Apt (Adenine Phosphoribosyltransferase) Mutation in Laboratory-Selected Vancomycin-Intermediate Staphylococcus aureus

Adaptive physiological and metabolic alterations in Staphylococcus aureus evolution under vancomycin exposure

Staphylococcus aureus can develop antibiotic resistance and evade immune responses, causing infections in different body sites. However, the metabolic changes underlying this process are poorly understood. A variant strain, C1V, was derived from the parental strain C1 by exposing it to increasing concentrations of vancomycin in vitro. C1V exhibited a vancomycin-intermediate phenotype and physiological changes compared to C1. It showed higher survival rates than C1 when phagocytosed by Raw264.7 cells. Metabolomics analysis identified significant metabolic differences pre- and post-induction (C1 + SC1 vs. C1V + SC1V: 201 metabolites) as well as pre- and post-phagocytosis (C1 vs. SC1: 50 metabolites; C1V vs. SC1V: 95 metabolites). The variant strain had distinct morphological characteristics, decreased adhesion ability, impaired virulence, and enhanced resistance to phagocytosis compared to the parental strain. Differential metabolites may contribute to S. aureus ' resistance to antibiotics and phagocytosis, offering insights into potential strategies for altering vancomycin nonsusceptibility and enhancing phagocyte killing by manipulating bacterial metabolism.

An induced mutation of ABC-transporter component VraF(K84E) contributes to vancomycin resistance and virulence in Staphylococcus aureus strain MW2

Staphylococcus aureus is a notorious pathogen responsible for various severe diseases. Due to the emergence of drug-resistant strains, the prevention and treatment of S. aureus infections have become increasingly challenging. Vancomycin is considered to be one of the last-resort drugs for treating most methicillin-resistant S. aureus (MRSA), so it is of great significance to further reveal the mechanism of vancomycin resistance. VraFG is one of the few important ABC (ATP-binding cassette) transporters in S. aureus that can form TCS (two-component systems)/ABC transporter modules. ABC transporters can couple the energy released from ATP hydrolysis to translocate solutes across the cell membrane. In this study, we obtained a strain with decreased vancomycin susceptibility after serial passaging and selection. Subsequently, whole-genome sequencing was performed on this laboratory-derived strain MWA2 and a novel single point mutation was discovered in vraF gene, leading to decreased sensitivity to vancomycin and daptomycin. Furthermore, the mutation reduces autolysis of S. aureus and downregulates the expression of lytM, isaA, and atlA. Additionally, we observed that the mutant has a less net negative surface charge than wild-type strain. We also noted an increase in the expression of the dlt operon and mprF gene, which are associated with cell surface charge and serve to hinder the binding of cationic peptides by promoting electrostatic repulsion. Moreover, this mutation has been shown to enhance hemolytic activity, expand subcutaneous abscesses, reflecting an increased virulence. This study confirms the impact of a point mutation of VraF on S. aureus antibiotic resistance and virulence, contributing to a broader understanding of ABC transporter function and providing new targets for treating S. aureus infections.

Resistance phenotype and genetic features of a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus strain from an immunocompromised patient

Strain C1 was successfully isolated from an immunosuppressed patient with persistent bacteremia, who had not previously been exposed to glycopeptide antibiotics. This strain was found to be a heterogeneous vancomycin intermediate-resistant Staphylococcus aureus (hVISA). It is noteworthy that, following a brief period of vancomycin treatment, strains C6, C8, and C9, which were obtained from blood and other body parts, exhibited a significant reduction in heterogeneity as determined by population analysis profile-area under the curve (PAP-AUC) detection. Genotyping analysis revealed that these bacterial strains belonged to the same SCCmecIVa-ST59-t437-agrI genotype and shared the same virulome and resistome. In this study, a comparative genomics analysis was conducted between strain C1 and strain N315 to identify potential hVISA-associated mutations. Ultimately, a total of 205 mutation sites in 19 candidate genes, likely associated with the hVISA phenotype, were identified.

The evolution of diverse antimicrobial responses in vancomycin-intermediate Staphylococcus aureus and its therapeutic implications

Staphylococcus aureus causes endocarditis, osteomyelitis, and bacteremia. Clinicians often prescribe vancomycin as an empiric therapy to account for methicillin-resistant S. aureus (MRSA) and narrow treatment based on culture susceptibility results. However, these results reflect a single time point before empiric treatment and represent a limited subset of the total bacterial population within the patient. Thus, while they may indicate that the infection is susceptible to a particular drug, this recommendation may no longer be accurate during therapy. Here, we addressed how antibiotic susceptibility changes over time by accounting for evolution. We evolved 18 methicillin-susceptible S. aureus (MSSA) populations under increasing vancomycin concentrations until they reached intermediate resistance levels. Sequencing revealed parallel mutations that affect cell membrane stress response and cell-wall biosynthesis. The populations exhibited repeated cross-resistance to daptomycin and varied responses to meropenem, gentamicin, and nafcillin. We accounted for this variability by deriving likelihood estimates that express a population's probability of exhibiting a drug response following vancomycin treatment. Our results suggest antistaphylococcal penicillins are preferable first-line treatments for MSSA infections but also highlight the inherent uncertainty that evolution poses to effective therapies. Infections may take varied evolutionary paths; therefore, considering evolution as a probabilistic process should inform our therapeutic choices.