Synergy Between Beta-Lactams and Lipo-, Glyco-, and Lipoglycopeptides, Is Independent of the Seesaw Effect in Methicillin-Resistant Staphylococcus aureus

Daptomycin and ceftaroline combination for the treatment of persistent methicillin-resistant Staphylococcus aureus bloodstream infections: a case series and literature review

Methicillin-resistant Staphylococcus aureus (MRSA) is challenging to treat due to a lack of guidance for clinicians. The daptomycin and ceftaroline combination is promising for treating persistent MRSA bloodstream infections (BSIs). In this report, we present a case series of 7 patients who failed vancomycin and then were treated with daptomycin and ceftaroline for persistent MRSA BSIs. The median age (IQR) of the included patients was 59 (48-67), with 5 male and 2 female patients. Six patients (85.7%) had a clinical cure for their persistent BSIs. The median time (IQR) for sterilization of MRSA BSIs after initiation of daptomycin and ceftaroline combination was 2 days (1-3). Among the patients who had clinical cures, the median time for clinical cures (IQR) was 6 weeks (4.5-6 weeks). The combination of daptomycin and ceftaroline could be an excellent treatment option for persistent MRSA BSIs.

Genomic investigation and clinical correlates of the in vitro β-lactam: NaHCO3 responsiveness phenotype among methicillin-resistant Staphylococcus aureus isolates from a randomized clinical trial

NaHCO3 responsiveness is a novel phenotype where some methicillin-resistant Staphylococcus aureus (MRSA) isolates exhibit significantly lower minimal inhibitory concentrations (MIC) to oxacillin and/or cefazolin in the presence of NaHCO3. NaHCO3 responsiveness correlated with treatment response to β-lactams in an endocarditis animal model. We investigated whether treatment of NaHCO3-responsive strains with β-lactams was associated with faster clearance of bacteremia. The CAMERA2 trial (Combination Antibiotics for Methicillin-Resistant Staphylococcus aureus) randomly assigned participants with MRSA bloodstream infections to standard therapy, or to standard therapy plus an anti-staphylococcal β-lactam (combination therapy). For 117 CAMERA2 MRSA isolates, we determined by broth microdilution the MIC of cefazolin and oxacillin, with and without 44 mM of NaHCO3. Isolates exhibiting ≥4-fold decrease in the MIC to cefazolin or oxacillin in the presence of NaHCO3 were considered "NaHCO3-responsive" to that agent. We compared the rate of persistent bacteremia among participants who had infections caused by NaHCO3-responsive and non-responsive strains, and that were assigned to combination treatment with a β-lactam. Thirty-one percent (36/117) and 25% (21/85) of MRSA isolates were NaHCO3-responsive to cefazolin and oxacillin, respectively. The NaHCO3-responsive phenotype was significantly associated with sequence type 93, SCCmec type IVa, and mecA alleles with substitutions in positions -7 and -38 in the regulatory region. Among participants treated with a β-lactam, there was no association between the NaHCO3-responsive phenotype and persistent bacteremia (cefazolin, P = 0.82; oxacillin, P = 0.81). In patients from a randomized clinical trial with MRSA bloodstream infection, isolates with an in vitro β-lactam-NaHCO3-responsive phenotype were associated with distinctive genetic signatures, but not with a shorter duration of bacteremia among those treated with a β-lactam.

