Salivary enzymes and exhaled air affect Streptococcus salivarius growth and physiological state in complemented artifici
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Salivary enzymes and exhaled air affect Streptococcus salivarius growth and physiological state in complemented artificial saliva P. Roger • S. Harn-Arsa • J. Delettre • C. Be´al
Received: 17 June 2011 / Revised: 25 July 2011 / Accepted: 5 August 2011 / Published online: 3 September 2011 Ó Springer-Verlag 2011
Abstract To better understand the phenomena governing the establishment of the oral bacterium Streptococcus salivarius in the mouth, the effect of some environmental factors has been studied in complemented artificial saliva, under oral pH and temperature conditions. Three salivary enzymes at physiological concentrations were tested: peroxidase, lysozyme and amylase, as well as injection of exhaled air. Injection of air containing 5% CO2 and 16% O2 induced a deleterious effect on S. salivarius K12, mainly by increasing redox potential. Addition of lysozyme slightly affected the physiological state of S. salivarius by altering membrane integrity. In contrast, peroxidase was not detrimental as it made it possible to decrease the redox potential. The addition of amylase reduced the specific growth rate of S. salivarius by formation of a complex with amylase and mucins, but led to high final biomass, as a result of enzymatic degradation of some nutrients. Finally, this work demonstrated that salivary enzymes had a slight impact on S. salivarius behaviour. It can thus be concluded that this bacterium was well adapted to in-mouth conditions, as it was able to resist certain salivary enzymes, even if tolerance to expired air was affected, as a result of an increased redox potential. Keywords Streptococcus salivarius Physiological state Salivary enzymes Artificial saliva Redox potential Growth rate
Communicated by Erko Stackebrandt. P. Roger S. Harn-Arsa J. Delettre C. Be´al (&) AgroParisTech, INRA, UMR 782 Ge´nie et Microbiologie des Proce´de´s Alimentaires, CBAI, 78850 Thiverval-Grignon, France e-mail: [email protected]
Introduction Saliva has many functions in the mouth such as lubrification of oral mucous membranes, buffering action, maintenance of tooth integrity, enhancement of taste and digestion, and protection of teeth and mucosal surfaces (Mandel 1987). Through these functions, saliva strongly interacts with microorganisms in the mouth. Due to its quick turnover linked to continuous saliva production and swallowing, it allows the oral cavity to maintain a relatively constant bacterial balance, thus limiting pathogen development (Mandel 1987). This phenomenon is enhanced by several salivary components such as mucins, amylase, statherin and agglutinins, which aggregate the bacteria including streptococci, thus helping them to be flushed out of the oral cavity (Kilian and Nyvad 1990). Another saliva protection role is linked to its content in specific antimicrobial factors such as lysozyme, peroxidase and others. Lysozyme hydrolyses bond between N-acetylmuramic acid and Nacetylglucosamine in the peptidoglycan layer of the bacterial cell wall, thus causing cell lysis (M
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