Discovery of potential anti-infectives against Staphylococcus aureus using a Caenorhabditis elegans infection model

Abstract

BackgroundThe limited antibiotic options for effective control of methicillin-resistant Staphylococcus aureus infections has led to calls for new therapeutic approaches to combat this human pathogen. An alternative approach to control MRSA is through the use of anti-infective agents that selectively disrupt virulence-mediated pathways without affecting microbial cell viability or by modulating the host natural immune defenses to combat the pathogen.MethodsWe established a C. elegans – S. aureus liquid-based assay to screen for potential anti-infectives against S. aureus. The assay was utilized to screen 37 natural extracts and 29 synthetic compounds for the ability to extend the lifespan of infected nematodes. Disc diffusion and MIC microdilution tests were used to evaluate the anti-microbial properties of these natural extracts and synthetic compounds whilst in vivo bacterial CFU within the C. elegans gut were also enumerated.ResultsWe screened a total of 37 natural extracts and 29 synthetic compounds for anti-infective properties. The screen successfully revealed 14 natural extracts from six plants (Nypa fruticans, Swietenia macrophylla, Curcuma longa, Eurycoma longifolia, Orthosiphon stamineus and Silybum eburneum) and one marine sample (Faunus ater) that improved the survival of S. aureus-infected worms by at least 2.8-fold as well as 14 synthetic compounds that prolonged the survival of S. aureus-infected nematodes by 4-fold or greater. An anti-microbial screen of all positive hits demonstrated that 8/28 hits had no effect on S. aureus growth. Of these 8 candidates, 5 of them also protected the worms from MRSA infection. We also noted that worms exposed to N. fruticans root and O. stamineus leaf extracts showed reduced intestinal colonization by live S. aureus. This suggests that these extracts could possibly activate host immunity to eliminate the bacteria or interfere with factor/s that prevents pathogen accumulation.ConclusionWe have successfully demonstrated the utility of this liquid-based screen to identify anti-infective substances that prolong S. aureus-infected host survival without affecting bacterial cell viability.

Identification of potential anti-infectives against Staphylococcus aureus using a Caenorhabditis elegans infection model

“…Consistent with our previous findings [6], use of a liquid-based assay facilitated detection of more hits than the conventional agar-based assay. It is possible that in an agar-based system, the addition of compound into the molten agar at high temperatures may have led to compound degradation.…”

Antibacterial activity of Orthosiphon stamineus towards Staphylococcus aureus and methicilin resistant Stahpylococcus aureus (MRSA)

“…Result of MIC test indicated that both extracts have antibacterial activity against S. aureus and MRSA strains. The results are comparable to the results reported by Kong (2014). In their study, aqueous extract of O. stamineus was observed to be able to protect Caenorhabditis elegan (nematode) from S. aureus and MRSA infection.…”

Comparison of antibiotic resistance, virulence gene profiles, and pathogenicity of methicillin-resistant and methicillin-susceptibleStaphylococcus aureususing aCaenorhabditis elegansinfection model

“…7 These initial successes have led to more recent use of C. elegans for the discovery of potential anti-infectives against S. aureus. 8,9 The objectives of this study were to compare the carriage of virulence determinants and antibiotic resistance phenotypes between MRSA and MSSA isolates and examine their virulence potential using the nematode, C. elegans.…”