Escherichia coli K88 receptor expression in intestine of disease-susceptible weaned pigs.

A challenge trial was carried out in which Escherichia coli O157 K88ac was administered to a litter of weaned pigs and the development of the disease monitored over a five-day experimental period. The eight animals in the trial were assigned to two groups depending on whether they exhibited disease symptoms. Six pigs developed diarrhoea and two appeared unaffected; these were designated as the test (or K88-susceptible) group and the control (or K88-resistant) group, respectively. The animals were euthanised and the intestine was removed and sections processed for brush border membrane vesicle preparation. Microscopic and biochemical assays were undertaken on tissue samples from each animal and a strong correlation was observed between the expression of a glycoprotein receptor complex associated with the brush border membrane and the development of disease symptoms. Further investigation revealed the presence of an analogous glycoprotein complex in the K88-resistant group which did not bind the K88-fimbriae antigen. These results suggest that genetic differences in the glycosyl moieties of the receptor complex provide the basis for disease susceptibility to K88-positive E. coli.

Evaluation of the susceptibility of dermatophytes to antifungal drugs: a new technique.

The evaluation of the minimal inhibitory concentration (MIC) for pathogenic fungi is still a technically difficult assay. Insufficient standardization of the technique is often the basis of problems which appear. Culture characteristic of dermatophytes do not favour techniques usually used in bacteriology (Steers agar dilution method). A study was undertaken to compare the Steers agar dilution method and a new culture method to evaluate the minimal inhibitory concentration of antifungal compounds on several species of dermatophytes. The new method involves dilution of the antifungal drug in solid medium in a Petri dish. Standardized agar cylinders are cut from the plates and filled with inocula of the same size cut from plates of dermatophyte cultures. Such inocula facilitate analysis of the fungus in its natural growth conditions in vitro without being submitted to a disruptive preparative technique. The MIC values were similar for the two methods of evaluation in spite of important differences between the inocula. The new technique is reliable, quick, and highly reproducible. It is more efficient than the Steers agar dilution method because it enables assays to be run on several strains simultaneously and avoids labour-intensive procedures for the preparation of the inocula.

Antifungal activity of allylamines on Epidermophyton floccosum: scanning electron microscopy study.

The action of allylamine antifungal agents on Epidermophyton floccosum was studied using scanning electron microscopy. After 7 days of culture on Sabouraud dextrose agar, Epidermophyton floccosum samples were brought in contact with concentrations of 0.2 and 2 micrograms ml-1 and 0.01 and 0.1 micrograms ml-1 of naftifine and terbinafine, respectively. Lesions observed after 24 h, 3 and 7 days of contact were mainly on the structure and rigidity of the mycelial and macroconidial wall. They were characterized by hyphal ballooning and twisting and by apical bulbous bulges. Deterioration of macroconidia was characterized by wall exfoliation. The intensity of the deterioration depended on the dose and only slightly on the length of time that the sample and the antifungal drug were in contact.

Low voltage scanning electron microscopy study of naftifine activity on Microsporum canis.

Scanning electron microscopy (SEM) is at present considered a good way to observe the morphological alterations induced by an antifungal on pathogenic fungi. Owing to its high precision, low voltage scanning electron microscopy (LVSEM) improves the quality of observations. The Microsporum canis morphology alterations induced by naftifine at a concentration of 0.9 microgram ml-1 (10 times the minimum inhibitory concentration (MIC) for 7 days were studied in LVSEM. The young lateral ramifications and the aborted buds take on a granulous aspect. These granulations can be localized as brassard shapes around hyphae. The mycelial filaments often appear irregularly swollen with bulbous tips. Macroconidia are selectively covered with a microfibrillar network. In addition, LVSEM on control samples reveals pavimentous angular structures on the macroconidial surface and fine granulations on the filament surface of M. canis unknown until now. A cytological study with transmission electron microscopy (TEM) of filaments altered by naftifine permitted us to observe the disorganization of cell wall fibrillar structure, an excessive plasma membrane undulation and an intracytoplasmic accumulation of large vesicles with probably lipidic contents.