Biofilms are surface-bound bacterial colonies that are held together by a self-produced extracellular polymeric matrix. They are highly resistant to antibiotics and host defence mechanisms, and are known to be the cause of persistent infections. Biofilm-degrading enzymes have been shown to prevent biofilm formation, remove mature biofilm, and enhance the efficacy of antibiotics. This study investigated the antibacterial and antibiofilm actions of the commercial enzyme Pectinex Ultra SP-L (Pectinex), alone and in combination with antibiotics, on standard and clinical cultures of Staphylococcus aureus and Pseudomonas aeruginosa. The cytotoxicity of Pectinex was determined on human cell cultures in vitro. Pectinex (7.42 – 950 PGU/ml) was not bactericidal, and had no effect on the antibacterial efficacy of amoxicillin-clavulanate and ciprofloxacin in cultures of S. aureus (ATCC 12600) and P. aeruginosa (ATCC 9027), respectively. However, in clinical cultures of P. aeruginosa, Pectinex caused an 89.0% (from 1.0 to 1.89 μg/ml) and 92.8% (from 1.67 to 3.22 μg/ml) increase in the MIC and MBC of ciprofloxacin, respectively. In clinical cultures of S. aureus, both bactericidal indices of amoxicillin-clavulanate were increased by 28.0% (from 2.0 to 2.56 μg/ml). In all bacterial cultures, low concentrations of Pectinex (≤ 118.75 PGU/ml) and prolonged incubation periods (≥ 6 h) were both associated with increased viability and biofilm biomass. Over a short incubation period (≤ 6 h), higher concentrations of Pectinex (237.5 – 950 PGU/ml) effectively inhibited biofilm formation in P. aeruginosa ATCC (237.5 – 950 PGU/ml) and clinical (950 PGU/ml) strains but not in S. aureus cultures. Pectinex (237.5 – 950 PGU/ml) was cytotoxic to HeLa cells, lymphocytes and neutrophils, and induced morphological features that included shrunken rounded cells, blebs, apoptotic bodies, cytoplasmic vacuoles and cell debris. The effects at 475 and 950 PGU/ml were comparable to mitomycin C 10 μg/ml and staurosporine 1 μg/ml. Pectinex was shown to either enhance or reduce biofilm biomass and cell viability in cultures of S. aureus and P. aeruginosa. The manifested effects depended on the concentration of the enzyme, the specific bacterial species and strain, and the maturity of the biofilms. Further studies are still needed in order to determine the actions of Pectinex on other clinical pathogens. / Thesis (PhD)--University of Pretoria, 2014. / lk2014 / Pharmacology / PhD / Unrestricted