Glutaraldehyde efficacy against biofilm bacteria was investigated using a model system of Pseudomonas aeruginosa entrapped in hydrated gel bead "artificial biofilms." Bacteria in biofilms were clearly less susceptible to glutaraldehyde than the same microorganisms when grown in a conventional suspension culture. For example, using 50 mg/L glutaraldehyde it took only approximately 20 minutes to achieve a 2 log reduction in viable cell numbers in planktonic experiments but almost 600 minutes to achieve this same level of killing in the biofilm. In general, the susceptibility of bacteria in biofilms was reduced by approximately an order of magnitude compared to planktonic bacteria. Biofilm results
indicated that glutaraldehyde penetration into the biofilms was retarded and that poor penetration likely contributed to biofilm reduced susceptibility. Treating biofilm bacteria with a brief, concentrated dose
of glutaraldehyde was more effective than a proportionally longer treatment at a lower concentration. For example, a 200 mg/L dose of glutaraldehyde for 40 minutes was as effective as a 50 mg/L dose
delivered for 600 minutes. The demonstration of unambiguous biofilm resistance to glutaraldehyde highlights the need to continue to employ biofilm testing methodologies in designing and optimizing applications of this agent. The insights obtained in this investigation suggest possible approaches for improving biofilm control with glutaraldehyde.