METHODS: TEM, SEM and ATP efflux assay were used to evaluate the effect of hybrid peptides on the integrity of the pneumococcal cell wall/membrane. DNA retardation assay was assessed to measure the impact of hybrid peptides on the migration of genomic DNA through the agarose gel. In vitro synergistic effect was checked using the chequerboard assay. ICR male mice were used to evaluate the in vivo toxicity and antibacterial activity of the hybrid peptides in a standalone form and in combination with ceftriaxone.

RESULTS: The results obtained from TEM and SEM indicated that the hybrid peptides caused significant morphological alterations in Streptococcus pneumoniae and disrupting the integrity of the cell wall/membrane. The rapid release of ATP from pneumococcal cells after one hour of incubation proposing that the antibacterial action for the hybrid peptides is based on membrane permeabilization and damage. The DNA retardation assay revealed that at 62.5 µg/ml all the hybrid peptides were capable of binding and preventing the pneumococcal genomic DNA from migrating through the agarose gel. In vitro synergy was observed when pneumococcal cells treated with combinations of hybrid peptides with each other and with conventional drugs erythromycin and ceftriaxone. The in vivo therapeutic efficacy results revealed that the hybrid peptide RN7-IN8 at 20 mg/kg could improve the survival rate of pneumococcal bacteremia infected mice, as 50% of the infected mice survived up to seven days post-infection. In vivo antibacterial efficacy of the hybrid peptide RN7-IN8 was signficantly improved when combined with the standard antibiotic ceftriaxone at (20 mg/kg + 20 mg/kg) as 100% of the infected mice survived up to seven days post-infection.

METHODS: Demographic data, underlying diseases, procedures and details on polymyxin B therapy were retrospectively analyzed in a cohort of 84 patients who received intravenous polymyxin B in an intensive care unit from 2010 to 2014.

RESULTS: Polymyxin B was used to treat bacteremia (46.4% of cases) and pneumonia (53.6%). Majority of the pathogens isolated were Acinetobacter spp. (96.4%). The mortality rate was 48.8%, of which 82.9% was attributed to polymyxin B treatment failure. The independent predictors of treatment failure were low doses of polymyxin B (p = 0.002), shorter duration of therapy (p = 0.009), not combining with cefoperazone/sulbactam (p = 0.030), female gender (p = 0.004), administered for treatment of bacteremia (p = 0.023) and renal impairment (p = 0.021). Low polymyxin B doses (p = 0.007), not combining with cefoperazone/sulbactam (p = 0.024), female gender (p = 0.048) and renal impairment (p = 0.022) were also significant predictors for in-hospital mortality.