Serious infections due to methicillin-resistant Staphylococcus aureus: an evolving challenge for physicians

Broad-Spectrum Therapeutic Potentials of the Multifaceted Triterpene Lupeol and Its Derivatives

Lupeol (LUP), a naturally occurring pentacyclic triterpene, is found in various fruits, vegetables, and medicinal plants and is evident to possess diverse pharmacological activities. This study aimed to consolidate its findings based on updated database reports. Findings suggest that LUP and some of its derivatives have promising biological roles, including anticancer effects. Notably, LUP induces apoptosis and cell cycle arrest in cancer cells while sparing normal cells, highlighting its selective cytotoxicity. By modifying pathways such as NF-κB and phosphatidyl inositol 3-kinase (PI3K)/Akt, LUP demonstrates anticancer activity, reducing LDL oxidation by 34.4% and causing cancer cells to undergo apoptosis while leaving healthy cells unaffected. Moreover, it has strong antioxidant and anti-inflammatory properties; thus, it may act against conditions like arthritis, asthma, and cardiovascular diseases. It has broad-spectrum antimicrobial activities and can be used as an alternative to conventional antibiotics. LUP and its nanoformulations (PEGylated liposomes) improved biopharmaceutical profiles in test systems. It also showed neuroprotective effects, particularly against Alzheimer's and Parkinson's diseases. Taken together, LUP has multi-target therapeutic approaches against various diseases and pathological conditions, advocating for its inclusion in future clinical trials.

Therapeutic drug monitoring of antibiotics for methicillin-resistant Staphylococcus aureus infections: an updated narrative review for clinicians

BACKGROUND

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are associated with high mortality rates. Optimal antibiotic dosage plays a crucial role in reducing MRSA burden; thus, the use of therapeutic drug monitoring (TDM) in the clinical practice, especially of new drugs such as ceftobiprole, ceftaroline, dalbavancin, and oritavancin, should be implemented.

OBJECTIVES

We aim to examine and summarize the available evidence about TDM of anti-MRSA molecules, with a focus on pneumonia, endocarditis and vascular infections, and bone and joint infections.

SOURCES

We applied 'therapeutic drug monitoring' and 'Staphylococcus aureus' as search terms in PubMed, considering a time frame of 24 years (2001-2024). Articles in English language, non-duplicated, evaluating antibiotic therapeutic target, and role of TDM were included in the study.

CONTENT

In this review, available data for therapeutic target and TDM were critically analysed and summarized and suggestions about the use of old and new anti-MRSA antibiotics were provided, focusing on optimal dosages, tissue penetration according to infection types, and toxicity. Limitations to the widespread use of TDM in clinical practice were discussed.

IMPLICATIONS

The use of TDM may play an important role for the optimal management of patients with MRSA infections and may impact on patient outcomes by increasing efficacy and reducing the risk of adverse events. TDM may be implemented in clinical practice; however, several limitations such as the wide variability in the methodology and the need for skilled personnel need to be considered.

Skin and soft tissue infections in the elderly

PURPOSE OF REVIEW

To highlight the peculiarity of skin and soft tissue infections (SSTIs) in elderly patients and to provide useful elements for their optimal management.

RECENT FINDINGS

In the COVID-19 era, early discharge from the hospital and implementation of outpatient management is of key importance.

SUMMARY

Elderly patients are at high risk of SSTIs due to several factors, including presence of multiple comorbidities and skin factors predisposing to infections. Clinical presentation may be atypical and some signs of severity, such as fever and increase in C-reactive protein, may be absent or aspecific in this patients population. An appropriate diagnosis of SSTIs in the elderly is crucial to avoid antibiotic overtreatment. Further studies should explore factors associated with bacterial superinfections in patients with pressure ulcers or lower limb erythema. Since several risk factors for methicillin-resistant Staphylococcus aureus (MRSA) may coexist in elderly patients, these subjects should be carefully screened for MRSA risk factors and those with high risk of resistant etiology should receive early antibiotic therapy active against MRSA. Physicians should aim to several objectives, including clinical cure, patient safety, early discharge and return to community. SSTIs in the elderly may be managed using long-acting antibiotics, but clinical follow-up is needed.

