Post-Antibiotic Effect of Moxifloxacin in Streptococcus pneumoniae: DNA-cleavage and Reactive Oxygen Species Production

Abstract

Background: Streptococcus pneumoniae is cause of community acquired pneumonia, meningitis, otitis media, sinusitis and conjunctivitis. Moxifloxacin (MFX) is a fluoroquinolone used for pneumococcal infections. The post-antibiotic effect (PAE) is useful to determine optimal dosage regimens for antibiotics. MFX forms intermediates of DNA-MFX-topoisomerase complexes, which generates double-stranded DNA breaks. Its lethality is enhanced by the production of reactive oxygen species (ROS), via the up-regulation of genes that increases pyruvate and stimulate the Fenton reaction. Objectives: To study the factors involved in PAE of MFX in S. pneumoniae. Methods: Streptococcus pneumoniae R6 strain was analyzed during the postantibiotic phase. Growth curves by viable counting, level of chromosome fragmentation by Pulse Field Gel Electrophoresis, ROS production by dihydrorhodamine 123 dye and gene expression by q-RT-PCR, were determined Results: Treatment of 1 h with MFX at (2.5 −5 – 10)  MIC induced PAE of 0.76 h, 1.33 h and 1.99 h, respectively. DNA breakage induced by the treatment decreased more than 3-fold after the PAE phase. Increase up to 3-fold of ROS level induced by the treatment reverted after the PAE-phase. MFX up-regulated the expression of fba and gpdA genes involved in the conversion of fructose 6- phosphate to pyruvate by glycolytic pathway. MFX also up-regulated the expression of pmi and tktA genes, which encode for enzymes that funnel phosphate sugars into the glycolytic pathway. MFX induces significant PAE representing the time necessary for the bacteria to recover their normal levels of ROS and intact DNA.