Abstract
The DNA topoisomerase complement of Streptococcus pneumoniae is constituted by two type II enzymes (topoisomerase IV and gyrase), and a single type I enzyme (topoisomerase I). These enzymes maintain the DNA topology, which is essential for replication and transcription. While fluoroquinolones target the type II enzymes, seconeolitsine, a new antimicrobial agent, targets topoisomerase I. We compared for the first time the in vitro effect of inhibition of topoisomerase I by seconeolitsine and of the type II topoisomerases by the fluoroquinolones levofloxacin and moxifloxacin. We used three isogenic non-encapsulated strains and five non-vaccine serotypes isolates belonging to two circulating pneumococcal clones, ST638 (2 strains) and ST1569V (3 strains). Each group contained strains with diverse susceptibility to fluoroquinolones. Minimal inhibitory concentrations, killing curves and postantibiotic effects were determined. Seconeolitsine demonstrated the fastest and highest bactericidal activity against planktonic bacteria and biofilms. When fluoroquinolone-susceptible planktonic bacteria were considered, seconeolitsine induced postantibiotic effects (1.00−1.87 h) similar than levofloxacin (1.00−2.22 h), but longer than moxifloxacin (0.39−1.71 h). The same effect was observed in sessile bacteria forming biofilms. Seconeolitsine induced postantibiotic effects (0.84−2.31 h) that were similar to those of levofloxacin (0.99−3.32 h) but longer than those of moxifloxacin (0.89−1.91 h). The greatest effect was observed in the viability and adherence of bacteria in the postantibiotic phase. Seconeolitsine greatly reduced the thickness of the biofilms formed in comparison with fluoroquinolones: 2.91 ± 0.43 μm (seconeolitsine), 7.18 ± 0.58 μm (levofloxacin), 17.08 ± 1.02 μm (moxifloxacin). When fluoroquinolone-resistant bacteria were considered, postantibiotic effects induced by levofloxacin and moxifloxacin, but not by seconeolitsine, were shorter, decreasing up to 5-fold (levofloxacin) or 2-fold (moxifloxacin) in planktonic cells, and up to 1.7 (levofloxacin) or 1.4-fold (moxifloxacin) during biofilm formation. Therefore, topoisomerase I inhibitors could be an alternative for the treatment of pneumococcal diseases, including those caused by fluoroquinolone-resistant isolates.
Highlights
Streptococcus pneumoniae is a main human pathogen
Pneumococcal biofilms are present in the nasopharynx, and in adenoid and mucosal epithelial tissues in children with recurrent middle-ear infections and otitis media [13], sinus mucosa of patients with chronic rhinosinusitis [14], and in the lungs of mice infected with S. pneumoniae [15]
The strains tested include three isogenic non-encapsulated strains (R6, T1 and T2), and five clinical isolates belonging to two circulating pneumococcal clones, ST638 (2 strains) and ST1569V (3 strains)
Summary
Streptococcus pneumoniae is a main human pathogen. The implementation of the 7-valent and 13-valent conjugate vaccines, which include the serotype-specific polysaccharides more often associated with resistance to antibiotics, have led to a decline of invasive pneumococcal disease and penicillin resistance [1]. Non-encapsulated isolates, which are the etiological agents of 3–19% of pneumococcal diseases [5,6] and more prone to form biofilm than encapsulated strains [7], have emerged. Dissemination leads to the development of sinusitis, conjunctivitis or acute otitis media and, eventually, invasive diseases, such as bacteremic pneumonia, meningitis and sepsis [11,12]. Pneumococcal biofilms are present in the nasopharynx, and in adenoid and mucosal epithelial tissues in children with recurrent middle-ear infections and otitis media [13], sinus mucosa of patients with chronic rhinosinusitis [14], and in the lungs of mice infected with S. pneumoniae [15]. Biofilms are 1000-fold more tolerant and/or resistant to antibiotics than planktonic cells [17]. Biofilm antibiotic therapy demands the use of higher doses of antibiotics over prolonged periods
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