Levofloxacin-Ceftriaxone Combination Attenuates Lung Inflammation in a Mouse Model of Bacteremic Pneumonia Caused by Multidrug-Resistant Streptococcus pneumoniae via Inhibition of Cytolytic Activities of Pneumolysin and Autolysin

Abstract

In this study, our objective was to determine whether a synergistic antimicrobial combination in vitro would be beneficial in the downregulation of pneumococcal virulence genes and whether the associated inflammation of the lung tissue induced by multidrug-resistant Streptococcus pneumoniae infection in vivo needs to be elucidated in order to consider this mode of therapy in case of severe pneumococcal infection. We investigated in vivo changes in the expression of these virulence determinants using an efficacious combination determined in previous studies. BALB/c mice were infected with 10 6 CFU of bacteria. Intravenous levofloxacin at 150 mg/kg and/or ceftriaxone at 50 mg/kg were initiated 18 h postinfection; the animals were sacrificed 0 to 24 h after the initiation of treatment. The levels of cytokines, chemokines, and C-reactive protein (CRP) in the serum and lungs, along with the levels of myeloperoxidase and nitric oxide the inflammatory cell count in bronchoalveolar lavage fluid (BALF), changes in pneumolysin and autolysin gene expression and COX-2 and inducible nitric oxide synthase (iNOS) protein expression in the lungs were estimated. Combination therapy downregulated inflammation and promoted bacterial clearance. Pneumolysin and autolysin expression was downregulated, with a concomitant decrease in the expression of COX-2 and iNOS in lung tissue. Thus, the combination of levofloxacin and ceftriaxone can be considered for therapeutic use even in cases of pneumonia caused by drug-resistant isolates.

Mechanism of Macrolide-Induced Inhibition of Pneumolysin Release Involves Impairment of Autolysin Release in Macrolide-Resistant Streptococcus pneumoniae

“…Mutations of the lytA gene in S. pneumoniae lead to a significantly decreased virulence of this organism compared to that of the wild-type strain in a mouse intraperitoneal infection model (34). Although it has been reported that the combination treatment of multidrug-resistant pneumococcus with both levofloxacin and ceftriaxone induces a slight reduction in lytA gene transcription (35), this is, to our knowledge, the first report to identify the inhibitory effect of macrolides on the release of LytA protein, leading to the inhibition of PLY release. Additional effects resulting from the inhibition of LytA release should be addressed in future studies.…”

Induction of Cyclooxygenase 2 by <b><i>Streptococcus pyogenes </i></b>Is Mediated by Cytolysins

“…Evidence has been provided that different bacterial toxins such as LPS [24] , C. difficile toxin A [13] and pneumolysin [19,25] are strong inducers of the expression of the inducible form of COX-2. This has been also shown for certain bacterial cytolysins like the ACT (adenylate cyclase toxin) of Bordetella pertussis [26] .…”

Effectiveness of combination therapy versus monotherapy with a third-generation cephalosporin in bacteraemic pneumococcal pneumonia: A propensity score analysis

“…and levofloxacin in 54% of the strains tested in one study (28) but not for macrolides (29,30), therefore, it seems unlikely that synergism was the beneficial effect of combination, 3) anti-inflammatory effect that has been described for macrolides and fluoroquinolones mediated in both cases by the inhibition of NF-kß transcription factor that leads to a reduction in the production of pro-inflammatory cytokines (31-33) and subsequent beneficial immunomodulatory effects (34,35), and 4) virulence reduction of S. pneumoniae by inhibiting the production of pneumolysin that has been demonstrated with macrolides and fluoroquinolones and it is independent of the strain susceptibility (36)(37)(38). Pneumolysin facilitates intraalveolar replication of pneumococci, penetration of bacteria from alveoli into the interstitium of the lung, and dissemination of pneumococci into the bloodstream during experimental pneumonia (39).…”