Selective sensitization of bacteria to peroxide damage associated with fluoride inhibition of catalase and pseudocatalase

Fluoride and sulfide are known inhibitors of heme catalases in acid environ ments. Staphylococcus aureus H cells were found to be sensitized by fluorid e or sulfide to H2O2 killing at acid pH values in the range of 3.5 to 4.0, and catalase activity was reduced concomitantly. In contrast, fluoride had little effect on H2O2 killing of Streptococcus mutans GS-5, which has fluor ide-insensitive peroxidase activity, but still is more sensitive to H2O2 th an is S. aureus in the absence of fluoride. Fluoride but not sulfide was in hibitory also for the Mn-containing, nonheme pseudocatalase of Lactobacillu s plantarum ATCC 14431 over a wide pH range, and this inhibitory effect was reflected in enhanced H2O2 killing in the presence of fluoride. In additio n, we found that catalase-positive S. aureus or Neisseria sicca could prote ct catalase-negative S. mutans against killing by H2O2 in mixed suspensions , but protection was compromised by fluoride or sulfide under acid conditio ns. Thus, catalase-positive organisms could protect a catalase-negative org anism against peroxide damage, but inhibition of catalase reduced protectio n. These findings are pertinent to the widespread use of fluoride and perox ide in oral health care products.