# Characteristics of Clinical Isolates of _Streptococcus mutans_
## 3 Results and Discussion  
Sixty clinical _S. mutans_ strains were isolated from 60 different individuals, 30 from adults and 30 from children with the symptoms of caries. The isolated strains grew only on sucrose medium. The strains were identified using the automated Vitek GP card system (bioMerieux). No significant differences were observed in the biochemical properties of strains from adults and children. The biochemical panel is shown in Table 3. The method of isolation and identification of strains was found to be effective and it provided reproducible results. The biochemical panel of the strain is typical for _S. mutans_ strains isolated from the oral cavity of Polish patients [18]. The drug resistance of each of the _S. mutans_ strains was determined. The system classified all tested isolates as sensitive (S) to the antibiotics listed in Table 4. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline AMY & + & PIPLC & – & dXYL & – & ADH1 & – & BGAL & – & AGLU & (\(-\)) \\ \hline APPA & \(-\) & CDEX & \(-\) & AspA & \(-\) & BGAR & \(-\) & AMAN & \(-\) & PHOS & \(-\) \\ \hline LeuA & (\(-\)) & ProA & \(-\) & BGURr & \(-\) & AGAL & \(-\) & Pyr A & \(-\) & BGUR & \(-\) \\ \hline Ala & + & TyrA & \(-\) & dSOR & + & URE & \(-\) & POLYB & + & dGAL & + \\ \hline dRIB & \(-\) & ILATk & \(-\) & Lac & + & NAG & \(-\) & dMAL & + & BACI & + \\ \hline NOVO & + & NC6.5 & \(-\) & dMAN & + & dMNE & + & MBdG & + & PUL & \(-\) \\ \hline dRAF & + & O129R & \(-\) & SAL & + & SAC & + & dTRE & + & ADH2s & \(-\) \\ \hline OPTO & + & & & & & & & & & \\ \hline \end{tabular}
\end{table} 
Table 3: Illustrative biochemical profile of _S. mutans_ (GP card) of a randomly selected strain. The biochemical profile was identical for all strains. Another element in the characterisation of the strains was the assessment of biofilm production capacity. The year 1986 marks the beginning of research into signal transduction phenomena in bacteria. At that time, [PERSON] et al. first used the term two-component system (TCS) [3]. The model two-component regulatory system consists of a membrane sensor protein, which is histidine kinase (HK), which receives a signal from the environment, and a cytoplasmic regulatory protein--the response regulator (RR), which, after a conformational change resulting from signal reception, regulates the expression of the target gene. As indicated in the literature, binary regulatory systems are involved in many _S. mutans_ life processes, including biofilm formation, which is the main virulence factor of this species and plays a fundamental role in plaque formation. Compared to _S. mutans_ reference strain UA159 ATCC 700610, strains with mutations in both vicK and vicR genes form a biofilm that differs from that typical of this species [19; 20; 21; 22]. Determination of the biofilm level was performed using the crystal violet staining method. The applied method gave reproducible results and showed that all tested strains formed biofilm in vitro at the expected high level, comparable to the reference strain _S. mutans_ UA 159 (Scheme 1, bar 2). **Scheme 1. ** Level of biofilm formation by 10 randomly selected clinical isolates of _S. mutans_. 1--non-biofilm forming strain, 2--reference strain _S. mutans_ UA159, 3--clinical isolates from adults, 7--12--clinical isolates from children. Bars represent mean values \(\pm\) standard deviation. \begin{table}
\begin{tabular}{c c c} \hline
**Antimicrobial** & **MIC** & **Interpretation** \\ \hline Benzylpenicillin & \(<\)=0.06 & Sensitive \\ \hline Ampicillin & \(<\)=0.25 & Sensitive \\ \hline Cefotaxime & \(<\)=0.12 & Sensitive \\ \hline Ceftriaxone & \(<\)=0.12 & Sensitive \\ \hline Erythromycin & \(<\)=0.12 & Insufficient evidence that species is good target for therapy \\ \hline Clindamycin & \(<\)=0.25 & Sensitive \\ \hline Vanomycin & 1 & Sensitive \\ \hline \end{tabular}
\end{table} 
Table 4: Drug susceptibility panel—AST-ST01 Card (bioMerieux). In preparing the multiplex PCR analysis, all amplifications were performed for the _S.