Challenges in the management of chronic wound infections

OBJECTIVES

Chronic wound infections may delay the healing process and are responsible for a significant burden on healthcare systems. Since inappropriate management may commonly occur in the care of these patients, this review aims to provide a practical guide underlining actions to avoid in the management of chronic wound infections.

METHODS

We performed a systematic review of the literature available in PubMed in the last 10 years, identifying studies regarding the management of patients with chronic wound infections. A panel of experts discussed the potential malpractices in this area. A list of 'Don'ts', including the main actions to be avoided, was drawn up using the 'Choosing Wisely' methodology.

RESULTS

In this review, we proposed a list of actions to avoid for optimal management of patients with chronic wound infections. Adequate wound bed preparation and wound antisepsis should be combined, as the absence of one of them leads to delayed healing and a higher risk of wound complications. Moreover, avoiding inappropriate use of systemic antibiotics is an important point because of the risk of selection of multidrug-resistant organisms as well as antibiotic-related adverse events.

CONCLUSION

A multidisciplinary team of experts in different fields (surgeon, infectious disease expert, microbiologist, pharmacologist, geriatrician) is required for the optimal management of chronic wound infections. Implementation of this approach may be useful to improve the management of patients with chronic wound infections.

Diabetes and acute bacterial skin and skin structure infections

Acute bacterial skin and skin structures infections (ABSSSIs) are associated with high morbidity, costs and mortality in patients with diabetes mellitus. Their appropriate management should include several figures and a well-organized approach. This review aims to highlight the interplay between diabetes and ABSSSIs and bring out the unmet clinical needs in this area. Pathogenetic mechanisms underlying the increased risk of ABSSSIs in diabetes mellitus are multifactorial: high glucose levels play a crucial pathogenetic role in the tissue damage and delayed clinical cure. Moreover, the presence of diabetes complications (neuropathy, vasculopathy) further complicates the management of ABSSSIs in patients with diabetes. Multidrug resistance organisms should be considered in this population based on patient risk factors and local epidemiology and etiological diagnosis should be obtained whenever possible. Moreover, drug-drug interactions and drug-related adverse events (such as nephrotoxicity) should be considered in the choice of antibiotic therapy. Reducing unnecessary hospitalizations and prolonged length of hospital stay is of primary importance now, more than ever. To achieve these objectives, a better knowledge of the interplay between acute and chronic hyperglycemia, multidrug resistant etiology, and short and long-term outcome is needed. Of importance, a multidisciplinary approach is crucial to achieve full recovery of these patients.

Cationic antimicrobial peptides: alternatives and/or adjuvants to antibiotics active against methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

Methicillin-resistant Staphylococcus aureus and multidrug-resistant Pseudomonas aeruginosa are becoming difficult to treat with antibiotics whereas Cationic Antimicrobial Peptides (CAMPs) represent promising alternatives. The effects of four CAMPs (LL-37: human cathelicidin, CAMA: cecropin(1-7)-melittin A(2-9) amide, magainin-II and nisin) were investigated against clinical and laboratory S. aureus (n = 10) and P. aeruginosa (n = 11) isolates either susceptible or resistant to antibiotics. Minimal Inhibitory Concentrations (MICs), Minimal Bactericidal Concentrations (MBCs), and bacterial survival rates (2 h post-treatment) were determined by microbroth dilution. The antipseudomonal effects of the antibiotics colistin or imipenem combined to LL-37 or CAMA were also studied. The toxicity of CAMPs used alone and in combination with antibiotics was evaluated on two human lung epithelial cell lines by determining the quantity of released cytoplasmic lactate dehydrogenase (LDH). Attempts to induce bacterial resistance to gentamicin, LL-37 or CAMA were also performed.

RESULTS

The results revealed the rapid antibacterial effect of LL-37 and CAMA against both antibiotic susceptible and resistant strains with almost a total reduction in bacterial count 2 h post-treatment. Magainin-II and nisin were less active against tested strains. When antibiotics were combined with LL-37 or CAMA, MICs of colistin decreased up to eight-fold and MICs of imipenem decreased up to four-fold. Cytotoxicity assays revealed non-significant LDH-release suggesting no cell damage in all experiments. Induction of bacterial resistance to LL-37 was transient, tardive and much lower than that to gentamicin and induction of resistance to CAMA was not observed.

