Annales de microbiologie最新文献

The effects of Bacillus thuringiensis var. israelensis delta-endotoxin were investigated on a cell culture of Aedes aegypti with the electron microscope. The ultrastructural changes following intoxication were: disintegration of endoplasmic reticula by the formation of spherical structures; condensation and then swelling of mitochondria with disappearance of internal cristae; frequent dilatation of the perinuclear space; cellular lysis. The action of a metabolic inhibitor, 2,6-dibromophenol (2,6-DBP), was tested for comparison: beyond condensation of mitochondria, no changes in other cell structures were observed. These data seem to indicate that the mode of action of delta-endotoxin is quite different from that of 2,6 DBP.

The susceptibility pattern of 459 strains of bifidobacteria, representing 15 species, to 16 antimicrobial agents was determined by the broth dilution method. The majority of the strains derived from human faeces. Penicillin G, erythromycin, clindamycin, vancomycin and bacitracin were the most active compounds; they inhibited 90% of the strains at less than 1.6 micrograms/ml. All strains were susceptible to chloramphenicol (MIC90 = 2.0-5.8 micrograms/ml) and also to lincomycin (MIC50 = 0.64-1.5 micrograms/ml). Neomycin, streptomycin and tetracycline presented a great variability in their activity. Most strains were resistant to polymyxin B, nalidixic acid, kanamycin, gentamicin and metronidazole. The only variation in susceptibility which was observed among the different species concerned Bifidobacterium suis, which generally appeared to be more resistant than other species.

Virulence of the five genomic groups of Listeria monocytogenes (sensu lato) was tested toward mice by determination of LD50 and growth or survival kinetics in vivo. Virulent strains included L. monocytogenes (sensu lato) (genomic group 1) and "L. bulgarica" (genomic group 2). The three other genomic groups, "L. innocua", "L. welshimeri" and "L. seeligeri", were apathogenic and avirulent under these experimental conditions.

After induction of pyelonephritis and cystitis in rabbits by a group D streptococcus, the authors measured the specific serum antibody response in the three major immunoglobulin classes. The enzyme-linked immunosorbent assay was performed using group D streptococcal antigen extracted by phenol. Before experimentation, all rabbits had low IgM, IgG and IgA titres against group D streptococcal antigen. A marked increase in IgM antibodies was detected during the first month of experimental pyelonephritis. A poor IgM antibody response was observed in rabbits with cystitis. During the three months of experimentation, a significant difference in mean IgG levels was observed between rabbits with pyelonephritis and those with cystitis.

Bacterial growth was studied in synthetic media containing guanidomethyl-, 2-guanidoethyl-, 3-guanidopropyl- or 4-guanido-1-aminobutyl-phosphonic acid, as a possible nitrogen or phosphorus source. Among these four compounds, 2-guanidoethylphosphonic acid (2-GEPh) appeared to be the only efficient nitrogen nutrient. Our results are discussed in light of recent data on Pseudomonas aeruginosa amidinohydrolases. In addition, 2-GEPh proved to be a valuable source of phosphorus; the phosphorus group of its higher homologue 3-guanidopropylphosphonic acid was also used, but the linear bacterial growth curve reflected a limited rate of phosphate release. The characterization of ethylguanidine and propylguanidine in the corresponding culture filtrates suggests a hydrolytic process similar to that described for 3-aminopropylphosphonic acid.

The K99 and F41 pili produced by most bovine enterotoxigenic Escherichia coli were composed of polypeptide subunits with molecular weights of 18,300 and 29,000. The glucose dependency of K99 pili biosynthesis in some strains of E. coli was evidenced by results of SDS-polyacrylamide gel electrophoresis. Differences in electrophoretic mobility in "Noble" agar between K99 pili from glucose-dependent and independent pathways were unrelated to differences in subunit molecular weight. The K99 and F41 pili displayed two kinds of mannose-resistant haemagglutination properties: 1) strong and thermostable; and 2) weaker than "1" and properties: 1) strong and thermostable; and 2) weaker than "1" and thermolabile. The reproducibility of results concerning "2" was poor and depended on the age of extracts and erythrocytes. It was therefore proposed that only "1" be retained, with sheep and guinea-pig erythrocytes for F41 pili and horse erythrocytes for K99 pili.

In a patient with Serratia marcescens bacteraemia, a variant resistant to cefotaxime and amikacin was isolated in a blood culture under combined treatment with cefotaxime and amikacin. In addition, in vitro selection on cefotaxime and/or amikacin yielded resistant mutants from the sensitive parent strain. These mutants displayed the same type of cross-resistance as the clinical strain to all beta-lactam and aminoglycoside antibiotics. The mechanism for this resistance was a decrease in the permeability of the cell. To our knowledge, the isolation of such strains from blood cultures and the mechanism responsible for this "broad-spectrum resistance" have not been previously described.

The role of complement in the bactericidal activity of human serum against a mutant strain of Pseudomonas aeruginosa used as a model was demonstrated. The involvement of complement in the bacterial destruction of P. aeruginosa, and the contribution of the alternative and classical pathways of the complement system were directly evidenced by using sera from complement-deficient patients.

Yeasts are found to a large extent in cheeses, more particularly in soft cheeses such as Camembert. The proximity between two species previously identified by standard methods was studied using a factorial discriminant analysis on 326 strains. Twenty-three fermentation and assimilation tests (discriminant variables) gave a fairly good discrimination between species. This treatment has allowed us to confirm the present tendencies noticed in yeast classification and has also enabled us to group some of the species.