title: Toxic effect of high concentration of sonochemically synthesized polyvinylpyrrolidone-coated silver nanoparticles on Citrobacter sp. A1 and Enterococcus sp. C1.
abstract: OBJECTIVE
  Currently, silver nanoparticles (AgNPs) have gained importance in various industrial applications. However, their impact upon release into the environment on microorganisms remains unclear. The aim of this study was to analyze the effect of polyvinylpyrrolidone-capped AgNPs synthesized in this laboratory on two bacterial strains isolated from the environment, Gram-negative Citrobacter sp. A1 and Gram-positive Enterococcus sp. C1.
  
  
  METHODS
  Polyvinylpyrrolidone-capped AgNPs were synthesized by ultrasound-assisted chemical reduction. Characterization of the AgNPs involved UV-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy. Citrobacter sp. A1 and Enterococcus sp. C1 were exposed to varying concentrations of AgNPs, and cell viability was determined. Scanning electron microscopy was performed to evaluate the morphological alteration of both species upon exposure to AgNPs at 1000 mg/L.
  
  
  RESULTS
  The synthesized AgNPs were spherical in shape, with an average particle size of 15 nm. The AgNPs had different but prominent effects on either Citrobacter sp. A1 or Enterococcus sp. C1. At an AgNP concentration of 1000 mg/L, Citrobacter sp. A1 retained viability for 6 hours, while Enterococcus sp. C1 retained viability only for 3 hours. Citrobacter sp. A1 appeared to be more resistant to AgNPs than Enterococcus sp. C1. The cell wall of both strains was found to be morphologically altered at that concentration.
  
  
  CONCLUSIONS
  Minute and spherical AgNPs significantly affected the viability of the two bacterial strains selected from the environment. Enterococcus sp. C1 was more vulnerable to AgNPs, probably due to its cell wall architecture and the absence of silver resistance-related genes.
authors.affiliation: Faculty of Biosciences and Medical Engineering (FBME), Universiti Teknologi Malaysia (UTM), Johor, Malaysia.
authors.forename: Chew Ping
authors.initials: CP
authors.lastname: Lau
authors.affiliation: Faculty of Biosciences and Medical Engineering (FBME), Universiti Teknologi Malaysia (UTM), Johor, Malaysia.
authors.forename: Mohd Firdaus
authors.initials: MF
authors.lastname: Abdul-Wahab
authors.affiliation: Faculty of Science, Universiti Teknologi Malaysia (UTM), Johor, Malaysia.
authors.forename: Jafariah
authors.initials: J
authors.lastname: Jaafar
authors.affiliation: School of Applied Science, Temasek Polytechnic, Singapore.
authors.forename: Giek Far
authors.initials: GF
authors.lastname: Chan
authors.affiliation: Faculty of Biosciences and Medical Engineering (FBME), Universiti Teknologi Malaysia (UTM), Johor, Malaysia. Electronic address: nooraini_nar@fbb.utm.my.
authors.forename: Noor Aini
authors.initials: NA
authors.lastname: Abdul Rashid
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002954:Citrobacter / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology; D016983:Enterococcus / Q000187:drug effects* / Q000302:isolation & purification / Q000502:physiology; D004783:Environmental Microbiology; D050296:Microbial Viability / Q000187:drug effects*; D008854:Microscopy, Electron; D053758:Nanoparticles / Q000737:chemistry*; D010084:Oxidation-Reduction; D011205:Povidone / Q000494:pharmacology*; D012834:Silver / Q000494:pharmacology*; D013057:Spectrum Analysis; D014463:Ultrasonography; D014961:X-Ray Diffraction
chemical_list: D000900:Anti-Bacterial Agents; D012834:Silver; D011205:Povidone
keywords: Citrobacter sp. A1; Enterococcus sp. C1; silver nanoparticles; tolerance level; toxic effect