Emergence of daptomycin resistance following vancomycin-unresponsive Staphylococcus aureus bacteraemia in a daptomycin-naïve patient—a review of the literature

Infected Emphysematous Bullae of the Lung: A Diagnostic Challenge

Infected emphysematous bullae of the lung present a diagnostic challenge due to their rarity and diverse clinical manifestations. We report the case of a 52-year-old female with chronic respiratory symptoms, including breathlessness and dry cough, persisting for six months. Imaging studies revealed characteristic features of infected emphysematous bullae, including large thick-walled cavities with air-fluid levels and associated parenchymal compression. Biomass exposure history and microbiological analysis, which isolated methicillin-resistant coagulase-negative Staphylococcus (MRCoNS), further supported the diagnosis. The patient responded well to antimicrobial therapy with doxycycline and linezolid. This case underscores the importance of considering environmental factors and multidisciplinary collaboration in managing complex respiratory conditions. Further research is warranted to elucidate optimal management strategies for infected emphysematous bullae of the lung.

Staphylococcus aureus response and adaptation to vancomycin

Antibiotic resistance is an increasing challenge for the human pathogen Staphylococcus aureus. Methicillin-resistant S. aureus (MRSA) clones have spread globally, and a growing number display decreased susceptibility to vancomycin, the favoured antibiotic for treatment of MRSA infections. These vancomycin-intermediate S. aureus (VISA) or heterogeneous vancomycin-intermediate S. aureus (hVISA) strains arise from accumulation of a variety of point mutations, leading to cell wall thickening and reduced vancomycin binding to the cell wall building block, Lipid II, at the septum. They display only minor changes in vancomycin susceptibility, with varying tolerance between cells in a population, and therefore, they can be difficult to detect. In this review, we summarize current knowledge of VISA and hVISA. We discuss the role of genetic strain background or epistasis for VISA development and the possibility of strains being 'transient' VISA with gene expression changes mediated by, for example, VraTSR, GraXSR, or WalRK signal transduction systems, leading to temporary vancomycin tolerance. Additionally, we address collateral susceptibility to other antibiotics than vancomycin. Specifically, we estimate how mutations in rpoB, encoding the β-subunit of the RNA polymerase, affect overall protein structure and compare changes with rifampicin resistance. Ultimately, such in-depth analysis of VISA and hVISA strains in terms of genetic and transcriptional changes, as well as changes in protein structures, may pave the way for improved detection and guide antibiotic therapy by revealing strains at risk of VISA development. Such tools will be valuable for keeping vancomycin an asset also in the future.

Population Analysis of Daptomycin-non-Susceptible Methicillin-Resistant Staphylococcus aureus Reveals the Presence of Variants That Contribute to Daptomycin Resistance

In this study, population analysis (PA) of methicillin-resistant Staphylococcus aureus (MRSA), before and after long-duration daptomycin (DAP) treatment, was used to detect subpopulations with different susceptibilities to DAP and to verify the changes in the number of resistant cells. Furthermore, we aimed to characterize the bacteriology of the variants present in the non-susceptible cell subpopulation. A DAP non-susceptible (NS) MRSA phenotype (D2) that emerged from a DAP- susceptible MRSA phenotype (D1) during treatment of an open wound, was used for testing. We performed bacteriological and genetic analyses of cryptic DAP-NS MRSA variants detected by PA to study the variants present in the resistant cell subpopulation. PA results suggest that MRSA adapted to survival in the presence of DAP are selected leading to reduced susceptibility. Within the cell population growing in media containing 2.0 mg/L of DAP, three variants with different pigment production and colony size were detected. Variant 3 was an orange colony due to enhanced production of staphyloxanthin. Our results revealed that the DAP minimum inhibitory concentration (MIC) value increased two-fold (4 mg/L) in variant 3, in which pigment production was most enhanced, compared to the parental strain D2. In conclusion, our results indicate that long-duration DAP treatment can lead to the emergence and increased proportion of DAP-NS subpopulations. Furthermore, slow-growing variants that can be detected only under antimicrobial selective pressure are present among DAP-NS cells, suggesting that these variants may also contribute to the development of DAP resistance.

Molecular Basis of Non-β-Lactam Antibiotics Resistance in Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most successful human pathogens with the potential to cause significant morbidity and mortality. MRSA has acquired resistance to almost all β-lactam antibiotics, including the new-generation cephalosporins, and is often also resistant to multiple other antibiotic classes. The expression of penicillin-binding protein 2a (PBP2a) is the primary basis for β-lactams resistance by MRSA, but it is coupled with other resistance mechanisms, conferring resistance to non-β-lactam antibiotics. The multiplicity of resistance mechanisms includes target modification, enzymatic drug inactivation, and decreased antibiotic uptake or efflux. This review highlights the molecular basis of resistance to non-β-lactam antibiotics recommended to treat MRSA infections such as macrolides, lincosamides, aminoglycosides, glycopeptides, oxazolidinones, lipopeptides, and others. A thorough understanding of the molecular and biochemical basis of antibiotic resistance in clinical isolates could help in developing promising therapies and molecular detection methods of antibiotic resistance.

Studies toward synthesis of the core skeleton of spiroaspertrione A

Bioassay-guided isolation of spiroaspertrione A from cultures of Aspergillus sp. TJ23 in 2017 demonstrated potent resensitization of oxacillin against methicillin-resistant Staphylococcus aureus by lowering the oxacillin minimal inhibitory concentration up to 32-fold. To construct this unique spiro[bicyclo[3.2.2]nonane-2,1′-cyclohexane] system, a protocol for ceric ammonium nitrate-induced intramolecular cross-coupling of silyl enolate is disclosed.

Can Amoxicillin and Clavulanic Acid Impregnated Plaster of Paris Beads Serve as an Effective Alternative to Systemic Antibiotics for Third Molar Surgeries? A Split Mouth Randomized Clinical Trial

Purpose

The present work was a pilot study undertaken to evaluate the effectiveness of amoxicillin and clavulanic acid impregnated plaster of paris beads for prevention of infection of third molar extraction sockets.

Materials and Methods

This was a prospective, randomized, split mouth clinical trial done on 16 patients (32 sites) who required surgical extraction of mandibular third molars. Control arm patients were given Tab. amoxicillin 500 mg with clavulanic acid 125 mg (Tab. Klavimed 625 mg, Indomed, India), thrice daily for 3 days after extraction, whereas test arm patients received Antibiotic Impregnated Microbeads (AIM), containing Amoxicillin 500 mg and Clavulanic Acid 100 mg placed in situ in the extraction socket. The primary outcome parameter was infection and the secondary outcome parameters were pain, trismus, swelling and wound healing.

Results

None of the patients in either group had post operative infection. There was no significant difference in pain intensity between the two groups (1st day p = 0.41; 3rd day p = 0.38, 7th day p = 0.37). Both the groups were also similar with respect to swelling (p = 0.596, 0.146, 0.871, 0.820 on 1st, 3rd, 7th, 15th post-op day ,respectively).

