Evaluation of telavancin susceptibility in isolates of Staphylococcus aureus with reduced susceptibility to vancomycin

Insights into the molecular basis of reduced vancomycin susceptibility among three prominent Staphylococcus aureus clonal complexes

Staphylococcus aureus is a leading cause of healthcare-associated infections globally. Vancomycin-resistant S. aureus (VRSA), those with high-level resistance [minimum inhibitory concentration (MIC) of 16-32 µg/mL vancomycin], are uncommon, whereas vancomycin-intermediate S. aureus (VISA; MIC of 4-8 µg/mL), are isolated more frequently and develop during long-term and/or repeated use of the antibiotic. VISA can be difficult to eradicate and infections may persist. Our knowledge of mechanisms that underlie the development of VISA is incomplete. We used a genomics approach to investigate the VISA phenotype in three prominent S. aureus lineages. All VISA clinical isolates tested had increased cell wall thickness compared with vancomycin-susceptible S. aureus strains. Growth rates of clonal complex (CC) 5, CC8, and CC45 clinical isolates were reduced in 2 µg/mL vancomycin compared to media alone. Culture in 2 and 4 µg/mL vancomycin sequentially for two weeks reduced susceptibility to daptomycin, televancin, tigecycline, and vancomycin in a majority of CC5, CC8, and CC45 isolates tested. We identified alleles reported previously to contribute to the VISA phenotype, but unexpectedly, these alleles were unique to each CC. A subtherapeutic concentration of vancomycin elicited changes in the VISA transcriptome-common and unique-among the three CCs tested. Multiple genes, including those encoding a glycerate kinase, an M50 family metallopeptidase, and an uncharacterized membrane protein, were upregulated among all three lineages and not reported previously as associated with VISA. Although there are lineage-specific changes in DNA sequence, our findings suggest changes in the VISA transcriptome constitute a general response to stress that confers reduced susceptibility to multiple antibiotics.

IMPORTANCE

Our understanding of the mechanisms that underlie the development of vancomycin-intermediate Staphylococcus aureus (VISA) is incomplete. To provide a more comprehensive view of this process, we compared genome sequences of clonal complex (CC) 5, CC8, and CC45 VISA clinical isolates and measured changes in the transcriptomes of these isolates during culture with a subtherapeutic concentration of vancomycin. Notably, we identified differentially expressed genes that were lineage-specific or common to the lineages tested, including genes that have not been previously reported to contribute to a VISA phenotype. Changes in gene expression were accompanied by reduced growth rate, increased cell wall thickness, and reduced susceptibility to daptomycin, televancin, tigecycline, and vancomycin. Our results provide support to the idea that changes in gene expression contribute to the development of VISA among three CCs that are a prominent cause of human infections.

Synthesis of a Two-Dimensional Molybdenum Disulfide Nanosheet and Ultrasensitive Trapping of Staphylococcus Aureus for Enhanced Photothermal and Antibacterial Wound-Healing Therapy

Photothermal therapy has been widely used in the treatment of bacterial infections. However, the short photothermal effective radius of conventional nano-photothermal agents makes it difficult to achieve effective photothermal antibacterial activity. Therefore, improving composite targeting can significantly inhibit bacterial growth. We inhibited the growth of Staphylococcus aureus (S. aureus) by using an extremely low concentration of vancomycin (Van) and applied photothermal therapy with molybdenum disulfide (MoS₂). This simple method used chitosan (CS) to synthesize fluorescein 5(6)-isothiocyanate (FITC)-labeled and Van-loaded MoS₂-nanosheet hydrogels (MoS₂-Van-FITC@CS). After modifying the surface, an extremely low concentration of Van could inhibit bacterial growth by trapping bacteria synergistically with the photothermal effects of MoS₂, while FITC labeled bacteria and chitosan hydrogels promoted wound healing. The results showed that MoS₂-Van-FITC@CS nanosheets had a thickness of approximately 30 nm, indicating the successful synthesis of the nanosheets. The vitro antibacterial results showed that MoS₂-Van-FITC with near-infrared irradiation significantly inhibited S. aureus growth, reaching an inhibition rate of 94.5% at nanoparticle concentrations of up to 100 µg/mL. Furthermore, MoS₂-Van-FITC@CS could exert a healing effect on wounds in mice. Our results demonstrate that MoS₂-Van-FITC@CS is biocompatible and can be used as a wound-healing agent.

Effect of silver nanoparticles on vancomycin resistant Staphylococcus aureus infection in critically ill patients

A prevalent increase in antimicrobial resistance represents a universal obstacle for the treatment of Staphylococcus aureus (S. aureus) infection, especially in critically ill patients. Silver nanoparticles are defined as broad spectrum bactericidal agents, which might be effective against vancomycin resistant S. aureus (VRSA). In this study, we examined the bactericidal efficacy of silver nanoparticles on VRSA in 150 blood and sputum samples isolated from intensive care patients. Methicillin resistant S. aureus (MRSA) isolates were identified in 83 samples, with an incidence of 55.3%. Meanwhile, VRSA isolates were found in 11 and 8 isolates (a total of 19 isolates out of 150) from sputum and blood samples, with an incidence of 14.67% and 10.67%, respectively, with a total incidence of 12.67%. Vancomycin intermediate S. aureus (VISA) isolates had an inhibitory zone ranging from 9 to 13 mm, which was found in 13 out of 19 isolates, whereas VRSA isolates had an inhibitory zone ranging from 0 to 6 mm, which was detected in 6 out of 19 isolates. The findings of this study confirm that silver nanoparticles are an effective treatment against VRSA.