Temperature-sensitive mutants of Pseudomonas aeruginosa: isolation and preliminary immunological evaluation

Temperature-sensitive mutants of Actinobacillus pleuropneumoniae induce protection in mice

Temperature-sensitive mutants of Actinobacillus pleuropneumoniae 4074, serotype 1, were isolated after treatment with nitrosoguanidine and enrichment with penicillin and D-cycloserine. Of the four temperature-sensitive mutants evaluated in mice, one (A-1) had a tight phenotype (i.e., it ceased replication immediately after transfer to the nonpermissive temperature [37 degrees C]) and three (1-2, 4-1, and 12-1) were coasters that continued replication for up to three generations after transfer to 37 degrees C. The reversion frequencies ranged from 10(-6) to 10(-9), and cutoff temperatures ranged from 33 to 35 degrees C. No major changes were detected in the biochemical profiles; agglutination reactions; electrophoretic profiles of the lipopolysaccharides, outer membrane proteins, and hemolysin proteins; hemolytic titers; or CAMP factor reactions of the mutants and the wild-type bacteria. Groups of 3- to 5-week-old, female ICR mice were immunized intranasally with three doses of 3.5 x 10(6) CFU of the mutants over 3 weeks and subsequently challenged intranasally with 5 50% lethal doses of the parental wild-type. Protection was induced by both the tight and the coaster mutants, with the 4-1 and 12-1 coasters eliciting greater protection (67 and 82%, respectively) than that induced by the A-1 tight mutant (57%). Intranasal immunization with both phenotypes induced serum antibody responses against the surface antigens and the hemolysin protein.

Interaction between granulocytes and antibodies in the enhancement of lung defenses against Staphylococcus aureus after intranasal immunization of mice with live-attenuated bacteria

Immunization with live-attenuated Staphylococcus aureus induced measurable levels of specific IgG and IgA in the lungs, but the pulmonary clearance of S. aureus in immunized mice did not differ from that of control mice. Aerosol exposure of mice to Pseudomonas aeruginosa induced a significant recruitment of polymorphonuclear leukocytes (PMNL) to the lungs in both immunized and control mice, whereas S. aureus challenge did not. However, challenge with a mixture of P. aeruginosa-S. aureus or exposure to an aerosol of Escherichia coli lipopolysaccharide (LPS) before S. aureus challenge induced PMNL migration and a significant enhancement of pulmonary clearance of S. aureus in immunized mice. The presence of both antibodies and PMNL was required for enhancement of S. aureus pulmonary clearance.

Oral immunization of mice with temperature-sensitive Pseudomonas aeruginosa enhances pulmonary clearance of the wild-type

DBA/2J mice were immunized daily for 3 days per os with 10(8)-10(9) colony forming units (c.f.u.) of two different temperature-sensitive (TS) mutants of Pseudomonas aeruginosa. At varying times after the final immunization the animals were exposed to aerosols of the parental immunotype 1, and the ability of the immunized and control mice to clear their lungs of the wild-type (WT) challenge was measured 4 h later. The number of c.f.u. remaining in the lungs of mice immunized with one mutant, D/1/8, was significantly less (p less than 0.01) than the number remaining in the lungs of control mice and mice immunized with a second TS mutant, E/9/9.

Biological evaluation of Mycoplasma pulmonis temperature-sensitive mutants for use as possible rodent vaccines

Temperature-sensitive mutants (TSMs) of Mycoplasma pulmonis were produced by treating the wild-type strain with N-methyl-N'-nitro-N-nitrosoguanidine. Three TSMs were selected at 38 degrees C, as a restrictive temperature, and at 34 degrees C, as a permissive temperature. Two TSMs, UTCMI and UTCMII, were proven to be nonpathogenic but immunogenic. In addition, they did not induce pneumonia, tracheitis, or tympanitis but did induce mild rhinitis. They were stable after 10 passages in vitro and in vivo. They elicited excellent antibody production and cell-mediated immunity in vaccinated rats. They also were not mitogenic to rat lymphocytes. Rats immunized intranasally with these TSMs were significantly protected against challenge with wild-type organisms. These mutants were morphologically and serologically indistinguishable from the wild-type organisms. The growth characteristics and antibiotic sensitivities were similar to those of wild-type organisms, except that they grew only at 34 degrees C. In contrast to wild-type organisms, they did not bind to or lyse sheep erythrocytes. Thus, these TSMs may qualify as a vaccine to prevent M. pulmonis infection in rats.

Differential growth characteristics and immunogenicity of tight and coasting temperature-sensitive mutants of Pseudomonas aeruginosa

Genetically attenuated vaccines capable of limited replication in the vaccinate may elicit stronger, longer-lasting immunity than that induced by component, killed whole-cell, or nonreplicating live vaccines. We have isolated and partially characterized temperature-sensitive Pseudomonas aeruginosa mutants of two different phenotypes: a tight mutant, which ceases all growth immediately after its transfer to 36 degrees C, and a coaster, which continues to replicate for five generations at 36 degrees C. The growth profiles of the two temperature-sensitive phenotypes were compared both in vitro and in vivo; maintenance of the coasting phenotype in vivo was confirmed. The immunogenicity of the two phenotypes was compared in two models. In model 1, ICR mice were immunized intraperitoneally (i.p.) with graded doses of either mutant and challenged 3 weeks later i.p. with lethal doses of the wild-type strain. In model 2, DBA/2J mice were immunized intranasally with either mutant and subsequently challenged with an aerosolized inoculum of the wild-type strain, and lung clearance was measured over 4 h. In both models, the coaster demonstrated slightly higher immunogenic potential and, in addition, induced significantly higher levels of immunotype-specific serum immunoglobulin G after i.p. immunization.

