infarct involving the posterior part of the temporal lobe. In September 1995, a second stroke occurred. Head CT scan revealed a recent right middle cerebral artery infarct within the posterior part of temporal cortex. Auditory agnosia was diagnosed. Auditory evoked potentials recording showed bilateral dysfunction of central auditory pathways mainly over the right hemisphere. Clinical data and evoked potentials suggest that auditory agnosia might be related to the right temporal lobe damage. This later is involved in linguistic processes as suggested by positron emission tomography studies.

Purification of the dissimilative nitrate reductase of Pseudomonas fluorescens and the cloning and sequencing of its corresponding genes.

The dissimilative membrane-bound nitrate reductase from Pseudomonas fluorescens strain AK15 was purified and the alpha subunit of the enzyme partially sequenced. On the basis of this partial amino acid sequence and of conserved stretches of amino acids between Escherichia coli and Bacillus subtilis, degenerate primers were design to amplify the narG gene and part of the narH gene in a PCR approach. The deduced amino acid sequence of narG shows 72% and 52% and narH 78% and 62% identity to the homologous subunit of E. coli and B. subtilis, respectively.

Influence of Two Plant Species (Flax and Tomato) on the Distribution of Nitrogen Dissimilative Abilities within Fluorescent Pseudomonas spp.

The distribution of nitrogen-dissimilative abilities among 317 isolates of fluorescent pseudomonads was studied. These strains were isolated from an uncultivated soil and from the rhizosphere, rhizoplane, and root tissue of two plant species (flax and tomato) cultivated on this same soil. The isolates were distributed into two species, Pseudomonas fluorescens (45.1%) and Pseudomonas putida (40.4%), plus an intermediate type (14.5%). P. fluorescens was the species with the greatest proportion of isolates in the root compartments and the greatest proportion of dissimilatory and denitrifying strains. According to their ability to dissimilate nitrogen, the isolates have been distributed into nondissimilatory and dissimilatory strains, nitrate reducers and true denitrifiers with or without N(inf2)O reductase. The proportion of dissimilatory isolates was significantly enhanced in the compartments affected by flax and tomato roots (55% in uncultivated soil and 90 and 82% in the root tissue of flax and tomato, respectively). Among these strains, the proportion of denitrifiers gradually and significantly increased in the root vicinity of tomato (44, 68, 75, and 94% in uncultivated soil, rhizosphere, rhizoplane, and root tissue, respectively) and was higher in the flax rhizoplane (66%) than in the uncultivated soil. A higher proportion of N(inf2)O reducers was also found in the root compartments. This result was particularly clear for tomato. It is hypothesized that denitrification could be a selective advantage for the denitrifiers in the root environment and that this process could contribute to modify the specific composition of the bacterial communities in the rhizosphere.

Use of tn5 mutants to assess the role of the dissimilatory nitrite reductase in the competitive abilities of two pseudomonas strains in soil.

We examined the influence of soil aeration state and plant root presence on the comparative survival of wild-type bacteria and isogenic Tn5 (Nir(sup-)) mutants lacking the ability to synthesize nitrite reductase. Two denitrifying Pseudomonas strains with different nitrite reductase types were used. Enumeration of bacteria in sterile and nonsterile soils was based on differential antibiotic resistance. The validity of the bacterial models studied (i.e., equal growth of wild-type and mutant bacteria under aerobic conditions and significantly better growth of wild-type bacteria under denitrifying conditions) was verified in pure-culture studies. In sterile soil, both strains survived better under aerobic than under anaerobic conditions. The lower efficiency of denitrification than O(inf2) respiration in supporting bacterial growth explained this result, and the physical heterogeneity of soil did not strongly modify the results obtained in pure-culture studies. In nonsterile soil, one of the Pseudomonas strains survived better under anaerobic conditions while the other competed equally with the indigenous soil microflora under aerobic and anaerobic conditions. However, when the Nir(sup-)-to-total inoculant ratios (wild type plus Nir(sup-) mutant) were analyzed, it appeared that the presence of nitrite reductase conferred on both Pseudomonas strains a competitive advantage for anaerobic environment or rhizosphere colonization. This is the first attempt to demonstrate with isogenic nondenitrifying mutants that denitrification can contribute to the persistence and distribution of bacteria in fluctuating soil environments.

Ecological study of twoNitrobacter serotypes coexisting in the same soil.

The problem of competition betweenNitrobacter strains was posed by the fact that two serotypes (N.w and L) coexisted in a soil, as shown by immunofluorescence. The L serotype had a lower growth rate in pure culture than serotype N.w, as well as a slower nitrifying activity when inoculated to a sterilized soil percolated with NO2 (-) solution. When both serotypes were inoculated together, only N.w was observed by immunofluorescence at the end of the percolation; when in the control soil the two serotypes were identified, strain L always adhered to particles. Maintenance of the two serotypes in the soil could be explained as their exploitation of distinct ecological niches. Thus the relative in situ importance of the two strains is governed by environmental conditions.

Isolation from soils ofNitrobacter and evidence for novel serotypes using immunofluorescence.

To study the ecology of chemoautotrophic nitrifying bacteria (Nitrobacter), the immunofluorescence technique has been used. Fluorescent antibodies againstNitrobacter winogradskyi andNitrobacter agilis, the two known serotypes, have not labeled strains isolated from soils of the Lyon region (pH 8.1 and pH 4.7). The pure-culture isolates appeared to belong to the same genus, but to be serologically different from the reference strains. These results led us to question the diversity of strains ofNitrobacter in soils.