Sphingoid Bases Are Taken Up by Escherichia coli and Staphylococcus aureus and Induce Ultrastructural Damage

Abstract

Sphingoid bases found in the outer layers of the skin exhibit antimicrobial activity against gram-positive and gram-negative bacteria. We investigated the uptake of several sphingoid bases by Escherichia coli and Staphylococcus aureus, and assessed subsequent ultrastructural damage. E. coli and S. aureus were incubated with <smlcap>d</smlcap>-sphingosine, dihydrosphingosine, or phytosphingosine at ten times their MIC for 0.5 and 4 h, respectively, to kill 50% of viable bacteria. Treated bacterial cells were immediately prepared for SEM, TEM, and analyzed for lipid content by QTLC. E. coli and S. aureus treated with sphingoid bases were distorted and their surfaces were concave and rugate. Significant differences were observed in the visual surface area relative to controls for both E. coli and S. aureus when treated with dihydrosphingosine and sphingosine (p < 0.0001) but not phytosphingosine. While sphingoid base-treated S. aureus exhibited disruption and loss of cell wall and membrane, E. coli cytoplasmic membranes appeared intact and the outer envelope uncompromised. Both E. coli and S. aureus cells contained unique internal inclusion bodies, likely associated with cell death. QTLC demonstrated extensive uptake of sphingoid bases by the bacteria. Hence, sphingoid bases induce both extracellular and intracellular damage and cause intracellular inclusions that may reflect lipid uptake.

Lack of Sphingosine Causes Susceptibility to Pulmonary Staphylococcus Aureus Infections in Cystic Fibrosis

“…Further, the exact mechanism of the antibacterial activity of sphingoid bases is still unclear. Electron microscopy of sphingosine-treated S. aureus revealed multiple lesions of cell wall, membrane evaginations, loss of ribosomes and leakage of cellular debris trough gaps in the wall [34,35]. In addition Fischer and colleagues (2013) demonstrated extensive uptake of sphingoid bases by bacteria and detected internal inclusion bodies, likely associated with cell death, but it is unknown whether such an uptake of sphingosine by the pathogen occurs in vivo after contact of the pathogen with mammalian membranes [35].…”

“…It is suspected that the positive charge of the nitrogen atom of sphingoid bases is relevant for the antibacterial effect of sphingosine [13,17,35]. The following observations support this hypothesis: First, an increase of the pH value (pH > 8) and consequent deprotonation of the sphingoid base lead to loss of antibacterial activity [17].…”

Ceramide and sphingosine in pulmonary infections

“…burgdorferi, and H. influenzae (Pewzner-Jung et al, 2014). At present it is unknown how sphingosine kills pathogens, although recently published findings suggest that sphingosine causes ultrastructural damage in E. coli and S. aureus (Fischer et al, 2013). Many details about this activity of sphingosine remain to be identified.…”

Antimicrobial Role of Human Meibomian Lipids at the Ocular Surface

“…19 Sphingoid bases found in skin also cause similar intracellular and extracellular damage to S. aureus, which has been revealed by SEM. 44 The mechanism of antimicrobial action of meibomian lipids would be difficult to predict due to its mixture nature. However, knowledge of the action of different lipid classes can help in understanding the likely effect of these lipids on bacteria.…”