Biofilm formation by Streptococcus pneumoniae strains and effects of human serum albumin, ibuprofen, N-acetyl-l-cysteine, amoxicillin, erythromycin, and levofloxacin.

Streptococcus pneumoniae ability to produce biofilms may induce persistent infections and difficulties for eradication in vivo. We investigated the ability of 11 pneumococcal strains (serotypes 3, 6B, 9V, 19F, and 23F) to form biofilms on polystyrene plates at 16 and 24 h. The extent of biofilm was greater at 24 h in 10 strains, being the highest magnitude for serotype 3 strains. Human serum albumin at 25,000 microg/mL and ibuprofen at 128 microg/mL significantly reduced biofilm formation in 7 and 5 strains, respectively. Amoxicillin, erythromycin, and levofloxacin at supra-MIC concentrations were very active against planktonic cells of 3 selected strains but lower on biofilm-associated organisms in 2 strains and null against the third. Although N-acetyl-l-cysteine had very little activity against both planktonic and biofilm-forming organisms, when combined with the 3 antibiotics, a slightly enhanced activity against biofilm-embedded organisms in 1 strain and combined with amoxicillin in another one was observed.

Correlation between in vitro and in vivo activity of levofloxacin and moxifloxacin against pneumococcal strains with different susceptibilities to fluoroquinolones.

In vitro and in vivo models were developed to evaluate the efficacy of levofloxacin and moxifloxacin against three serotype 3 pneumococcal strains with different susceptibilities to fluoroquinolones (wild-type, parC mutant, and parC, parE and gyrA mutant). Levofloxacin and moxifloxacin reduced the bacterial burden in the in vitro pharmacodynamic and animal models for the wild-type strain but had very little activity against the fully resistant strain (parC, parE and gyrA mutant). Levofloxacin showed very little activity both in the in vitro pharmacodynamic model and in the animal model for the strain having a mutation in parC (levofloxacin and moxifloxacin minimum inhibitory concentrations, 2mg/L and 0.25mg/L, respectively). However, moxifloxacin still had a significant in vitro and in vivo activity against this strain.