Cellular and molecular characterization of Phytophthora parasitica appressorium-mediated penetration.

Data on plant pathogenic oomycetes are scarce and little is known about the early events leading to the onset of infection. The aim of this work was to analyze the penetration process of the soil-borne plant pathogen Phytophthora parasitica, which has a wide host range. Here, we performed a cytological analysis of the colonization of the first plant cell and developed an inoculation assay for characterizing the entire penetration process through cellular and molecular analyses. We showed that P. parasitica infects roots by producing a specialized structure, the appressorium. We produced the first cDNA library for the penetrating stage of a Phytophthora species and showed it to be highly enriched in pathogenicity-related sequences. These included coding sequences for many cell-degrading enzymes, effectors such as RXLR-containing proteins and proteins involved in protection against plant defense responses. Characterization of the appressorium cDNA library and identification of genes overrepresented early in P. parasitica infection provided us with an unprecedented opportunity to decipher the molecular mechanisms involved in penetration of the plant cells during the initiation of infection by a soil-borne oomycete.

A family of repeated DNA in the genome of the oomycete plant pathogen Phytophthora cryptogea.

We have identified a family of repetitive sequences, called PCISs (Phytophthora Cryptogea Insertion Sequences), in the genome of Phytophthora cryptogea. They vary greatly in size (in a 100-1200 bp range) and appear to represent 3' terminal fragments of a larger element. Two subfamilies were characterised on the basis of nucleotide sequences. PCISs exhibit insertion polymorphism, as well as a very low sequence divergence. Most copies are flanked by terminal direct repeats, suggesting that their spreading involves insertion events rather than rearrangements. PCISs are found in very few copies in Phytophthora cinnamomi. The spreading of these sequences within the genus Phytophthora is discussed.

[Community-acquired bacterial meningitis in the Loire-Atlantic region: evolution of pneumococcal and meningococcal sensitivity to penicillin]. / Les méningites bactériennes communautaires en Loire-Atlantique: évolution de la sensibilité à la pénicilline des pneumocoques et méningocoques.

OBJECTIVES: An epidemiological study of community-acquired bacterial meningitis was conducted in Loire-Atlantique in subjects aged over 1 month. Risk factors and changes in pneumococcal and meningococcal susceptibility to betalactams were analyzed. PATIENTS AND METHODS: All cases of proven or presumed bacterial meningitis registered by Loire-Atlantic bacteriology laboratories between May 1995 and April 1998 were analyzed. RESULTS: One hundred two cases were registered (annual incidence: 3.12 cases per 100,000 inhabitants). In children (33 cases) the main germs were meningococci (51%), pneumococci (24%) and Haemophilus influenzae (6%). In adults (69 cases), pneumococci (49%), meningococci (14%) and Listeria (4%) predominated. An underlying disease was noted 44% of the cases. Mortality was 17.6%. Sequellae were observed in 9.5%. Some degree of penicillin resistance was observed in 45% of the pneumococcal strains and in 50% of the meningococcal strains. Half of the pneumococcal strains were also resistant to third generation cephalosporins (C3G). No risk factor was significantly related to resistant strains. Susceptibility to antibiotics was not correlated with mortality for either pneumococcal or meningococcal strains, but sequellae were more frequent after meningitis caused by resistant pneumococci. CONCLUSION: For cases of community-acquired meningococcal meningitis diagnosed in 1999, it would be advisable to prescribe a combination C3G-vancomycin regimen as the first line empirical treatment while waiting for results of susceptibility tests. Certain guidelines proposed by the February 1996 consensus conference on community-acquired purulent meningitis would thus need to be amended.

Characterization of a gene cluster of Phytophthora cryptogea which codes for elicitins, proteins inducing a hypersensitive-like response in tobacco.

Elicitins, proteinaceous elicitors secreted by Phytophthora spp., act as inducers of a hypersensitive-like response in tobacco during incompatible interactions. We have isolated and cloned sequences encoding cryptogein and related isoforms from P. cryptogea that belong to the elicitin family. The isolation of a genomic clone led to the characterization of four clustered genes. Two of these genes encode distinct elicitins, and two genes would encode, if expressed, a class of highly acidic elicitins which had not been observed so far. Northern blots indicate that elicitin genes are expressed in the fungus grown in vitro, though at different levels. Southern hybridization revealed that elicitins are encoded by a multigene family in several other species of Phytophthora. Moreover, isolates of Phytophthora parasitica var. nicotianae, pathogenic to tobacco, which do not produce elicitins, possess several elicitin-encoding genes. Involvement of elicitins in plant-pathogen interactions is discussed.

[Pulmonary infection with Pasteurella multocida in an immuno-deficient patient (author's transl)]. / Infection pulmonaire a Pasteurella multocida chez un patient immunodéprimé.

A seventy-seven-year-old woman, under intermittent treatment with chlorambucil for chronic lymphocytic leukemia, developed acute pneumonia (diffuse interstitial pneumonitis) due to Pasteurella multocida. No direct traumatism had been caused by her cat. Bacteriologic study material was obtained by guided transtracheal distal bronchial brushing and washing. Therapy with tetracyclin was rapidly successful. Pasteurella multocida is an opportunistic organism which can be responsible for severe infections in high-risk patients.

[Septicemia due to an unusual micro-organism: Actinobacillus actinomycetum comitans (author's transl)]. / Septicémie à un germe inhabituel: Actinobacillus actinomycetem comitans.

A new case of septicemia (without endocarditis) due to Actinobacillus actinomycetum comitans is described. The patient was a 59-year-old man with an intraventricular pacemaker. He was successfully treated by a combination of gentamicin and ampicillin. Human infections due to this demanding and slow-growing micro-organism, which is not related to actinomycosis, are only exceptionally reported. In 73% of the cases the endocarditis is subacute. The study of the literature demonstrates the prevalence of male patients and the usual absence of leukocytosis.

In vitro susceptibility of Listeria monocytogenes to some antibiotics and their combinations.

The Listeria monocytogenes strains isolated during recent years in our hospital have been tested for in vitro susceptibility against eleven antibiotics. The following tests were used: antibiotics discs method on Mueller-Hinton agar, determination of MICs by agar dilution method, study of the bactericidal potency of antibiotics combinations. Antibiotic discs method gives some too optimistic results, not confirmed by the MICs determined with agar dilution method. Ther are a few antibiotics used alone which are bactericidal upon Listeria monocytogenes at the concentration reached with usual therapeutic doses, and none regularly bactericidal. Bêtalactam-aminoglycoside combinations are the most effective ones but the ones involving gentamicin are more bactericidal than the ones involving streptomycin. Pristinamycin-aminoglycoside combinations have interesting activities and might be used as an alternative to betalactam-aminoglycoside ones in some peculiar and restricted indications. The other tested combinations are antagonistic or without interest.