Optimal detection of extended-spectrum
β-lactamase producers,
carbapenemase producers, polymyxin-resistant Enterobacterales, and
vancomycin-resistant enterococci from stools
Mustafa Sadek
a, Laurent Poirel
a,b,c, Patrice Nordmann
a,b,c,d,⁎
a
Medical and Molecular Microbiology, Faculty of Science and Medicine, University of Fribourg, Fribourg, Switzerland b
INSERM European Unit (IAME, France), University of Fribourg, Fribourg c
Swiss National Reference Center for Emerging Antibiotic Resistance (NARA), University of Fribourg, Fribourg d
Institute for Microbiology, University of Lausanne and University Hospital Centre, Lausanne, Switzerland
Keywords:
syphilis serum repository nontreponemal test treponemal test serological diagnostic assay syphilis stage
serum bank
syphilis diagnostic assay
This study compared the impact of different approaches, namely, nonenrichment, nonselective enrichment, and selective (antibiotic-containing) enrichment steps, for detecting extended-spectrum β-lactamase producing Enterobacterales (ESBL-E), carbapenemase-producing Enterobacterales (CPE), polymyxin-resistant Enterobacterales (PMR-E), and vancomycin-resistant enterococci (VRE) from spiked stools. The use of a nonse-lective 18-h enrichment broth culture significantly improved the recovery rate of all types of resistant bacteria after their plating onto selective media. In addition, the detection of ESBL-E, CPE, PMR-E, and VRE was further im-proved when using an enrichment step using antibiotic-supplemented broths respectively supplemented with cefotaxime (0.1 μg/mL), ertapenem (0.1 μg/mL), colistin (0.5 μg/mL), and vancomycin (1 μg/mL). Therefore, we showed here that a screening strategy based on a selective broth enrichment step significantly contributes to an increased rate of detection of multidrug-resistant bacteria, which may be crucial in term of improvement of infection control.
1. Introduction
Infections caused by multidrug-resistant (MDR) bacteria are associated with increased morbidity and mortality due to the limited treatment options (Cerceo et al. 2016). Therefore, the early detection of patients colonized with MDR bacteria is becoming fundamental for the prompt implementation of optimal infection control strategies
(Fang et al. 2012). In many institutions and hospitals, screening of
patients colonized by MDR bacteria is performed as part of the infection control measures. However, limited data exist regarding the optimal screening strategy for MDR bacteria. For vancomycin-resistant entero-cocci (VRE), use of a selective culture medium containing vancomycin is known to improve their detection from stool samples (Cuzon et al.
2008; Nordmann et al. 2012). Although it is clear that the use of
chromogenic and antibiotic-containing media is useful for improving
the identification and recovery of MDR bacteria from stool samples
(Cuzon et al. 2008;Fang et al. 2012;Nordmann et al. 2012;Cerceo
et al. 2016;Poirel et al. 2017), the use of an enrichment step for their
detection is not a common practice, and the added-value of this approach remains unclear.
Extended-spectrumβ-lactamase producing Enterobacterales (ESBL-E) are increasingly reported worldwide. Gastrointestinal colonization with ESBL-E is associated with an increased risk of bacteremia
(Cornejo-Juárez et al. 2016). Detection of carbapenemase-producing
Enterobacterales (CPE) is also challenging since the level of resistance to carbapenems may vary significantly depending on the nature of the carbapenemase itself, on the level of expression of the carbapenemase gene, and also on the resistance background of the strain (variability of the outer membrane permeability). Finally, polymyxins are now considered as last-resort antibiotics against MDR Enterobacterales in re-gions endemic for CPE, such as Italy and Greece (Poirel et al. 2017). Concomitantly, resistance to polymyxins in Gram-negative bacteria is now increasingly reported (Poirel et al. 2017). Therefore, rapid and
⁎ Corresponding author. Tel: +41-26-300-9581.
E-mail address:patrice.nordmann@unifr.ch(P. Nordmann).
