Lisa W. Plano, M.D., Ph.D.

Associate Professor of Clinical Pediatrics and Microbiology and Immunology
Room 3066 (Office), Room 3087 (Lab)
Rosenstiel Medical Sciences Building (RMSB)
1600 N.W. 10th Avenue
Office: 305-243-2598
Lab: 305-243-3259
E-mail: lplano@miami.edu

Research Interests:

Molecular Analysis of Staphylococcus aureus Exfoliative toxins 

In our laboratory, we are primarily interested in studying the mechanisms of pathogenesis of the remarkable human pathogen Staphylococcus aureus. We have concentrated on the study of a distinctive set of secreted toxins, the exfoliative toxins (ETA and ETB) which are unique serine proteases, and their target in the skin, desmoglein 1 (Dsg1). These protein toxins are responsible for contributing to significant local skin infections (primarily seen in children) as well as causing Staphylococcal scalded skin syndrome (SSSS), a systemic manifestation of exposure to the toxins. SSSS, is a disease primarily of the young and immunocompromised that is rarely seen in healthy adults and continues to be present as outbreaks in hospital nurseries. It is associated with as high as 60% mortality when occurring in adults. Our hypothesis is that characteristics of the interaction between the exfoliative toxins of S. aureus and their target, desmoglein 1, explain the species, target and age specificity demonstrated by these toxins as well as contribute to the pathogenicity of the bacteria. Using molecular techniques we are attempting to characterize the interaction between these toxins, primarily ETA, and their target, Dsg1 of humans and mice. The goal of our research is to provide insight into the mechanisms for the age and species specificity of these unique serine proteases.

Exfoliative toxins and Staphylococcal scalded skin syndrome

SSSS is characterized by specific exfoliation of the upper epidermis in the stratum granulosum of the skin of infected humans at a site distal to a focus of infection with exfoliative toxin (ET) producing S. aureus. These characteristic findings are replicated in a newborn mouse model. The mechanism by which these toxins result in exfoliation involves cleavage of desmoglein 1 (Dsg1), a desmosomal protein member of the cadherin family of cell adhesion molecules, by a unique serine protease activity of the ETs. Cleavage of this protein fits the clinical picture of SSSS as Dsg1 is primarily expressed at this layer of this skin. The ETs are members of the trypsin-like serine protease family containing the characteristic catalytic triad (S195, H72, D120), but do have some significant structural differences. In comparisons to other family members, the N– and C- termini and loop regions of the ETs appear unique and the catalytic site (the “oxyanion hole”) is in the closed or inactive conformation in crystalized ETA. The similarity of the catalytic site in both ET structures to glutamate-specific serine proteases suggests a similar catalytic mechanism, however the structural differences might contribute to the uniqueness of these toxins. Ourselves and others have postulated that the unique amphipathic helix at the N-terminus might be involved in regulating the accessibility of the catalytic site residues by binding and opening the “oxyanion hole” or might contribute to specific target recognition. The exact mechanism by which adults remain relatively protected against the action of these toxins whereas newborns are susceptible is currently not known and structural differences might contribute to these characteristics as well.

In the animal model skin manifestations can result from a single injection of one of two species-specific exfoliative toxins, ETA or ETB. We have shown that protection is not a gradual process but in the animal model occurs abruptly between 7 and 8 days of life and is associated with serum clearance of the toxins. This time frame corresponds with the development of the adaptive immune response in mice, however our studies have failed to identify a primary role of the adaptive immune response in protection of adult mice. Neither adult SCID mice or T-cell depleted mice were adversely effected by injection with purified toxin at levels that would have been lethal in newborns. Much remains to be determined about the age specificity of these toxins.

Significance

Staphylococcus aureus is well established as a major cause of hospital acquired as well as significant community associated infections. As many as 5% of all clinical isolates of S. aureus are capable of expressing an exfoliative toxin. SSSS, the result of an infection with ET producing S. aureus, is an exfoliative dermatitis primarily of infants, young children and immunocompromised individuals. The mechanism by which adults are normally protected from the actions of the ETs is not totally understood; and while it might involve neutralizing antibodies , the kinetics of protection in naive adult mice suggest that an adaptive antibody response is not the sole mechanism. Although mortality due to SSSS in children is rare in the USA with appropriate antibiotic therapy, it is significant in adults. S. aureus infections, especially hospital acquired, are occurring with increasing incidence of resistance to multiple antibiotics including resistance to methicillin/oxacillin and vancomycin. There remains a continued threat for outbreaks of SSSS in newborn nurseries and adult intensive care units and understanding the varied mechanisms of pathogenesis of these bacteria may ultimately aid in the fight against them.

Relevant Publications.

Plano , L R. W. 2004. Staphylococcus aureus exfoliative toxins: How they cause disease. Journal of Investigative Dermatology, 122: 1070-1077.

Rieger-Fackeldey, E., Plano, L. R. W., Kramer, A. and Schulze, A. 2002. Staphylococcal scalded skin syndrome related to an exfoliative toxin A- and B-producing strain in preterm infants. Eur. J. Pediatr., 161:649-652.

Plano , L. R. W. , R. D. Adkins, M. Woichnick, R. Ewing, C. M. Collins. 2001. Toxin Levels in Serum Correlate with the Development of Staphylococcal Scalded Skin Syndrome in a Murine Model. Infect. Immun., 69: 5193-5197.

Plano , L.R.W. , D. Gutman, M. Woischnik, and C. M. Collins. 2000. Recombinant Staphylococcus aureus exfoliative toxins are not bacterial superantigens. Infect. Immun., 68:3048-3052.

Papageorgiou, A. C., L. R. W. Plano, C. M. Collins, and K. R. Acharya. 2000. Structural differences in Staphylococcus aureus exfoliative toxins A and B as revealed from their crystal structures. Protein Science, 9:610-618.