A rapid single-phase extraction for polar staphylococcal lipids

The lipid membrane is gaining appreciation as a critical factor in the emergence of antibiotic resistance, both for antibiotics that target lipid synthesis or the membrane directly and for cell-wall-targeting antibiotics. The methods used to study the emergence of antibiotic resistance in vitro can generate a large number of samples that may be low in volume and in cell density. As in eukaryotic/mammalian lipidomics, two-phase liquid-liquid extractions are the most commonly used approach to recover lipids from bacteria. The need to separate the lipid layer is cumbersome for high-throughput applications and can be a source of poor reproducibility or contaminant introduction. While several single-phase extractions have been proposed for serum, tissue, and eukaryotic cells, there have been far fewer efforts to adapt or develop such methods for bacteria lipidomics. Here, we describe a simple, single-phase lipid extraction method based on methanol, acetonitrile, and water-the MAW method. The merits of the MAW method are evaluated against the Bligh & Dyer (B&D) method for the recovery of the major membrane lipids (phosphatidylglycerols, diglycosyldiacylglycerols, and lysyl-phosphatidylglycerols) in the Gram-positive pathogen Staphylococcus aureus. We demonstrate that the MAW method achieves recoveries that are comparable to that of the B&D extraction (≥ 85% for PG 15:0/d₇-18:1). The benefits of the MAW method enable the detection of lipids from lower amounts of bacteria than the B&D method (0.57 vs 0.74 McFarlands for PG 32:0, respectively) and is easily scaled down to microplate volumes to facilitate high-throughput studies of bacterial lipids.

Emergence of Dalbavancin, Vancomycin, and Daptomycin Nonsusceptible Staphylococcus aureus in a Patient Treated With Dalbavancin: Case Report and Isolate Characterization

A patient with end-stage renal disease received 2 doses of dalbavancin for methicillin-resistant Staphylococcus aureus (MRSA) arteriovenous fistula infection and presented 5 weeks later with infective endocarditis secondary to vancomycin, daptomycin, and dalbavancin nonsusceptible MRSA. Resistance was associated with walK and scrA mutations, reduced long-chain lipid content, and reduced membrane fluidity.

Evolution of Enterococcus faecium in Response to a Combination of Daptomycin and Fosfomycin Reveals Distinct and Diverse Adaptive Strategies

Infections caused by vancomycin-resistant Enterococcus faecium (VREfm) are an important public health threat. VREfm isolates have become increasingly resistant to the front-line antibiotic daptomycin (DAP). As such, the use of DAP combination therapies with other antibiotics like fosfomycin (FOS) has received increased attention. Antibiotic combinations could extend the efficacy of currently available antibiotics and potentially delay the onset of further resistance. We investigated the potential for E. faecium HOU503, a clinical VREfm isolate that is DAP and FOS susceptible, to develop resistance to a DAP-FOS combination. Of particular interest was whether the genetic drivers for DAP-FOS resistance might be epistatic and, thus, potentially decrease the efficacy of a combinatorial approach in either inhibiting VREfm or in delaying the onset of resistance. We show that resistance to DAP-FOS could be achieved by independent mutations to proteins responsible for cell wall synthesis for FOS and in altering membrane dynamics for DAP. However, we did not observe genetic drivers that exhibited substantial cross-drug epistasis that could undermine the DAP-FOS combination. Of interest was that FOS resistance in HOU503 was largely mediated by changes in phosphoenolpyruvate (PEP) flux as a result of mutations in pyruvate kinase (pyk). Increasing PEP flux could be a readily accessible mechanism for FOS resistance in many pathogens. Importantly, we show that HOU503 was able to develop DAP resistance through a variety of biochemical mechanisms and was able to employ different adaptive strategies. Finally, we showed that the addition of FOS can prolong the efficacy of DAP and slow down DAP resistance in vitro.

New Perspectives on Antimicrobial Agents: Long-Acting Lipoglycopeptides

The long-acting lipoglycopeptides (LGPs) dalbavancin and oritavancin are semisynthetic antimicrobials with broad and potent activity against Gram-positive bacterial pathogens. While they are approved by the Food and Drug Administration for acute bacterial skin and soft tissue infections, their pharmacological properties suggest a potential role of these agents for the treatment of deep-seated and severe infections, such as bloodstream and bone and joint infections. The use of these antimicrobials is particularly appealing when prolonged therapy, early discharge, and avoidance of long-term intravascular catheter access are desirable or when multidrug-resistant bacteria are suspected. This review describes the current evidence for the use of oritavancin and dalbavancin in the treatment of invasive infections, as well as the hurdles that are preventing their optimal use. Moreover, this review discusses the current knowledge gaps that need to be filled to understand the potential role of LGPs in highly needed clinical scenarios and the ongoing clinical studies that aim to address these voids in the upcoming years.