title: Characterization of the modified Hodge test-positive isolates of Enterobacteriaceae in Taiwan.
abstract: OBJECTIVE
  The modified Hodge test is a phenotypic test to detect KPC-type carbapenemase producers among Enterobacteriaceae, as recommended by the Clinical Laboratory Standards Institute. However, false positive results were reported. In this study, we aimed to large-scale investigate the characterization of the modified Hodge test-positive isolates of Enterobacteriaceae collected between 2006 and 2010 in Taiwan.
  
  
  METHODS
  Fifty-six isolates, including 24 Enterobacter cloacae, 17 Escherichia coli, 10 Klebsiella pneumoniae, and 5 Citrobacter freundii, tested positive with the modified Hodge test. The in vitro activities of 10 antimicrobial agents were determined by the agar dilution method. Boronic acid combined-disk test was used to further confirm the KPC producers. Phenotype of ESBL, AmpC, class B carbapenemases, and profile of outer membrane proteins were investigated by the confirmatory test, boronic acid disk method, 2-mercaptopropionic acid double-disk method, and urea/sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), respectively. β-lactamase genes were examined by PCR and sequencing.
  
  
  RESULTS
  These isolates were resistant to ceftazidime (100%), aztreonam (82.1%), ertapenem (64.3%), gentamicin (53.6%), ciprofloxacin (50%), levofloxacin (48.2%), cefepime (19.6%), imipenem (16.1%), meropenem (12.5%), and amikacin (8.9%). Phenotypic testing among isolates revealed the production of ESBLs, metallo-β-lactamases (MBLs), and AmpC in 10 (17.9%), 16 (28.6%), and 12 (44.4%) isolates, respectively. Carbapenemase and non-carbapenemase β-lactamase genes bla(TEM-1), bla(SHV), bla(CTX-M), bla(IMP-8), bla(CMY-2), and bla(DHA-1) were found in 32 (57.1%), 19 (33.9%), 4 (7.1%), 16 (28.6%), 14 (25%), and 5 (8.9%) of the strains, respectively. No class A and D carbapenemase genes were detected. Outer membrane protein profile showed obviously decreased expression in 49 (87.5%) isolates with positive result of modified Hodge test.
  
  
  CONCLUSIONS
  Our data show that ESBLs, AmpC, and imipenemase-8 (IMP-8) carbapenemase coupled with decreased expression of outer membrane protein were prevalent in Enterobacteriaceae isolates testing positive for the modified Hodge test in Taiwan.
authors.affiliation: Department of Medical Laboratory Science and Biotechnology, College of Medicine, National Cheng Kung University, Taiwan.
authors.forename: Kuei-Hsiang
authors.initials: KH
authors.lastname: Hung
authors.forename: Jing-Jou
authors.initials: JJ
authors.lastname: Yan
authors.forename: Jang-Jih
authors.initials: JJ
authors.lastname: Lu
authors.forename: Hung-Mo
authors.initials: HM
authors.lastname: Chen
authors.forename: Jiunn-Jong
authors.initials: JJ
authors.lastname: Wu
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000032:analysis; D004591:Electrophoresis, Polyacrylamide Gel; D004755:Enterobacteriaceae / Q000201:enzymology* / Q000302:isolation & purification; D004756:Enterobacteriaceae Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D016133:Polymerase Chain Reaction; D020543:Proteome / Q000032:analysis; D013624:Taiwan; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D020543:Proteome; D001618:beta-Lactamases