Tetracycline resistance can be achieved through tet genes, which code for efflux pumps, ribosomal protection proteins and inactivation enzymes. Some of these genes have only been described in either Gram-positive or Gram-negative bacteria. This is the case of tet(B), which codes for an efflux pump and, so far, had only been found in Gram-negative bacteria. In this study, tet(B) was detected in two clinical Streptococcus oralis strains isolated from the gingival sulci of two subjects. In both cases, the gene was completely sequenced, yielding 100% shared identity and coverage with other previously published sequences of tet(B). Moreover, we studied the expression of tet(B) using RT-qPCR in the isolates grown with and without tetracycline, detecting constitutive expression in only one of the isolates, with no signs of expression in the other one.

This is the first time that the presence and expression of the tet(B) gene has been confirmed in Gram-positive bacteria, which highlights the potential of the genus Streptococcus to become a reservoir and a disseminator of antibiotic resistance genes in an environment so prone to horizontal gene transfer as is the oral biofilm.

四环素耐药性可通过tet基因实现，该基因编码外排泵，核糖体保护蛋白和失活酶。其中一些基因仅在革兰氏阳性或革兰氏阴性细菌中有描述。tet（B）就是这种情况，其编码外排泵，到目前为止，仅在革兰氏阴性细菌中发现。在这项研究中，在从两个受试者的牙龈沟分离的两个临床链球菌链球菌中检测到tet（B）。在这两种情况下，基因均已完全测序，与其他先前发表的tet（B）序列具有100％的共享同一性和覆盖率。此外，我们研究了tet的表达（B）使用RT-qPCR在有和没有四环素的情况下生长的分离株中，仅在其中一个分离株中检测到组成型表达，而在另一分离株中没有表达迹象。

这是首次在革兰氏阳性细菌中证实了tet（B）基因的存在和表达，这突显了链球菌属在如此容易发生的环境中成为抗生素抗性基因的贮藏和传播者的潜力。向水平基因转移，就像口服生物膜一样。