Survival of Enterococcus faecalis in seawater microcosms is limited in the presence of bacterivorous zooflagellates.

The survival and persistence of growing and starved cells of Enterococcus faecalis in untreated and differentially filtered (20 microm, 5 microm, 3 microm, 1.2 microm, and 0.1 microm) seawater was analyzed in samples taken at different times over a 1-year period by plate counts and scanning electron microscopy. Whereas seawater filtered through a 0.1-microm mesh was not at all or only slightly bactericidal during incubation at 16 degrees C in the dark, culturability of E. faecalis in the other systems decreased as a function of increasing pore size of the filters. Recovery of culturable, glucose pre-starved cells was always higher than that of cells harvested from the exponential growth phase. Electron microscopic analysis showed that the disappearance of enterococci appeared related to the presence and multiplication of various zooflagellates.

Characterization and analysis of a new gene involved in glucose starvation response in Enterococcus faecalis.

The genome sequence of Enterococcus faecalis, led us to discover that gls24, encoding a general stress protein, seems to be in the second last position of a putative six-gene operon structure. Interestingly, another gene named orf4 located just upstream from gls24 shows strong identity (72%) with this last. To determine the role of the orf4 gene in E. faecalis, we have constructed a mutant strain by homologous recombination. Phenotypic analysis of these cells, reveals that Orf4 is probably involved in cell structure in stationary phase.

Antimicrobial spectrum and target site of D-3-phenyllactic acid.

Geotrichum candidum excretes D-3-phenyllactic acid, which inhibits the growth of Listeria monocytogenes. It was found to inhibit a range of gram-positive bacteria found in humans and foodstuffs, such as Staphylococcus aureus and Enterococcus faecalis, and gram-negative bacteria from humans, such as Providencia stuartii and Klebsiella oxytoca. Scanning electron microscope studies on the effect of D-3-phenyllactic acid on L. monocytogenes showed that it caused changes in bacterial behavior and structure. The bacteria formed aggregates and secreted polysaccharides; their cell walls lost their rigidity, causing the cells to swell. Finally the bacteria broke down completely and the cells disintegrate.

[In vitro changes induced by phenylmercury nitrate on fungi causing keratitis. Scanning electron microscopy study]. / Modifications induites in vitro par le nitrate de phénylmercure sur des champignons responsables de kératites. Examen en microscopie électronique à balayage.

Antifungal activity of phenylmercury nitrate was studied on fungi from keratitis. Important deterioration and bursting were observed with 2 mg/100 ml phenylmercury nitrate concentration on Aspergillus flavus, Scedosporium and Candida albicans spores.

[Morphological characteristics and physiological properties of aflatoxin B1 producing and non-producing Aspergillus flavus strains]. / Caractères morphologiques et propriétés physiologiques de souches d'Aspergillus flavus, productrices ou non d'aflatoxine B1.

Comparison between about 80 strains of Aspergillus flavus, belonging to the series flavus and oryzae, obtained from international collections but also isolated from French or African substrates revealed the following observations: 1. Cultural and morphological characteristics of toxicogenic and atoxicogenic strains of A. flavus are similar. However, the former produce a diffusible yellow pigment in 83% of isolates. 2. The two groups of conidiospores have the same resistance to UV irradiation (254 nm, 5 and 10 min). All the strains are equally sensitive to 4 antifungal antibiotics: nystatine, ketoconazole, clotrimazole and amphotericine. 3. A difference was seen in the capacity to produce enzymes as alpha-galactosidase, beta-galactosidase and beta-glucosidase, implicated in the glucid metabolism. The specific hydrolytic activity has been confirmed by the characterization of a large amount of beta-galactosidase and by a diauxic growth on glucose medium supplemented by lactose. Possible relationship between these characters and aflatoxin B1 production by A. flavus strains is discussed.

[Cytologic alterations induced in Bacillus thuringiensis (Berliner) by zearalenone]. / Altérations cytologiques induites par la zéaralénone chez Bacillus thuringiensis (Berliner).

Zearalenone (F-2 toxin) an estrogenic mycotoxin secreted by some species of Fusarium exhibits an antibacterial activity which can be easily demonstrated in Gram-positive spore forming bacteria, especially in Bacillus sp. Morphologically abnormal cells were produced by Bacillus thuringiensis (Berliner) in response to zearalenone. The most significant ultrastructural alterations obtained with the mycotoxin at 2.5 or 5.0 micrograms/ml, are: increase of number of mesosomes which are hypertrophied, decrease of ribosomes, formation of imperfect cell septa and unknown 'crystalloïd inclusion'. These effects which provoke induction of atypical long cells, resemble those obtained with one other mycotoxin which possesses as zearalenone an unsaturated lactone structure: aflatoxin B1.

[Morphologic alterations induced by aflatoxin B1 in Bacillus thuringiensis (Berliner)]. / Altérations morphologiques induites par l'aflatoxine B1 chez Bacillus thuringiensis (Berliner).

Significative ultrastructural alterations shown in aflatoxin B1, treated cells of Bacillus thuringiensis are: increase of number of mesosomes which are hypertrophied, decrease of ribosomes and formation of imperfect cell septa.