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INFECTION AND IMMUNITY, July 1979, 304-309 Vol. 25, No. 1 0019-9567/79/07-0304/06$02.00/0 Lactoperoxidase Binding to Streptococci KENNETH M. * PRUITT, MICHAEL ADAMSON, AND ROLAND ARNOLD2 Laboratory ofMolecular Biology and Department ofMicrobiology,2 University ofAlabama in Birmingham, Birmingham, Alabama 35294 Received for publication 26 April 1979 There have been conflicting reports regarding the binding of lactoperoxidase to bacterial cell surfaces. We describe here the effects of cell-bound lactoperoxidase on acid production by suspensions of Streptococcus mutans (NCTC10449) in the presence of hydrogen peroxide and thiocyanate. Saline suspensions of log-phase bacteria were treated with 0.1 mg of lactoperoxidase per ml and were then washed thoroughly. The addition ofhydrogen peroxide and thiocyanate markedly reduced the acid production of these lactoperoxidase-treated bacteria but had no effect on the acid production of untreated controls. After a 3-h incubation in saline, the lactoperoxidase-treated bacteria produced acid in the presence of hydrogen per- oxide and thiocyanate at the same rate as untreated bacteria. These observations suggest that lactoperoxidase is initially bound to the cell surface in an enzymati- cally active form at a concentration sufficient to inhibit acid production. The lactoperoxidase is slowly degraded or desorbed as the bacteria stand in saline suspension. Lactoperoxidase (LPO) catalyzes the oxida- unable to reproduce the observations of Steele tion of thiocyanate ions by hydrogen peroxide to and Morrison (10). He suggested that cell b