Computerised gas-liquid chromatography of bacterial cellular fatty acids in analysis of bacterial mixtures

A simple and fast method for metabolomic analysis by gas liquid chromatography-mass spectrometry

INTRODUCTION

The metabolomic profile is an essential tool for understanding the physiological processes of biological samples and their changes. In addition, it makes it possible to find new substances with industrial applications or use as drugs. As GC-MS is a very common tool for obtaining the metabolomic profile, a simple and fast method for sample preparation is required.

OBJECTIVES

The aim of this research was to develop a direct derivatization method for GC-MS to simplify the sample preparation process and apply it to a wide range of samples for non-targeted metabolomic analysis purposes.

METHODS

One pot combined esterification of carboxylic acids with methanol and silylation of the hydroxyl groups was achieved using a molar excess of chlorotrimethylsilane with respect to methanol in the presence of pyridine.

RESULTS

The metabolome profile obtained from different samples, such as bilberry and cherry cuticles, olive leaves, P. aeruginosa and E. coli bacteria, A. niger fungi and human sebum from the ceruminous gland, shows that the procedure allows the identification of a wide variety of metabolites. Aliphatic fatty acids, hydroxyfatty acids, phenolic and other aromatic compounds, fatty alcohols, fatty aldehydes dimethylacetals, hydrocarbons, terpenoids, sterols and carbohydrates were identified at different MSI levels using their mass spectra.

CONCLUSION

The metabolomic profile of different biological samples can be easily obtained by GC-MS using an efficient simultaneous esterification-silylation reaction. The derivatization method can be carried out in a short time in the same injection vial with a small amount of reagents.

Identification and characterization of Streptococcus agalactiae isolates using 16S rRNA sequencing and cellular fatty acid composition analysis

This study was undertaken to apply 16S rRNA sequence and Cellular Fatty Acid (CFA) composition analysis techniques for the identification and characterization of seven individual bacteria isolates obtained from seven infected fish samples. All samples were cultured on brain heart infusion agar. All the seven isolates were Gram positive and were identified as Streptococcus sp. The 16S rRNA sequencing method yielded about 1500 bps for each strain where upon the sequence was compared to nucleotide data in Gene Bank using BLASTN 2.2.1 sequence alignment from NCBI for the nucleotide comparison. The 16S rRNA gene sequence for all the seven samples had no sequence variation between the isolates and gave a 100% similarity to plus, plus strand with Streptococcus agalactiae strain A909 Accession number NC_007432.1 and S. agalactiae strain H36B (Accession number AAJS01000007). Also the 16S rRNA sequence showed a high (92-93%) similarity between S. agalactiae and S. equi, S. suis and S. uberis. All strains appeared to be nearly identical to each other after CFA analysis using Library Generation System (LGS) software (MIDI) and were consistent to that of S. agalactiae ATCC 12386, the CFA analysis not only confirmed the results of 16S rRNA sequence but also indicated a possibility of single source of infection. Despite their accuracy to identify the poorly described, rarely isolated, or phenotypically aberrant strains, 16S rRNA gene sequence analysis and CFA analysis lacks widespread use beyond the large and reference laboratories because of technical and cost considerations.

Identifying bacteria in human urine: current practice and the potential for rapid, near-patient diagnosis by sensing volatile organic compounds

Urinary tract infection (UTI) represents a significant burden for the National Health Service. Extensive research has been directed towards rapid detection of UTI in the last thirty years. A wide range of microbiological and chemical techniques are now available to identify and quantify bacteria in urine. However, there is a clear and present need for near, rapid, sensitive, reliable analytical methods, preferably with low-running costs, that could allow early detection of UTI and other diseases in urine. Here we review the "state of the art" of current practice for the detection of bacteria in urine and describe the advantages of the recent "e-nose" technology as a potential tool for rapid, near-patient diagnosis of UTI, by sensing volatile organic compounds (VOCs).

Stability of cyclopropane and conjugated linoleic acids during fatty acid quantification in lactic acid bacteria

Seven methods commonly used for fatty acid analysis of microorganisms and foods were compared to establish the best for the analysis of lyophilized lactic acid bacteria. One of these methods involves fat extraction followed by methylation of fatty acids, while the other methods use a direct methylation of the samples, under different operating conditions (e.g., reaction temperature and time, reagents, and pH). Fatty acid methyl esters were identified by gas chromatography-mass spectrometry and quantified by on-column capillary gas chromatography. Two reliable methods for the analysis of fatty acids in bacteria were selected and further improved. They guarantee high recovery of classes of fragile fatty acids, such as cyclopropane and conjugated acids, and a high degree of methylation for all types of fatty acid esters. These two direct methylation methods have already been successfully applied to the analysis of fatty acids in foods. They represent a rapid and highly reliable alternative to classical time- and solvent-consuming methods and they give the fatty acid profile and the amount of each fatty acid. Using these methods, conjugated linoleic acids were identified and quantified in lactic acid bacteria.