Streptococcus pneumoniae, a
penicillin-sensitive bacterium, is recognized as a major cause of
pneumonia and is treated clinically with
penicillin-based
antibiotics. The rapid increase in resistance to
penicillin and other
antibiotics affects 450 million people globally and results in 4 million deaths every year. To unveil the mechanism of resistance of S. pneumoniae is thus an important issue to treat streptococcal disease that might consequently save millions of lives around the world. In this work, we isolated a streptococci-conserved L-ascorbate 6-phosphate lactonase, from S. pneumoniae ATCC 49136. This
protein reveals a metallo-β-lactamase activity in vitro, which is able to deactivate an
ampicillin-based
antibiotic by hydrolyzing the
amide bond of the β-
lactam ring. The Michaelis parameter (Km) = 25 μM and turnover number (kcat) = 2 s(-1) were obtained when
nitrocefin was utilized as an optically measurable substrate. Through confocal images and western blot analyses with a specific antibody, the indigenous
protein was recognized in S. pneumoniae ATCC 49136. The
protein-overexpressed S.
pneumonia exhibits a high
ampicillin-tolerance ability in vivo. In contrast, the
protein-knockout S.
pneumonia reveals the
ampicillin-sensitive feature relative to the wild type strain. Based on these results, we propose that this
protein is a membrane-associated metallo-β-lactamase (MBL) involved in the
antibiotic-resistant property of S. pneumoniae.