Biomedical subjects

L K Husmann

Publications and source records attributed to L K Husmann.

6 recordsLinked to original sources

PubMed1997

Role of putative virulence factors of Streptococcus pyogenes in mouse models of long-term throat colonization and pneumonia.

To investigate the role of putative virulence factors of Streptococcus pyogenes (group A streptococcus; GAS) in causing disease, we introduced specific mutations in GAS strain B514, a natural mouse pathogen, and tested the mutant strains in two models of infection. To study late stages of disease, we used our previously described mouse model (C3HeB/FeJ mice) in which pneumonia and systemic spread of the streptococcus follow intratracheal inoculation. To study the early stages of disease, we report here a model of long-term (at least 21 days) throat colonization following intranasal inoculation of C57BL/10SnJ mice. When the three emm family genes of GAS strain B514-Sm were deleted, the mutant showed no significant difference from the wild type in induction of long-term throat colonization or pneumonia. We inactivated the scpA gene, which encodes a complement C5a peptidase, by insertion of a nonreplicative plasmid and found no significant difference from the wild type in the incidence of throat colonization. However, there was a small but statistically significant decrease in the incidence of pneumonia caused by the scpA mutant. Finally, we demonstrated a very important effect of the hyaluronic acid capsule in both models. Following intranasal inoculation of mice with a mutant in which a nonreplicative plasmid was inserted into the hasA gene, which encodes hyaluronate synthase, we found that all bacteria recovered from the throats of the mice were encapsulated revertants. Following intratracheal inoculation with the hasA mutant, the incidence of pneumonia within 72 h was significantly reduced from that of the control strain (P = 0.006). These results indicate that the hyaluronic acid capsule of S. pyogenes B514 confers an important selective advantage for survival of the bacteria in the upper respiratory tract and is also an important determinant in induction of pneumonia in our model system.

Adhesins, Bacterial↗

PubMed1996

Streptococcus pyogenes infection in mice.

We inoculated 5 to 7-week-old female C3HeB/FeJ mice with Streptococcus pyogenes strain B514-Sm (type M50) by both an intranasal and intratracheal route and characterized the resulting illness. Following intranasal inoculation, the animals developed signs of illness within 1 to 8 days post-inoculation which correlated with acute, suppurative, bronchopneumonia during histopathologic analysis; however, the relationship of response to dose was non-linear, as seen previously in a small group of mice. Intratracheal inoculations were then performed to increase the quantitative reliability of the model. Following intratracheal inoculation, the animals succumbed to an illness that was indistinguishable from that seen after intranasal inoculation, and the incidence of pneumonia followed a steep dose response curve. The dose at which 50% of the animals exhibited signs of respiratory illness within 72 h was 1.0 x 10(7) colony forming units. All of the animals that appeared ill had lung lesions as determined by gross and histopathologic examination. Bacteraemia followed pneumonia in two-thirds of the intratracheally inoculated animals, indicating that the S. pyogenes had crossed tissue barriers. We hope that this model will be useful in future studies concerning the role of suspected streptococcal virulence factors in the later stages of pathogenesis of invasive S. pyogenes infection.

Animals↗

PubMed1995

Expression of the Arp protein, a member of the M protein family, is not sufficient to inhibit phagocytosis of Streptococcus pyogenes.

Many Streptococcus pyogenes immunoglobulin-binding proteins have structural similarities to the antiphagocytic M protein, including the well-known C repeats. One of these molecules is the immunoglobulin A-binding protein Arp, which is expressed by a serotype 4 strain for which no antiphagocytic M protein has yet been described. We expressed Arp4 in an S. pyogenes strain from which the structural gene for the M protein has been deleted and found that Arp4 is not sufficient to inhibit phagocytosis.

Antigens, Bacterial↗

PubMed1994

Cytotoxicity of extracellular Legionella pneumophila.

Legionella pneumophila, the causative agent of Legionnaire's disease and Pontiac fever, is known to produce a cytopathic effect on macrophages. The capacity of extracellular L. pneumophila to mediate toxicity for guinea pig peritoneal macrophages and J774 mouse macrophages was assessed. Extracellular organisms were found to be capable of mediating toxicity; however, toxic activity appeared to require close proximity with the mononuclear cell surface. Serogroup 1 strains grown on supplemented Mueller-Hinton agar exhibited variable expression of toxic activity. One strain positive on supplemented Mueller-Hinton agar was cytotoxic and unable to replicate in J774 macrophages but remained virulent for guinea pigs at high doses.

Animals↗

PubMed1993

Virulence of two Streptococcus pyogenes strains (types M1 and M3) associated with toxic-shock-like syndrome depends on an intact mry-like gene.

The major virulence factor of Streptococcus pyogenes, the M protein, is positively regulated at the transcriptional level by mry in the M type 6 strain studied. We show here that in two S. pyogenes strains isolated from cases of toxic-shock-like syndrome, a type M1 strain and a type M3 strain, an mry-like gene is also required for resistance to phagocytosis.

Antigens, Bacterial↗

PubMed1992

Adherence of Legionella pneumophila to guinea pig peritoneal macrophages, J774 mouse macrophages, and undifferentiated U937 human monocytes: role of Fc and complement receptors.

Legionella pneumophila, the causative agent of Legionnaires' disease, is a facultative intracellular pathogen of alveolar macrophages. Although previous studies have demonstrated that specific antibody facilitates uptake of L. pneumophila by phagocytic cells, the role of complement has been unclear. Thus, we have examined the relative contributions of Fc gamma- and complement receptor-mediated adherence to guinea pig peritoneal macrophages, U937 human monocytic cells, and J774 mouse macrophage cells. Opsonization of L. pneumophila (Philadelphia 2) with polyclonal immunoglobulin G promoted maximum adherence to guinea pig macrophages. In contrast, incubation in the presence of 20% fresh nonimmune human serum from a single donor did not promote adherence. The results obtained with U937 and J774 cells paralleled those obtained with guinea pig macrophages. In the absence of specific antibody, opsonization with guinea pig complement did not enhance adherence of the Philadelphia 1, Philadelphia 2, or Knoxville strain. However, when complement was added to heat-inactivated, specific antiserum, a fourfold increase in the number of adherent organisms was observed. Blocking studies utilizing membrane receptor-specific monoclonal antibodies demonstrated that both Fc and complement receptors mediated adherence of organisms treated with complement in the presence of specific antibody. These results suggest that complement augments adherence of L. pneumophila only when acting in concert with specific antibody.

Animals↗