Conclusion

Amoxycillin with clavulanic acid impregnated PoP beads appears to be as effective as oral 3 day amoxicillin with clavulanic acid regime for prevention of 3 M socket infection.

Elasnin Effectively Eradicates Daptomycin-Resistant Methicillin-Resistant Staphylococcus aureus Biofilms

Elasnin is a recently reported antibiofilm agent that is effective against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). Remarkably, we observed that elasnin has a superior activity in eradicating daptomycin-resistant MRSA strain biofilm, with a lower minimum biofilm eradication concentration (MBEC) value of 0.625 μg/mL, compared to 2.5 μg/mL for the wild type. Confocal microscopy further confirmed the higher biofilm eradication on the daptomycin-resistant strain, displaying ∼53% decrease in cell density upon elasnin treatment, while the wild-type strain was only decreased by ∼15%. Quantitative proteomics revealed that the daptomycin-resistant strain has a lower expression of the membrane, cell wall, and extracellular proteins, and also proteins involved in the arginine biosynthesis, pathogenesis, and cell adhesion compared to the wild type, which may result in weaker biofilm development. This study highlights the potential clinical application of elasnin through its superior biofilm eradication activity against a daptomycin-resistant MRSA strain, and revealed the associated processes governing this superior activity through proteomics analysis. IMPORTANCE Due to the increased use of daptomycin for the treatment of MRSA infections, the emergence of daptomycin-resistant strains has become prevalent in recent years. In this study, we discovered that elasnin, a newly reported antibiofilm compound, has a superior activity in eradicating daptomycin-resistant MRSA strain biofilms compared to the wild type. Follow-up analysis revealed the reason behind this superior activity, which is the lower expression of key proteins that play a role in pathogenesis and cell adhesion in the daptomycin-resistant strain, leading to weaker biofilm development. This showcases the potential use of elasnin in clinical settings where daptomycin-resistant strains and biofilm formation are prevalent. Altogether, our study provides new insights into the mechanism of elasnin in MRSA biofilm cells and identified its superior biofilm eradicating activity in the daptomycin-resistant strain.

An atomic perspective on improving daptomycin's activity

BACKGROUND

Recently, through comprehensive medicinal chemistry efforts, we have found a new daptomycin analogue, termed kynomycin, showing enhanced activity against both methicillin-resistant S. aureus and vancomycin-resistant Enterococcus in vitro and in vivo, with improved pharmacokinetics and lower cytotoxicity than daptomycin.

METHODS

In this study we compared the physicochemical properties of kynomycin with those of daptomycin from an atomic perspective by using Nuclear Magnetic Resonance spectroscopy and Molecular Dynamics simulations.

RESULTS AND CONCLUSION

We observed that kynurenine methylation changes daptomycin's key physicochemical properties; its calcium dependent oligomerization efficiency is improved and the modified kynurenine strengths contacts with the lipid tail and tryptophan residues. In addition, it is observed that, compared to daptomycin, kynomycin tetramer is more stable and binds stronger to calcium. The combined experiments provide key clues for the improved antibacterial activity of kynomycin.

GENERAL SIGNIFICANCE

We expect that this approach will help study the calcium binding and oligomerization features of new calcium dependent peptide antibiotics.

Evaluating the Rapid Emergence of Daptomycin Resistance in Corynebacterium: a Multicenter Study

Members of the genus Corynebacterium are increasingly recognized as pathobionts and can be very resistant to antimicrobial agents. Previous studies have demonstrated that Corynebacterium striatum can rapidly develop high-level daptomycin resistance (HLDR) (MIC, ≥256 μg/ml). Here, we conducted a multicenter study to assay for this in vitro phenotype in diverse Corynebacterium species. Corynebacterium clinical isolates (n = 157) from four medical centers were evaluated. MIC values to daptomycin, vancomycin, and telavancin were determined before and after overnight exposure to daptomycin to identify isolates able to rapidly develop daptomycin nonsusceptibility. To investigate assay reproducibility, 18 isolates were evaluated at three study sites. In addition, the stability of daptomycin nonsusceptibility was tested using repeated subculture without selective pressure. The impact of different medium brands was also investigated. Daptomycin nonsusceptibility emerged in 12 of 23 species evaluated in this study (C. afermentans, C. amycolatum, C. aurimucosum, C. bovis, C. jeikeium, C. macginleyi, C. pseudodiphtheriticum, C. resistens, C. simulans, C. striatum, C. tuberculostearicum, and C. ulcerans) and was detected in 50 of 157 (31.8%) isolates tested. All isolates displayed low (susceptible) MIC values to vancomycin and telavancin before and after daptomycin exposure. Repeated subculture demonstrated that 2 of 9 isolates (22.2%) exhibiting HLDR reverted to a susceptible phenotype. Of 30 isolates tested on three medium brands, 13 (43.3%) had differences in daptomycin MIC values between brands. Multiple Corynebacterium species can rapidly develop daptomycin nonsusceptibility, including HLDR, after a short daptomycin exposure period.

Clinical Pharmacokinetics of Daptomycin

Due to the low level of resistance observed with daptomycin, this antibiotic has an important place in the treatment of severe Gram-positive infections. It is the first-in-class of the group of calcium-dependent, membrane-binding lipopeptides, and is a cyclic peptide constituted of 13 amino acids and an n-decanoyl fatty acid chain. The antibacterial action of daptomycin requires its complexation with calcium. Daptomycin is not absorbed from the gastrointestinal tract and needs to be administered parenterally. The distribution of daptomycin is limited (volume of distribution of 0.1 L/kg in healthy volunteers) due to its negative charge at physiological pH and its high binding to plasma proteins (about 90%). Its elimination is mainly renal, with about 50% of the dose excreted unchanged in the urine, justifying dosage adjustment for patients with renal insufficiency. The pharmacokinetics of daptomycin are altered under certain pathophysiological conditions, resulting in high interindividual variability. As a result, therapeutic drug monitoring of daptomycin may be of interest for certain patients, such as intensive care unit patients, patients with renal or hepatic insufficiency, dialysis patients, obese patients, or children. A target for the ratio of the area under the curve to the minimum inhibitory concentration > 666 is usually recommended for clinical efficacy, whereas in order to limit the risk of undesirable muscular effects the residual concentration should not exceed 24.3 mg/L.