1
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Published in "Diagnostic Microbiology and Infectious Disease doi: 10.1016/
j.diagmicrobio.2019.114919, 2020" which should be cited to refer to this work.
early identification of patients colonized with polymyxin-resistant Enterobacterales (PMR-E) is also important.
The aim of our study was to determine whether an enrichment step, with and without antibiotics, prior to inoculation on selective agar plates increased the sensitivity of MDR screening. Our evaluation of different screening strategies focused on 4 clinically relevant MDR bacteria, i.e., VRE, ESBL-E, CPE, and PMR-E.
2. Material and methods 2.1. Bacterial strains
This study was carried out with a well-characterized collection (16S rRNA sequencing) of multidrug bacterial isolates from the Medical and Molecular Microbiology Unit, Faculty of Science and Medicine, Univer-sity of Fribourg, Switzerland (Tables 1–4). Isolates were obtained from various clinical sources and from various countries and continents. Resistance mechanisms to the selected antibiotics were previously determined at the molecular level using PCR approaches.
2.2. Susceptibility testing
MIC values of antibiotics except for colistin were determined using ETEST strips (bioMérieux, La Balme-les-Grottes, France) on Mueller-Hinton agar plates at 37 °C, and the results were interpreted according
to the latest EUCAST breakpoints (www.eucast.org). Broth
microdilution was performed for determination of MICs of colistin in cation-adjusted Mueller-Hinton broth (Bio-Rad, Marnes-La-Coquette, France), and results were interpreted according to the EUCAST/CLSI
joint guidelines (www.eucast.org) (resistance, N2 μg/mL for
Enterobacterales) (CLSI, 2018). E. coli ATCC 25922 and E. faecalis ATCC 29212 were used as quality control strains for susceptibility testing of Enterobacterales and enterococci, respectively.
2.3. Spiking experiments
Serial 10-fold dilutions were made in 0.85% saline solution with bac-terial suspensions of MDR bacteria starting with an optical density at a 0.5 McFarland standard (inoculum of ~1.5 × 108CFU/ml). To quantify
the viable bacteria in each dilution step, tryptic soy (TS) agar plates
were inoculated with 100 μL of each suspension and incubated
overnight at 37 °C. The number of colonies that grew was counted the following day. Then, spiked fecal samples were made by adding 100μL of serial-fold bacterial dilutions to 900 μl of stool suspension. Stool suspensions were obtained by suspending 6 g of pooled feces from healthy volunteers in 60 mL of distilled water. Healthy volunteers were previously screened to be negative for the VRE, ESBL-E, CPE, and PMR-E. Stool suspensions without addition of bacterial strains were used as negative controls.
For all the enrichment strategies, 2 procedures were compared, namely, an 18-h enrichment step in TS broth without antibiotic supple-mentation and an enrichment step using TS broth containing a given concentration of antibiotic. Several antibiotic concentrations were tested, remaining below the breakpoints of resistance of each tested antibiotic, according to EUCAST (www.eucast.org) and CLSI (https://
clsi.org/2018/) guidelines.
Aliquots of 100μL of the stool suspension spiked with ESBL-E were inoculated a) directly onto chromID ESBL agar (bioMérieux), b) into 5 mL of nonselective TS broth, or c) into 5 mL of TS broth with cefotax-ime (Acros Organics, Chemie Brunschwig AG, Switzerland) at 0.1 or 0.5μg/mL (Blane et al., 2016) . Aliquot of 100μL of the fecal suspension without the addition of ESBL-E directly spread onto chromID ESBL agar (bioMérieux) was used as a negative control. Aliquot of 100μL of the fecal suspension without the addition of ESBL-E inoculated into 5 mL of TSB was used as a negative control. Aliquot of 100μL of the fecal sus-pension without the addition of ESBL-E inoculated into 5 mL of TS broth with cefotaxime was used as negative control. Agar plates and enrich-ment broths were incubated overnight at 37 °C. The following day, ali-quots of 100μL of nonselective TS broth and selective TS broth were inoculated onto selective chromID ESBL agar.
