Probing Interkingdom Signaling Molecules via Liquid Extraction Surface Analysis-Mass Spectrometry

Comparative lipidomics profiles of planktonic and biofilms of methicillin-resistant and -susceptible Staphylococcus aureus

Staphylococcus aureus is a significant human pathogen causing acute life-threatening, and chronic infections often linked to biofilms. This study conducted a comparative lipidomic analysis of a methicillin-resistant (MRSA) and a methicillin-susceptible (MSSA) S. aureus strain in both planktonic and biofilm cultures using liquid chromatography-mass spectrometry (LC-MS) and nuclear magnetic resonance (NMR) spectroscopy. The developed protocol successfully differentiates between the strains in various living states (planktonic and biofilm) and growth media (Tryptic Soy Broth and Brain Heart Infusion) using S. aureus USA300 LAC (MRSA) and S. aureus Newman (MSSA). LC-MS and NMR lipidomics profiles revealed global differences and particular ones among the following classes of bacterial lipids: phosphatidylglycerols, diacylglycerols, monoglycosyldiacylglycerols, diglycosyldiacylglycerols, and cardiolipins. Lipid content was higher in the biofilm states for most of these classes. Growth media differences were significant, while differences between MRSA and MSSA were less pronounced but still detectable. Additionally, we provide data on hundreds of unknown compounds that differ based on living state, strain background, or growth media. This study offer insights into the dynamic nature of S. aureus lipid composition and the used methods are adaptable to other organisms.

Development, characterization, and evaluation of a simple polymicrobial colony biofilm model for testing of antimicrobial wound dressings

Chronic wound infections are generally of polymicrobial nature with aerobic and anaerobic bacteria, as well as fungi frequently observed in them. Wound treatment involves a series of steps, including debridement of the wound, flushing, and often the use of multiple wound dressings many of which are antimicrobial. Yet, many wound dressings are tested versus single species of planktonic microbes, which fails to mirror the real-life presence of biofilms.

AIMS

Simple biofilm models are the first step to testing of any antimicrobial and wound dressing; therefore, the aim of this study was to develop and validate a simple polymicrobial colony biofilm wound model comprised of Pseudomonas aeruginosa, Staphylococcus aureus, and Candida albicans on RPMI-1640 agar. The model was then used to evaluate the topical disinfectant chlorohexidine and four commercially available wound dressings using the polymicrobial model. The model used was as a starting point to mimic debridement in clinical care of wounds and the effectiveness of wound dressings evaluated afterwards.

METHODS AND RESULTS

Planktonic assessment using AATCC100-2004 demonstrated that all antimicrobial wound dressings reduced the planktonic microbial burden below the limit of detection; however, when challenged with polymicrobial colony biofilms, silver wound dressings showed limited effectiveness (1-2 log CFU reductions). In contrast, a single iodine releasing wound dressing showed potent antibiofilm activity reducing all species CFUs below the limit of detection (>6-10 log) depending on the species. A disrupted biofilm model challenge was performed to represent the debridement of a wound and wound silver-based wound dressings were found to be marginally more effective than in whole colony biofilm challenges while the iodine containing wound dressing reduced microbial recovery below the limit of detection.

CONCLUSIONS

In this model, silver dressings were ineffective versus the whole colony biofilms but showed some recovery of activity versus the disrupted colony biofilm. The iodine wound dressing reduced the viability of all species below the level of detection. This suggests that mode of action of wound dressing should be considered for the type of biofilm challenge as should the clinical use, e.g. debridement.