title: Effects of pH and Temperature on Antibacterial Activity of Zinc Oxide Nanofluid Against Escherichia coli O157: H7 and Staphylococcus aureus.
abstract: BACKGROUND
  Zinc oxide nanoparticles (ZnO NPs) are known as one of the important inorganic materials used in research and health-related applications with effective antibacterial activities. Although the toxic effects of ZnO NPs have already been evaluated, more information is required to understand the possible mechanisms.
  
  
  OBJECTIVE
  The aim of the present study was to determine the influences of pH and temperature on antibacterial activity of ZnO NPs against some strains of pathogenic bacteria. Identifying the interrelationship between toxicity and cultural conditions helps us to have a better understanding of the optimum reaction conditions for maximum antimicrobial activity.
  
  
  METHODS
  ZnO NPs were prepared and characterized and then dispersed in glycerol with the help of ammonium citrate as the dispersant. The antibacterial tests were performed by measuring the growth of Escherichia coli O157:H7 and Staphylococcus aureus with different concentrations of ZnO NPs in glycerol. All the experiments were conducted at different incubation temperatures (25-42(°)C) and pH levels (4-10 for E. coli O157:H7 and 5-10 for S. aureus).
  
  
  RESULTS
  The results showed that ZnO nanofluid have antibacterial activity against E. coli O157:H7 and S. aureus and the inhibitory effect increases with increasing the nanofluid concentration. The experiments showed that the antibacterial activity of ZnO NPs was influenced by temperature and pH. Higher antibacterial activity was observed at acidic pH levels with the maximum toxicity at pH = 4 and pH = 5 for E. coli O157: H7 and S. aureus, respectively. By raising the temperature, the toxicity of ZnO nanofluid increased, with the highest antibacterial activity at 42°C for both bacterial types in comparison with positive controls under the same conditions.
  
  
  CONCLUSIONS
  Analysis of the results demonstrated that exposure media of ZnO NPs and cultural factors play a role in their cytotoxic effects. It could be attributed to the principal mechanism at different reaction conditions.
authors.affiliation: Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, IR Iran.
authors.forename: Mahsa
authors.initials: M
authors.lastname: Saliani
authors.affiliation: Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, IR Iran ; Cell and Molecular Biotechnology Research Group, Institute of Biotechnology, Ferdowsi University of Mashhad, Mashhad, IR Iran.
authors.forename: Razieh
authors.initials: R
authors.lastname: Jalal
authors.affiliation: Department of Chemistry, Faculty of Sciences, Ferdowsi University of Mashhad, Mashhad, IR Iran.
authors.forename: Elaheh
authors.initials: E
authors.lastname: Kafshdare Goharshadi
keywords: Escherichia coli O157: H7; Nanoparticles; Staphylococcus aureus; Treatment
references.citation: Environ Toxicol Chem. 2010 Dec;29(12):2814-22
references.pmid: 20931607
references.citation: Langmuir. 2008 Apr 15;24(8):4140-4
references.pmid: 18341364
references.citation: Nanomedicine. 2011 Apr;7(2):184-92
references.pmid: 21034861
references.citation: J Appl Toxicol. 2009 Jan;29(1):69-78
references.pmid: 18756589
references.citation: Toxicol Appl Pharmacol. 2010 Aug 1;246(3):116-27
references.pmid: 20434478
references.citation: Environ Sci Technol. 2011 Jan 15;45(2):755-61
references.pmid: 21133426
references.citation: J Colloid Interface Sci. 2004 Jul 1;275(1):177-82
references.pmid: 15158396
references.citation: Appl Microbiol Biotechnol. 2003 Jun;61(5-6):424-8
references.pmid: 12684849
references.citation: Environ Pollut. 2013 Jan;172:76-85
references.pmid: 22995930
references.citation: Science. 2007 Jun 15;316(5831):1600-3
references.pmid: 17569859
references.citation: J Appl Microbiol. 2009 Oct;107(4):1193-201
references.pmid: 19486396
references.citation: Aquat Toxicol. 2013 Jul 15;136-137:49-59
references.pmid: 23643724
references.citation: Environ Sci Technol. 2011 Mar 1;45(5):1977-83
references.pmid: 21280647
references.citation: Environ Toxicol Chem. 2012 Jan;31(1):93-9
references.pmid: 21994124