A similar procedure was followed for screening CPE, and aliquots of 100 μL of spiked stool suspension were inoculated i) directly on SuperCarba agar (CHROMAgar Ltd., Paris, France) (Nordmann et al. 2012)), ii) in 5 mL of nonselective TS broth, or iii) in 5 mL of TS broth with ertapenem (0.1 and 0.5μg/mL) (Acros Organics).
For PMR-E, aliquots of 100μL of spiked stool suspensions were inoculated i) directly on SuperPolymyxin agar (ELITech Microbiology, Puteaux, France) (Nordmann et al. 2016;Jayol et al. 2018), ii) in 5 mL of nonselective TS broth, or iii) in 5 mL of TS broth with colistin (0.5 and 2μg/mL) (Sigma Aldrich Chemie GmbH, Buchs, Switzerland).
For VRE, aliquots of 100μL of the spiked stool suspension were inoculated i) directly on ChromID VRE agar (bioMérieux), ii) in 5 mL of nonselective TS broth, or iii) in 5 mL of TSB with vancomycin (1 and 3μg/mL) (Duchefa Biochemie, Haarlem, the Netherlands).
Colony-forming units were counted after 18 h of incubation at 37 °C. All experiments were performed in duplicate. Data were statistically an-alyzed with SPSS using Wilcoxon signed rank test.
3. Results and discussion
The impact of direct plating, nonselective broth enrichment, and selective broth enrichment for the detection of ESBL-E, CPE, PMR-E, and VRE revealed remarkable differences. Following enrichment in TS broth, many more ESBL-E were recovered when compared to direct plating onto agar plates (PN 0.05) (Table 1). Furthermore, the use of selective enrichment with cefotaxime - regardless of the concentration - further improved the detection of ESBL-E compared to non-selective enrichment step (PN 0.05). However, no significant difference was
Table 1
Evaluation of direct plating on ChromID ESBL agar of spiked stools, with and without an 18-h enrichment step in TSB and TSB + cefotaxime (CTX) at 0.1μg/mL for the detection of ESBL-E. Strain Species β-Lactamase contenta
MIC of cefotaxime (μg/mL) ChromID ESBL agar (CFU/mL) Enrichment broth (CFU/mL) TSB TSB + CTX R889 K. pneumoniae CTX-M-15 16 101 3.1 × 104 5.5 × 107 R1003 E. coli CTX-M-15 + SHV-1 16 4 × 101 1.93 × 104 2.75 × 107 R1063 K. pneumoniae CTX-M-3 + TEM-1+ SHV-11 16 3 × 101 1.2× 106 1.2× 109 R1907 E coli CTX-M-3 + TEM-1 16 5 × 101 2.7 × 104 5.8 × 108 R985 E. coli CTX-M-9 + TEM-1 32 1 × 102 4.5 × 104 3 × 107 R1095 K. pneumoniae SHV-5 8 1 × 102 8 × 105 1.77 × 109 R1097 K. pneumoniae SHV-12 2 6 × 101 2.4 × 106 6.9 × 108 R1099 K. pneumoniae TEM-3 + SHV-28 4 9 × 101 3 × 105 1.21 × 109 R1101 K. pneumoniae TEM-52 + SHV-28 N32 4 × 101 2.2 × 106 8.2 × 108 R 301 K. pneumoniae SHV-11 + KPC-2 N32 1 × 102 2.8 × 106 3.1 × 108 R3092 K. pneumoniae CTX-M-55 + TEM-1 N32 3 × 101 1.5 × 105 4.5 × 108 aESBL enzymes are in bold.
2
observed when comparing enrichment steps using any of the tested concentrations of cefotaxime (0.1 versus 0.5μg/mL) (data not shown). Consequently, data presented inTable 1refer to a single concentration of antibiotic for each enrichment procedure, but same results would apply for the second concentration tested.