CONCLUSION

This study showed the potent and rapid antibacterial activity of CAMPs on both laboratory and clinical isolates of S. aureus and P. aeruginosa either susceptible or resistant to antibiotics. Most importantly, CAMPs synergized the efficacy of antibiotics, had non toxic effects on human cells and were associated with transient and low levels of induced resistance.

Synergistic effect of linezolid with fosfomycin against Staphylococcus aureus in vitro and in an experimental Galleria mellonella model

BACKGROUND/PURPOSES

Treatment of Staphylococcus aureus infections is challenging owing to widespread multidrug resistance. There is now considerable interest in the potential of combination therapies. Although linezolid/fosfomycin combination appears to be a promising treatment option based on in vitro data, further preclinical work is needed. In this study, the Galleria mellonella system was employed to study the in vivo efficacy of this combination in order to determine whether it should be explored further for the treatment of S. aureus infections.

METHODS

The antimicrobial activity of linezolid and fosfomycin alone and in combination was assessed versus four S. aureus. Synergy studies were performed using the microtitre plate chequerboard assay and time-kill methodology. The in vivo activity of linezolid/fosfomycin combination was assessed using a G. mellonella larvae model.

RESULTS

The combination of linezolid and fosfomycin was synergistic and bacteriostatic against four tested strains. Treatment of G. mellonella larvae infected with lethal doses of S. aureus resulted in significantly enhanced survival rates when low-dose of combination has no significant differences with high-dose combination (P > 0.05), G. mellonella hemolymph burden of S. aureus suggest that combination therapy with rapid and sustained bacteriostatic activity compared monotherapy.

CONCLUSION

This work indicated that linezolid combination with fosfomycin has synergistic effect against S. aureus in vitro and in an experimental G. mellonella model, and it suggests that high-dose of linezolid and fosfomycin may not necessary.

Acute bacterial skin and skin structure infections in internal medicine wards: old and new drugs

Skin and soft tissue infections (SSTIs) are a common cause of hospital admission among elderly patients, and traditionally have been divided into complicated and uncomplicated SSTIs. In 2010, the FDA provided a new classification of these infections, and a new category of disease, named acute bacterial skin and skin structure infections (ABSSSIs), has been proposed as an independent clinical entity. ABSSSIs include three entities: cellulitis and erysipelas, wound infections, and major cutaneous abscesses This paper revises the epidemiology of SSTIs and ABSSSIs with regard to etiologies, diagnostic techniques, and clinical presentation in the hospital settings. Particular attention is owed to frail patients with multiple comorbidities and underlying significant disease states, hospitalized on internal medicine wards or residing in nursing homes, who appear to be at increased risk of infection due to multi-drug resistant pathogens and treatment failures. Management of ABSSSIs and SSTIs, including evaluation of the hemodynamic state, surgical intervention and treatment with appropriate antibiotic therapy are extensively discussed.

mecA Gene Dissemination Among Staphylococcal and Non-staphylococcal Isolates Shed in Surface Waters

Aquatic ecosystems represent important vehicles for the dissemination of antibiotic resistant bacteria and antibiotic resistance genes. Of particular interest are methicillin-resistant staphylococci (MRS) harboring mecA gene that confers their resistance to β-lactams. Therefore, in this study, water samples collected from different locations of a river impacted by surrounding facilities and domestic effluents were analyzed to learn more about the occurrence of MRS and mecA gene. Out of 290, 12 surface water isolates displayed resistance to both cefoxitin and oxacillin antibiotics. Resistant staphylococcal and non-staphylococcal isolates, identified by 16S rRNA sequencing, were found to harbor mecA gene. The phylogenetic tree of partial mecA sequences obtained from staphylococcal and non-staphylococcal isolates showed sequence similarity values of 8 %-100 %. Surface water bodies receive contaminated waters via runoff, effluents from industrial, agricultural, and municipal discharges. Therefore, surface waters are not only hot spots for mecA harboring staphylococcal isolates but also non-staphylococcal isolates and require special scientific consideration.

