LYSOZYME-CAFFEIC ACID CONJUGATES - POSSIBLE NOVEL PRESERVATIVES FOR DERMAL FORMULATIONS

An equivalent mixture of a recently developed lysozyme-caffeic acid co njugate and lysozyme was tested as possible preservative-system for de rmal products. Whereas bacterial growth of Escherichia coli (ATCC 8793 ) was strongly inhibited by the lysozyme-caffeic acid conjugate, the e fficacy towards Staphylococcus aureus (ATCC 6538) was slightly reduced . In order to compensate for this effectivity loss, a combination of l ysozyme-caffeic acid conjugate and lysozyme was required. Microbial ef ficacy was studied in Various hydrogels based on the following polymer s: hydroxypropylmethylcellulose (HPMC), sodium chitosan-EDTA (NaChito- EDTA) and sodium carbopol 980 (NaC980), and the effectiveness as a pre servative tested with E. coli as Gram-negative and S. aureus as Gram-p ositive representatives. Colony forming units (cfu) of samples were co unted immediately and 1, 7, 14, 21 and 28 days after inoculation. The effectiveness of the preservative-system depended on the polymer type, the bacterial strains (Gram-negative or Gram-positive) and on the app lied concentration. Almost no antibacterial effect could be detected i n NaC980 gels, which may be caused by the attachment of lysozyme to th e polymer. Our results show that a concentration of 0.2% (w/w) of the lysozyme-caffeic acid conjugate/lysozyme mixture (1+1) was required fo r HPMC- and NaChito-EDTA gels to exert a bactericidal effect for Gram- negative as well as for Gram-positive bacteria with the exception of H PMC gels towards E. coli, where only a bacteriostatic effect could be detected at this concentration. (C) 1998 Elsevier Science B.V. All rig hts reserved.