Figure 2

An overview of the high-throughput protocol for metal susceptibility testing using the MBEC assay. (A) Frozen stocks of bacteria were streaked out on the appropriate agar medium to obtain a first- and a subsequent second-subculture. (B) Colonies were collected from second-subcultures and suspended in broth medium to a 1.0 McFarland Standard. (C) This suspension was diluted 30-fold in broth, and the 1 in 30 dilution was used to inoculate the MBEC assay. (D) The inoculated device was placed on a rocking table in an incubator. (E) Serial dilutions of metal cations and oxyanions were set up along length of a microtiter plate along (the challenge plate). (F) The biofilms were rinsed to remove loosely adherent planktonic bacteria. (G) The first peg from each row was removed. These pegs were used to verify growth of the biofilms on the pegs. The peg lid was then inserted into the challenge plate. (H) During exposure, metals diffuse into the biofilm while planktonic cells are shed from the surface of the biofilm. Sloughed cells serve as the inoculum for planktonic MIC and MBC determinations. (I) The exposed biofilms were rinsed twice and the peg lid was inserted into fresh recovery medium containing the appropriate neutralizing agent (the recovery plate). The biofilms were disrupted into the recovery medium by sonciation on a water table sonicator. (J) Aliquots of planktonic cultures were transferred from the challenge plate to a microtiter plate containing the appropriate neutralizing agents (the neutralizing plate). (K) An aliquot from the recovery and neutralizing plates were spotted onto rich agar media. (L) MIC values are determined by reading the optical density at 650 nm (OD₆₅₀) of the challenge plate after the desired period of incubation using a microtiter plate reader. Spot plates were qualitatively scored for growth to obtain MBC and MBEC values. MBEC values were redundantly determined by determining the A₆₅₀ of the recovery plates after incubation.