Lytic transglycosylase contributes to the survival of lipooligosaccharide-deficient, colistin-dependent Acinetobacter baumannii

J-Y Lee; H Lee; M Park; C-J Cha; D Shin; K S Ko

doi:10.1016/j.cmi.2019.02.004

Lytic transglycosylase contributes to the survival of lipooligosaccharide-deficient, colistin-dependent Acinetobacter baumannii

Clin Microbiol Infect. 2019 Sep;25(9):1156.e1-1156.e7. doi: 10.1016/j.cmi.2019.02.004. Epub 2019 Feb 18.

Authors

J-Y Lee¹, H Lee², M Park³, C-J Cha⁴, D Shin², K S Ko⁵

Affiliations

¹ Division of Antimicrobial Resistance, Korea Centers for Disease Control and Prevention, Cheongju, South Korea.
² Department of Molecular Cell Biology and Samsung Medical Center, Sungkyunkwan University School of Medicine, Suwon, South Korea.
³ Department of Integrative Biotechnology, College of Biotechnology and Bioengineering, Sungkyunkwan University, Suwon, South Korea.
⁴ Department of Systems Biotechnology, Chung-Ang University, Anseong, South Korea.
⁵ Department of Molecular Cell Biology and Samsung Medical Center, Sungkyunkwan University School of Medicine, Suwon, South Korea. Electronic address: ksko@skku.edu.

PMID: 30790686
DOI: 10.1016/j.cmi.2019.02.004

Abstract

Objectives: The phenomenon of colistin dependence in Acinetobacter baumannii has been described in a situation in which colistin is now considered as the last resort for the treatment of infections caused by multidrug-resistant Gram-negative bacteria. In this study, we aimed to reveal a gene associated with colistin dependence in A. baumannii.

Methods: The colistin-dependent A. baumannii H08-391D strain was isolated from a patient, and target gene-inactivation mutants were constructed. We investigated the effects of target gene on colistin dependence with quantitative real-time PCR and endotoxin assay. Also, we observed the change of cell morphology by electron microscopy.

Results: The expression of ACICU_02898, encoding a soluble lytic transglycosylase associated with cell-wall degradation and recycling, was increased by eight-to 42-fold in colistin-dependent mutants, and deletion of ACICU_02898 in a colistin-dependent strain led to colistin susceptibility (MIC = 8 mg/L). Endotoxin activity was significantly low in a colistin-dependent derivative ACICU_02898-inactivated mutant and a complemented mutant. In addition, the ACICU_02898-inactivated mutant showed a highly reduced growth rate. The colistin-dependent derivative and ACICU_02898-inactivated mutant showed clearly distinguished absorption profiles in the red/green fluorescence dot blot with regard to their membrane potential. Electron microscopy revealed that the deletion mutant cells were elongated compared to the colistin-susceptible wild-type strain and colistin-dependent strain.

Conclusions: A colistin-dependent A. baumannii strain exhibited a deficiency in its outer membrane integrity and high expression of lytic transglycosylase was required for survival. This study reveals why the colistin-dependent mutant can tolerate high antibiotic concentrations.

Keywords: Acinetobacter baumannii; Colistin dependence; Lytic transglycosylase; relA; spoT.

MeSH terms

Acinetobacter Infections / microbiology
Acinetobacter baumannii / drug effects
Acinetobacter baumannii / enzymology*
Acinetobacter baumannii / genetics
Acinetobacter baumannii / growth & development*
Anti-Bacterial Agents / metabolism*
Anti-Bacterial Agents / pharmacology
Cell Membrane / physiology
Colistin / metabolism*
Colistin / pharmacology
Drug Resistance, Multiple, Bacterial / genetics
Endotoxins / metabolism
Gene Expression Regulation, Bacterial
Glycosyltransferases / genetics*
Humans
Lipopolysaccharides / deficiency
Microbial Sensitivity Tests
Microbial Viability
Mutation

Substances

Anti-Bacterial Agents
Endotoxins
Lipopolysaccharides
lipid-linked oligosaccharides
Glycosyltransferases
murein transglycosylase
Colistin