Optimizing antibiotic therapy of bacteremia and endocarditis due to staphylococci and enterococci: new insights and evidence from the literature

Gram-positive cocci are a well-recognised major cause of nosocomial infection worldwide. Bloodstream infections due to methicillin-resistant Staphylococcus aureus, methicillin-resistant coagulase-negative staphylococci, and multi-drug resistant enterococci are a cause of concern for physicians due to their related morbidity and mortality rates. Aim of this article is to review the current state of knowledge regarding the management of BSI caused by staphylococci and enterococci, including infective endocarditis, and to identify those factors that may help physicians to manage these infections appropriately. Moreover, we discuss the importance of an appropriate use of antimicrobial drugs, taking in consideration the in vitro activity, clinical efficacy data, pharmacokinetic/pharmacodynamic parameters, and potential side effects.

Linezolid-resistant staphylococcal bacteraemia: A multicentre case-case-control study in Italy

The aim of this multicentre study was to analyse the characteristics of patients with bloodstream infections due to staphylococcal strains resistant to linezolid. This was a retrospective case-case-control study of patients hospitalised in three large teaching hospitals in Italy. A linezolid-resistant (LIN-R) Staphylococcus spp. group and a linezolid-susceptible (LIN-S) Staphylococcus spp. group were compared with control patients to determine the clinical features and factors associated with isolation of LIN-R strains. All LIN-R Staphylococcus spp. strains underwent molecular typing. Compared with the LIN-S group, central venous catheters were the main source of infection in the LIN-R group. The LIN-R and LIN-S groups showed a similar incidence of severe sepsis or septic shock, and both showed a higher incidence of these compared with the control group. Overall, patients in the LIN-R group had a higher 30-day mortality rate. Multivariate analysis found previous linezolid therapy, linezolid therapy >14 days, antibiotic therapy in the previous 30 days, antibiotic therapy >14 days, previous use of at least two antibiotics and hospitalisation in the previous 90 days as independent risk factors associated with isolation of a LIN-R strain. The G2576T mutation in domain V of 23S rRNA was the principal mechanism of resistance; only one strain of Staphylococcus epidermidis carried the cfr methylase gene (A2503), together with L4 insertion (71GGR72) and L3 substitution (H146Q). LIN-R strains are associated with severe impairment of clinical conditions and unfavourable patient outcomes. Reinforcement of infection control measures may have an important role in preventing these infections.

Brazilian experience in EU-CORE: daptomycin registry and treatment of serious Gram-positive infections

Objectives

To collect data about non-controlled prescribing use of daptomycin and its impact among Brazilian patients with serious Gram positive bacterial infection, as well as the efficacy and safety outcomes.

Materials and methods

This is a multi-center, retrospective, non-interventional registry (August 01, 2009 to June 30, 2011) to collect data on 120 patients (44 patients in the first year and 76 patients in the second year) who had received at least one dose of commercial daptomycin in Brazil for the treatment of serious Gram-positive bacterial infection.

Results

Right-sided endocarditis (15.8%), complicated skin and soft tissue infections (cSSTI)-wound (15.0%) and bacteremia-catheter-related (14.2%) were the most frequent primary infections; lung (21.7%) was the most common site for infection. Daptomycin was used empirically in 76 (63.3%) patients, and methicillin-resistant Staphylococcus aureus (MRSA) was the most common suspected pathogen (86.1%). 82.5% of the cultures were obtained prior to or shortly after initiation of daptomycin therapy. Staphylococcus spp. – coagulase negative, MRSA, and methicillin-susceptible S. aureus were the most frequently identified pathogens (23.8%, 23.8% and 12.5%, respectively). The most common daptomycin dose administered for bacteremia and cSSTI was 6 mg/kg (30.6%) and 4 mg/kg (51.7%), respectively. The median duration of inpatient daptomycin therapy was 14 days. Most patients (57.1%) did not receive daptomycin while in intensive care unit. Carbapenem (22.5%) was the most commonly used antibiotic concomitantly. The patients showed clinical improvement after two days (median) following the start of daptomycin therapy. The clinical success rate was 80.8% and the overall rate of treatment failure was 10.8%. The main reasons for daptomycin discontinuation were successful end of therapy (75.8%), switched therapy (11.7%), and treatment failure (4.2%). Daptomycin demonstrated a favorable safety and tolerability profile regardless of treatment duration.