It was previously shown that an overnight preenrichment step in TS broth improves the detection of ESBL-E and allows an earlier recogni-tion of patients that are ESBL-E carriers (Murk et al. 2009). Likewise,
Jazmati et al. (2017)showed the added value of an enrichment step
for the screening of broad-spectrum cephalosporins-resistant Enterobacterales. In another study, an enrichment step was shown to increase the sensitivity of detection of ESBL-E from 75% to 97% in stool samples (Blane et al. 2016).
Detection of CPE was also improved by the use of a similar enrich-ment step when compared to direct plating on selective medium (PN 0.05) (Table 2). Moreover, the use of selective broth enrichment containing ertapenem (0.1 or 0.5μg/mL) further improved the detec-tion of CPE compared to non-selective broth (PN 0.05) regardless of the ertapenem MIC (Table 2). Two new methods of CPE detection from stool samples have been recently proposed: an automated broth medium method (Arena et al. 2018) and a temocillin-containing broth to improve detection of a specific group of CPE, namely the OXA-48 producers (Cieselinczuk et al. 2018). The use of temocillin as an enrich-ment factor is related to the high resistance level to this antibiotic con-ferred by OXA-48-like. Based on our results, specific enrichment of OXA-48-like producers with temocillin would not be necessary since all tested strains including OXA-48 and OXA-181 producers were well detected after the ertapenem-based enrichment step. Similarly,Glaser
et al. (2015)report that a growth step in a meropenem-containing
broth may enhance the selection of CPE. On the opposite, by using clinical rectal swabs,Simner et al. (2016)did not evidence higher CPE recovery by using an ertapenem-containing broth.
For detection of carbapenemase-producing Klebsiella spp. and E. coli, the Centers for Disease Control and Prevention (CDC) recommendation includes an overnight selective broth enrichment culture of the rectal swab in 5 mL of TS broth supplemented with a 10-μg ertapenem or 5-μg meropenem disk followed by a subculture onto MacConkey agar
plates (CDC 2009;Viau et al. 2016). The addition of ertapenem at a given concentration that we propose is following the same principle of selection. However, our strategy is based on screening not only of carba-penem-resistant Enterobacterales but concomitantly of other MDR bacteria.
A significant benefit of an enrichment step was also observed for PMR-E detection, regardless of the type of polymyxin-resistance mechanism (Table 3). A higher detection yield was achieved by using a selective enrichment TS broth containing colistin (at 0.5 or 2μg/mL) prior to plating on selective agar (Table 3). To our knowledge, this is thefirst study evaluating the impact of direct plating, broth enrichment, and selective broth enrichment for an optimal recovery of PMR-E. In a context of growing polymyxin resistance worldwide, this detection strategy may be clinically significant.
The same increase in sensitivity of the screening test was observed
for VRE when using a nonselective enrichment step (P N 0.05)
(Table 4). However, a selective enrichment step with addition of
vanco-mycin resulted in a further increase of recovery of VRE compared to the nonselective enrichment, although these differences were not found to be statistically significant (P b 0.05). This result is consistent with previ-ous studies indicating that a preculture step in broth with or without
vancomycin (15μg/mL) enhances the recovery of VRE from feces
(Palladino et al. 2003;Novicki et al. 2004).
4. Conclusion
The use of selective enrichment broths prior to direct inoculation onto selective culture media resulted in significant increases of recovery of the MDR bacteria tested. Although such enrichment steps require an additional overnight culture, consequently delaying turnaround time, the present data demonstrate the increased sensitivity of an enrichment procedure. In clinical practice, use of an enrichment procedure may be particularly important in outbreak situations to decrease false-negative results. This enrichment procedure shall be performed in addition to direct plating of stools on screening culture media. From a practical point of view, antibiotic concentrations may be prepared in advance as a set and kept at−20 °C to be used on demand.
