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Effect of Fluoride-Resistant Microorganisms on Dental Caries S. ROSEN, J. I. FREA, and Su M. Hsu College of Dentistry and Department of Microbiology, The Ohio State University, Columbus, Ohio 43210, USA J Dent Res 57(2): 180, February 1978. Several strains of Streptococcus mutans were treated with mutagens and fluoride resistant mutants were obtained. Strains S-126 (obtained from W. W. Briner) and 6715 (obtained from Paul Keyes) were made resistant to 600 ppm Fby exposure to ultraviolet light. FA-1 (obtained from R. Fitzgerald) was made resistant to 600 ppm F- by exposure to acriflavin. * Tolerance to fluoride was based on abundant fluocculant growth. All of the mutant isolates possessed the same basic carbohydrate degradative pathways as the wild-type. Each isolate resistant to fluoride was tested for its ability to produce intracellular polysaccharide (IPS) by the method of VAN HOUTE (Caries Res., 2:47-56, 1968). Most isolates were found to produce IPS readily in the presence of fluoride. It was also noted that the greater the fluoride resistance of the mutant isolates, the higher was the fluoride concentrations at which IPS formation was evident. All mutants were checked for acid production under increasing levels of fluoride in the growth medium. Those organisms which were found to produce the most acid at high fluoride levels were also those isolates which showed the greatest IPS formation. So, in general, IPS formation, acid production, and tolerance to high fluoride levels appeared to be related. In order to determine the amount of growth that was occurring under increased fluoride levels, dry weight determinations were carried out. The dry weights of these organisms increased with increasing levels of fluoride in the growth medium. The parent and mutant strains were inoculated into gnotobiotic rats and parent and mutant strains of 6715 were superimposed upon the microflora of conventional animals. Diet 2000t (KEYES and JORDAN, Arch Oral Biol, 9:377-400, 1964) was fed ad libitum and sodium fluoride was administered in the drinking water (45 ppm F-) or a neutral 1 % solution (4,500 ppm F-) was used to swab the teeth twice a day, five days per week. After 9 weeks, the rats were sacrificed and scored for caries by a Received for publication August 5, 1977. Accepted for publication January 10, 197 8. *Aldrich Chemical Company, Inc... Milwaukee, Wi. 'Teklad Mills, Madison, Wi.
modified method of COX ET AL (J Dent Res., 18:469-480, 1939). Before sacrifice, the teeth of the conventional animals were swabbed and recovery of resistant microorganisms was made by replicate plating in media containing fluoride. Sterility checks and recoveries were made from fecal material and drinking water in the isolators. Our data show that the cariogenicity of the mutant strains of S-126 (Exp 1 and 2) and FA-1 (Exp 3) was sharply reduced but the cariogenicity of the fluoride-resistant strain of 6715 was not (Exp 4). It appears that that cariogenicity of this strain was enhanced, but one of the animals in this group had an extremely high score. The results with 6715 were encouraging. We repeated the experiment and included animals in conventional environment. The data show that the mutant strain was as cariogenic as the wild-type in gnotobiotic and conventional animals not given fluoride (Exp 5 and 6). Animals given fluoride had lower scores. Recovery of fluoride resistant bacteria from conventional rats was greater from mutant inoculated animals (37% of the recovered bacteria were resistant to 400 ppm F-) than from wild-type inoculated animals (5% of the recovered bacteria were resistant to 400 ppm F-). Thus, the mutant was established in the oral cavity of these animals and could have contributed to the production of caries. Therefore, the low caries scores in the animals treated with fluoride occurred even in the presence of the cariogenic mutant. Since fluoride inhibits the production of caries by fluoride-resistant cariogenic bacteria, the theory that fluoride inhibits caries by decreasing enamel solubility is supported. Re-isolation of fluoride resistant S mutans from the animals two months after inoculation revealed that these mutants retain resistance to fluoride at the same levels as before inoculation. This indicates the stability of the mutants in an animal environment. We have shown that certain strains of S mutans resistant to fluoride are less cariogenic than their parent strains. This suggests the possibility that in the human oral cavity fluorideresistant strains may be selected out by fluoride treatment. Since these organisms may be less cariogenic, this could be another mechanism by which fluoride inhibits dental caries.