Verification of a Novel Approach to Predicting Effects of Antibiotic Combinations: In Vitro Dynamic Model Study with Daptomycin and Gentamicin against Staphylococcus aureus

To explore whether susceptibility testing with antibiotic combinations at pharmacokinetically derived concentration ratios is predictive of the antimicrobial effect, a Staphylococcus aureus strain was exposed to daptomycin and gentamicin alone or in combination in multiple dosing experiments. The susceptibility of the S. aureus strain to daptomycin and gentamicin in combination was tested at concentration ratios equal to the ratios of 24 h areas under the concentration–time curve (AUC₂₄s) of antibiotics simulated in an in vitro dynamic model in five-day treatments. The MICs of daptomycin and gentamicin decreased in the presence of each other; this led to an increase in the antibiotic AUC₂₄/MIC ratios and the antibacterial effects. Effects of single and combined treatments were plotted against the AUC₂₄/MIC ratios of daptomycin or gentamicin, and a significant sigmoid relationship was obtained. Similarly, when the effects of single and combined treatments were related to the total exposure of both drugs (the sum of AUC₂₄/MIC ratios (∑AUC₂₄/MIC)), a significant sigmoid relationship was obtained. These findings suggest that (1) the effects of antibiotic combinations can be predicted by AUC₂₄/MICs using MICs of each antibacterial determined at pharmacokinetically derived concentration ratios; (2) ∑AUC₂₄/MIC is a reliable predictor of the antibacterial effects of antibiotic combinations.

Predicting the antistaphylococcal effects of daptomycin-rifampicin combinations in an in vitro dynamic model

To predict the effects of combined use of antibiotics on their pharmacodynamics, the susceptibility of Staphylococcus aureus to daptomycin-rifampicin combinations was tested at concentration ratios equal to the ratios of daptomycin and rifampicin 24-h areas under the concentration-time curve (AUC₂₄s) simulated in an in vitro dynamic model. In combination with rifampicin, daptomycin MICs decreased 2- to 31-fold, whereas rifampicin MICs were similar with or without daptomycin. The enhanced susceptibility of S. aureus to daptomycin combined with rifampicin resulted in both an increase of the actual AUC₂₄/MIC ratios and also more pronounced antibacterial effects compared with single treatments. The areas between the control growth and time-kill curves (ABBCs) determined in combined and single daptomycin treatments were plotted against AUC₂₄/MIC on the same graph (r² 0.90). These findings suggest that the effects of daptomycin-rifampicin combinations can be predicted by AUC₂₄/MICs of daptomycin using its MIC determined at pharmacokinetically derived daptomycin-to-rifampicin concentration ratios.

Daptomycin Resistance and Tolerance Due to Loss of Function in Staphylococcus aureus dsp1 and asp23

Lipopeptide daptomycin is a last-line cell-membrane-targeting antibiotic to treat multidrug-resistant Staphylococcus aureus Alarmingly, daptomycin-resistant S. aureus isolates have emerged. The mechanisms underlying daptomycin resistance are diverse and share similarities with resistances to cationic antimicrobial peptides and other lipopeptides, but they remain to be fully elucidated. We selected mutants with increased resistance to daptomycin from a library of transposon insertions in sequent type 8 (ST8) S. aureus HG003. Insertions conferring increased daptomycin resistance were localized to two genes, one coding for a hypothetical lipoprotein (SAOUHSC_00362, Dsp1), and the other for an alkaline shock protein (SAOUHSC_02441, Asp23). Markerless loss-of-function mutants were then generated for comparison. All transposon mutants and knockout strains exhibited increased daptomycin resistance compared to those of wild-type and complemented strains. Null and transposon insertion mutants also exhibited increased resistance to cationic antimicrobial peptides. Interestingly, the Δdsp1 mutant also showed increased resistance to vancomycin, a cell-wall-targeting drug with a different mode of action. Null mutations in both dsp1 and asp23 resulted in increased tolerance as reflected by reduced killing to both daptomycin and vancomycin, as well as an increased tolerance to surfactant (Triton X-100). Neither mutant exhibited increased resistance to lysostaphin, a cell-wall-targeting endopeptidase. These findings identified two genes core to the S. aureus species that make previously uncharacterized contributions to antimicrobial resistance and tolerance in S. aureus.

Characterization of compensatory mutations associated with restoration of daptomycin-susceptibility in daptomycin non-susceptible methicillin-resistant Staphylococcus aureus and the role mprF mutations

The objective of this study was to investigate the underlying mechanism explaining reversion of clinical DAP non-susceptible (NS) MRSA isolates to DAP-susceptible (S) by analysis of genomic and cell wall characteristics of clinical DAP-NS MRSA and DAP-S MRSA isolates as well as in vitro revertant DAP-S MRSA using whole genome sequencing (WGS) and analysis of biological properties. WGS of the 4 clinical DAP-NS MRSA revealed mprF mutations resulting in amino acid substitutions or deletion. These same amino acid substitutions and deletion were also observed in the 4 in vitro revertant DAP-S strains. While WGS identified the presence of the same mprF mutations in both the DAP-NS and in vitro DAP-S revertant strains, new mutations were also detected in other genes and intergenic regions of in vitro DAP-S revertant strains. Transmission electron microscopy to assess cell-wall (CW) thickness of 4 sets strains (pre- and post-DAP therapy isolates and in vitro DAP-S revertant) showed that 3 of the 4 isolates developed increased thickness of the CW after DAP therapy. After reversion to DAP susceptibility, CW thickness was decreased to the same level as DAP-S MRSA. Our results indicate that in vitro conversion of DAP-NS MRSA to DAP-S is independent of mprF gene mutations and may be partially explained by a change in CW thickness. However, as some strains showed no change in the CW, further studies are required to elucidate the different mechanisms of resistance to DAP, and factors for conversion of DAP-NS to DAP-S.

Daptomycin

Daptomycin is a cyclic lipopeptide antibiotic used for the treatment of Gram-positive infections including complicated skin and skin structure infections, right-sided infective endocarditis, bacteraemia, meningitis, sepsis and urinary tract infections. Daptomycin has distinct mechanisms of action, disrupting multiple aspects of cell membrane function and inhibiting protein, DNA and RNA synthesis. Although daptomycin resistance in Gram-positive bacteria is uncommon, there are increasing reports of daptomycin resistance in Staphylococcus aureus, Enterococcus faecium and Enterococcus faecalis. Such resistance is seen largely in the context of prolonged treatment courses and infections with high bacterial burdens, but may occur in the absence of prior daptomycin exposure. Furthermore, use of inadequate treatment regimens, irregular drug supply and poor drug quality have also been recognized as other important risk factors for emergence of daptomycin-resistant strains. Antimicrobial susceptibility testing of Gram-positive bacteria, communication between clinicians and laboratories, establishment of internet-based reporting systems, development of better and more rapid diagnostic methods and continuous monitoring of drug resistance are urgent priorities.

