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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 ( K   m  ) = 25 μM and turnover number ( k   cat  ) = 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 .

A Novel Metallo-β-Lactamase Involved in the Ampicillin Resistance of Streptococcus pneumoniae ATCC 49136 Strain