Evaluation Synergistic Effect of TiO2, ZnO Nanoparticles and Amphiphilic Peptides (Mastoparan-B, Indolicidin) Against Drug-Resistant Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii

Backgound: The aims of this study were to evaluate the antimicrobial properties and synergistic effects of nano-titanium dioxide (TiO2), nano- zinc oxide (ZnO) and two synthetic peptides (mastoparan-B, indolicidin) against drug-resistant strains of Pseudomonas aeruginosa, Klebsiella pneumoniae, and Acinetobacter baumannii.
From March to August 2015, a total of 30 (10 each) isolates of the above bacteria were recovered from patients in the ICU of two referral hospitals in Kerman, Iran. The sizes and purities of nano-TiO2, nano-ZnO were determined by scanning electron microscope (SEM) and X-ray diffraction (XRD). Similarly, mass spectroscopy and HPLC were used for checking the genunity of the peptides. Antibiotic sensitivity was determined by agar disk diffusion assay. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) activities of nanometals and synthetic peptides were assessed by CLSI broth microdilution test. Similarly, checkerboard and time-kill curve analysis were performed to determine the synergistic activities of these compounds.
Mastoparan-B had potent toxicity to all isolates with an average MIC 4 ± 0.2 mg/L, while TiO2-NP had lowest antimicrobial activity with MIC range 1280 ≥ ± 0.2 mg/L (P. aeruginosa growth was not inhibited by TiO2 and ZnO NPs). The bactericidal activity against the isolates in descending order was mastoparan-B, indolicidin, nano ZnO, and nano TiO2, respectively. Further investigation on synergism using fractional inhibitory concentration index (FIC) revealed that, nano-TiO2 and nano-ZnO combination had an additive effect (FIC = 0.95 ± 0.1) on A. baumannii and K. pneumoniae strains, whereas, P. aeruginosa isolates were indifferent to this combination (FIC ≥ 2 ± 0.2). In contrast, mastoparan-B and indolicidin combination displayed broad synergistic effect (FIC = 0.5 ± 0.1) on all the isolates and caused rapid killing of the organisms within 4 h of incubation.
Our results showed that the combination of mastoparan-B and indolicidin peptides is a suitable candidate for substitution of the antibiotics for topical treatment of infections caused by drug- resistant bacteria. to determine the incidence and prevalence of Shiga Toxin producing E. coli (STEC), as a cause of urinary tract infection in Iran.