Identification of unique cardiolipin and monolysocardiolipin species in Acinetobacter baumannii

Patrizia Lopalco,Cosimo Annese,Beate Averhoff,Angela Corcelli,Julia Stahl

doi:10.1038/s41598-017-03214-w

Abstract

Acidic glycerophospholipids play an important role in determining the resistance of Gram-negative bacteria to stress conditions and antibiotics. Acinetobacter baumannii, an opportunistic human pathogen which is responsible for an increasing number of nosocomial infections, exhibits broad antibiotic resistances. Here lipids of A. baumannii have been analyzed by combined MALDI-TOF/MS and TLC analyses; in addition GC-MS analyses of fatty acid methyl esters released by methanolysis of membrane phospholipids have been performed. The main glycerophospholipids are phosphatidylethanolamine, phosphatidylglycerol, acyl-phosphatidylglycerol and cardiolipin together with monolysocardiolipin, a lysophospholipid only rarely detected in bacterial membranes. The major acyl chains in the phospholipids are C16:0 and C18:1, plus minor amounts of short chain fatty acids. The structures of the cardiolipin and monolysocardiolipin have been elucidated by post source decay mass spectrometry analysis. A large variety of cardiolipin and monolysocardiolipin species were found in A. baumannii. Similar lysocardiolipin levels were found in the two clinical strains A. baumannii ATCC19606T and AYE whereas in the nonpathogenic strain Acinetobacter baylyi ADP1 lysocardiolipin levels were highly reduced.

Highlights

Acinetobacter baumannii is a well-adapted hospital pathogen responsible for an increasing number of intensive care unit (ICU)-acquired pneumonia cases, as well as wound, tissue and urinary tract infections[1,2,3]
In order to obtain detailed information on the lipid composition of A. baumannii ATCC 19606T, cells were grown in LB medium to the stationary phase, harvested and subjected to lipid extraction and the total lipid extract of A. baumannii was analyzed by MALDI-TOF/MS in the negative ion mode (Fig. 1)
By comparatively analysing the fragmentation patterns, we propose that the peak at m/z 1183.5 and 1293.6 correspond to a cardiolipin species carrying short fatty acid chains likely C12:0 and/or C14:0 in agreement with above gas chromatography with mass spectrometry (GC-MS) analyses

Summary

Introduction

Acinetobacter baumannii is a well-adapted hospital pathogen responsible for an increasing number of intensive care unit (ICU)-acquired pneumonia cases, as well as wound, tissue and urinary tract infections[1,2,3]. Survival in the human host, resistance to antibiotics and desiccation stress resistance are promoted by distinct features of the cell surface[7, 8]. In Gram-negative bacteria the outer membrane, consisting of a monolayer of glycerophospholipids and an exposed monolayer of lipopolysaccharides (LPS) serves as the outermost barrier restricting the transfer of toxic compounds and maintaining a hydrated layer around the cell thereby enhancing resistance to different environmental stresses. Lipid A alterations directly affect pathogenesis, by modifying the outer membrane permeability barrier and promoting resistance to antibiotics and desiccation[12, 13]. In the Gram-negative bacterium Salmonella thiphimurium, glycerophospholipids cooperate with lipid A to form a critical barrier for antibiotic resistance and intracellular survival in the host. Correspondence and requests for materials should be addressed to A.C

Methods

Results

Conclusion