Enzyme-linked immunosorbent assay antibody responses to a temperature-sensitive mutant of Pseudomonas aeruginosa

The serum immunoglobulin G and M responses induced by immunization of mice with temperature-sensitive mutant A/10/25 of Pseudomonas aeruginosa were evaluated by enzyme-linked immunosorbent assay. These antibody responses were immunotype specific, and the immunoglobulin G antibody level, although low, was still significant by day 52 after vaccination.

Effect of chemotactins released by Staphylococcus aureus and Pseudomonas aeruginosa on the murine respiratory tract

Staphylococcus aureus, the Pseudomonas aeruginosa temperature-sensitive (ts) mutant A/10/25, and the P. aeruginosa parental wild type were aerosolized to C5-deficient mice, and the total number of polymorphonuclear leukocytes (PMN) recovered by lung lavage was determined 4 h after aerosol exposure. S. aureus induced a slight but significant recruitment of PMN, as compared with the effect of a saline aerosol. Both wild-type P. aeruginosa and the ts mutant induced a significant PMN recruitment of a magnitude ca. 180 times higher than that produced by S. aureus. Gentamicin-killed ts P. aeruginosa induced a PMN recruitment of a magnitude similar to that produced by live ts P. aeruginosa. Thorough washing of the bacteria, however, removed ca. 90% of the chemotactic activity. Exposure of the animals to a ts P. aeruginosa culture supernatant aerosol induced significant PMN recruitment into the lower airways. The same culture supernatants were chemotactic for mouse PMN in a dose-dependent fashion when tested in vitro in the absence of serum. Culture supernatants of S. aureus exhibited weak chemotactic activity in vitro and did not induce PMN recruitment in the lungs when aerosolized to DBA/2J mice. The results suggest that chemotactins released by P. aeruginosa may be an important virulence factor and play a significant role in lung tissue damage.

Quantitative determination of bacterial replication in vivo

A new methodology which permits the quantitative measurement of absolute bacterial replication in vivo is proposed. Mice were inoculated with mixtures of temperature-sensitive mutants and parental wild types, and the changes in the ratios of the two strains were measured. The number of wild-type generations was calculated from the declining ratios over time with the formula n = log (r0/rt)/log 2; n is the number of generations, and r0 and rt are the ratio of temperature-sensitive mutants to the parental wild type at time zero and at the times sampled throughout the experiment. The replication rate was determined by regression analysis. A mathematical argument for the formula is presented. Using this technique, we determined the mean generation times of Escherichia coli (33 min) and Pseudomonas aeruginosa (20 min) in the peritoneal cavities of mice, in the face of host clearance mechanisms during the first stages of infection.

Live attenuated bacterial vaccines: new approaches for safety and efficacy

Problems arising from reversion to virulence in genetically attenuated bacterial vaccines can be overcome by the combination, in one strain, of multiple temperature-sensitive mutations of identical phenotype. Immunogenicity of attenuated strains may be enhanced by incorporation of mutations which permit limited replication in the vaccinee (thereby increasing antigen mass while minimising the possibility of vaccine reactions) and the expression of genes coding for antigens which are synthesised only during infection of the host.

Enhancement of Pseudomonas aeruginosa lung clearance after local immunization with a temperature-sensitive mutant

We investigated the capacity of the temperature-sensitive mutant strain A/10/25 of Pseudomonas aeruginosa (ts-Psa) to induce enhancement of lung defenses against wild type P. aeruginosa (wt-Psa). Mice of the DBA/2J inbred strain were immunized by aerosolization with a single dose of 2 x 10(5) to 4 x 10(5) CFU of ts-Psa and were challenged 7, 14, and 21 days later with wt-Psa. The uncleared bacteria ratio was determined 4 h after aerosol exposure; significant enhancement in lung clearance of wt-Psa (P less than 0.01) was evident as early as 7 days after immunization and detectable for at least 21 days. Aerosol immunization with Staphylococcus aureus did not enhance lung clearance of wt-Psa; however, slight but significant enhancement in S. aureus clearance was observed in mice immunized 7 days before with ts-Psa. No enhancement of S. aureus clearance was seen in ts-Psa immunized animals after 14 and 21 days. Analysis of the cell composition of lung lavage fluids revealed a transient cell response characterized by rapid increase in the absolute number of polymorphonuclear leukocytes, followed later by an increase in alveolar macrophages. The characteristics of lung lavages returned to base-line values 6 days after aerosol immunization, and a second exposure to a ts-Psa aerosol produced a response of similar magnitude and quality. We conclude that aerosol immunization with a temperature-sensitive mutant of P. aeruginosa enhances specific pulmonary defense mechanisms against the parental pathogen in mice.