Annales de microbiologie最新文献

Oscillations in population densities in the bacterial predator-prey Bdellovibrio bacteriovorus-Escherichia coli system were investigated both experimentally and theoretically. Experimental conditions for observing (damped) oscillations were first determined in a closed system and then used in an open system, i.e. in a chemostat, when an adequate flux of nutritive medium was added. The experimentally observed oscillations were always unstable with poorly reproducible amplitude and period. A theoretical model was used in order to explain this behaviour. It was first presented and satisfactorily tested for the same bacterial couple operating in a closed system, and allowed an experimental determination of its kinetic parameters. When adapted to open system conditions, it yielded computer-simulations which showed oscillations of the population densities in good agreement with those experimentally observed. It also showed that stable oscillations were not possible, the only "focus" in the predator-prey-density plane being an unstable one with no surrounding limit cycle.

Susceptibility of 121 isolates of coagulase-negative staphylococci to two antimicrobial agents, novobiocin and fosfomycin, was determined using the agar dilution method. Isolates included 45 strains of Staphylococcus saprophyticus, 26 strains of S. cohnii and S. xylosus, 24 strains of S. epidermidis and 26 strains of S. hominis, S. capitis, S. warneri and S. auricularis . The minimal inhibitory concentration average of fosfomycin for S. saprophyticus differed (p less than 0.001) from that other for novobiocin-resistant staphylococci (S. cohnii and S. xylosus) and for S. epidermidis (p less than 0.001). Out of 45 isolates of S. saprophyticus, 42 were resistant to fosfomycin. The results were very heterogeneous with regard to fosfomycin for all of the other coagulase-negative staphylococci. Resistance to fosfomycin, like resistance to novobiocin, could be used as a presumptive test for the identification of S. saprophyticus.

In order to improve our knowledge of the effect of daylight on freeze-dried and rehydrated BCG, 8 BCG vaccines prepared with four BCG strains--Danish 1331, French 1173-P2, English (Glaxo-1077) and Japanese 172--were studied. Four of them were in amber-coloured ampoules manufactured in Copenhagen (K. Bunch -Christensen) and four were in colourless ampoules manufactured by Institut Pasteur Production (Paris). Samples of these vaccines, both freeze-dried and rehydrated for use in children, were exposed to both factors and checked regularly for their viability. Daylight had a deleterious effect on the viability of both freeze-dried and (especially) rehydrated BCG vaccines. The fall in viability began after 2-h exposure of rehydrated vaccines and after 8-h exposure of freeze-dried ones. BCG survival was improved by coloured ampoules. Differences were observed between BCG strains in terms of the light effect, with the French strain being most resistant, the Danish least resistant and the others intermediate. UV irradiation was even more deleterious: 50% survival after 30-min exposure at 20 microW /cm2. In conclusion, since BCG vaccines are sensitive to these factors, they must therefore be protected and their viability checked during BCG vaccination campaigns.

One hundred and five strains of Salmonella, including 103 clinical isolates, were examined for resistance to beta-lactams (ampicillin, carbenicillin). The resistance frequency was 5.9 and 40.6%, respectively, according to the geographical source: France or Senegal. The mechanism of resistance to beta-lactam antibiotics was always related to the biosynthesis of one constitutive beta-lactamase (beta la+). By analytical isoelectric focusing on gel of all crude sonic extracts, four types of enzymes were identified: TEM-1, TEM-2, OXA-1 and SHV -1. TEM-1, the most prevalent, was observed among 17 serotypes, TEM-2 among 3 including S. poona , and OXA-1 among 2 serotypes. SHV -1 was detected in all isolates of S. ordonez (38) but only among strains of this serotype. Among others factors involved in their distribution, differences were reported according to the geographical origin of the studied strains. In France, the three types, TEM-1, TEM-2 and OXA-1, were isolated only in the north. Moreover, the resistance frequency was 4-fold higher (7.3%) than in the south (1.8%). In Africa (Senegal), three types were individualized: TEM-1, TEM-2 and SHV -1. The SHV -1 type was only detected in clinical isolates of S. ordonez from Senegal, all of which were multi-resistant to other antibiotics (chloramphenicol, sulfonamides and tetracyclines).

