The Relationship Between Lipidome and Antibiotic Resistance

Antibiotic resistance is a serious threat which could reduce the body sensitivity to the drugs. The Centers for Disease and Control (CDC) in  the United States reported and listed several antibiotic-resistant pathogens which are considered threats, such as Carbapenem-resistant Acinetobacter, Candida aureus, Clostridioides difficile, Drug-resistant Neisseria gonorrhoeae and Methicillin-resistant Staphylococcus aureus (MRSA), among which MRSA is the most serious threats.

In 2018, CDC in the US reported five core actions to help slow down and prevent antibiotic-resistant pathogens in the future, including Infection Prevention and Control, Tracking and Data, Antibiotic Use and Access, Vaccines, Therapeutics and Diagnostics and Environment and Sanitation.

In order to develop the new vaccines, improve existing therapeutics and find out better ways to diagnose infections caused by the pathogens, we need to fully understand the pathogens themselves. Researchers are interested in understanding the antibiotic resistance applying bioanalytical methods using ion mobility-mass spectrometry (IM-MS) to enhance lipidomics and metabolomics experiments. With the techniques, they could show us the metabolic change in antibiotic-resistant pathogens and test antibiotic sensibility and small molecule screening.

Staphylococcus aureus (S. aureus) has a complex lipidome compose of saturated-chain fatty acids (SCFAs) and branched-chain fatty acids (BCFAs). As the ratio of SCFA and BCFA determines the characteristics of the membrane, such as packing, rigidity, fluidity and net surface charge, the understanding of the ratio in diverse lipids is the key to developing the test of antibiotic sensibility and screening small molecules. Previously, gas chromatography in the form of fatty acid methyl esters (GC-FAME) and reversed-phase liquid chromatography-mass spectrometry (RPLC-MS) were used to separate and quantify fatty acid isomers. However, both of the methods require the fatty acids to be separated from the backbone of the glycerol which eliminates the information of fatty acids distributed among various lipids. Besides, eukaryotes do not have high concentrations of BCFAs. The high concentration of diverse BCFAs in S. aureus provides a great opportunity for the study of alternative methods to identify and quantify SCFAs and BCFAs.

In a word, the researchers accurately assigned glycerol backbone positions of fatty acids using RPLC, a commonly used separating technique, and ion mobility separation technique. In addition, by using isotopically labelled exogenous SCFAs and endogenous BCFAs, they confirmed that lipids containing two BCFAs elute before lipids containing one BCFA and one SCFA, and those elute before lipids containing two SCFAs. The method can also help distinguish the iso- and anteiso-forms of BCFAs almost to a baseline level. What is the most important is that the method does not need to remove the fatty acids from glycerol backbone through hydrolysis and all the information that comes from lipids can be retained.

Nowadays, the technique can be used to study the fatty acid composition of many pathogens. By understanding more about their lipidome and metabolome, we could develop more vaccines, therapeutic methods and diagnostic tools that could prevent us from antibiotic resistant infections in the future.

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