Comparative study of the biological characteristics of mucoid and non-mucoid Pseudomonas aeruginosa strains isolated from chronic respiratory infections.

Morphological, culture and enzymatic characteristics, as well as virulence, susceptibility to antimicrobial agents and epidemiological markers, were studied for 100 mucoid and 100 non-mucoid Ps. aeruginosa strains isolated from chronic respiratory infections. For 10 mucoid and 10 non-mucoid strains was performed the active protection test in mice, both with inactivated germs (10(9) germs), and LPS extracted by Westphal method. It was ascertained that mucoid Ps. aeruginosa strains differ from non-mucoid strains by the slow growth on culture media, more reduced proteolytic activity (81% as compared to 99%), slow oxidation of carbohydrates (5-7 days), reduced virulence in mice (8%) or avirulence (92%), higher sensitivity to some antibiotics (amikacin, dibekacin, ticarcillin, tetracycline, cefotaxime, ceftriaxone), lysoresistance (74%) and polyagglutinability (67%). The mucoid strains ensure a reduced active protection in mice, 70% of strains did not protect the mice against the infection with virulent homologous strains, while the non-mucoid strains ensured 80%-100% protection.

Investigations on the efficacy of monovalent Pseudomonas aeruginosa vaccine for oral administration in Pseudomonas aeruginosa experimental infection.

Therapeutic efficacy of Pseudomonas aeruginosa vaccine for oral use (10(10) killed germs/ml), prepared from strain 4922, belonging to serotype XV, by Meitert-Meitert scheme, on 4 experimental models in mice (pneumonia, infected burn, septicaemia and urinary tract infection) was studied in comparison with monovalent Ps. aeruginosa vaccine serotype XV (10(9) killed germs/ml) for subcutaneous use and also with associated administration of the two vaccine variants. Mice immunization by using vaccine for oral use was performed by 0.5 ml vaccine per day, for 10 days and vaccine for subcutaneous use was administrated in a volume of 0.5 ml x 2, at 3 days interval. Mice immunization by using the two vaccine types, in association was concomitantly performed and in the same quantity as for separate immunization. In experimental pneumonia, Ps. aeruginosa vaccine for oral use protected mice in 35% of cases, those with infected burns were protected in 33.3% of cases, those with septicemia--in 96.6% of cases and those with urinary tract infection in 50% of cases. As compared to Ps. aeruginosa vaccine for subcutaneous use, the results obtained by vaccine for oral use are less favourable but associated administration of both vaccine variants led to superior results. Thus, in experimental pneumonia, it was obtained a surviving rate of 65% for animals immunized with both vaccine types, in comparison with 50% for animals immunized with vaccine for subcutaneous use only, and in Ps. aeruginosa infected burn, it was obtained a recovering rate of 79.1% for the animals immunized by using both vaccines, in comparison with 70.8% surviving for animals immunized with vaccine for subcutaneous use. In experimental septicaemia and urinary tract infection, combined use of both vaccine variants determined animals surviving and recovering in percents similar to those obtained by separate administration of vaccine for subcutaneous use (in septicemia--100% protection; in urinary tract infection--75% protection).

Specific and nonspecific protection of mice by Pseudomonas aeruginosa lipopolysaccharides.

The role of lipopolysaccharide (LPS) in eliciting a predominant cellular or humoral protection of mice is determined by the amount administered and the immunization schedule. Three basically different experimental conditions could be characterized. Five days after immunization with 100 micrograms of LPS, a nonspecific protection was observed due to the immunomodulatory capacity of lipid A. After 14 days, the same amount of LPS results in an O-specific humoral protection. On the other hand, 0.1 micrograms of LPS lead to a specific protection within 5 days after immunization due to a synergistic action of a specific humoral response (induced by the O-side chain) and a nonspecific signal modulated by lipid A. In order to study the role of each LPS region for protection, the free side chain was conjugated to albumin, followed by complexation with lipid A. To induce a nonspecific protection 5 days after immunization, the presence of lipid A was mandatory, in either the conjugated or free form. Removal of ester-linked fatty acids from free lipid A reduced its protective and mitogenic capacities by 50, and 25%, respectively.