Iron is an essential nutrient for the growth of bacteria, and iron is needed for various biochemical and physiological responses of bacteria [1-3]. Oral streptococci that reside in human oral cavity are gram-positive bacteria and play an important role in plaque formation . Some of them cause dental caries and infective endocarditis [5,6].
Currently, there are three known mechanisms for iron accumulation in bacteria. One is the mechanism by which siderophores present in bacteria act. The siderophore binds to iron to form a ferric siderophore complex, and ferric siderophore binds to a complex present in bacteria. Through this, the bacteria obtain iron . The second mechanism is the use of host iron binding proteins (transferrin, lactoferrin, etc.) [9,10]. Some bacteria have low-iron-inducible outer membrane proteins capable of binding to the human iron binding protein, transferrin or lactoferrin, and are used to obtain iron through human iron binding proteins [9,10]. The third is the mechanism of using heme compounds. It is a mechanism to obtain iron by using hemin binding protein of bacteria that can bind with heme or heme compounds [11,12]. Heme compounds can act as an iron source for bacterial growth . Heme compounds can provide a sufficient supply of iron for bacterial growth, even at low concentrations (<10 μM) .
Several previous studies report that the hemin binding ability of bacteria is closely related to the Congo red binding of bacteria [13,15-18]. According to Surgalla and Beesley , strains binding to hemin in
Congo red was reported as one of the identification markers used to distinguish the toxicity and harmlessness of certain bacteria . For example, in vitro experiment on
In this study, the binding of Congo red was analyzed in oral streptococcus,
After binding of
Statistical significance was determined using a two-sample Student t-test. The Student t-test was run through the Software Package for Social Sciences (SPSS version 23; IBM Corp., Armonk, NY, USA) program.
To determine whether the Congo red binding capacity of
To determine the association between hemin binding and Congo red binding, Congo red binding of bacteria was analyzed after hemin prebinding of
Congo red binds structurally to receptors capable of recognizing this substance, and Congo red binding can be inhibited by structurally very similar compounds . This was suggested by showing that Congo red binding of oral spirochetes is inhibited by hemin and protophorphysin IX in studies on oral spirochetes (
In this study, the binding of
Studies on the association between hemin and Congo red binding have been conducted in several bacteria. Daskaleros and Payne  showed that Congo red binding of
The authors declare that they have no competing interests.