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

Norihisa Yamamoto,Yukihiro Akeda,Rumiko Asada,Rathina Kumar Shanmugakani,Kazunori Tomono,Kazuhiro Maeda,Yumi Sasaki,Shigeyuki Hamada,Isao Nishi,Satomi Yukawa,Ryuji Kawahara,Noriko Sakamoto,Naohiro Hara,Hisao Yoshida,Hideharu Hagiya

doi:10.1186/s12879-017-2312-1

Abstract

BackgroundIdentification of carbapenemase-producing Enterobacteriaceae (CPE) in faecal specimens is challenging. This fact is particularly critical because low-level carbapenem-resistant organisms such as IMP-producing CPE are most prevalent in Japan. We developed a modified selective medium more suitable for IMP-type CPE.MethodsFifteen reference CPE strains producing different types of β-lactamases were used to evaluate the commercially available CHROMagar KPC and chromID CARBA as well as the newly prepared MC-ECC medium (CHROMagar ECC supplemented with meropenem, cloxacillin, and ZnSO4) and M-ECC medium (CHROMagar ECC supplemented with meropenem and ZnSO4). A total of 1035 clinical samples were then examined to detect CPE using chromID CARBA and M-ECC medium.ResultsAll tested strains producing NDM-, KPC-, and OXA-48-carbapenemases were successfully cultured in the media employed. Although most of the IMP-positive strains did not grow in CHROMagar KPC, chromID CARBA, or MC-ECC, all tested strains grew on M-ECC. When faecal samples were applied to the media, M-ECC medium allowed the best growth of IMP-type CPE with a significantly higher sensitivity (99.3%) than that of chromID CARBA (13.9%).ConclusionsM-ECC medium was determined as the most favourable selective medium for the detection of IMP-type CPE as well as other types of CPE.

Highlights

Identification of carbapenemase-producing Enterobacteriaceae (CPE) in faecal specimens is challenging
We evaluated three major selective media, the chromID CARBA, CHROMagar KPC, and MC-ECC that was made in reference to SuperCarba medium [15]
The NDM, KPC, and OXA-48-positive strains were recovered with both chromID CARBA and CHROMagar

Summary

Introduction

Identification of carbapenemase-producing Enterobacteriaceae (CPE) in faecal specimens is challenging. This fact is critical because low-level carbapenem-resistant organisms such as IMP-producing CPE are most prevalent in Japan. Isolation of CPE from faecal specimens is difficult because CPE usually exists as a small proportion of the overall bacterial load [4, 5]. The sensitivity of screening largely depends on the minimum inhibitory concentration (MIC) of the drug for the isolate and the bacterial load. This phenomenon is especially important in Japan because the most prevalent CPE in Japan are IMP-1 and IMP-6- types, which show low-level

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Conclusion