Daptomycin in combination with other antibiotics for the treatment of complicated methicillin-resistant Staphylococcus aureus bacteremia

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.

Phytochemical Composition and Antibacterial Activity of Hydroalcoholic Extracts of Pterospartum tridentatum and Mentha pulegium against Staphylococcus aureus Isolates

Pterospartum tridentatum and Mentha pulegium are largely used in Portuguese folk medicine to treat several human disorders and inflammatory processes but without any consistent evidence for those beneficial pointed properties. Thus, the aim of the current work is to evaluate its benefits and phytochemicals related to those beneficial properties. A distinct polyphenol profile between P. tridentatum and M. pulegium was found. Taxifolin, myricetin, ginestin, ginestein, and ginestein derivatives, biochanin A-glucoside, and biochanin A were identified in P. tridentatum, whilst in M. pulegium the luteolin-7-rutinoside, diosmin, and apigenin and respective derivatives were most representative polyphenols. These variations had implications in the antiradical and antibacterial activity and the P. tridentatum exhibited the highest antibacterial activity against methicillin-resistant and methicillin-sensitive Staphylococcus aureus MSSA, which was mainly dose-dependent. This antibacterial activity seems to be related to high content of flavonols, flavones, and isoflavones, which can act synergistically with each other against this type of bacteria. Our results showed consistent evidence that Pterospartum tridentatum and Mentha pulegium are an important reservoir of phytochemicals with antiradical activity and antibacterial capacity and thus they might be used in a preventive way or in a combined pharmaceutical and antibiotic therapy against pathogenic bacteria.

Mechanisms of drug resistance: daptomycin resistance

Daptomycin (DAP) is a cyclic lipopeptide with in vitro activity against a variety of Gram-positive pathogens, including multidrug-resistant organisms. Since its introduction into clinical practice in 2003, DAP has become an important key frontline antibiotic for severe or deep-seated infections caused by Gram-positive organisms. Unfortunately, DAP resistance (DAP-R) has been extensively documented in clinically important organisms such as Staphylococcus aureus, Enterococcus spp., and Streptococcus spp. Studies on the mechanisms of DAP-R in Bacillus subtilis and other Gram-positive bacteria indicate that the genetic pathways of DAP-R are diverse and complex. However, a common phenomenon emerging from these mechanistic studies is that DAP-R is associated with important adaptive changes in cell wall and cell membrane homeostasis with critical changes in cell physiology. Findings related to these adaptive changes have provided novel insights into the genetics and molecular mechanisms of bacterial cell envelope stress response and the manner in which Gram-positive bacteria cope with the antimicrobial peptide attack and protect vital structures of the cell envelope, such as the cell membrane. In this review, we will examine the most recent findings related to the molecular mechanisms of resistance to DAP in relevant Gram-positive pathogens and discuss the clinical implications for therapy against these important bacteria.

Multiple pathways of cross-resistance to glycopeptides and daptomycin in persistent MRSA bacteraemia

BACKGROUND

The development of non-susceptibility to glycopeptides and daptomycin in MRSA during persistent bacteraemia has become a significant therapeutic challenge. However, the in vivo evolution and mechanism of the dual resistance have remained incompletely understood.

METHODS

A series of MRSA blood isolates with incremental non-susceptibility to glycopeptides and daptomycin were consecutively recovered from a bacteraemic patient who was failing chemotherapy. The evolutionary pathways during conversion from a glycopeptide- and daptomycin-susceptible phenotype into a vancomycin-intermediate Staphylococcus aureus (VISA) and a daptomycin-resistant S. aureus (DRSA) phenotype were then traced by WGS of the isogenic strains.

RESULTS

A total of six non-synonymous mutations and three evolutionary pathways were identified during the development of the VISA/DRSA phenotype. The first pathway involved two steps of evolution, with an initial 1 bp insertion into yycH and a subsequent gain-in-function point mutation in mprF (S295L). The two mutations were correlated with heteroresistance to daptomycin/vancomycin and full development of the VISA/DRSA phenotype. The second pathway involved an 11 bp deletion mutation in yycH and point mutations at two genes, correlating with the development of the VISA phenotype and heteroresistance to daptomycin. Mutation in mprF (S295L) and a 5 bp deletion mutation in yycH were identified in the third pathway and corresponded to conversion into the full VISA/DRSA phenotype. The mutations in yycH resulted in premature terminations of YycH with variable lengths.

CONCLUSIONS

Multiple evolutionary pathways involving yycH and mprF can proceed simultaneously and may mediate cross-resistance to glycopeptides and daptomycin during persistent MRSA bacteraemia under antibiotic selective pressure.