Scott M. Walsh

Lysostaphin Cream Eradicates Staphylococcus aureus Nasal Colonization in a Cotton Rat Model

ABSTRACT The anterior nares are a primary ecologic niche for Staphylococcus aureus, and nasal colonization by this opportunistic pathogen increases the risk of development of S. aureus infection. Clearance of S. aureus nasal colonization greatly reduces this risk. Mupirocin ointment is the current standard of care for clearance of S. aureus nasal colonization, but resistance to this antibiotic is emerging. Lysostaphin is a glycylglycine endopeptidase which specifically cleaves the cross-linking pentaglycine bridges in the cell walls of staphylococci. Lysostaphin is extremely staphylocidal (MIC at which 90% of isolates are inhibited, 0.001 to 0.064 μg/ml) and rapidly lyses both actively growing and quiescent S. aureus. This study demonstrates that a single application of 0.5% lysostaphin (actual dose, ∼150 μg of lysostaphin), formulated in a petrolatum-based cream, dramatically reduces S. aureus nasal colonization in 100% of animals tested and eradicates S. aureus nasal colonization in 93% of animals in a cotton rat model. A single dose of lysostaphin cream is more effective than a single dose of mupirocin ointment in eradicating S. aureus nasal colonization in this animal model. The lantibiotic peptide nisin, which has potent in vitro antistaphylococcal activity, was ineffective in reducing staphylococcal nasal carriage in this model. Nasal colonization was not reduced after three treatments with 5% nisin (∼1,500 μg/dose) in any of the treated animals. Lysostaphin formulated in cream may prove to be a superior alternative to mupirocin ointment for clearance of S. aureus nasal colonization.

Improved Pharmacokinetics and Reduced Antibody Reactivity of Lysostaphin Conjugated to Polyethylene Glycol

ABSTRACT Lysostaphin is a 27-kDa endopeptidase that enzymatically disrupts the cell wall of Staphylococcus aureus and is a promising candidate for treating S. aureus blood-borne infections. It would be extremely useful to define conditions that would both increase lysostaphins in vivo half-life to allow for more effective tissue distribution and reduce its immunogenicity. Conjugation of polyethylene glycol (PEG) to lysostaphin (PEGylation) was investigated as a means to accomplish these goals. Rather than using linear forms of PEG, branched PEGs were chosen as the initial candidates because their large spatial volumes prevent entry of the polymer into the enzymes active sites, which could potentially reduce enzymatic function. Enzymatic activity for most PEGylated lysostaphins was reduced, but these compounds were still considerably active compared to unconjugated lysostaphin, with conjugates that had lower degrees of PEG modification having greater activity than those with higher degrees. PEGylated lysostaphin injected intravenously had a serum drug half-life of up to 24 h and resulted in much higher plasma drug concentrations than an equal dose of unconjugated lysostaphin, which had a half-life of less than 1 h. Finally, reduced binding affinity was shown for PEGylated lysostaphin in an antilysostaphin capture enzyme-linked immunosorbent assay, with some PEG-lysostaphin conjugates having binding affinities that were reduced more than 10-fold compared to unconjugated lysostaphin. These findings demonstrate that PEGylation of lysostaphin, while diminishing its S. aureus killing activity, results in prolonged serum drug persistence and reduced antibody binding. These features should significantly enhance lysostaphins therapeutic value as an intravenous “antibiotic” against S. aureus.

Lysostaphin-Coated Catheters Eradicate Staphylococccus aureus Challenge and Block Surface Colonization

ABSTRACT Lysostaphin is an endopeptidase that kills Staphylococcus aureus, a predominant organism in catheter-related infections. Lysostaphin-coated catheters prevented catheter colonization by several strains of S. aureus, and activity was maintained for at least 4 days. Prophylactic use of lysostaphin in catheters may help prevent the occurrence of catheter-related staphylococcal infections.

Extended Nasal Residence Time of Lysostaphin and an Anti-Staphylococcal Monoclonal Antibody by Delivery in Semisolid or Polymeric Carriers

AbstractPurpose. Eradication of Staphylococcus aureus nasal colonization reduces the risk of nosocomial and community acquired infections with this organism. This study describes the formulation and use of lysostaphin and BSYX-A110, an anti-lipoteichoic acid monoclonal antibody, for eradication of S. aureus nasal colonization. Methods. Lysostaphin was formulated into a hydrophilic cream that forms an emulsion with the secretions of the nasal mucosa, and aqueous formulations of BSYX-A110 were made containing the mucoadhesive polymers polystyrene sulfonate and chitosan. Intranasal pharmacokinetics of the drugs was measured in mice and cotton rats. Results. Lysostaphin formulated in the cream increased nasal retention of the drug by 10-fold at 3 h post-cream installation and 50-fold at 24 h as compared to lysostaphin in saline drops. Furthermore, the levels of lysostaphin in the nose 24 h post-cream instillation are still above the minimum bactericidal concentration for most bacterial strains. The liquid polymer formulations also resulted in prolonged retention of antibody in the nose, with 4-fold higher levels at 3 h post-instillation as compared to antibody in saline drops. Conclusions. These results demonstrate that cream and polymer delivery systems significantly decrease the clearance rate of lysostaphin and BSYX-A110 from the nose, thereby enhancing their therapeutic potential for eradicating S. aureus nasal colonization.