Table 2
Evaluation of direct plating on SUPERCARBA agar of spiked stools, with and without an 18-h enrichment step in TSB and in TSB+ ertapenem (ETP) at 0.1μg/mL for the detection of CPE. Strain Species β-Lactamase contenta MIC of ertapenem (μg/mL)
SUPERCARBA agar (CFU/mL) Enrichment broth (CFU/mL) TSB TSB + ETP R293 E. coli KPC-2 + TEM-1 + OXA-1 N32 2.4 × 102
8 × 106
5 × 107 R300 K. pneumoniae KPC-2 + TEM-1 + OXA-9 N32 4.4 × 102
6 × 106 45 × 107 R24 K. pneumoniae NDM-1 0.38 6 × 101 3.9 × 105 9 × 107 R61 E. coli VIM-1 0.5 7 × 101 8 × 105 3 × 107 R68 K. pneumoniae IMP-1 + SHV-12 0.25 3 × 101 4.5 × 105 4 × 106 R83 K. pneumoniae KPC-3 0.25 5 × 101 2.2 × 105 4 × 108
R721 E. coli OXA-48 + TEM-1 0.12 5 × 101
1 × 107 4.8 × 108 R753 K. pneumoniae OXA-48 + SHV-1 N32 6 × 101 4 × 106 7 × 107 R2815 E. coli OXA-181 0.5 1.3 × 102 3 × 106 3 × 107 R2854 K. pneumoniae OXA-181 N32 8 × 101 1 × 106 3.2 × 108 a
Carbapenemase names are in bold.
Table 3
Evaluation of direct plating on SuperPolymyxin agar plates of spiked stools, with and without an 18-h enrichment step in TSB and selective enrichment in TSB + colistin (CST) at 0.5μg/mL for the detection of PMR-E.
Strain Species Resistance mechanism MIC of colistin (μg/mL) SuperPolymyxin Agar (CFU/mL) Enrichment broth (CFU/mL) TSB TSB + CST R2739 E. coli MCR-1 4 4.1 × 102 3.5 × 106 4.3 × 108 R3330 E. coli MCR-1 8 6 × 101 4 × 106 3.5 × 108 R3193 K pneumoniae IS1R into mgrB prom−45/−46 64 3 × 102
4.38 × 107 1.2 × 109 R3218 K. pneumoniae G53S PmrA 128 1 × 102 2.5 × 106 3 × 108 R3210 K. pneumoniae R16C in PhoQ 128 2 × 101 2 × 105 1.4 × 108 R3222 K. pneumoniae T157P substitution in PmrB 32 4 × 101 7 × 105 5 × 107 3
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Noteworthy, our study showed that the detection rate of MDR bacte-ria may be improved thanks to a pre-enrichment step, especially in the case of patients with low inoculum in their stools. Even though these patients may represent a low risk of dissemination and generate rare secondary cases (D'Agata et al. 2002), our clinical experience indicates us that those patients with low inoculum shall be identified as early as possible to prevent a hidden dissemination of MDR bacteria.
Noticeably, we did not identify any difference of MDR recovery when using 2 different antibiotic concentrations in the selective enrich-ment strategies, showing that the presence rather than the absolute concentration of selective antibiotics is indeed crucial. We retained an-tibiotic concentrations of 0.1 μg/mL of cefotaxime, 0.1 μg/mL of ertapenem, 0.5μg/mL of colistin, and 1 μg/mL of vancomycin for optimal detection of ESBL-E, CPE, PMR-E, and VRE, respectively. Those antibiotic concentrations were defined for the first time by precisely quantifying the bacterial inocula in stools, the antibiotic concentrations, and the re-sistant bacteria type. To our knowledge, this is thefirst study to show that an enrichment step containing a defined concentration of colistin improves the detection of PMR-E.