Conclusions

Daptomycin had a relevant role in the treatment of Gram-positive infections in the clinical practice setting in Brazil.

Clinical impact of broad-spectrum empirical antibiotic therapy in patients with healthcare-associated pneumonia: a multicenter interventional study

Healthcare-associated pneumonia (HCAP) has been proposed as a new category of pneumonia distinct from community-acquired pneumonia (CAP). A multicenter observational study in 2008 finds that patients with HCAP have a mortality rate significantly higher than patients with CAP, and a worse outcome is associated at logistic regression analysis with a low adherence to empirical antibiotic therapy recommended by ATS/IDSA guidelines. We designed a prospective interventional study to establish whether administration of a broad-spectrum antibiotic therapy consistent with the 2005 ATS/IDSA guidelines has an effect on the clinical outcome of hospitalized patients with HCAP. All patients with HCAP prospectively admitted in 25 medical wards of 20 Italian hospitals during a 1-month period were included in the study. All patients were assigned to receive an empirical therapy including a fluoroquinolone plus an anti-MRSA agent plus either piperacillin-tazobactam or a carbapenem. Main measures for improvement were duration of antibiotic therapy, length of hospital stay, and in-hospital mortality rate. Patients were compared with a historical control group of 90 patients, and followed up to discharge or death. HCAP patients receiving a guideline-concordant therapy had a shorter duration of antibiotic therapy (median 15 vs. 12 days, p = 0.0002), a shorter duration of hospitalization (median 18 vs. 14 days, p = 0.02), and a lower mortality rate (17.8 vs. 7.1 %, p = 0.03). Our results suggest that an empirical broad-spectrum therapy is associated with improved outcome in patients with HCAP.

Pneumonia in frail older patients: an up to date

Despite advances in diagnosis, antimicrobial therapy and supportive care modalities, community-acquired pneumonia (CAP) remains an important cause of morbidity and mortality, especially in patients who require hospitalization. Elderly patients with poor functional status are characterized by a higher risk of developing severe CAP, due to the frequent presence of underlying respiratory and cardiac diseases, alteration of mental status, and immunosuppression. In recent years, changes in the healthcare system have shifted a considerable part of older patient care from hospitals to the community, and the traditional distinction between community- and hospital-acquired infections has become less clear. Pneumonia occurring among outpatients in contact with the healthcare system has been termed healthcare-associated pneumonia. Older frail patients have a high frequency of aspiration pneumonia and pneumonia due to gram-negative bacilli and other multidrug resistant pathogens. The contemporary presence of renal impairment usually requires specific dose adjustment of antibiotic therapy, which may be toxic in this specific patient population. This review produces a summary of therapeutic recommendations on the basis of the most updated clinical and pharmacological data.

Negative impact of linezolid on human neutrophil functions in vitro

BACKGROUND/AIMS

In a recent phase III clinical trial on linezolid, more patients in the linezolid treatment arm acquired Gram-negative catheter-related bloodstream infections despite the adequate therapy of infections caused by Gram-negative bacteria. We tested our hypothesis that linezolid impairs phagocytosis and the killing of Gram-negative bacteria by polymorphonuclear leukocytes (PMN).

METHODS

The influence of clinically relevant concentrations (5, 20 and 50 mg/l) of linezolid on granulocyte function in vitro was tested. Phagocytosis was determined by flow cytometry, and killing of bacteria was evaluated by plate counting. Chemotaxis was examined by an under-agarose cell migration assay. Gram-positive and Gram-negative bacteria were used.

RESULTS

Linezolid significantly impaired phagocytosis of a specific Escherichia coli strain in a concentration-dependent manner, whereas the effect on Pseudomonas aeruginosa was less prominent. No such effects were observed with a different E. coli strain or Staphylococcus aureus. Neither killing nor the chemotactic behaviour of PMN was significantly affected by linezolid.

CONCLUSIONS

The observed concentration-dependent impairment of the phagocytic function might contribute to the higher frequency of catheter-related Gram-negative bloodstream infections in patients treated with linezolid. Individual patient risk may also depend on the causative Gram-negative strain.