Daptomycin Resistance in Clinical MRSA Strains Is Associated with a High Biological Fitness Cost

Daptomycin remains as one of the main treatment options for Methicillin-Resistant Staphylococcus aureus (MRSA). Sporadic resistance cases reported in patients treated with either daptomycin or glycopeptides are a growing concern. In a previous study, we described a clinical case of a patient with a community-acquired MRSA infection resistant to daptomycin and with intermediate resistance to vancomycin who developed a recurrent infection with a susceptible isogenic strain. In the present work, we further investigated the sequential events to determine whether the switch from a daptomycin resistance to a susceptible phenotype was due to a phenomenon of resistance reversion or recurrent infection with a susceptible strain. Pairwise competition experiments showed that the susceptible clinical recurrent SA6850 strain had increased fitness when compared to the resistant counterpart SA6820 strain. In fact, although we have demonstrated that reversion of daptomycin resistance to daptomycin susceptible can occur in vitro after serial passages in drug-free media, phylogenetic analysis suggested that the in vivo process was the result of a recurrent infection with a previous susceptible isolate carried by the patient rather than a resistance reversion of the strain. Whole genome sequence of evolved strains showed that daptomycin resistance in MRSA is associated with a high fitness cost mediated by mutations in mprF gene, revealed as a key element of the biological cost. Moreover, we determined that daptomycin resistance-associated fitness cost was independent of vancomycin intermediate resistance phenotype, as demonstrated in additional clinical MRSA vancomycin susceptible strains. This study highlights important observations as, despite daptomycin offers a useful treatment option for the patients with persistent infections, it has to be carefully monitored. The high fitness cost associated to daptomycin resistance may explain the reduced dissemination of daptomycin resistance and the absence of daptomycin reported outbreaks.

When Good Bugs Go Bad: Epidemiology and Antimicrobial Resistance Profiles of Corynebacterium striatum, an Emerging Multidrug-Resistant, Opportunistic Pathogen

Infections with Corynebacterium striatum have been described in the literature over the last 2 decades, with the majority being bacteremia, central line infections, and occasionally, endocarditis. In recent years, the frequency of C. striatum infections appears to be increasing; a factor likely contributing to this is the increased ease and accuracy of the identification of Corynebacterium spp., including C. striatum, from clinical cultures. The objective of this study was to retrospectively characterize C. striatum isolates recovered from specimens submitted as part of routine patient care at a 1,250-bed, tertiary-care academic medical center. Multiple strain types were recovered, as demonstrated by repetitive-sequence-based PCR. Most of the strains of C. striatum characterized were resistant to antimicrobials commonly used to treat Gram-positive organisms, such as penicillin, ceftriaxone, meropenem, clindamycin, and tetracycline. The MIC₅₀ for ceftaroline was >32 μg/ml. Although there are no interpretive criteria for susceptibility with telavancin, it appeared to have potent in vitro efficacy against this species, with MIC₅₀ and MIC₉₀ values of 0.064 and 0.125 μg/ml, respectively. Finally, as previously reported in case studies, we demonstrated rapid in vitro development of daptomycin resistance in 100% of the isolates tested (n = 50), indicating that caution should be exhibited when using daptomycin for the treatment of C. striatum infections. C. striatum is an emerging, multidrug-resistant pathogen that can be associated with a variety of infection types.

Emergence of Daptomycin-Nonsusceptible Methicillin-Resistant Staphylococcus aureus Clinical Isolates Among Daptomycin-Naive Patients in Korea

This study was conducted to assess emergence of daptomycin-nonsusceptible (DAP-NS) phenotype in DAP-naive patients with invasive Staphylococcus aureus (ISA) infections in Korea. A total of 208 S. aureus clinical isolates were selected from a previous prospective study on ISA infections and evaluated for DAP-NS. Although DAP has never been introduced in Korea, five DAP-NS S. aureus strains (2.4%) were identified among 208 S. aureus strains collected from ISA infections. The DAP-NS phenotype was observed only in methicillin-resistant S. aureus (MRSA) strains, but not in methicillin-susceptible S. aureus strains. One DAP-NS MRSA strain belonged to sequence type 72 (ST72) and four were ST5 MRSA strains, three of which were heteroresistant vancomycin (VAN)-intermediate S. aureus. All these five DAP-NS MRSA strains were from healthcare-associated infections without prior exposure to VAN within 30 days. While the ST72 MRSA strain exhibited DAP-NS phenotype via charge repulsion mechanism, four ST5 DAP-NS S. aureus strains had charge-independent DAP-NS mechanism. None of the five DAP-NS strains displayed significant increase in cell wall thickness, indicating that altered cell wall thickness was not associated with the observed DAP-NS phenotype.

Septic Thrombophlebitis with Persistent Methicillin-Resistant Staphylococcus Aureus Bacteremia and de Novo Resistance to Vancomycin and Daptomycin

Persistent methicillin-resistant Staphylococcus aureus (MRSA) bacteremia is associated with significant risk of mortality, especially when it occurs while on appropriate antimicrobial therapy. We herein describe an unusual case of a patient with prosthetic aortic tissue valve, who suffered from central venous catheter related MRSA bacteremia with septic thrombus formation in the superior vena cava. MRSA bacteremia persisted despite removal of the catheter and appropriate antimicrobial therapy including vancomycin, rifampin, and daptomycin. Subsequently, the MRSA strain exhibited de novo resistance to vancomycin, rifampin and daptomycin. Eventually, salvage combination therapy with high dose daptomycin and trimethoprim-sulfamethoxazole was successful and achieved clearance of MRSA bacteremia. The case illustrates the growing complexity of treating MRSA infections.

Ceftaroline fosamil monotherapy for methicillin-resistant Staphylococcus aureus bacteremia: a comparative clinical outcomes study

OBJECTIVES

Vancomycin is the treatment of choice for methicillin-resistant Staphylococcus aureus (MRSA) bacteremia; however, its use has been subject to scrutiny due to failure in severe infections. Ceftaroline fosamil (CPT-F) is approved for MRSA acute bacterial skin and skin structure infections, but not for bloodstream infections. The clinical outcomes of treatment with CPT-F in patients with MRSA bacteremia were evaluated.

METHODS

Patients diagnosed with MRSA bacteremia at Henry Ford Hospital in Detroit, Michigan, USA, involving isolates with a vancomycin minimum inhibitory concentration ≥1.0mg/l and susceptible in vitro to CPT-F, were systematically reviewed retrospectively. Ceftaroline fosamil-treated patients were matched with at least two vancomycin- and/or one daptomycin-treated control patient based on age-patients age 65 years or greater or less than 65 years of age. Outcomes evaluated included the duration of hospitalization, duration of therapy, adverse events, relapse, hospital readmission, and death.

RESULTS

Thirty consecutive cases of MRSA bacteremia treated with CPT-F during the period May 2011 to June 2013 were identified; these patients were matched to 56 MRSA bacteremia patients treated with vancomycin and 46 MRSA bacteremia patients treated with daptomycin. The primary source of MRSA bacteremia in the cohort treated with CPT-F was endocarditis (n=7, 23%), skin/wound (n=9, 30%), and bone/joint (n=8, 27%). The MRSA bacteremia in those treated with CPT-F was community-acquired in 43% of cases, healthcare-associated in 43%, and hospital-acquired in 13%. The mean length of hospital stay for these patients was 22 days. The overall 30-day mortality rate was 13% (n=4) in CPT-F patients versus 24% (n=11) in daptomycin patients and 11% (n=6) in vancomycin patients (p=0.188).

