Spectinomycin sp

S. mutans wild-type UA159 and its derivatives (Table 1) were maintained and grown in brain heart infusion (BHI, Difco Laboratories, Detroit, MI, USA) at 37 °C in an aerobic incubator with 5% CO₂, unless otherwise specifically stated. When necessary, antibiotic spectinomycin (Sp, Sigma-Aldrich, St. Louis, MO, USA), erythromycin (Erm, Sigma-Aldrich), and/or kanamycin (Kan, Sigma-Aldrich) were added to the growth medium at the level of 1 mg/mL, 10 µg/mL, and 1 mg/mL, respectively. For growth studies, BHI broth medium adjusted to pH 6.0 or supplemented with methyl viologen at the concentration of 12.5 mM were also used, and the optical density of the bacterial cultures were measured and recorded continuously using Bioscreen C (Growth Curves USA, Piscataway, NJ, USA) with or without a layer of sterile mineral oil [17 (link)]. For E. coli strains, Sp, Erm and Kan were used at 100 µg/mL, 300 µg/mL, and 40 µg/mL, respectively.

Streptococcusagalactiae GD201008-001 was isolated in 2010 from tilapia with meningoencephalitis in Guangdong Province, China [21 (link)]. GD201008-001 wild-type strain (WT) and its derived luxS mutant strain (ΔluxS) and the luxS complemented strain (CΔluxS) [13 (link)] were maintained in Todd-Hewitt broth (THB) or in chemically defined medium (CDM) [22 (link)]. Escherichia coli was cultured in Luria–Bertani (LB) medium. For plasmids screening required, media were supplemented with antibiotics using the concentration below: 100 μg/mL spectinomycin (Sp, Sigma, St. Louis, MO, USA), 10 μg/mL erythromycin (Em, Sigma), 100 μg/mL kanamycin (Km, Sigma) or 100 μg/mL ampicillin (Ap, Sigma). The details of bacterial strains and plasmids are listed in Additional file 1. Macrophage cell line RAW 264.7 were maintained in DMEM (Gibco, Grand Island, NY, USA) supplemented with 10% fetal bovine serum (FBS, Gibco).