Adaptation of Staphylococcus aureus in a Medium Mimicking a Diabetic Foot Environment

Abstract

Staphylococcus aureus is the most prevalent pathogen isolated from diabetic foot infections (DFIs). The purpose of this study was to evaluate its behavior in an in vitro model mimicking the conditions encountered in DFI. Four clinical S. aureus strains were cultivated for 16 weeks in a specific environment based on the wound-like medium biofilm model. The adaptation of isolates was evaluated as follows: by Caenorhabditis elegans model (to evaluate virulence); by quantitative Reverse Transcription-Polymerase Chain Reaction (qRT-PCR) (to evaluate expression of the main virulence genes); and by Biofilm Ring test® (to assess the biofilm formation). After 16 weeks, the four S. aureus had adapted their metabolism, with the development of small colony variants and the loss of b-hemolysin expression. The in vivo nematode model suggested a decrease of virulence, confirmed by qRT-PCRs, showing a significant decrease of expression of the main staphylococcal virulence genes tested, notably the toxin-encoding genes. An increased expression of genes involved in adhesion and biofilm was noted. Our data based on an in vitro model confirm the impact of environment on the adaptation switch of S. aureus to prolonged stress environmental conditions. These results contribute to explore and characterize the virulence of S. aureus in chronic wounds.

The High Impact of Staphylococcus aureus Biofilm Culture Medium on In Vitro Outcomes of Antimicrobial Activity of Wound Antiseptics and Antibiotic

“…Although the wound fluid immersing factual biofilm differs from these media, it has only been recently that this seemingly obvious fact and phenomena have been related to it, with it now starting to be thoroughly explored [33,34]. Presently, numerous research teams have aimed to develop a method that allows for the wound conditions to be reflected in in vitro conditions as closely as possible [26,[35][36][37]. Of note, the media used in biofilm analyses should mimic the composition of wound exudate because host-derived components, which commonly occur in the wound bed, can determine biofilm formation and interact with antimicrobials [33,38].…”

Long-Term Intrahost Evolution of Staphylococcus aureus Among Diabetic Patients With Foot Infections

“…However, we could not exclude the influence of the “environment” encountered by S. aureus in this chronic wound. If we previously highlighted that the diabetic foot medium modifies the virulence of S. aureus ( Pouget et al, 2021 ), we also know that the competition between microorganisms in these polymicrobial infections directly impacts the invasiveness of S. aureus ( Pouget et al, 2020 ). The importance of the bacterial adaptation could also be observed by the formation of small colony variants ( Tuchscherr et al, 2020 ), as previously observed in isolates from CF patients ( Schwerdt et al, 2018 ) and DFU ( Cervantes-Garcia et al, 2015 ).…”

Characteristics of Staphylococcus aureus small colony variants isolated from wound specimen of a tertiary care hospital in China

“…***p < 0.05 increased expression of adhesion and biofilm formation genes, slow growth rate, and formation of SCVs. 34 Therefore, the formation of SCVs may be the result of the interaction between S. aureus and the host immune system and antimicrobial. Since the insufficient SCVs and the lack of parent wild-type strains, it is unable to confirm the pathogenic characteristics of SCVs.…”

“…aureus infection models, long‐term environmental adaptation leads to the down‐regulation of virulence genes such as toxin‐encoding genes, increased expression of adhesion and biofilm formation genes, slow growth rate, and formation of SCVs. 34 Therefore, the formation of SCVs may be the result of the interaction between S . aureus and the host immune system and antimicrobial.…”