Lysogeny broth agar

The plasmid (rAAV5-hSyn-eNpHR3.0-eYFP) was provided by courtesy of Karl Deisseroth’s Lab (Stanford University). We directly transfected plasmid-DNA into chemically competent Stbl3 E. coli cells (Invitrogen, Darmstadt, Germany) in order to amplify the plasmid containing the eNpHR3.0 construct. The vector possessed an ampicillin resistance. Therefore, transfected Stbl3 cells were transferred on Lysogeny broth (LB)-Agar with ampicillin (100 mg/ml) (Carl Roth GmbH, Karlsruhe, Germany) and incubated over night at 37°C. On the next day, we picked one colony and transferred it into 250 ml liquid LB-medium with 100 mg/ml ampicillin. After overnight incubation, we harvested bacterial cells by centrifugation at 4000 rpm for 15 min at 4°C and purified the plasmids with the Qiagen EndoFree Plasmid Maxi Kit (Qiagen, Hilden, Germany) according to the manufacturers’ protocol. We sent 300 μg of amplified plasmid for AAV vector production (serotype 2 pseudotyped with serotype 5) to the viral vector core at the University of North Carolina (UNC Vector Core, Chapel Hill, NC, USA) and received viral vectors with a titer of 4.0 × 10¹² genome copies (g.c.) ml^-1.

Brain Heart Infusion (BHI) agar (LAB M, Lancashire, UK) and Lysogeny Broth (LB) agar (Carlroth, Karlsruhe, Germany) plates (composition given in Supplementary Table 2), containing 1.5% (v/w) agar, were used to determine the bacterial load on the face masks before and after wearing and cleaning. The bacterial load was determined in colony forming units per ml (CFU/ml) of resuspension medium and recalculated to CFU/mask. The face mask suspension was diluted 10 times and 100 μl of undiluted and diluted suspensions were plated out on both growth media. Plates were incubated overnight at 37°C in aerobic conditions. CFUs were counted and a total of 47 colonies were isolated, subjected to colony PCR and identified using Sanger sequencing as described below. For isolation, colonies were transferred to BHI or LB liquid medium, grown statically at 37°C overnight and used for making glycerol stocks in 25% v/v glycerol stored at −80°C. To determine antibiotic resistance, the isolates were plated out on LB or BHI agar containing ampicillin and erythromycin, each at 100 μg/mL; final concentration.

E. coli ATCC 25922 were provided by the American Type Culture Collection (Manassas, VA). Freeze-dried peptide powders of LF11-215 (H-FWRIRIRR-NH₂), LF11-324 (H-PFFWRIRIRR-NH₂), and O-LF11-215 (octanoyl-FWRIRIRR-NH₂), purity >95%, were purchased from the Polypeptide Laboratories (San Diego, CA). Lysogeny broth (LB)-agar and LB medium were obtained from Carl Roth (Karlsruhe, Germany). All the other chemicals were purchased from Sigma-Aldrich (Vienna, Austria).