In vitro activity of meropenem/piperacillin/tazobactam triple combination therapy against clinical isolates of Staphylococcus aureus, Staphylococcus epidermidis, Staphylococcus pseudintermedius and vancomycin-resistant Enterococcus spp

Pharmacokinetics, Tissue Distribution, and Efficacy of VIO-001 (Meropenem/Piperacillin/Tazobactam) for Treatment of Methicillin-Resistant Staphylococcus aureus Bacteremia in Immunocompetent Rabbits with Chronic Indwelling Vascular Catheters

Methicillin-resistant Staphylococcus aureus (MRSA) infections of surgically implanted subcutaneous vascular catheters (SISVCs) cause serious morbidity in patients with chronic illnesses. Previous in vitro and murine models demonstrated the synergistic interaction of equimolar concentrations of meropenem/piperacillin/tazobactam (MPT) (VIO-001) against MRSA infection. We investigated the pharmacokinetics (PK) and efficacy of VIO-001 for the treatment of MRSA bacteremia in immunocompetent rabbits with SISVCs. In PK studies, we determined that optimal dosing to achieve a time above 4× MIC (T_>4×MIC) of a duration of 3 to 3.30 h required a 1-h infusion with every-4-h (Q4h) dosing. Study groups in efficacy experiments consisted of MPT combinations of 100/150/100 mg/kg of body weight (MPT100), 200/300/200 mg/kg (MPT200), and 400/600/400 mg/kg (MPT400); vancomycin (VAN) at 15 mg/kg; and untreated controls (UC). The inoculum of MRSA isolate USA300-TCH1516 (1 × 10³ organisms) was administered via the SISCV on day 1 and locked for 24 h. The 8-day therapy started at 24 h postinoculation. There was a significant reduction of MRSA in blood cultures from the SISVCs in all treatment groups, with full clearance on day 4, versus UCs (P < 0.05). Consistent with the clearance of SISVC-related infection, full eradication of MRSA was achieved in lungs, heart, liver, spleen, and kidneys at the end of the study versus UC (P < 0.01). These results strongly correlated with time-kill data, where MPT in the range of 4/6/4 μg/ml to 32/48/32 μg/ml demonstrated a significant 6-log decrease in the bacterial burden versus UC (P < 0.01). In summary, VIO-001 demonstrated a favorable PK/pharmacodynamic (PD) profile and activity against SISCV MRSA infection, bacteremia, and disseminated infection. This rabbit model provides a new system for understanding new antimicrobial agents against MRSA SISVC-related infection, and these data provide a basis for future clinical investigation.

Trans-Cinnamaldehyde Exhibits Synergy with Conventional Antibiotic against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen worldwide and has acquired multiple resistance to a wide range of antibiotics. Hence, there is a pressing need to explore novel strategies to overcome the increase in antimicrobial resistance. The present study aims to investigate the efficacy and mechanism of plant-derived antimicrobials, trans-cinnamaldehyde (TCA) in decreasing MRSA’s resistance to eight conventional antibiotics. A checkerboard dilution test and time–kill curve assay are used to determine the synergistic effects of TCA combined with the antibiotics. The results indicated that TCA increased the antibacterial activity of the antibiotics by 2-16-fold. To study the mechanism of the synergism, we analyzed the mecA transcription gene and the penicillin-binding protein 2a level of MRSA treated with TCA by quantitative RT-PCR or Western blot assay. The gene transcription and the protein level were significantly inhibited. Additionally, it was verified that TCA can significantly inhibit the biofilm, which is highly resistant to antibiotics. The expression of the biofilm regulatory gene hld of MRSA after TCA treatment was also significantly downregulated. These findings suggest that TCA maybe is an exceptionally potent modulator of antibiotics.

Case Commentary: Imipenem/Cilastatin and Fosfomycin for Refractory Methicillin-Resistant Staphylococcus aureus Infection: a Novel Combination Therapy

Given that it is unlikely that randomized clinical trials will yield answers for treating the most challenging bacteremic infections caused by methicillin-resistant Staphylococcus aureus, clinicians, microbiologists, and pharmacists will have to cooperate to discover novel ways to select successful individualized antimicrobial therapy for these patients. An example of such a strategy was demonstrated in the identification and utilization of imipenem/cilastatin plus fosfomycin to treat a particularly recalcitrant MRSA bacteremia and spinal abscess.

Prevention and Killing Efficacy of Carbapenem Resistant Enterobacteriaceae (CRE) and Vancomycin Resistant Enterococci (VRE) Biofilms by Antibiotic-Loaded Calcium Sulfate Beads

Carbapenem-resistant Enterobacteriaceae (CRE) and vancomycin-resistant Enterococci (VRE) have emerged as multidrug-resistant (MDR) pathogens associated with periprosthetic joint infections (PJI). In this study, we evaluated the efficacy of antibiotic-loaded calcium sulfate beads (ALCSB) in inhibiting bacterial growth, encouraging biofilm formation and killing preformed biofilms of CRE and VRE. Three strains of Klebsiella pneumoniae (KP) and a strain of Enterococcus faecalis (EF) were used. ALCSB of 4.8-mm diameter were loaded with vancomycin (V) and gentamicin (G), V and rifampicin (R), V and tobramycin (T) or R and meropenem (M), and placed onto tryptic soy agar (TSA), spread with one of the test strains and incubated for 24 h at 37 °C. Beads were transferred daily onto fresh TSA spread plates and the zone of inhibition (ZOI) was recorded until no inhibition was observed. ALCSB containing R + M or R + V produced the most extensive ZOI up to 5 weeks. Biofilm prevention efficacy was investigated by challenging ALCSB daily with 5 × 10⁵ CFU/mL bacterial cells and analyzing for biofilm formation at challenges 1, 2 and 3. In the biofilm killing experiments, ALCSB were added to pre-grown 3-day biofilms of KP and EF strains, which were then analyzed at days 1 and 3 post-exposure. The CFU counts and confocal images of the attached cells showed that ALCSB treatment reduced colonization and biofilm formation significantly (5–7 logs) with combinations of R + M or R + V, compared to unloaded beads. This study provides evidence that the local release of antibiotics from ALCSB may be useful in treating the biofilms of multidrug-resistant strains of CRE and VRE.