CONCLUSIONS

CPT-F demonstrated comparable clinical outcomes in MRSA bacteremia patients compared with the other agents, especially as salvage therapy.

Combination Therapy With Vancomycin and Ceftaroline for Refractory Methicillin-resistant Staphylococcus aureus Bacteremia: A Case Series

PURPOSE

Although vancomycin has been the mainstay of therapy for methicillin-resistant Staphylococcus aureus (MRSA) infections, its effectiveness has been challenged. Combination therapy may be used for patients with persistent MRSA bacteremia refractory to initial therapy. Studies have reported in vitro synergy between vancomycin and ceftaroline; however, clinical experience with this therapy is limited. Here, we report our experience with 5 cases of vancomycin-refractory MRSA bacteremia treated with the combination of vancomycin and ceftaroline.

METHODS

Between January 2014 and August 2016, 5 patients were identified who received vancomycin and ceftaroline combination therapy due to persistent bacteremia or deterioration of their clinical status on vancomycin alone (despite a vancomycin MIC within the susceptible range).

FINDINGS

Five patients presented with MRSA bacteremia secondary to endocarditis (n = 2), epidural abscess (n = 2), or left iliopsoas abscess (n = 1). Four of the 5 patients experienced microbiologic cure, and 1 patient transitioned to palliative care.

IMPLICATIONS

This case series serves to describe additional clinical experience with vancomycin and ceftaroline combination therapy. This combination may be considered when vancomycin monotherapy does not lead to microbiological and/or clinical improvement in patients with metastatic MRSA bacteremia. Additional studies are warranted to further define its role in salvage therapy for persistent MRSA bacteremia.

Resistance to Non-glycopeptide Agents in Serious Staphylococcus aureus Infections

The role of vancomycin in the treatment of serious Staphylococcus aureus infections, both methicillin-susceptible and methicillin-resistant, is becoming increasingly ineffective due to increasing MIC and failure. The development of reduced vancomycin susceptibility by S. aureus to glycopeptides highlights the need for clinicians to reexamine the roles of non-glycopeptide therapy. As the use of these alternative non-glycopeptides antimicrobials increases, it will become pertinent to monitor the rates of resistance. Large surveillance programs have provided data for resistance against S. aureus for the non-glycopeptides (daptomycin, ceftaroline, tigecycline, linezolid, and tedizolid). The current published literatures suggest that worldwide resistance rates to these non-glycopeptides for serious MRSA infections are still low. Implementation of antimicrobial stewardship programs will be crucial in prevention of resistance of these antimicrobials against S. aureus.

Multidrug-resistant organisms in liver transplant: Mitigating risk and managing infections

Liver transplant (LT) recipients are vulnerable to infections with multidrug-resistant (MDR) pathogens. Risk factors for colonization and infection with resistant bacteria are ubiquitous and unavoidable in transplantation. During the past decade, progress in transplantation and infection prevention has contributed to the decreased incidence of infections with methicillin-resistant Staphylococcus aureus. However, even in the face of potentially effective antibiotics, vancomycin-resistant enterococci continue to plague LT. Gram-negative bacilli prove to be more problematic and are responsible for high rates of both morbidity and mortality. Despite the licensure of novel antibiotics, there is no universal agent available to safely and effectively treat infections with MDR gram-negative organisms. Currently, efforts dedicated toward prevention and treatment require involvement of multiple disciplines including transplant providers, specialists in infectious diseases and infection prevention, and researchers dedicated to the development of rapid diagnostics and safe and effective antibiotics with novel mechanisms of action. Liver Transplantation 22 1143-1153 2016 AASLD.

Study on daptomycin use and implementation of an antimicrobial stewardship program

BACKGROUND

Treatment of Gram-positive pathogens remains a major health issue due to the presence of methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-Resistant Enterococcus spp. Daptomycin offers an alternative after therapeutic failure using glycopeptides. Yet its use requires strict control given its financial impact and environmental risks. Since 2014, the use of daptomycin within our hospital has intensified, occasionally outside the scope of its approved indications.

OBJECTIVES

The aim of this study is to analyze the appropriateness of daptomycin prescriptions.

SETTING

This work was conducted in a 1500-bed University Hospital.

METHOD

A descriptive retrospective study was conducted from November 2013 to July 2014. All patients having received at least 2 days of treatment were included. Analysis of the appropriateness of daptomycin prescriptions was conducted by a multidisciplinary team comprised of infectious diseases specialists, pharmacists and a microbiologist. The appropriateness of daptomycin prescriptions was established based on Infectious Diseases Society of America recommendations published in 2011.

MAIN OUTCOME MEASURES

The indicators chosen to determine appropriateness of prescription were: treatment indication, prescribed dose and other antibiotics associated with the daptomycin prescription.

RESULTS

19 patients (14 men/5 women) were included. Observed indications were: bone and joint infection (n = 6; 32 %), infectious endocarditis (n = 5; 26 %), bacteremia (n = 5; 26 %) and complicated skin and soft tissue infection (n = 3; 16 %). Identified pathogens were: MRSA (n = 14; 74 %), methicillin-resistant coagulase-negative Staphylococcus (n = 4; 21 %) and Streptococcus mitis (n = 1; 5 %). Daptomycin was prescribed as first-line treatment in 32 % of cases (n = 6). The mean dosage was 9 mg/kg/day (5-11 mg/kg/day) for a mean duration of 11 days (2; 55 days). Clinical success was observed in 42 % of cases (n = 8). Appropriateness for daptomycin use was only established for 15 % of prescriptions (n = 3).

CONCLUSION

Faced with a lack of recent recommendations on the subject, our multidisciplinary team issued a local consensus, defining the indications and dosage modalities for this reserve antibiotic. This multidisciplinary approach enables improved use of recent anti-MRSA drugs.

Daptomycin > 6 mg/kg/day as salvage therapy in patients with complex bone and joint infection: cohort study in a regional reference center

Background

Even if daptomycin does not have approval for the treatment of bone and joint infections (BJI), the Infectious Diseases Society of America guidelines propose this antibiotic as alternative therapy for prosthetic joint infection. The recommended dose is 6 mg/kg/d, whereas recent data support the use of higher doses in these patients.

Methods

We performed a cohort study including consecutive patients that have received daptomycin >6 mg/kg/d for complex BJI between 2011 and 2013 in a French regional reference center. Factors associated with treatment failure were determined on univariate Cox analysis and Kaplan-Meier curves.