We believe that this screening protocol should be repeated with a larger and more diverse collection of isolates including the producers of other types of carbapenemases, particularly those conferring unusual and difficult-to-detect susceptibility profiles, such as OXA-244 known to be difficult to detect when relying only on phenotypic approaches
(Potron et al. 2016;Hoyos-Mallecot et al. 2017). Also, there is need for
additional experiments to test other MDR organisms and different marketed screening agar plates. Furthermore, testing other specimen such as skin or throat samples through the same approach would signif-icantly add to the knowledge in thefield.
A limitation of our study was the use of spiked stools rather than stools recovered from colonized patients. Therefore, clinical evaluation of the proposed procedures may be interesting as well as the evaluation of a similar screening strategy for identification of colonization by MDR Acinetobacter baumannii and Pseudomonas aeruginosa. Finally, our proposed MDR screening technique may be a relatively low-cost, easy-to-implement strategy to perform extended surveys in humans, animals, or environmental settings.
Acknowledgments
This work wasfinanced by the University of Fribourg, Switzerland. It has also been funded by the Swiss National Science Foundation (project FNS-407240_177382). We warmly thank L.S. Munoz-Price for critical reading of our manuscript.
References
Arena F, Giani T, Antonelli A, Colavecchio OL, Pecile P, Viaggi B, et al.A new selective broth enrichment automated method for detection of carbapenem-resistant Enterobacteri-aceae from rectal swabs. J Microbiol Methods 2018;147:66–8.
Blane B, Brodrick HJ, Gouliouris T, Ambridge KE, Kidney AD, Ludden CM, et al.Comparison of two chromogenic media for the detection of extended-spectrumβ-lactamase
pro-ducing Enterobacteriaceae stool carriage in nursing home residents. Diag microb. In-fect Dis 2016;84:181–3.
Centers for Disease Control and Prevention. Laboratory protocol for detection of carbapenem-resistant or carbapenemase-producing. Atlanta, GA: Klebsiella spp. and E. coli from rectal swabs. Centers for Disease Control and Prevention; 2009.
Cerceo E, Deitelzweig SB, Sherman BM, Amin AN.Multidrug-resistant gram-negative bac-terial infections in the hospital setting: overview, implications for clinical practice. and emerging treatment options Microb Drug Resist 2016;22:412–31.
Cieselinczuk H, Phee LM, Dolphin H, Wilks M, Cherian BP, Wareham DW.Optimal detec-tion of carbapenemase-producing Enterobacteriaceae from rectal samples: a role for enrichment. J Hosp Infect 2018;98:270–4.
Clinical and Laboratory Standards Institute.Performance standards for antimicrobial sus-ceptibility testing; 28th informational supplement (M100–S28). Wayne (PA): The In-stitute; 2018.
Cornejo-Juárez P, Suárez-Cuenca JA, Volkow-Fernández P, Silva-Sánchez J, Barrios-Camacho H, Nájera-León E, et al.Fecal ESBL Escherichia coli carriage as a risk factor for bacteremia in patients with hematological malignancies. Supp Care Cancer 2016;24:253–9.
Cuzon G, Naas T, Fortineau N, Nordmann P. Novel chromogenic medium for detection of vancomycin-resistant Enterococcus faecium and Enterococcus faecalis. J Clin Microbiol 2008;46:2442–
D'Agata EM, Gautam S, Green WK, Tang YW.High rate of false-negative results of the rec-tal swab culture method in detection of gastrointestinal colonization with vancomycin-resistant enterococci. Clin Infect Dis 2002;34:167–72.
Fang H, Ohlsson AK, Jiang GX, Ullberg M.Screening for vancomycin-resistant enterococci: an efficient and economical laboratory-developed test. Eur J Clin Microbiol Infect Dis 2012;31:261–5.
Glaser L, Andreacchio K, Lyons M, Alby K.Improved surveillance for carbapenem resistant Enterobacteriaceae using chromogenic media with a broth enrichment. Diagn Microbiol Infect Dis 2015;82:284–5.
