Abstract
In vitro cultivation of staphylococci is fundamental to both clinical and research microbiology, but few studies, to-date, have investigated how the differences in rich media can influence the volatilome of cultivated bacteria. The objective of this study was to determine the influence of rich media composition on the chemical characteristics of the volatilomes of Staphylococcus aureus and Staphylococcus epidermidis. S. aureus (ATCC 12600) and S. epidermidis (ATCC 12228) were cultured in triplicate in four rich complex media (brain heart infusion (BHI), lysogeny broth (LB), Mueller Hinton broth (MHB), and tryptic soy broth (TSB)), and the volatile metabolites produced by each culture were analyzed using headspace solid-phase microextraction combined with comprehensive two-dimensional gas chromatography—time-of-flight mass spectrometry (HS-SPME-GC×GC-TOFMS). When comparing the chemical compositions of the staph volatilomes by the presence versus absence of volatiles produced in each medium, we observed few differences. However, when the relative abundances of volatiles were included in the analyses, we observed that culturing staph in media containing free glucose (BHI and TSB) resulted in volatilomes dominated by acids and esters (67%). The low-glucose media (LB and MHB) produced ketones in greatest relative abundances, but the volatilome compositions in these two media were highly dissimilar. We conclude that the staphylococcal volatilome is strongly influenced by the nutritional composition of the growth medium, especially the availability of free glucose, which is much more evident when the relative abundances of the volatiles are analyzed, compared to the presence versus absence.
Highlights
In vitro cultivation of staphylococci is fundamental to both clinical and research microbiology, and the selection of growth medium substantially influences staph growth rates, genetic integrity, pathogenicity, and metabolic capacity [1,2,3,4,5]
Sixty-eight compounds from this study were named for the first time as volatile metabolites of either S. aureus (n = 9), S. epidermidis (n = 37), or both (n = 22), and 12 of them have not been previously described for any bacterium (Table 1)
In the glucose-free media of lysogeny broth (LB) and Mueller Hinton broth (MHB), we observed substantial media-dependent differences in the volatilome chemical composition, while in brain heart infusion (BHI) and tryptic soy broth (TSB) media containing free glucose, half or more of the volatilome was comprised of acids and esters, and the remaining portion was of unique chemical composition by the medium
Summary
In vitro cultivation of staphylococci is fundamental to both clinical and research microbiology, and the selection of growth medium substantially influences staph growth rates, genetic integrity, pathogenicity, and metabolic capacity [1,2,3,4,5]. Staph is able to survive under host sequestration ( known as nutritional immunity) and microbial competition, both of which influence the availability of essential nutrients and carbon sources [1,4,6,7,8,9,10,11,12,13,14,15]. Glucose is the preferred carbon and energy source for staphylococci, which employ catabolite repression control to regulate metabolism in glucose-rich environments. Under catabolite repression control in glucose-replete conditions, the tricarboxylic acid cycle is markedly downregulated, forcing catabolism through the Embden–Meyerhof–Parnas pathway (EMP; glycolysis) and the pentose phosphate pathway (PPP) [16,17,18,19]. Once glucose and other hexose sugars are depleted, other nutrient sources, such as Metabolites 2020, 10, 347; doi:10.3390/metabo10090347 www.mdpi.com/journal/metabolites
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