Results

Forty-three patients (age, 61 ± 17 years) received a mean dose of 8 ± 0.9 mg/kg/d daptomycin, for a mean 81 ± 59 days (range, 6–303 days). Most had chronic (n = 37, 86 %) implant-associated (n = 37, 86 %) BJI caused by coagulase-negative staphylococci (n = 32, 74 %). A severe adverse event (SAE) occurred in 6 patients (14 %), including 2 cases of eosinophilic pneumonia, concomitant with daptomycin C_min >24 mg/L. Outcome was favorable in 30 (77 %) of the 39 clinically assessable patients. Predictors for treatment failure were age, non-optimal surgery and daptomycin withdrawal for SAE.

Conclusions

Prolonged high-dose daptomycin therapy was effective in patients with complex BJI. However, optimal surgery remains the cornerstone of medico-surgical strategy; and a higher incidence of eosinophilic pneumonia than expected was recorded.

Emergence of Daptomycin-Resistant Staphylococcus aureus during Treatment

A 68-year-old man with persistent bacteremia accompanying a large iliopsoas abscess, vertebral osteomyelitis, discitis and central venous port infection caused by methicillin-resistant Staphylococcus aureus (MRSA) was admitted to our hospital. During the course of treatment, the emergence of a daptomycin (DAP)-resistant MRSA strain was confirmed; the minimum inhibitory concentration was 1 to 2 μg/mL for vancomycin and more than 1 μg/mL for DAP. Although the bacterial cell wall was not significantly thickened, an increased positive surface charge and single-nucleotide polymorphism within mprF have been confirmed in DAP-resistant strains. Still rare, but clinicians need to be cautious of the emergence of DAP-resistant MRSA during treatment.

Daptomycin non-susceptible, vancomycin-intermediate Staphylococcus aureus endocarditis treated with ceftaroline and daptomycin: case report and brief review of the literature

We report a case of clearance of persistent bacteremia due to daptomycin non-susceptible, vancomycin-intermediate Staphylococcus aureus native mitral valve endocarditis with a combination of ceftaroline and daptomycin, in an 81-year-old medically complex patient who was not an operative candidate.

Towards a definition of daptomycin optimal dose: Lessons learned from experimental and clinical data

Daptomycin exhibits excellent antibacterial activity against a wide range of Gram-positive bacteria. The on-label standard daily doses for daptomycin are 4 mg/kg for skin infections and 6 mg/kg for bacteraemia or right-sided endocarditis. Daptomycin bactericidal activity is predominantly concentration-dependent and by considering the values of pharmacokinetic targets established by several authors as well as the peak and trough concentrations of daptomycin obtained at various daily dosages, it appears that these targets can easily be reached with a dose of 6 mg/kg but only for a minimum inhibitory concentration (MIC) at 0.1 mg/L, and that for increasing MICs (e.g. 0.5 mg/L or 1 mg/L) these targets may only be attained with higher dosages (i.e. ≥10 mg/kg). High-dose (HD) daptomycin therapy has also been proven to be effective for reducing the risk of selection of daptomycin-resistant strains. Given the concentration-dependent bactericidal activity of daptomycin, the absence of a dose-toxicity relationship and the need to prevent the selection of resistant strains, we propose to consider for staphylococcal (i) skin and soft-tissue infections, daily doses of daptomycin of 6 mg/kg (new standard dose) and (ii) endocarditis or bacteraemia including those associated with intravascular catheter and implant-related infections, ≥10 mg/kg (HD) when the MIC is unknown or >0.25 mg/L, and 6-10 mg/kg (intermediate doses) when the MIC is ≤0.25 mg/L. For severe and deep-seated enterococcal infections, we propose high (≥10 mg/kg) daily doses of daptomycin in combination with another active agent, especially a β-lactam.

Synergistic, collaterally sensitive β-lactam combinations suppress resistance in MRSA

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent multidrug-resistant pathogens worldwide, exhibiting increasing resistance to the latest antibiotic therapies. Here we show that the triple β-lactam combination meropenem-piperacillin-tazobactam (ME/PI/TZ) acts synergistically and is bactericidal against MRSA subspecies N315 and 72 other clinical MRSA isolates in vitro and clears MRSA N315 infection in a mouse model. ME/PI/TZ suppresses evolution of resistance in MRSA via reciprocal collateral sensitivity of its constituents. We demonstrate that these activities also extend to other carbapenem-penicillin-β-lactamase inhibitor combinations. ME/PI/TZ circumvents the tight regulation of the mec and bla operons in MRSA, the basis for inducible resistance to β-lactam antibiotics. Furthermore, ME/PI/TZ subverts the function of penicillin-binding protein-2a (PBP2a) via allostery, which we propose as the mechanism for both synergy and collateral sensitivity. Showing in vivo activity similar to that of linezolid, ME/PI/TZ demonstrates that combinations of older β-lactam antibiotics could be effective against MRSA infections in humans.

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.

Impact of Molecular Epidemiology and Reduced Susceptibility to Glycopeptides and Daptomycin on Outcomes of Patients with Methicillin-Resistant Staphylococcus aureus Bacteremia

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) bacteremia was associated with high mortality, but the risk factors associated with mortality remain controversial.

METHODS

A retrospective cohort study was designed. All patients with MRSA bacteremia admitted were screened and collected for their clinical presentations and laboratory characteristics. Minimum inhibitory concentration (MIC) and staphylococcal cassette chromosome mec (SCCmec) type of bacterial isolates were determined. Risk factors for mortality were analyzed.

RESULTS

Most MRSA isolates from the 189 enrolled patients showed reduced susceptibility to antibiotics, including MIC of vancomycin ≥ 1.5 mg/L (79.9%), teicoplanin ≥ 2 mg/L (86.2%), daptomycin ≥ 0.38 mg/L (73.0%) and linezolid ≥ 1.5 mg/L (64.0%). MRSA with vancomycin MIC ≥ 1.5 mg/L and inappropriate initial therapy were the two most important risk factors for mortality (both P < 0.05; odds ratio = 7.88 and 6.78). Hospital-associated MRSA (HA-MRSA), carrying SCCmec type I, II, or III, was associated with reduced susceptibility to vancomycin, teicoplanin or daptomycin and also with higher attributable mortality (all P < 0.05). Creeping vancomycin MIC was linked to higher MIC of teicoplanin and daptomycin (both P < 0.001), but not linezolid (P = 0.759).

CONCLUSIONS

Giving empirical broad-spectrum antibiotics for at least 5 days to treat catheter-related infections, pneumonia, soft tissue infection and other infections was the most important risk factor for acquiring subsequent HA-MRSA infection. Choice of effective anti-MRSA agents for treating MRSA bacteremia should be based on MIC of vancomycin, teicoplanin and daptomycin. Initiation of an effective anti-MRSA agent without elevated MIC in 2 days is crucial for reducing mortality.