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Effect of Fluoride-Resistant Microorganisms on Dental Caries S. ROSEN, J. I. FREA, and Su M. Hsu College of Dentistry and Department of Microbiology, The Ohio State University, Columbus, Ohio 43210, USA J Dent Res 57(2): 180, February 1978. Several strains of Streptococcus mutans were treated with mutagens and fluoride resistant mutants were obtained. Strains S-126 (obtained from W. W. Briner) and 6715 (obtained from Paul Keyes) were made resistant to 600 ppm Fby exposure to ultraviolet light. FA-1 (obtained from R. Fitzgerald) was made resistant to 600 ppm F- by exposure to acriflavin. * Tolerance to fluoride was based on abundant fluocculant growth. All of the mutant isolates possessed the same basic carbohydrate degradative pathways as the wild-type. Each isolate resistant to fluoride was tested for its ability to produce intracellular polysaccharide (IPS) by the method of VAN HOUTE (Caries Res., 2:47-56, 1968). Most isolates were found to produce IPS readily in the presence of fluoride. It was also noted that the greater the fluoride resistance of the mutant isolates, the higher was the fluoride concentrations at which IPS formation was evident. All mutants were checked for acid production under increasing levels of fluoride in the growth medium. Those organisms which were found to produce the most acid at high fluoride levels were also those isolates which showed the greatest IPS formation. So, in general, IPS formation, acid production, and tolerance to high fluoride levels appeared to be related. In order to determine the amount of growth that was occurring under increased fluoride levels, dry weight determinations were carried out. The dry weights of these organisms increased with increasing levels of fluoride in the growth medium. The parent and mutant strains were inoculated into gnotobiotic rats and parent and mutant strains of 6715 were superimposed upon the microflora of conventional animals. Diet 2000t (KEYES and JORDAN, Arch Oral Biol, 9:377-400, 1964) was fed ad libitum and sodium fluoride was administered in the drinking water (45 ppm F-) or a neutral 1 % solution (4,500 ppm F-) was used to swab the teeth twice a day, five days per week. After 9 weeks, the rats were sacrificed and scored for caries by a Received for publication August 5, 1977. Accepted for publication January 10, 197 8. *Aldrich Chemical Company, Inc... Milwaukee, Wi. 'Teklad Mills, Madison, Wi.
modified method of COX ET AL (J Dent Res., 18:469-480, 1939). Before sacrifice, the teeth of the conventional animals were swabbed and recovery of resistant microorganisms was made by replicate plating in media containing fluoride. Sterility checks and recoveries were made from fecal material and drinking water in the isolators. Our data show that the cariogenicity of the mutant strains of S-126 (Exp 1 and 2) and FA-1 (Exp 3) was sharply reduced but the cariogenicity of the fluoride-resistant strain of 6715 was not (Exp 4). It appears that that cariogenicity of this strain was enhanced, but one of the animals in this group had an extremely high score. The results with 6715 were encouraging. We repeated the experiment and included animals in conventional environment. The data show that the mutant strain was as cariogenic as the wild-type in gnotobiotic and conventional animals not given fluoride (Exp 5 and 6). Animals given fluoride had lower scores. Recovery of fluoride resistant bacteria from conventional rats was greater from mutant inoculated animals (37% of the recovered bacteria were resistant to 400 ppm F-) than from wild-type inoculated animals (5% of the recovered bacteria were resistant to 400 ppm F-). Thus, the mutant was established in the oral cavity of these animals and could have contributed to the production of caries. Therefore, the low caries scores in the animals treated with fluoride occurred even in the presence of the cariogenic mutant. Since fluoride inhibits the production of caries by fluoride-resistant cariogenic bacteria, the theory that fluoride inhibits caries by decreasing enamel solubility is supported. Re-isolation of fluoride resistant S mutans from the animals two months after inoculation revealed that these mutants retain resistance to fluoride at the same levels as before inoculation. This indicates the stability of the mutants in an animal environment. We have shown that certain strains of S mutans resistant to fluoride are less cariogenic than their parent strains. This suggests the possibility that in the human oral cavity fluorideresistant strains may be selected out by fluoride treatment. Since these organisms may be less cariogenic, this could be another mechanism by which fluoride inhibits dental caries.
180 Downloaded from jdr.sagepub.com at MICHIGAN STATE UNIV LIBRARIES on June 13, 2015 For personal use only. No other uses without permission.