Wax moth larva (Galleria mellonella): an in vivo model for assessing the efficacy of antistaphylococcal agents

OBJECTIVES

To investigate whether the wax moth larva, Galleria mellonella, is a suitable host for assessing the in vivo efficacy of antistaphylococcal agents against Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) infections.

METHODS

Wax moth larvae were infected with increasing doses of S. aureus to investigate the effect of inoculum size on larval survival. In addition, infected wax moth larvae were treated with daptomycin, penicillin or vancomycin to examine whether these agents were effective against S. aureus and MRSA infections in vivo.

RESULTS

Increasing inoculum doses of live S. aureus cells resulted in greater larval mortality, but heat-killed bacteria and cell-free culture filtrates had no detrimental effects on survival. Larval mortality rate also depended on the post-inoculation incubation temperature. After larvae were infected with S. aureus, larval survival was enhanced by administering the antistaphylococcal antibiotics daptomycin or vancomycin. Larval survival increased with increasing doses of the antibiotics. Moreover, penicillin improved survival of larvae infected with a penicillin-susceptible methicillin-susceptible S. aureus (MSSA) strain, but it was ineffective at similar doses in larvae infected with MRSA (penicillin resistant). Daptomycin and vancomycin were also effective when administered to the larvae prior to infection with bacteria.

CONCLUSIONS

This is the first report to demonstrate that antibiotics are effective in the wax moth larva model for the treatment of infections caused by Gram-positive bacteria. The new wax moth larva model is a useful preliminary model for assessing the in vivo efficacy of candidate antistaphylococcal agents before proceeding to mammalian studies, which may reduce animal experimentation and expense.

Inactivation of the Ecs ABC transporter of Staphylococcus aureus attenuates virulence by altering composition and function of bacterial wall

BACKGROUND

Ecs is an ATP-binding cassette (ABC) transporter present in aerobic and facultative anaerobic gram-positive Firmicutes. Inactivation of Bacillus subtilis Ecs causes pleiotropic changes in the bacterial phenotype including inhibition of intramembrane proteolysis. The molecule(s) transported by Ecs is (are) still unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In this study we mutated the ecsAB operon in two Staphylococcus aureus strains, Newman and LS-1. Phenotypic and functional characterization of these Ecs deficient mutants revealed a defect in growth, increased autolysis and lysostaphin sensitivity, altered composition of cell wall proteins including the precursor form of staphylokinase and an altered bacterial surface texture. DNA microarray analysis indicated that the Ecs deficiency changed expression of the virulence factor regulator protein Rot accompanied by differential expression of membrane transport proteins, particularly ABC transporters and phosphate-specific transport systems, protein A, adhesins and capsular polysaccharide biosynthesis proteins. Virulence of the ecs mutants was studied in a mouse model of hematogenous S. aureus infection. Mice inoculated with the ecs mutant strains developed markedly milder infections than those inoculated with the wild-type strains and had consequently lower mortality, less weight loss, milder arthritis and decreased persistence of staphylococci in the kidneys. The ecs mutants had higher susceptibility to ribosomal antibiotics and plant alkaloids chelerythrine and sanguinarine.

CONCLUSIONS/SIGNIFICANCE

Our results show that Ecs is essential for staphylococcal virulence and antimicrobial resistance probably since the transport function of Ecs is essential for the normal structure and function of the cell wall. Thus targeting Ecs may be a new approach in combating staphylococcal infection.

Antimethicillin-resistant Staphylococcus aureus (MRSA) activity of 'pacific propolis' and isolated prenylflavanones

The need to discover and develop alternative therapies to treat methicillin-resistant Staphylococcus aureus (MRSA) infections is timely. This study was undertaken to purify and identify some anti-MRSA constituents from propolis, a natural product from the beehive traditionally used in folk medicine for its antimicrobial properties. A crude extract of propolis originating from the Solomon Islands ('Pacific propolis') was screened, using an agar dilution assay, in vitro against 15 MRSA clinical isolates. Results revealed activity worthy of further investigation, and subsequent purification work on this crude extract afforded 23 fractions. Further purification of active fractions led to the isolation of compounds 1-4, characterized upon analysis of their spectroscopic data (1D- and 2D-NMR, MS) and by comparison with the literature, as the prenylflavanones propolin H (1), propolin G (2), propolin D (3), and propolin C (4). This study is the first to report the anti-MRSA activity of 'Pacific propolis' and the presence of prenylflavanones in the propolis sample selected. The anti-MRSA activity of propolin D (3) (MIC 8-16 mg/L) and propolin C (4) (MIC 8-32 mg/L) is reported for the first time.

