Relative Resistance of Biofilms and Planktonic Cells of Common Molds and Yeasts to Antimicrobials

Various antimicrobials, including benzalkonium chloride, dimethyl benzyl ammonium chloride, Chlorhexidine, polyhexamethylene biguanide and hydrogen peroxide, were screened for their inhibitory effects against planktonic and adhered cells of selected yeasts and molds. A resistant strain of Serratia marcescens was employed as a control. Quaternary compounds often merely damaged cells; recoveries varied with the neutralizing medium and whether agar or broths were used. In general, quaternary compounds and biguanides at concentrations of less than 1.0% gave static inhibition, but with borate ions present biocidal activity was observed for certain compounds. Cells dried to polyethylene surfaces were usually more resistant to disinfectant concentrations than planktonic cells, but in a few instances dried biofilms showed increased susceptibility. Molds such as Aspergillus flavus and A. fumigatus were more resistant to certain biguanides than the yeasts Candida albicans ano C. parapsilosis. Hydrogen peroxide tested at a maximum concentration of 3.0%, in general, was one of the most effective disinfectants for adhered and planktonic cells.