Abstract
Methicillin-susceptible (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) is a pathogen commonly found in bone and joint infections, including septic arthritis. S. aureus virulence and the frailty of affected patients can cause several complications; a prompt and specific antibiotic treatment can positively affect the outcome of patients. We carried out an in-depth genomic characterization by Illumina whole genome sequencing and bioinformatics of two biofilm-producing M1 and M2 ST398 MSSA causing septic knee arthritis not-responding to antimicrobial therapy. The strains were characterized for antibiotic resistance, biofilm and adhesive properties as well as genomics, single nucleotide polymorphism phylogeny, resistomics and virulomics. Our results showed that M1 and M2 MSSA were ST398-t1451-agrI-Cap5, susceptible to cefoxitin and resistant to erythromycin and clindamycin, traits consistent with the lack of the SCCmec-locus and the presence of the sole blaZ and ermT. Furthermore, M1 and M2 were biofilm-producing and largely potentially adhesive strains, as indicated by the adhesion gene profile. Our data characterized a new human-adapted ST398 MSSA lineage, representing a “fusion” between the human-animal independent ST398 and the Livestock Associated (LA) ST398 lineages, forming biofilm and genomically predicted high adhesive, characterized by different genomic adaptation conferring a great ability to adhere to the host’s extracellular matrix causing septic knee arthritis.
Highlights
Invasive Staphylococcus aureus can cause severe and chronic septic arthritis associated with a high rate of relapse [1], in part explained by its ability to produce biofilm and small colony variants (SCVs) [2]
ST398 S. aureus has recently emerged worldwide and is a frequent source of human infections, being involved in serious infectious diseases such as bloodstream infections (BSI) [31,32], prosthetic joint infections (PJI) [33,34] and in diabetic foot osteomyelitis (DFO) [35], whereas ST398 methicillin-resistant Staphylococcus aureus (MRSA) is mainly associated with infections in humans and animals [36]
Our investigations characterized two ST398 methicillin-susceptible S. aureus (MSSA) isolates, being M2 a genetic evolution of M1 MSSA emerging under antimicrobial treatments, with a sticky behavior due to their in vitro slime and biofilm production
Summary
Biofilms are sessile microbial communities embedded in an extracellular polymeric slime (EPS) matrix composed of polysaccharide, protein or external. Bacterial communities in biofilms alter some of their phenotypic (susceptibility to disinfectants and antimicrobial agents) and genotypic features (gene expression and protein production profiling) [5]. A biofilm’s life cycle has various steps: (1) a reversible attachment to a surface by van der Waals forces, steric interactions, an electrostatic (double layer) interaction and irreversible adhesion mediated by hydrophobic and hydrophilic interactions between bacteria and surfaces; (2) bacterial adhesion to the host matrix via microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) and secretable expanded repertoire adhesive molecules (SERAMs); (3) production of microcolonies, with bacteria attaching to each other and producing additional polymeric sub-
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