S aureus xen31

For this study, we used XL10-Gold (200314 Stratagene) as E. coli strain and S. aureus – Xen31 (119242 Perkin Elmer, Milano, Italy) as the bioluminescent pathogenic bacteria. All microbial strains were stored at –80 °C in cryovial and 40% (v/v) glycerol. The bacteria were grown overnight at 30 °C in Luria Bertani (LB) medium, from which an inoculum was taken and adjusted to an OD 600 nm of 0.20 ± 0.02 (1 × 10⁸ colony-forming units [CFU]/mL). Subsequently, for each bacterium, at least four wells of sterile 96-well microtiter plates were filled with cells and sample (3D chitosan, GA, and HL-3D chitosan-GA). These were tested at two different concentrations (1.0 and 0.5 mg/mL). Cell suspensions with acidified water and cell suspension without sample were used as controls. The microtiter plates were then incubated for 24 h at 30 °C in an orbital shaker (150 rpm). The absorbance was measured at 600 nm using the EnSpire Multimode Plate Reader (Perkin Elmer, Milano, Italy).

Staphylococcus and Enterococcus strains were grown in brain heart infusion (BHI) broth (Oxoid, United Kingdom) at 37°C under aerobic conditions without shaking. For in vivo imaging of bacterial infection in mice, S. aureus Xen31 (Perkin Elmer, Waltham, MA) was used. The strain was derived from the parental strain S. aureus ATCC 33591, a clinical MRSA strain isolated from Elmhurst Hospital in New York, NY, USA (44 (link)). S. aureus Xen31 possesses a stable copy of the modified Photorhabdus luminescensluxABCDE operon at a single integration site on the bacterial chromosome. Other strains were taken from our collection (Laboratory of Microbial Gene Technology, Norwegian University of Life Sciences).

All bacterial strains used in this study are listed in Table 1 and Supplemental Table 1. S. equorum KAVA and S. equorum WS 2733 were MP1 producers; the former obtained from this study while the latter from a previous study (25 (link)). For in vivo imaging of bacterial infection in mice and antimicrobial synergy study, S. aureus Xen31 (Perkin Elmer, Waltham, MA) was used. The strain was derived from the parental strain S. aureus ATCC 33591, a clinical MRSA isolated from Elmhurst Hospital in New York (26 (link)). S. aureus Xen31 possesses a stable copy of the modified Photorhabdus luminescens luxABCDE operon at a single integration site on the bacterial chromosome. To define the inhibition spectrum of MP1, a panel of bacteria from different genera and species were used (see Supplemental Table 1). All bacterial strains were grown in brain heart infusion (BHI) broth (Oxoid, United Kingdom) at 30°C overnight without shaking unless stated otherwise.