Insights and clinical perspectives of daptomycin resistance in Staphylococcus aureus: A review of the available evidence

Towards Profiles of Resistance Development and Toxicity for the Small Cationic Hexapeptide RWRWRW-NH2

RWRWRW-NH₂ (MP196) is an amphipathic hexapeptide that targets the bacterial cytoplasmic membrane and inhibits cellular respiration and cell wall synthesis. In previous studies it showed promising activity against Gram-positive bacteria and no significant cytotoxicity or hemolysis. MP196 is therefore used as lead structure for developing more potent antibiotic derivatives. Here we present a more comprehensive study on the parent peptide MP196 with regard to clinically relevant parameters. We found that MP196 acts rapidly bactericidal killing 97% of initial CFU within 10 min at two times MIC. We were unable to detect resistance in standard 24 and 48 h resistance frequency assays. However, MP196 was effective against some but not all MRSA and VISA strains. Serum binding of MP196 was intermediate and we confirmed its low toxicity against mammalian cell lines. MP196 did neither induce NFκB activation nor cause an increase in IL8 levels at 250 μg/mL, and no IgE-dependent activation of basophil granulocytes was detected at 500 μg/mL. Yet, MP196 demonstrated acute toxicity in mice upon injection into the blood stream. Phase contrast microscopy of mouse blood treated with MP196 revealed a shrinking of erythrocytes at 250 μg/mL and severe morphological changes and lysis of erythrocytes at 500 μg/mL. These data suggest that MP196 derivatization directed at further lowering hemolysis could be instrumental in overcoming acute toxicity. The assessment of hemolysis is a critical step in the evaluation of the clinical potential of promising antimicrobial peptides and should be accompanied by microscopy-based morphological analysis of blood cells.

Hot topics in the diagnosis and management of skin and soft-tissue infections

Eighteen hot topics regarding the diagnosis and management of skin and soft-tissue infections (SSTIs) were selected and reviewed by members of the SSTI Working Group of the International Society of Chemotherapy (ISC). Despite the large amount of literature available on the issue selected, there are still many unknowns with regard to many of them and further studies are required to answer these challenging issues that face clinicians on a daily basis.

Daptomycin: an evidence-based review of its role in the treatment of Gram-positive infections

Infections caused by Gram-positive pathogens remain a major public health burden and are associated with high morbidity and mortality. Increasing rates of infection with Gram-positive bacteria and the emergence of resistance to commonly used antibiotics have led to the need for novel antibiotics. Daptomycin, a cyclic lipopeptide with rapid bactericidal activity against a wide range of Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, has been shown to be effective and has a good safety profile for the approved indications of complicated skin and soft tissue infections (4 mg/kg/day), right-sided infective endocarditis caused by S. aureus, and bacteremia associated with complicated skin and soft tissue infections or right-sided infective endocarditis (6 mg/kg/day). Based on its pharmacokinetic profile and concentration-dependent bactericidal activity, high-dose (>6 mg/kg/day) daptomycin is considered an important treatment option in the management of various difficult-to-treat Gram-positive infections. Although daptomycin resistance has been documented, it remains uncommon despite the increasing use of daptomycin. To enhance activity and to minimize resistance, daptomycin in combination with other antibiotics has also been explored and found to be beneficial in certain severe infections. The availability of daptomycin via a 2-minute intravenous bolus facilitates its outpatient administration, providing an opportunity to reduce risk of health care-associated infections, improve patient satisfaction, and minimize health care costs. Daptomycin, not currently approved for use in the pediatric population, has been shown to be widely used for treating Gram-positive infections in children.

In vivo development of daptomycin resistance in vancomycin-susceptible methicillin-resistant Staphylococcus aureus severe infections previously treated with glycopeptides

Our aim was to describe the clinical and microbiological features of four cases of severe vancomycin-susceptible methicillin-resistant Staphylococcus aureus (MRSA) infections in which the vancomycin non-susceptibility development and daptomycin resistance occurred under therapy with teicoplanin (three cases) and daptomycin switched to vancomycin (one case). Clinical data were retrospectively reviewed. On nine clinical epidemiologically unrelated daptomycin-susceptible (DAP-S) and daptomycin-resistant (DAP-R) MRSA, we performed: (i) DAP-VAN-TEC-CFX-RIF minimum inhibitory concentrations (MICs); (ii) glycopeptide resistance detection (GRD) by δ-hemolysis; (iii) glycopeptide population analysis; (iv) molecular characterization by PFGE-MLST-SCCmec-agr-typing; (v) rpoB and mprF single nucleotide polymorphisms (SNPs); (vi) dltA-mprF-atl-sceD expression by real-time quantitative polymerase chain reaction (qPCR). Three out of the four patients did not survive despite salvage treatment; two died with active MRSA infection and one died because of Stenotrophomonas maltophilia sepsis. The fourth patient, in which a reversion to a DAP-S phenotype occurred, survived with daptomycin plus trimethoprim/sulfamethoxazole and oxacillin treatment, and endovascular device removal. Daptomycin resistance development was preceded by a stable heterogeneous vancomycin-intermediate S. aureus (hVISA) or VISA phenotype acquisition, while in one case, daptomycin resistance was preceded by an unstable daptomycin heteroresistance (hDAP) behavior reverting to DAP-S during vancomycin plus rifampin therapy followed by high doses of daptomycin. All DAP-R strains showed hVISA or DAP-R traits, including mutations and/or up-regulation of genes involved in cell wall turnover and cell membrane perturbation. In our study, daptomycin resistance arose during glycopeptide therapy. The emergence of DAP-R isolates was preceded by a stable VISA or hVISA phenotype or by instability reverting to a DAP-S heteroresistant phenotype. Daptomycin, as first-line therapy for the treatment of severe MRSA infections, should be used at optimal dosage combined with other agents such as beta-lactams, to prevent daptomycin resistance occurrence.

Bacterial lipid membranes as promising targets to fight antimicrobial resistance, molecular foundations and illustration through the renewal of aminoglycoside antibiotics and emergence of amphiphilic aminoglycosides

Membrane anionic lipids as attractive targets in the design of amphiphilic antibacterial drugs active against resistant bacteria: molecular foundations and examples.