Ecological Control:In VitroInhibition of Anaerobic Bacteria by Oral Streptococci

Abstract

It has been proposed that oral malodour occurs at neutral and alkaline pH, and is inhibited by an acid environment. Thus the production of lactic and acetic acids from carbohydrate fermentation by oral streptococci generates a low pH that can interfere with the growth of other microorganisms. Additionally, some streptococci may produce hydrogen peroxide (H 2 O 2 ) and/or bacteriocins. The purpose of this study was to investigate whether products of streptococcal growth and carbohydrate metabolism had any effect in vitro on the growth of selected anaerobes associated with oral malodour. Oral streptococci were compared for their ability to ferment glucose or sucrose using acid indicator media and pH measurement, and for their ability to produce H 2 O 2 . The inhibition of anaerobes by end products of streptococcal growth in glucose-containing medium was evaluated using both an agar overlay technique and a cross-streak technique. Anaerobic bacteria were inhibited by products of growth of oral streptococci, particularly strains of Streptococcus mutans and Streptococcus salivarius in the presence, but not in the absence, of glucose. It is most likely that this inhibition results from the production of lactic acid rather than H 2 O 2 or bacteriocins, because the pattern of inhibition agreed more with acidogenicity than with any other variable. Oral streptococci may play an important role in the ecology of the oral flora and in the control of oral malodour. Key words : oral malodour, anaerobic bacteria, oral streptococci.