Efficacy of fosfomycin and its combination with linezolid, vancomycin and imipenem in an experimental peritonitis model caused by a Staphylococcus aureus strain with reduced susceptibility to vancomycin

The objective of this study was to evaluate the in vitro and in vivo efficacies of therapies including fosfomycin against clinical Staphylococcus aureus isolates with reduced susceptibility to vancomycin (hGISA). Time-kill curves were performed over 24 h. Peritonitis in C57BL/6 mice was induced by intraperitoneal inoculation of 10(8) CFU/ml. Four hours later (0 h), therapy was started and the treatment groups were: control (not treated), fosfomycin (100 mg/kg/5 h), vancomycin (60 mg/kg/5 h), imipenem (30 mg/kg/5 h), fosfomycin plus linezolid, fosfomycin plus vancomycin and fosfomycin plus imipenem, receiving subcutaneous therapy over 25 h. Bacterial counts in peritoneal fluid, bacteraemia and mortality rates were determined. In vitro, fosfomycin showed a synergistic effect when combined with the other antimicrobials tested. In the animal model, fosfomycin combinations were effective and significantly reduced the bacteraemia rates achieved in the control, imipenem and vancomycin groups (p < 0.05). The best combination in vivo was fosfomycin plus imipenem. Also, fosfomycin plus linezolid was significantly better than vancomycin alone, reducing the bacterial concentration in the peritoneal fluid. In conclusion, in vitro and in vivo, fosfomycin in combination with linezolid, vancomycin or imipenem exerted a good activity. Fosfomycin plus imipenem was the most active combination, decreasing 3 log CFU/ml, and appears to be a promising combination for clinical practice.

In vitro activity of the new multivalent glycopeptide-cephalosporin antibiotic TD-1792 against vancomycin-nonsusceptible Staphylococcus isolates

TD-1792 is a glycopeptide-cephalosporin heterodimer antibiotic with activity against a broad spectrum of gram-positive pathogens that includes methicillin-susceptible and -resistant Staphylococcus aureus. The objective of the present study was to evaluate the in vitro activity of TD-1792 against a collection of clinical isolates of vancomycin-intermediate Staphylococcus spp. (VISS), heteroresistant VISS (hVISS), and vancomycin-resistant S. aureus (VRSA). The TD-1792, vancomycin, daptomycin, linezolid, and quinupristin-dalfopristin MICs and minimum bactericidal concentrations (MBCs) were determined for 50 VISS/hVISS isolates and 3 VRSA isolates. Time-kill experiments (TKs) were then performed over 24 h with two vancomycin-intermediate S. aureus strains and two VRSA strains, using each agent at multiples of the MIC. TD-1792 and daptomycin were also evaluated in the presence and absence of 50% human serum to determine the effects of the proteins on their activities. Most of the VISS/hVISS isolates were susceptible to all agents except vancomycin. TD-1792 exhibited the lowest MIC values (MIC(90) = 0.125 microg/ml), followed by quinupristin-dalfopristin and daptomycin (MIC(90) = 1 microg/ml) and then linezolid (MIC(90) = 2 microg/ml). The presence of serum resulted in a 2- to 8-fold increase in the TD-1792 and daptomycin MIC values. In TKs, QD demonstrated bactericidal activity at multiples of the MIC that simulated therapeutic levels, whereas linezolid was only bacteriostatic. Both TD-1792 and daptomycin demonstrated rapid bactericidal activities against all isolates tested. The presence of proteins had only a minimal impact on the activity of TD-1792 in TKs. TD-1792 exhibited significant in vitro activity against multidrug-resistant Staphylococcus isolates and represents a promising candidate for the treatment of infections caused by gram-positive organisms.