title: Tracing of false negative results in phenotypic methods for identification of carbapenemase by Real-time PCR.
abstract: BACKGROUND
  Carbapenemase production causes multi antibiotics resistant in Gram-negative bacteria. A simple rapid and accurate phenotypic test for detection of Gram-negative carbapenemase-producing bacteria is useful for the treatment of infections. The aim of this study was to track the negative results in carbapenemase phenotypic test by Real-time PCR.
  
  
  METHODS
  In this study, 161 imipenem resistant Gram-negative bacteria were surveyed. Modified Hodge Test (MHT), boronic acid (BA), EDTA and dipicolinic acid were used for detection of Klebsiella pneumoniae carbapenemase (KPC) and metallo-beta-lactamase (MBLs). Different phenotypic methods and PCR confirmation followed by Real-time PCR for determination of phenotypic false-negative results were used.
  
  
  RESULTS
  Our results indicated that 85, 51 and 112 strains were MHT, BA and dipicolinic acid positive, respectively. No synergistic effect was observed between imipenem and EDTA. Sixty-nine strains were confirmed as carbapenemase-producers according to the results of molecular tests. All of the isolates carried the gene and expressed carbapenemase.
  
  
  CONCLUSIONS
  Comparison between the results of phenotypic and genotypic methods showed that the phenotypic methods could be used as the primary screening and the PCR remains as the gold standard for detection of carbapenemase positive strains.
authors.affiliation: Pediatric Infectious Research Center, Mofid Children Hospital, Shahid Beheshti University of Medical Sciences, Tehran, Iran.
authors.forename: Leila
authors.initials: L
authors.lastname: Azimi
authors.affiliation: Department of Microbiology, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Malihe
authors.initials: M
authors.lastname: Talebi
authors.affiliation: Molecular Microbiology Research Center, Shahed University, Tehran, Iran.
authors.forename: Parviz
authors.initials: P
authors.lastname: Owlia
authors.affiliation: Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran.
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Pourshafie
authors.affiliation: Department of Biochemistry, Iran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohamad
authors.initials: M
authors.lastname: Najafi
authors.affiliation: Luxembourg University, Faculty of Science Technology and Communication, Belgium; Liege University, Faculty of Science and Environment, Belgium.
authors.forename: Elnaz Rastegar
authors.initials: ER
authors.lastname: Lari
authors.affiliation: Department of Microbiology, Iran University of Medical Sciences, Tehran, Iran. Electronic address: azizlari@gmail.com.
authors.forename: Abdolaziz Rastegar
authors.initials: AR
authors.lastname: Lari
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D005188:False Negative Reactions; D006090:Gram-Negative Bacteria / Q000201:enzymology / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods*; D018440:beta-Lactam Resistance / Q000235:genetics*; D001618:beta-Lactamases / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D001618:beta-Lactamases; C063912:carbapenemase
keywords: Carbapenemase; Genotypic; Phenotypic