title: Overexpression of an outer membrane protein associated with decreased susceptibility to carbapenems in Proteus mirabilis.
abstract: Proteus mirabilis isolates commonly have decreased susceptibility to imipenem. Previously, we found P. mirabilis hfq mutant was more resistant to imipenem and an outer membrane protein (OMP) could be involved. Therefore, we investigated the role of this OMP in carbapenem susceptibility. By SDS-PAGE we found this OMP (named ImpR) was increased in hfq mutant and LC-MS/MS revealed it to be the homologue of Salmonella YbfM, which is a porin for chitobiose and subject to MicM (a small RNA) regulation. We demonstrated that ImpR overexpression resulted in increased carbapenem MICs in the laboratory strain and clinical isolates. Chitobiose induced expression of chb (a chitobiose utilization operon). Real-time RT-PCR and SDS-PAGE were performed to elucidate the relationship of hfq, impR, chb and MicM in P. mirabilis. We found MicM RNA was decreased in hfq mutant and chbBC-intergenic region (chbBC-IGR) overexpression strain (chbIGRov), while impR mRNA was increased in hfq mutant, micM mutant and chbIGRov strain. In addition, mutation of hfq or micM and overexpression of chbBC-IGR increased ImpR protein level. Accordingly, chitobiose made wild-type have higher levels of ImpR protein and are more resistant to carbapenems. Hfq- and MicM-complemented strains restored wild-type MICs. Mutation of both impR and hfq eliminated the increase in carbapenem MICs observed in hfq mutant and ImpR-complementation of hfq/impR double mutant resulted in MICs as hfq mutant, indicating that the ImpR-dependent decreased carbapenem susceptibility of hfq mutant. These indicate MicM was antisense to impR mRNA and was negatively-regulated by chbBC-IGR. Together, overexpression of ImpR contributed to the decreased carbapenem susceptibility in P. mirabilis.
authors.affiliation: Department and Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Yi-Lin
authors.initials: YL
authors.lastname: Tsai
authors.affiliation: Department and Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Min-Cheng
authors.initials: MC
authors.lastname: Wang
authors.affiliation: Departments of Laboratory Medicine and Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Po-Ren
authors.initials: PR
authors.lastname: Hsueh
authors.affiliation: Department and Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Ming-Che
authors.initials: MC
authors.lastname: Liu
authors.affiliation: Department of Biomedical Informatics, Asia University, Taichung, Taiwan, Republic of China.
authors.forename: Rouh-Mei
authors.initials: RM
authors.lastname: Hu
authors.affiliation: Department of Applied Chemistry, National Chiao Tung University, Taiwan, Republic of China.
authors.forename: Yue-Jin
authors.initials: YJ
authors.lastname: Wu
authors.affiliation: Department and Graduate Institute of Clinical Laboratory Sciences and Medical Biotechnology, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China; Departments of Laboratory Medicine and Internal Medicine, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan, Republic of China.
authors.forename: Shwu-Jen
authors.initials: SJ
authors.lastname: Liaw
mesh_terms: D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D015780:Carbapenems / Q000494:pharmacology*; D002874:Chromosome Mapping; D015870:Gene Expression; D005798:Genes, Bacterial; D008826:Microbial Sensitivity Tests; D011513:Proteus mirabilis / Q000187:drug effects / Q000378:metabolism*; D018440:beta-Lactam Resistance
chemical_list: D001425:Bacterial Outer Membrane Proteins; D015780:Carbapenems