Biofilm formation and autoinducer‐2 signaling in Streptococcus intermedius: role of thermal and pH factors

Abstract

Bacteria sense their population density using autoinducer (AI) signaling systems. The AI-2 signal is thought to mediate communication among and within bacterial species. Streptococcus intermedius is a commensal organism frequently associated with periodontitis and purulent infections. We investigated the role of AI-2 signaling in S. intermedius biofilm formation under temperatures and pH levels relevant to human physiology. Bioluminescence was used to monitor the change in AI-2 levels at various temperatures. Growth and biofilm formation in S. intermedius and its luxS mutant SI006 were measured at 35, 37, 39, and 41 degrees C and in pH ranging from 5.7 to 7.5. To confirm the role of AI-2 signals in biofilm formation, the AI-2 precursor (S)-4,5-dihydroxy-2,3-pentanedione (DPD) was used to complement SI006 biofilm formation. S. intermedius AI-2 signals were detected at all growth temperatures but reached the highest levels at 37 degrees C. SI006 displayed significantly less biofilm formation than S. intermedius wild-type (WT); however, the role of AI-2 on biofilm formation was confined to 37 degrees C. DPD supplementation significantly increased SI006 biofilm formation to the S. intermedius WT level. The role of AI-2 in S. intermedius biofilm formation was not influenced by pH. High temperatures and low pH enhanced biofilm formation in both S. intermedius and its luxS mutant. High temperature and acidic conditions may favor biofilm formation by S. intermedius. The role of AI-2 in biofilm formation by S. intermedius, however, varies with physiological temperature changes. These results may assist in understanding possible behavior relative to health and disease.