Hoyos-Mallecot Y, Naas T, Bonnin RA, Patino R, Glaser P, Fortineau N, et al. OXA-244-producing Escherichia coli isolates, a challenge for clinical microbiology laboratories. Antimicrob Agents Chemother 2017;61:pii: e00818–17.
Jayol A, Poirel L, André C, Dubois V, Nordmann P.Detection of colistin-resistant gram-neg-ative rods by using the SuperPolymyxin medium. Diagn Microbiol Infect Dis 2018;92: 95–101.
Jazmati N, Jazmati T, Hamprecht A.Importance of pre-enrichment for detection of third-generation cephalosporin-resistant Enterobacteriaceae (3GCREB) from rectal swabs. Eur J Clin Microbiol Infect Dis 2017;36:1847–51.
Murk JLA, Heddema ER, Hess DL, Bogaards JA, Vandenbroucke-Grauls CM, Debets-Ossenkopp YJ.Enrichment broth improved detection of extended-spectrum-β-lactamase-producing bacteria in throat and rectal surveillance cultures of samples from patients in intensive care units. J Clin Microbiol 2009;47:1885–7.
Nordmann P, Girlich D, Poirel L.Detection of carbapenemase producers in Entero-bacteriaceae by use of a novel screening medium. J Clin Microbiol 2012;50: 2761–6.
Nordmann P, Jayol A, Poirel L.A universal culture medium for screening polymyxin-resistant Gram-negative isolates. J Clin Microbiol 2016;54:1395–9.
Novicki TJ, Shapiro JM, Ulness BK, Sebeste A, Busse-Johnston L, Swanson KM, et al.
Convenient selective differential broth for isolation of broth of vancomycin-resistant enterococcus from fecal material. J Clin Microbiol 2004;42:1637–40.
Palladino S, Kay ID, Flexman JP, Boehm I, Costa AM, Lambert EJ, et al.Rapid detection of of vanA and vanB genes directly from clinical specimens and enrichment broths by real-time multiplex assay. J Clin Microbiol 2003;41:2483–6.
Poirel L, Jayol A, Nordmann P.Polymyxins: antibacterial activity, susceptibility testing, and resistance mechanisms encoded by plasmids or chromosomes. Clin Microbiol Rev 2017;30:557–96.
Potron A, Poirel L, Nordmann P.Characterization of OXA-244, a chromosomally-encoded OXA-48 likeβ-lactamase from Escherichia coli. Int J Antimicrob Agents 2016;47:102–3.
Simner P, Martin I, Opene B, Tamma PD, Karoll KC, Milstone AM.Evaluation of multiple methods for detection of gastro-intestinal colonization of carbapenem-resistant organisms from rectal swabs. J Clin Microbiol 2016; 54:1664–7.
Viau R, Frank KM, Jacobs MR, Wilson B, Kaye K, Donskey CJ, et al.Intestinal carriage of carbapenemase-producing organisms: current status of surveillance methods. Clin Microbiol Rev 2016;29:1–27.
Table 4
Evaluation of direct plating on VRE agar plates of spiked stools, with and without an 18-h enrichment step in TSB and selective enrichment in TSB+ vancomycin (VAN) at 1μg/mL for the detection of VRE.
Strain Species Resistance mechanism MIC of vancomycin (μg/mL) VRE Agar (CFU/mL) Enrichment brotha (CFU/mL) TSB TSB + VAN
R2953 Enterococcus faecalis VanB 64 4.7 × 102
4.85 × 107
5.9 × 107
R2961 Enterococcus faecium VanA 256 5.1 × 102
1.2 × 108
1.77 × 108
R2147 Enterococcus faecalis VanB 96 7 × 101 7 × 105 1 × 107
R2148 Enterococcus faecalis VanA 256 5 × 101 2.6 × 107 1 × 107
R2150 Enterococcus faecium VanB 12 8 × 101
1.8 × 107
3 × 108
R2152 Enterococcus faecium VanA 256 1 × 102
3.1 × 106
2 × 107
4
