Production of Antimicrobial Substances by Lactic Acid Bacteria I: Determination of Hydrogen Peroxide

Abstract

Restoration of the balance of different ecological niches has been proposed as a way to control the income of pathogenic microorganisms (1). The genus Lactobacillus has been used in different human and animal tracts as probiotic microorganisms with this objective in mind (2). The characteristics of the strains proposed as probiotics have been published (3) or patented under the process of elaboration of different types of products (4–6). One of the mechanisms suggested to control the vaginal ecosystem is the production of antagonistic substances (lactic acid, bacteriocins, or H₂O₂) (7–9). The H₂O₂-producing microorganisms present in the vagina of healthy women have been suggested as some of the bacteria responsible for maintenance of ecological balance, mainly in pregnant women (10,11). The absence of these microorganisms is related to a higher risk of: bacterial vaginosis (12), recurrent urinary tract infections by Escherichia coli (13), and acquisition of human immunodeficiency virus type 1 (HIV-1) (14). Bauer (15) has proposed that H₂O₂-producing lactobacilli also might exert control over vaginal cancer through specific interactions of reactive oxygen species, such as superoxide anion, hydroxyl radicals, and hypochlorous acid. The conversion of H₂O₂ into more toxic compounds during the oxidative process is potentiated by peroxidase and halures. This enzyme and some halures, such as chloride and bromide, are present in vaginal washes in sufficient amounts (16) to allow an optimal environment for successful inhibition of pathogens.