Comparative evaluation of a prototype chromogenic medium (ChromID CARBA) for detecting carbapenemase-producing Enterobacteriaceae in surveillance rectal swabs

J Clin Microbiol. 2012 Jun;50(6):1841-6. doi: 10.1128/JCM.06848-11. Epub 2012 Mar 29.

Abstract

Carbapenemase-producing Enterobacteriaceae (CPE) are an increasing problem worldwide, and rectal swab surveillance is recommended as a component of infection control programs. The performance of a prototype chromogenic medium (chromID CARBA) was evaluated and compared with media tested by four other screening methods: (i) overnight selective enrichment in 5 ml tryptic soy broth with a 10-μg ertapenem disk followed by plating onto MacConkey agar (CDC-TS), (ii) short selective enrichment in 9 ml brain heart infusion broth with a 10-μg ertapenem disk followed by plating onto chromID ESBL medium (ESBL-BH), (iii) direct plating onto chromID ESBL, and (iv) direct plating onto MacConkey agar supplemented with meropenem (1 μg/ml) (MCM). The screening methods were applied to detect CPE in 200 rectal swab specimens taken from different hospitalized patients. Identification and antimicrobial susceptibility were performed by the Vitek 2 system. Carbapenem MICs were checked by Etest. Carbapenemase production was confirmed using the modified Hodge test, combined-disk tests, and PCR assays. In total, 133 presumptive CPE strains were detected. Phenotypic and genotypic assays confirmed 92 strains to be CPE (56 KPC-positive Klebsiella pneumoniae, 29 VIM-positive K. pneumoniae, and 7 KPC-positive Enterobacter aerogenes strains) recovered from 73 patients, while the remaining 41 strains were confirmed to be CPE negative (19 ESBL producers and 22 nonfermenters). chromID CARBA, ESBL-BH, and chromID ESBL exhibited the highest sensitivity (92.4%), followed by CDC-TS and MCM (89.1%) (P = 0.631). The specificity was greater for chromID CARBA (96.9%) and ESBL-BH (93.2%) than for CDC-TS (86.4%), MCM (85.2%), and chromID ESBL (84.7%) (P = 0.014). In conclusion, chromID CARBA was found to be a rapid and accurate culture screening method for active CPE surveillance.

Publication types

  • Comparative Study
  • Evaluation Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Bacteriological Techniques / methods*
  • Carbapenems / pharmacology
  • Culture Media / chemistry*
  • Enterobacter aerogenes
  • Enterobacteriaceae / enzymology*
  • Enterobacteriaceae / isolation & purification*
  • Enterobacteriaceae Infections / microbiology*
  • Genotype
  • Humans
  • Klebsiella pneumoniae
  • Mass Screening / methods
  • Microbial Sensitivity Tests
  • Phenotype
  • Polymerase Chain Reaction
  • Rectum / microbiology*
  • Sensitivity and Specificity
  • beta-Lactamases / genetics
  • beta-Lactamases / metabolism*

Substances

  • Bacterial Proteins
  • Carbapenems
  • Culture Media
  • beta-Lactamases
  • carbapenemase