title: The modified Hodge test is a useful tool for ruling out Klebsiella pneumoniae carbapenemase.
abstract: OBJECTIVE
  Enterobacteriaceae bacteria harboring Klebsiella pneumoniae carbapenemase are a serious worldwide threat. The molecular identification of these pathogens is not routine in Brazilian hospitals, and a rapid phenotypic screening test is desirable. This study aims to evaluate the modified Hodge test as a phenotypic screening test for Klebsiella pneumoniae carbapenemase.
  
  
  METHODS
  From April 2009 to July 2011, all Enterobacteriaceae bacteria that were not susceptible to ertapenem according to Vitek2 analysis were analyzed with the modified Hodge test. All positive isolates and a random subset of negative isolates were also assayed for the presence of blaKPC. Isolates that were positive in modified Hodge tests were sub-classified as true-positives (E. coli touched the ertapenem disk) or inconclusive (distortion of the inhibition zone of E. coli, but growth did not reach the ertapenem disk). Negative results were defined as samples with no distortion of the inhibition zone around the ertapenem disk.
  
  
  RESULTS
  Among the 1521 isolates of Enterobacteriaceae bacteria that were not susceptible to ertapenem, 30% were positive for blaKPC, and 35% were positive according to the modified Hodge test (81% specificity). Under the proposed sub-classification, true positives showed a 98% agreement with the blaKPC results. The negative predictive value of the modified Hodge test for detection was 100%. KPC producers showed high antimicrobial resistance rates, but 90% and 77% of these isolates were susceptible to aminoglycoside and tigecycline, respectively.
  
  
  CONCLUSIONS
  Standardizing the modified Hodge test interpretation may improve the specificity of KPC detection. In this study, negative test results ruled out 100% of the isolates harboring Klebsiella pneumoniae carbapenemase 2. The test may therefore be regarded as a good epidemiological tool.
authors.affiliation: Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, Pathology Department, Microbiology Laboratory, São Paulo/SP, Brazil. anapaulacury@gmail.com
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Cury
authors.forename: Denise
authors.initials: D
authors.lastname: Andreazzi
authors.forename: Márcia
authors.initials: M
authors.lastname: Maffucci
authors.forename: Hélio Hehl
authors.initials: HH
authors.lastname: Caiaffa-Junior
authors.forename: Flávia
authors.initials: F
authors.lastname: Rossi
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D004269:DNA, Bacterial / Q000032:analysis; D000077727:Ertapenem; D006801:Humans; D007710:Klebsiella Infections / Q000382:microbiology*; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology / Q000302:isolation & purification*; D008826:Microbial Sensitivity Tests / Q000379:methods; D011237:Predictive Value of Tests; D018440:beta-Lactam Resistance / Q000187:drug effects / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D047090:beta-Lactams; D001618:beta-Lactamases; C531581:carbapenemase-2, Klebsiella pneumoniae; D000077727:Ertapenem