Small Changes in Environmental Parameters Lead to Alterations in Antibiotic Resistance, Cell Morphology and Membrane Fatty Acid Composition in Staphylococcus lugdunensis

Abstract

Staphylococcus lugdunensis has emerged as a major cause of community-acquired and nosocomial infections. This bacterium can rapidly adapt to changing environmental conditions to survive and capitalize on opportunities to colonize and infect through wound surfaces. It was proposed that S. lugdunensis would have underlying alterations in metabolic homeostasis to provide the necessary levels of adaptive protection. The aims of this project were to examine the impacts of subtle variations in environmental conditions on growth characteristics, cell size and membrane fatty acid composition in S. lugdunensis. Liquid broth cultures of S. lugdunensis were grown under varying combinations of pH (6–8), temperature (35–39°C) and osmotic pressure (0–5% sodium chloride w/w) to reflect potential ranges of conditions encountered during transition from skin surfaces to invasion of wound sites. The cells were harvested at the mid-exponential phase of growth and assessed for antibiotic minimal inhibitory concentration (MIC), generation time, formation of small colony variants, cell size (by scanning electron microscopy) and membrane fatty acid composition. Stress regimes with elevated NaCl concentrations resulted in significantly higher antibiotic resistance (MIC) and three of the combinations with 5% NaCl had increased generation times (P<0.05). It was found that all ten experimental growth regimes, including the control and centroid cultures, yielded significantly different profiles of plasma membrane fatty acid composition (P<0.0001). Alterations in cell size (P<0.01) were also observed under the range of conditions with the most substantial reduction occurring when cells were grown at 39°C, pH 8 (514±52 nm, mean ± Standard Deviation) compared with cells grown under control conditions at 37°C with pH 7 (702±76 nm, P<0.01). It was concluded that S. lugdunensis responded to slight changes in environmental conditions by altering plasma membrane fatty acid composition, growth rates and morphology to achieve optimal adaptations for survival in changing environments.

The Bacterial Alarmone (p)ppGpp Activates the Type III Secretion System in Erwinia amylovora

“…Similarly, ppGpp mutant cells of E. coli were considerably longer than WT cells when cultured under starvation conditions (49). It has also been reported that cells of smaller sizes become increasingly resistant to abiotic stresses, including osmotic and oxidative stresses, thus enhancing their ability to survive under harsh environmental conditions (33,36,(68)(69)(70). This may provide an explanation for why dksA and ppGpp 0 mutants fail to grow in HMM, suggesting that E. amylovora might require both ppGpp and DksA to coregulate cell size and resistance to environmental stresses, thus contributing to overall survival (59).…”

“…In general, ppGpp directly interacts with the interface of the ␤= and subunits of RNAP to orchestrate fine-tuning of cellular processes through direct inhibition and activation of genes (26)(27)(28), whereas the DksA protein, which binds to the RNAP secondary channel, greatly enhances the effect of ppGpp by modulating the direct interaction between RNAP and ppGpp (18,28). In addition, ppGpp inhibits RNAP binding to 70 -dependent stringent promoters, thus indirectly allowing RNAP to bind to alternative sigma factors, such as RpoN, and promoting the expression of alternative sigma factor-dependent genes (19,29). Importantly, inhibition of 70 binding by ppGpp is transient and reversible, thus enabling rapid and reversible control of stress response genes (17).…”

“…In addition, ppGpp inhibits RNAP binding to 70 -dependent stringent promoters, thus indirectly allowing RNAP to bind to alternative sigma factors, such as RpoN, and promoting the expression of alternative sigma factor-dependent genes (19,29). Importantly, inhibition of 70 binding by ppGpp is transient and reversible, thus enabling rapid and reversible control of stress response genes (17).…”

Amino acids and proteomic acclimation of Staphylococcus aureus when incubated in a defined minimal medium supplemented with 5% sodium chloride

“…The changes observed in the metabolome and proteome may represent a phenotypic shift that can occur within an existing population of cells without cell division. Such a shift may be indicative, for example, of the formation of small colony variants that have been previously shown to form in response exposures to NaCl, with accompanying reduced metabolism compared to wild‐type bacteria (Crompton et al, ; Onyango et al, ; Proctor et al, ; von Eiff, ). Prior investigations have shown that small colony variants have slower growth rates, reduced production of virulence factors and some are auxotrophic for important compounds such as haemin and menadione (Bui et al, ; Moisan et al, ; Proctor et al, ; von Eiff et al, ).…”

Maximising the potential for bacterial phenotyping using time‐of‐flight secondary ion mass spectrometry with multivariate analysis and Tandem Mass Spectrometry

“…high osmotic pressure, the properties of the bacterial cell envelope may be altered in a way that contributes to persistence and the development of resistance. [1,2] To identify such phenotypic alterations in the cell envelope of intact bacterial cells, time-of-flight secondary ion mass spectrometry (ToF-SIMS) appears to be a promising method as it is uniquely capable of probing the chemistry in this region. Investigation of bacterial surfaces may also include bacterial biofilms, which are amorphous and dynamic bacterial community structures.…”