Evaluation of Multiple Methods for Detection of Gastrointestinal Colonization of Carbapenem-Resistant Organisms from Rectal Swabs

Abstract

bRectal swabs from high-risk patients were screened for carbapenem-resistant organisms (CROs) using several methods. The direct MacConkey plate method was the most sensitive for CROs (95%), while chromID CARBA and the Check-Direct CPE screen assay were the most sensitive for the detection of carbapenemase-producing organisms (CPOs) (100%; all bla KPC ). All methods had a specificity of >90% for CROs, and for CPOs, the specificity ranged from 85 to 98%. Broth enrichment methods performed poorly compared to direct inoculation methods, negating the need for the broth enrichment step. In 2013, the U.S. Centers for Disease Control and Prevention (CDC) assigned the highest threat level to carbapenem-resistant Enterobacteriaceae (CRE). Additionally, the CDC designated multidrug-resistant (MDR) Pseudomonas aeruginosa and Acinetobacter baumannii as serious threats because they are resistant to nearly all available antibiotics, including carbapenems-declaring that they require urgent public health attention (1). Optimal screening methods for rapid detection of carbapenem-resistant organisms (CROs) have yet to be established (2). Currently described methods include broth enrichment, direct selective culture, chromogenic media, and detection of carbapenemase genes directly from rectal swabs (3-9). The objectives of this study were to (i) evaluate multiple methods for screening CROs from rectal swabs and (ii) to determine the prevalence of gastrointestinal colonization with CROs among high-risk inpatient populations.Two-hundred thirteen remnant vancomycin-resistant enterococcus (VRE) surveillance rectal ESwabs (Copan, Murrieta, CA) were collected in a non-outbreak setting from four distinct inpatient populations at The Johns Hopkins Hospital, Baltimore, MD. ESwabs were collected upon hospital unit admission and weekly thereafter until unit discharge. Consecutive rectal ESwabs were collected from medical and surgical intensive care units (MICUs and SICUs, respectively), an oncology ward, and an organ transplant ward over a 2-week period. The ESwabs were vortexed, and the remnant liquid Amies broth was aliquoted to cryovials and frozen at Ϫ70°C until further testing was performed. From each ESwab broth, five different methods for the detection of CRO were set up in parallel. The five methods included (i) the CDC broth enrichment method with ertapenem for selection (3), (ii) a modified CDC broth enrichment method using ertapenem and vancomycin for selection (3), (iii) a direct MacConkey plate with ertapenem disks (4, 6), (iv) a chromogenic chromID CARBA agar plate method (with the new reformulated medium; package insert version 20157 A-en-2013/02, reference no. 414012 [bioMérieux, Marcy l'Étoile, France]), and (v) the Check-Direct CPE screen assay for the BD MAX instrument (Check-Points, Wageningen, The Netherlands; Becton Dickinson, Sparks, MD). The ESwab broth was first vortexed for 5 s, 100 l of ESwab broth was inoculated into each of the medium types, and 25 l was inoculated into a DNA sample buffer tube (SBT) for the Check...

Development of selective medium for IMP-type carbapenemase-producing Enterobacteriaceae in stool specimens

“…MC-ECC showed better recoveries than chromID CARBA and CHROMagar KPC, although six IMP-positive strains were not recovered. This result is similar to previous reports [7, 16, 17]. IMP-producing CPE was also difficult to detect when a small number was inoculated.…”

“…Furthermore, among several types of carbapenemases, enzymes such as OXA-48 and IMP have low capability of hydrolysing carbapenems [6]. These data indicate the difficulties in screening for CPE in stool specimens [3–5, 7]. …”

How frequently are hospitalized patients colonized with carbapenem-resistant Enterobacteriaceae (CRE) already on contact precautions for other indications?

“…3 Colonies growing within 27 mm of ertapenem and 32 mm of meropenem were identified by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (Bruker Daltonics), and carbapenem antimicrobial susceptibility testing (ertapenem, meropenem and imipenem) was performed by disk diffusion applying Clinical and Laboratory Standards Institute guidelines. 4 Enterobacteriaceae resistant to ertapenem, meropenem, and/or imipenem were categorized as CRE.…”

Carbapenem-Resistant Non-Glucose-Fermenting Gram-Negative Bacilli: the Missing Piece to the Puzzle

“…Some data suggest that directly inoculating chromogenic agar from rectal swabs may compromise the sensitivity for detecting CRE (48). However, other studies have found that broth enrichment is not required and that direct inoculation of rectal swabs on chromogenic medium is comparable or superior to that in the CDC broth enrichment method (15,81).…”

“…Another significant disadvantage is the long turnaround time of up to 4 days. Additionally, although the broth enrichment was designed to increase sensitivity, it may in fact hinder the recovery of CROs with low carbapenem MICs or low inocula in the presence of high inocula of competing organisms (15,81). A second method using standard laboratory medium involves direct inoculation of a MacConkey agar plate and the placement of carbapenem disks between the juncture of quadrants 1 and 2 and juncture of quadrants 2 and 3.…”