Project description:Recently, we have reported on a highly drug-resistant carbapenemase-producing isolate of Enterobacter cloacae (Nepal et al., Virulence. 2018; 9: 1377-1389). In the present study, we asked the question whether and, if so, how this isolate responds to a sub-inhibitory challenge with the antibiotic imipenem. To answer this question, we applied a SILAC proteomics approach that allowed the quantification of changes in the relative abundance of bacterial protein in response to imipenem. The results show that the investigated E. cloacae isolate mounts a highly specific response to counteract the detrimental effects of imipenem.
Project description:Background: Efflux pumps are important cofactors for carbapenem resistance in Enterobacter cloacae. The regulatory mechanism by which asmA influences efflux pump function in this species remains unclear. This study explored the regulatory role of asmA on efflux pumps in carbapenem-resistant Enterobacter cloacae. Results: Sixteen carbapenem-resistant Enterobacter cloacae were collected. All strains carried blaNDM, 87.5% of which were blaNDM-1 and 12.5% were blaNDM-5. PAβN had weak inhibition on carbapenem resistance in ST78 and strong inhibition in ST2260. ST2260(CY-8) was still resistant to carbapenems after elimination of blaNDM and could be inhibited by PAβN. However, ST78(CY-9) lost its resistance to carbapenems. Knockout of asmA reduced the MIC of ST2260 by 16-fold. ST78 showed no such changes. Growth curves revealed impaired growth only in ST2260ΔasmA. Transcriptomics/qRT-PCR revealed no significantly altered acrAB-tolC or marA expression in either strain. Membrane proteomics detected AcrB loss specifically in ST2260ΔasmA. The loss of asmA affected a wide range of membrane proteins, especially OmpW. Molecular docking predicted that AsmA could bind to AcrB, with stronger binding energy in ST78. The buried area of the CY-8 model involved 110 contact residues, while the number of contacts of the CY-9 model increased to 144. The AsmA chain of the two models had 46 common contact residues, and the AcrB chain had 60 common contact residues. AcrB of ST78 generally carries the I277V mutation. Conclusion: asmA is highly conserved in Enterobacter cloacae. It has functional heterogeneity in different ST types. In ST2260, asmA can affect efflux pump-mediated carbapenem resistance. AsmA can regulate AcrAB-TolC not by affecting marA. It is predicted that AsmA can maintain the carbapenem resistance of Enterobacter cloacae ST2260 by helping AcrB anchor to the inner membrane. The difference in carbapenem resistance mediated by efflux pumps between ST78 and ST2260 suggests that ST78 commonly carries the AcrB I277V mutation, which is a key site for efflux of β-lactams.
Project description:Enterobacter cloacae is a Gram-negative nosocomial pathogen of the ESKAPE (Enterococcus, Staphylococcus, Klebsiella, Acinetobacter, Pseudomonas, and Enterobacter spp.) priority group with increasing multi-drug resistance via the acquisition of resistance plasmids. However, E. cloacae can also display forms of antibiotic refractoriness, such as heteroresistance and tolerance. Here, we report that E. cloacae displays transient heteroresistance to aminoglycosides, which is accompanied with the formation of small colony variants (SCVs) with increased minimum inhibitor concentration (MIC) of gentamicin and other aminoglycosides used in the clinic, but not other antibiotic classes. To explore the underlying mechanisms, we performed RNA sequencing of heteroresistant bacteria, which revealed global gene-expression changes and a signature of the CpxRA cell envelope stress response. Deletion of the cpxRA two-component system abrogated aminoglycoside heteroresistance and SCV formation, pointing to its indispensable role in these processes. The introduction of a constitutively active allele of cpxA led to high aminoglycoside MICs, consistent with cell envelope stress response driving these behaviours in E. cloacae. Cell envelope stress can be caused by environmental cues, including heavy metals. Indeed, bacterial exposure to copper increased gentamicin MIC in the wild-type, but not in the ΔcpxRA mutant. Moreover, copper exposure also elevated the gentamicin MICs of clinical isolates from bloodstream infections, suggesting that CpxRA- and copper-dependent aminoglycoside resistance is broadly conserved in E. cloacae strains. Altogether, we establish that E. cloacae relies on transcriptional reprogramming via the envelope stress response pathway for transient resistance to a major class of frontline antibiotic.