Polystyrene petri dish

Two days prior to honey bee pupal cell experiments, a brood frame containing purple-eyed pupae was brought into the lab. Fine-point, curved-tip forceps (Bioquip) were used to carefully remove the wax capping from pupae. Wide-tip, featherweight forceps (Bioquip) were used to gently grasp pupae between the eyes to remove them from the wax comb cells in which they develop. Pupae were incubated at 28 °C overnight in 12-well plates, and wounded (i.e., melanized) pupae were discarded. Primary cells were harvested from surface-sterilized honey bee pupae in a biosafety cabinet (Class II type A/B3, Nuaire). Surface sterilization was carried out in a sterile polystyrene petri dish (100 mm × 15 mm, Fisher), in which pupae were swirled in 0.6% hypochlorite solution (diluted bleach) for 3 min, 70% ethanol for 3 min, and briefly in sterile water for injection (Gibco). In groups of two, pupae were dissected into head, thorax, and abdomen segments in 2 mL WH2 medium in a 47 mm dish using sterile 18-gauge needles to vigorously disturb tissues and release cells into the medium [175 (link)]. The media containing the cells was then transferred to a 50 mL conical tube, and cells from individual pupa (~24 × 10⁶ cells) were pooled. Cell suspensions with approximately 10⁶ cells per 300 μL were plated into each well of a 48-well plate and incubated at room temperature overnight before infection.

The acrylate plastic block (McMaster-Carr) presented in Fig. 4a had a thickness of 5 mm and an area of 50 mm × 50 mm. The polystyrene petri dish (Fisher Scientific) presented in Fig. 4b had a bottom thickness of 1 mm and a diameter of 150 mm. The borosilicate glass coverslip (Fisher Scientific) measured in Supplementary Fig. S6a had a thickness of 0.15 mm and an area of 24 mm × 50 mm. The copper foil (All Foils Inc.) measured in Supplementary Fig. S6b had a thickness of 0.3 mm and an area of 15 mm × 40 mm. The glass coverslip and the copper foil were placed on a lens holder so that the sample was bounded by the air on two sides.

Lawn biofilms of PA-Xen 41 were generated by spreading the overnight culture on TSA with the Ag electrodes embedded underneath the agar layer, which is approximately 3.6 mm thick. Briefly, 100 µL of the overnight PA-Xen41 culture grown in TSB was mixed with 9.9 mL TSB to make a 1:100 dilution. 400 µL of the diluted culture was spread onto the TSA with embedded electrodes contained in a polystyrene petri-dish (150 mm × 15 mm, Fisher Scientific, USA). The petri-dishes were incubated at 37 °C in 5% CO₂ for 24 h to develop lawn biofilms of PA-Xen41. The PA lawns were verified as being biofilms by measuring their response to the antibiotic, tobramyacin (Fig. S1).