CHICAGO -- Oral bacteria can exchange genes, raising the possibility that organisms in the oral cavity can be transformed from harmless to destructive, and from antibiotic-susceptible to antibiotic-resistant, oral biologists at the University at Buffalo School of Dental Medicine have found.
In findings presented here today (March 9, 2001) at the annual meeting of the American Association for Dental Research, UB dental researchers showed direct experimental evidence that horizontal gene transfer can occur between two different families of bacteria commonly found in the mouth.
"We carried out these experiments to examine the possibility that bacteria in dental plaque may exchange genetic information between each other," said Howard K. Kuramitsu, Ph.D., UB professor of oral biology and microbiology and senior author on the study.
"Our studies demonstrated genetic exchange between two markedly distinct oral bacteria -- an oral spirochete and a streptococcus. Therefore, exchange between two closely related bacteria, such as the one responsible for dental caries -- Streptococcus mutans -- and the harmless Streptococcus gordonii is highly probable."
Kuramitsu and Bingyan Wang, M.D., a post-doctoral researcher, used an erythromycin-resistant plasmid as a marker of gene transfer. A plasmid is an extra-chromosomal self-replicating structure found in bacteria cells that carries genes for a variety of functions not essential for cell growth, such as antibiotic resistance.
The researchers cultivated Streptococcus gordonii in the presence of the plasmid alone and separately with the bacteria Treponema denticola harboring the plasmid marker. After a period of cultivation, they detected genes from the marker plasmid within S. gordonii under both growth scenarios. Isolation of plasmids from the later strain could be followed by transformation into Escherichia coli.
"These findings could be important in the transfer of antibiotic resistance between plaque organisms, as well as with more harmful bacteria that temporarily colonize the oral cavity," Kuramitsu said. "In addition, this process could be important in understanding the evolution of plaque bacteria and could explain why some organisms exhibit certain virulent properties, such as the ability to colonize teeth."
The research was supported by grants from the National Institutes of Health.
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