A complex extracellular proteolytic system was produced by Aeromonas hydrophila LP50 on glucose- polypeptone medium. Partial purification of this system was accomplished by ammonium sulphate precipitation, acetone precipitation, gel filtration on Sephacryl- S200 and chromatography on DEAE-Sephacel. Every stage was controlled by electrophoresis. This proteolytic system was constituted of three aminopeptidase and two endopeptidase components.

The main lipids synthesized by Mycobacterium ulcerans are specific for the species. Three products were isolated by chromatography. Their structures were determined by means of spectrographic methods performed on the natural substances or on their split products. The most abundant products were phthiodiolone diphthioceranate and phenolphthiodiolone diphthioceranate . These structures have some analogies with those of phthiocerol dimycocerosate synthesized by M. tuberculosis and M. bovis, and with those of phenolphthiocerol mycocerosate synthesized by M. bovis. The reverse configuration of the polymethyl-branched-chain fatty acids isolated from the substances, according to their origin, remains to be pointed out. Little attention has generally been paid to the stereochemistry of such molecules. We verified that the branched-chain fatty acids found in diacyl phthiocerol and in the mycoside of M. leprae have the same configuration as in the analogous molecules isolated from M. tuberculosis or M. bovis, contrary to M. ulcerans. Another peculiarity of phenolphthiodiolone isolated from M. ulcerans is the occurrence of the phenol group in free form.

In order to determine the cutaneous and digestive colonization of S. epidermidis in germ-free HRS mice, several groups of animals were contaminated with this strain according to different methods. The bacterial cutaneous enumerations were performed after preliminary crushing of the cutaneous biopsy. In this study, whatever the method of contamination of germ-free HRS mice, the kinetics of S. epidermidis cutaneous colonization was parallel to the kinetics of intestinal colonization. The isolation of bacteria on skin was possible only when microorganisms were eliminated in faeces (6 h after contamination). During a single experiment, there was only slight variability in colonization, whether intestinal or cutaneous. Some differences could be found from one experiment to another, but all animals in the same trial showed the same cutaneous bacterial count. This experimental model is characterized by an interrelation between the intestinal and cutaneous ecosystems.

The effect of bran ingestion on the flora of the human digestive tract was studied using two methods: quantitative enumeration of various microbial populations of the faecal flora, and a demonstration of the antagonistic effect exerted by the faecal flora against various potentially pathogenic bacteria of the environment. Since this latter study cannot be effected in human subjects, we used a model constituted by axenic mice inoculated with patients' flora. Faecal samples from 3 human donors receiving bran-containing diets were obtained prior to treatment and 30 days thereafter. These faecal samples were inoculated into axenic mice fed a diet with or without bran. The dominant floras of the human donors, before and after bran ingestion, were highly similar. The faecal floras of the gnotoxenic mice resembled those of the donors and no change resulting from the presence of bran in the diet could be observed. The drastic or permissive barrier effects exerted in the gnotoxenic mice by the human donors against Clostridium perfringens, Staphylococcus aureus, Candida albicans and Pseudomonas aeruginosa were not modified by the presence of bran in the diet. The large variability between animals in the barrier effect against Clostridium difficile masked any possible role of the bran. Study of the transit of Bacillus spores in the digestive tract of various mouse groups showed the existence of differences according to the origin of the inoculated floras, but not according to the presence or absence of bran in the diet.

The contagious pleuropneumonia syndrome is easily reproduced in goats, using cultures and lung lesion homogeneizate, given by endobronchial inoculation and by aerosol. The latter route causes hyperacure evolution, with septicaemia, multiple and disseminated lesions and death within three days following the onset of clinical signs. The same strains seem to be poorly pathogenic toward chick embryos inoculated in the yolk-sac. The nature of Mycoplasma capripneumoniae pathogenicity remains undetermined.

Cells of Legionella suspended in water were heated for 15 to 60 min, at temperatures between 40 and 70 degrees C, and their survival determined over 9 log-cycles. The survival curves were identical for the 6 strains, and were non-logarithmic. Implications of the resistance plateau observed are discussed.