The effect of inoculum size on selection of in vitro resistance to vancomycin, daptomycin, and linezolid in methicillin-resistant Staphylococcus aureus

OBJECTIVES

The inoculum effect (IE) is an increase in the minimum inhibitory concentration (MIC) at high bacterial densities. The effect of three inoculum sizes on the selection of resistance to vancomycin, daptomycin, and linezolid was investigated in methicillin-resistant Staphylococcus aureus (MRSA).

METHODS

Low (10(4) CFU/ml), medium (10(6) CFU/ml), and high (10(8) CFU/ml) inocula of MRSA were exposed to twofold increasing concentrations of either drug during 15 days of cycling. MICs for low (MICL), medium (MICM), and high (MICH) inocula were determined daily. Conventional MICs were measured at days 1, 5, 10, and 15. Experiments were performed in triplicate.

RESULTS

At the beginning of the experiment a small IE was observed for vancomycin (MICL=1 μg/ml, MICM=1-2 μg/ml, and MICH=2 μg/ml) and a significant IE for daptomycin (MICL=0.25 μg/ml, MICM=0.25-0.5 μg/ml, and MICH=2 μg/ml). Linezolid exhibited no IE at low and medium inocula (MICL=1 μg/ml and MICM=1-2 μg/ml), but with the high inoculum, concentrations up to 2,048 μg/ml did not fully inhibit visual growth. During cycling, increase of MIC was observed for all antibiotics. At day 15, MICL, MICM, and MICH of vancomycin were 2-4, 4-8, and 4-16 μg/ml and of daptomycin were 0.5-2, 8-128, and 64-256 μg/ml, respectively. MICL and MICM of linezolid were 1 and 2-4 μg/ml, respectively. Conventional MICs showed vancomycin and daptomycin selection of resistance since day 5 depending on the inocula. No selection of linezolid resistance was observed.

CONCLUSIONS

Our results showed the importance of the inoculum size in the development of resistance. Measures aimed at lowering the inoculum at the site of infection should be used whenever possible in parallel to antimicrobial therapy.

Prevalence of vancomycin-intermediate Staphylococcus aureus (VISA) and heterogeneous VISA among methicillin-resistant S. aureus with high vancomycin minimal inhibitory concentrations in Taiwan: A multicenter surveillance study, 2012-2013

BACKGROUND/PURPOSE

Intermediate-resistance and heteroresistance to vancomycin in methicillin-resistant Staphylococcus aureus (MRSA) is reported worldwide. A surveillance study in 2003 showed that the prevalence rates of vancomycin-intermediate S. aureus (VISA) and heterogeneous VISA (hVISA) in Taiwan were 0.2% and 0.7%, respectively. This study aimed to investigate the updated prevalence of VISA and hVISA in Taiwan.

METHODS

MRSA isolates from sterile sites with minimal inhibitory concentrations (MICs) of 1 μg/mL or more to vancomycin were collected from 15 participating hospitals in Taiwan. Enrolled MRSA isolates were submitted to antimicrobial susceptibility testing, staphylococcal cassette chromosome mec (SCCmec) element typing, and multilocus sequence typing. Isolates with vancomycin MIC of 1 μg/mL or 2 μg/mL were screened for vancomycin heterogeneous resistance by Etest glycopeptide-resistance detection (GRD). Those with positive GRD screening results were then analyzed by modified population analysis profiling-area under the curve method for confirmation of vancomycin heteroresistance.

RESULTS

Between 2012 and 2013, a total of 622 MRSA isolates from sterile sites with vancomycin MIC of 1 μg/mL or more were studied. The prevalence rates of hVISA and VISA among these isolates were 10.0% and 2.7%, respectively. The hVISA prevalence increased significantly compared to that in 2003. Compared with vancomycin-susceptible S. aureus, hVISA and VISA isolates were less susceptible to ciprofloxacin, clindamycin, daptomycin, gentamicin, rifampin, and trimethoprim/sulfamethoxazole, and are thus, more likely to have SCCmec II or III element. A twofold increase in either vancomycin or teicoplanin MIC doubled the probability of being hVISA.

CONCLUSION

Growing hVISA prevalence was highly suspected. Longitudinal surveillance of this phenomenon and monitoring of its clinical impact are necessary.

Potential role for telavancin in bacteremic infections due to gram-positive pathogens: focus on Staphylococcus aureus

Staphylococcus aureus bacteremia (SAB) is one of the most common serious bacterial infections and the most frequent invasive infection due to methicillin-resistant S. aureus (MRSA). Treatment is challenging, particularly for MRSA, because of limited treatment options. Telavancin is a bactericidal lipoglycopeptide antibiotic that is active against a range of clinically relevant gram-positive pathogens including MRSA. In experimental animal models of sepsis telavancin was shown to be more effective than vancomycin. In clinically evaluable patients enrolled in a pilot study of uncomplicated SAB, cure rates were 88% for telavancin and 89% for standard therapy. Among patients with infection due to only gram-positive pathogens enrolled in the 2 phase 3 studies of telavancin for treatment of hospital-acquired pneumonia, cure rates for those with bacteremic S. aureus pneumonia were 41% (9/22, telavancin) and 40% (10/25, vancomycin) with identical mortality rates. These data support further evaluation of telavancin in larger, prospective studies of SAB.

Ceftaroline Fosamil for the Treatment of Staphylococcus aureus Bacteremia Secondary to Acute Bacterial Skin and Skin Structure Infections or Community-Acquired Bacterial Pneumonia

BACKGROUND

The Clinical Assessment Program and Teflaro® Utilization Registry is designed to collect information on the clinical use of ceftaroline fosamil in the Unites States. This report presents data on the treatment of patients with Staphylococcus aureus bacteremia (SAB) secondary to acute bacterial skin and skin structure infections (ABSSSIs) or community-acquired bacterial pneumonia (CABP).

METHODS

Patients diagnosed with ABSSSI or CABP were identified through sequential review of randomly ordered charts generated from pharmacy listings from August 2011 to February 2013. Data were collected by chart review 30 days or more after completion of ceftaroline fosamil therapy.

RESULTS

Secondary SAB was reported in a total of 48 of 1428 evaluable patients (27 with ABSSSI, 21 with CABP). The mean (SD) patient age was 61 (15) years. At least 1 comorbidity was recorded for 74% of patients with ABSSSI and 81% with CABP. Methicillin-resistant S. aureus was isolated from 59% of patients with ABSSSI and 76% with CABP. The mean (SD) duration of ceftaroline fosamil therapy was 5.8 (4.8) days for ABSSSI and 7.0 (3.8) days for CABP. Clinical success among all patients with SAB treated with ceftaroline fosamil was 58% (52% for SAB secondary to ABSSSI, 67% for SAB secondary to CABP). Clinical success rates of methicillin-resistant S. aureus SAB were 50% (8/16) for ABSSSI and 63% (10/16) for CABP.

