Antibacterial activity of hydrogen peroxide and the lactoperoxidase-hydrogen peroxide-thiocyanate system against oral streptococci

Abstract

In secreted fluids, the enzyme lactoperoxidase (LP) catalyzes the oxidation of thiocyanate ion (SCN-) by hydrogen peroxide (H202), producing the weak oxidizing agent hypothiocyanite (OSCN-), which has bacteriostatic activity. However, H202 has antibacterial activity in the absence of LP and thiocyanate (SCN-). Therefore, LP may increase antibacterial activity by using H202 to produce a more effective inhibitor of bacterial metabolism and growth, or LP may protect bacteria against the toxicity of H202 by converting H202 to a less-potent oxidizing agent. To clarify the role of LP, the antibacterial activities of H202 and the LP-H202-SCNsystem were compared by measuring loss of viability and inhibition of bacterial metabolism and growth. The relative toxicity of H202 and the LP system to oral streptococci was found to depend on the length of time that the bacteria were exposed to the agents. During incubations of up to 4 h, the LP system was from 10 to 500 times more effective than H202 as an inhibitor of glucose metabolism, lactic acid production, and growth. However, if no more H202 was added, the concentration of the inhibitor OSCNfell because of slow decomposition of OSCN-, and when OSCNfell below 0.01 mM, the bacteria resumed metabolism and growth. In contrast, the activity of H202 increased with time. H202 persisted in the medium for long periods of time because H202 reacted slowly with the bacteria and streptococci lack the enzyme catalase, which converts H202 to oxygen and water. After 24 h of exposure, H202 was as effective as the LP system as an inhibitor of metabolism. H202 also caused a time-dependent loss of viability, whereas the LP system had little bactericidal activity. The concentration of H202 required to kill half the bacteria within 15 s was 1.8 M (6%) but fell to 0.3 M (1%) at 2 min, to 10 mM (0.03%) at 1 h, and to 0.2 mM (0.0007%) with a 24-h exposure. The results indicate that if high levels of H202 can be sustained for long periods of time, H202 is an effective bactericidal agent, and the presence of LP and SCNprotects streptococci against killing by H202. Nevertheless, the combination of LP, H202, and SCNis much more effective than H202 alone as an inhibitor of bacterial metabolism and growth.

Antimicrobial properties of hydrogen peroxide and potash alum alone and in combination against clinical bacterial isolates

“…Another study reported that the combination of alum with antibiotics (tetracycline and cefotaxime) was more effective than antibiotic combination and the combination effect was more efficient than an individual effect [40]. Similarly, hydrogen peroxide in combination with lactoperoxidase and thiocyanate is reported much more effective than hydrogen peroxide alone as an inhibitor of bacterial metabolism and growth [41]. Thus, the combination strategy provides us with an opportunity to improve their efficacy at low concentration.…”

Chewing sticks: timeless natural toothbrushes for oral cleansing

“…Darout et al (81) hypothesized that thiocyanate leaching out from miswak while in the oral cavity may lead to an elevated level of salivary thiocyanate. This, in turn, may enhance the ecacy of the salivary hydrogenperoxide-peroxidase-thiocyanate system, a known antimicrobial component of human saliva (84,85). This may partly explain the observation that adult Sudanese miswak users had signi®cantly lower numbers of cariogenic bacteria, except S. mutans, in their saliva while the matched toothbrush users demonstrated lower salivary levels of periodontopathogens (Darout et al 2000, unpublished observations).…”

The role of reactive oxygen species in the antibacterial photodynamic treatment: photoinactivationvsproliferation

“…Therefore their destroying effect is expected to be low (3). However, lower concentration of ROS can stimulate different biochemical pathways in the cells causing cell survival and proliferation (Imlay and Linn 1987;Thomas et al 1994;Miller and Britigan 1997;Davies 1999;Ruiz-Gines 2000;Palma et al 2004;Salunkhe et al 2005;Bartosz 2009). The two distinct effects of laser applications were studied in independent tracts in the literature, that is, proliferation effect for the cells (Karu et al 1995) or inhibitory/ killing effect for unwanted cancer cells (Tseng et al 2003;Almeida et al 2004;Crescenzi et al 2004).…”