engleski

Bactericidal activity of modified zeolites against clinical isolates of Acinetobacter baumannii.

Objectives: Clinical isolates of Acinetobacter baumannii persist in the environment for extended periods of time, representing the transmission route for occurrence of outbreaks in the hospital environment. The survival in environment is attributed to its resistance to antibiotics, disinfectants, drying and the ability to form biofilms on abiotic surfaces. The aim of this work was to study the bactericidal activity of the modified natural zeolite (MNZ) against clinical isolates of A. baumannii. Methods: The antibacterial activity of MNZ containing (in wt%): 5.07 of Ag+ (AgNZ), 2.60 of Cu2+ (CuNZ), 0.52 of Ni2+ (NiNZ), 1.47 of Zn2+ (ZnNZ), 8.50 of benzalkonium ion (BCNZ) or 8.50 of benzalkonium ion and 1.90 of acetylsalicylic acid (BCASNZ) were tested against clinical isolates of A. baumannii collected during two different outbreaks, first from 2002-2007 (EU I) and second from 2009-2010 (EU II) in Clinical Hospital Center Split, Croatia. Experiments were set up according to the standard dilution method and tubes were shaken during 24 h at 36°C. Number of bacteria was determined as CFU after 1 and 24 h of contact. The antibacterial activity of the MNZ was expressed as the percent reduction of log CFU as compared to the corresponding control and minimum bactericidal concentration (MBC) was determined after 24 h of contact. In tubes showing MBC the leaching of cations from MNZ was examined. The presence of extracellular substances in A. baumannii was confirmed by alcian blue staining. Results: The EU II was more sensitive to AgNZ and CuNZ with MBC 31.2 and 125 mg/L, respectively than isolate from EU I with MBC of 250 mg/L for both AgNZ and CuNZ. The EU I was more sensitive to BCNZ and BCASNZ with MBC 250 mg/L than EU II with MBC 500 mg/L. For NiNZ and ZnNZ no MBC was found. The bactericidal activity of AgNZ, CuNZ, BCNZ and BCASNZ was due to the activity of Ag, Cu or BC cations loaded onto NZ and not to NZ itself. Both clones of A. baumannii showed the resistance to Ni and Zn, while AS showed slight antibacterial activity. Low leaching of Cu and Ag suggest possible reuse of AgNZ and CuNZ. The change of pH was not the reason for the bactericidal activity of MNZ found in aerobic conditions. It seems that the extracellular polymers protect A. baumannii from the bactericidal activity of MNZ. Conclusion: The obtained results open a possibility for further clinical investigations and application of the MNZ as coatings or filters for use in hospitals.

Benzalkonium; Copper; Silver

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