CONCLUSIONS

This study supports the use of ceftaroline fosamil as a viable treatment option in hospitalized patients with SAB secondary to ABSSSI or CABP. Further studies evaluating the use of ceftaroline fosamil for the treatment of SAB are warranted.

Rapid emergence of daptomycin resistance in clinical isolates of Corynebacterium striatum… a cautionary tale

The objective of this study was to investigate the observation of daptomycin resistance in Corynebacterium striatum, both in vivo and in vitro. We describe a case of C. striatum bacteremia in a patient with a left ventricular assist device (LVAD); the initial isolate recovered was daptomycin susceptible with a minimum inhibitory concentration (MIC) of 0.125 μg/ml. Two months later, and after daptomycin therapy, the individual became bacteremic with an isolate of C. striatum with a daptomycin MIC of >256 μg/ml. To study the prevalence of daptomycin resistance in C. striatum, clinical isolates of C. striatum were grown in broth culture containing daptomycin to investigate the emergence of resistance to this antimicrobial. Molecular typing was used to evaluate serial isolates from the index patient and the clinical isolates of C. striatum we assayed. In vitro analysis of isolates from the index patient and 7 of 11 additional C. striatum isolates exhibited the emergence of high-level daptomycin resistance, despite initially demonstrating low MICs to this antimicrobial agent. This phenotype was persistent even after serial subculture in the absence of daptomycin. Together, these data demonstrate that caution should be taken when using daptomycin to treat high-inoculum infections and/or infections of indwelling medical devices with C. striatum. To our knowledge, this is the first report characterizing the emergence of daptomycin resistance in C. striatum.

Penetration of daptomycin into bone and synovial fluid in joint replacement

Daptomycin exhibits clinical activity in the treatment of infections with Gram-positive organisms, including infections due to methicillin-resistant Staphylococcus aureus. However, little is known about its penetration into bone and synovial fluid. The aim of our study was to assess the penetration of daptomycin into bone and synovial fluid after a single intravenous administration. This study was conducted in 16 patients who underwent knee or hip replacement and received a single intravenous dose of 8 mg of daptomycin per kg of body weight prior to surgery. Plasma daptomycin concentrations were measured 1 h after the end of daptomycin infusion and when bone fragments were removed. Daptomycin concentrations were also measured on bone fragments and synovial fluid collected at the same time during surgery. All samples were analyzed with a diode array-high-performance liquid chromatography (HPLC) method. After a single-dose intravenous infusion, bone daptomycin concentrations were above the MIC of daptomycin for Staphylococcus aureus in all subjects, and the median bone penetration percentage was 9.0% (interquartile range [IQR], 4.4 to 11.4). These results support the use of daptomycin in the treatment of Staphylococcus aureus bone and joint infections.

The impact of initial antibiotic therapy (linezolid, vancomycin, daptomycin) on hospital length of stay for complicated skin and soft tissue infections

Background

Empiric therapy of inpatient skin and soft tissue infections (SSTIs) generally require methicillin resistant Staphylococcus aureus (MRSA) coverage. Limited data are available to directly compare the effect of initial antibiotic choice on treatment outcomes and length of stay (LOS).

Objective

To assess potential differences in length of hospital stay when inpatients with complex skin and soft tissue infections (SSTIs) were initially treated with either vancomycin, linezolid, or daptomycin.

Methods

A retrospective review of 219 patients diagnosed with inpatient SSTI who received linezolid, vancomycin, or daptomycin for >48 hours was performed. Data collected included demographics, comorbidities, microbiologic/laboratory data, additional management (surgical, non-study antibiotics), hospital LOS, treatment outcome and morbidity/mortality.

Results

The three groups evaluated were linezolid (n = 45), vancomycin (n = 90) daptomycin (n = 84). There was no difference between the three groups with respect to gender, age, comorbidities, leukocytosis, fever, antibiotics prior to admission, site of infection culture results and surgical intervention. One death was recorded, not associated with diagnosis of SSTI. No significant difference in LOS was found (P = 0.525) between the 3 groups. The mean LOS in entire cohort was 4.5 days (SD ± 2.5); thirty patients had prolonged LOS for non-SSTI reasons; reanalyzing the data without these 30 patients did not produce any difference in the mean LOS between the 3 groups. Switching vancomycin just prior to discharge to facilitate outpatient therapy was common but did not impact LOS.

Conclusions

No difference was detected in hospital length of stay with respect to the initial choice of antibiotic (linezolid, vancomycin, or daptomycin) for SSTI. The three antibiotic regimens were equally effective in treating SSTIs as judged by LOS, irrespective of age, gender, comorbidities or baseline severity of SSTI. Given the large standard deviation in LOS, this result should be confirmed by larger studies.

Treatment of infections due to resistant Staphylococcus aureus

This chapter reviews data on the treatment of infections caused by drug-resistant Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA). This review covers findings reported in the English language medical literature up to January of 2013. Despite the emergence of resistant and multidrug-resistant S. aureus, we have seven effective drugs in clinical use for which little resistance has been observed: vancomycin, quinupristin-dalfopristin, linezolid, tigecycline, telavancin, ceftaroline, and daptomycin. However, vancomycin is less effective for infections with MRSA isolates that have a higher MIC within the susceptible range. Linezolid is probably the drug of choice for the treatment of complicated MRSA skin and soft tissue infections (SSTIs); whether it is drug of choice in pneumonia remains debatable. Daptomycin has shown to be non-inferior to either vancomycin or β-lactams in the treatment of staphylococcal SSTIs, bacteremia, and right-sided endocarditis. Tigecycline was also non-inferior to comparator drugs in the treatment of SSTIs, but there is controversy about whether it is less effective than other therapeutic options in the treatment of more serious infections. Telavancin has been shown to be non-inferior to vancomycin in the treatment of SSTIs and pneumonia, but has greater nephrotoxicity. Ceftaroline is a broad-spectrum cephalosporin with activity against MRSA; it is non-inferior to vancomycin in the treatment of SSTIs. Clindamycin, trimethoprim-sulfamethoxazole, doxycycline, rifampin, moxifloxacin, and minocycline are oral anti-staphylococcal agents that may have utility in the treatment of SSTIs and osteomyelitis, but the clinical data for their efficacy is limited. There are also several drugs with broad-spectrum activity against Gm-positive organisms that have reached the phase II and III stages of clinical testing that will hopefully be approved for clinical use in the upcoming years: oritavancin, dalbavancin, omadacycline, tedizolid, delafloxacin, and JNJ-Q2. Thus, there are currently many effective drugs to treat resistant S. aureus infections and many promising agents in the pipeline. Nevertheless, S. aureus remains a formidable adversary, and despite our deep bullpen of potential therapies, there are still frequent treatment failures and unfortunate clinical outcomes. The following discussion summarizes the clinical challenges presented by MRSA, the clinical experience with our current anti-MRSA antibiotics, and the gaps in our knowledge on how to use these agents to most effectively combat MRSA infections.