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First Report of bla IMP-4 and bla SRT-2 Coproducing Serratia marcescens Clinical Isolate in China
Xiangning Huang1, Siquan Shen2,3, Qingyu Shi2,3
1Department of Laboratory Medicine, Sichuan Provincial People's Hospital, University of Electronic Science and Technology of China, Chengdu, China.
Abstract:
Carbapenem-resistant Enterobacterales (CRE) has become a major therapeutic concern in clinical settings, and carbapenemase genes have been widely reported in various bacteria. In Serratia marcescens, class A group carbapenemases including SME and KPC were mostly identified. However, there are few reports of metallo-β-lactamase-producing S. marcescens. Here, we isolated a carbapenem-resistant S. marcescens (S378) from a patient with asymptomatic urinary tract infection which was then identified as an IMP-4-producing S. marcescens at a tertiary hospital in Sichuan Province in southwest of China. The species were identified using MALDI-TOF MS, and carbapenemase-encoding genes were detected using PCR and DNA sequencing. The results of antimicrobial susceptibility testing by broth microdilution method indicated that the isolate S. marcescens S378 was resistant to meropenem (MIC = 32 μg/ml) and imipenem (MIC = 64 μg/ml) and intermediate to aztreonam (MIC = 8 μg/ml). The complete genomic sequence of S. marcescens was identified using Illumina (Illumina, San Diego, CA, United States) short-read sequencing (150 bp paired-end reads); five resistance genes had been identified, including bla IMP-4, bla SRT-2, aac(6')-Ic, qnrS1, and tet(41). Conjugation experiments indicated that the bla IMP-4-carrying plasmid pS378P was conjugative. Complete sequence analysis of the plasmid pS378P bearing bla IMP-4 revealed that it was a 48,780-bp IncN-type plasmid with an average GC content of 50% and was nearly identical to pP378-IMP (99% nucleotide identity and query coverage).
Insights
Carbapenem-resistant Enterobacterales (CRE) are a growing threat. This study identifies a novel IMP-4-producing Serratia marcescens strain, highlighting the emergence of metallo-beta-lactamase-producing S. marcescens.
Area of Science:
- Microbiology
- Genetics
- Infectious Diseases
Background:
- Carbapenem-resistant Enterobacterales (CRE) pose a significant clinical challenge.
- Serratia marcescens typically harbors Class A carbapenemases; metallo-beta-lactamase (MBL) producers are less common.
- The emergence of MBL-producing S. marcescens warrants investigation due to treatment implications.
Purpose of the Study:
- To characterize a carbapenem-resistant Serratia marcescens isolate.
- To identify the carbapenemase genes and mobile genetic elements involved in resistance.
- To assess the antimicrobial susceptibility profile of the identified strain.
Main Methods:
- Species identification using MALDI-TOF MS.
- Detection of carbapenemase genes via PCR and DNA sequencing.
- Antimicrobial susceptibility testing using broth microdilution.
- Whole-genome sequencing and plasmid analysis (Illumina).
- Conjugation experiments to assess plasmid transfer.
Main Results:
- An IMP-4-producing Serratia marcescens strain (S378) was isolated from an asymptomatic UTI patient in China.
- The isolate exhibited resistance to meropenem and imipenem, and intermediate resistance to aztreonam.
- Whole-genome sequencing revealed five resistance genes, including bla_IMP-4, bla_SRT-2, aac(6')-Ic, qnrS1, and tet(41).
- The bla_IMP-4 gene was located on a conjugative IncN-type plasmid (pS378P), highly similar to pP378-IMP.
Conclusions:
- This study reports the first isolation of an IMP-4-producing Serratia marcescens in China.
- The presence of a conjugative IncN plasmid carrying bla_IMP-4 facilitates the potential spread of carbapenem resistance.
- This finding underscores the need for enhanced surveillance of MBL-producing S. marcescens.
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