Cai Yanling, Liao Ying, Brandt Bernd W, Wei Xi, Liu Hongyan, Crielaard Wim, Van Loveren Cor, Deng Dong Mei
Department of Operative Dentistry and Endodontics, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen UniversityGuangzhou, China.
Guangdong Province Key Laboratory of StomatologyGuangzhou, China.
Front Microbiol. 2017 Aug 28;8:1630. doi: 10.3389/fmicb.2017.01630. eCollection 2017.
The cariogenic bacterium can develop stable resistance to fluoride through chromosomal mutations . Fluoride-resistant has seldom been isolated in clinical settings, despite the wide application of fluoride in oral-care products. One explanation is that the fluoride-resistant strains have decreased fitness. However, so far, there has been no conclusive evidence to support this idea. The aim of this study was to investigate the fitness cost of 48-h biofilms of two fluoride-resistant strains, UF35 and UA159-FR (UAFR), using the wild-type fluoride-sensitive strain UA159 as a reference. The engineered UF35 strain contains one point mutation, whereas UAFR, selected from NaF-containing agar plates, has multiple chromosomal mutations. All biofilms were formed for 48 h under a constantly neutral pH or a pH-cycling (8 h of neutral pH and 16 h of pH 5.5) condition in the absence of fluoride. The biomass of the biofilms was quantified with a crystal violet assay. The biofilms were also treated with chlorhexidine or solutions at pH 3.0, after which their lactic acid production was quantified. Compared to the UF35 and UA159 biofilms, the biomass of UAFR biofilms was two-four fold higher, and the UAFR biofilms were more resistant to chlorhexidine and low pH in terms of lactic acid production. No difference in biomass and lactic acid production was detected between UF35 and UA159 biofilms. The fluoride resistance of UAFR and UF35 strains in biofilms was further confirmed by treating the biofilms with NaF solutions. The level of NaF resistance of the three biofilms is generally ranked as follows: UAFR > UF35 > UA159. In conclusion, there is indeed a fitness consequence in UAFR, but surprisingly, this fluoride-resistant strain performs better than UF35 and UA159 under the described conditions. In addition, UF35 did not display a reduced fitness; it performed as well as the wild-type fluoride-sensitive strain.
致龋细菌可通过染色体突变对氟化物产生稳定抗性。尽管氟化物在口腔护理产品中广泛应用，但耐氟菌株在临床环境中很少被分离出来。一种解释是耐氟菌株的适应性有所下降。然而，到目前为止，尚无确凿证据支持这一观点。本研究的目的是以野生型氟敏感菌株UA159为参照，研究两种耐氟菌株UF35和UA159-FR（UAFR）48小时生物膜的适应性代价。工程改造的UF35菌株含有一个点突变，而从含氟化钠的琼脂平板上筛选出的UAFR有多个染色体突变。所有生物膜均在无氟条件下，于恒定中性pH值或pH循环（8小时中性pH值和16小时pH 5.5）条件下形成48小时。用结晶紫测定法对生物膜的生物量进行定量。生物膜还用洗必泰或pH 3.0的溶液处理，之后对其乳酸产量进行定量。与UF35和UA159生物膜相比，UAFR生物膜的生物量高出两到四倍，并且就乳酸产生而言，UAFR生物膜对洗必泰和低pH更具抗性。UF35和UA159生物膜之间未检测到生物量和乳酸产生的差异。用氟化钠溶液处理生物膜进一步证实了UAFR和UF35菌株在生物膜中的耐氟性。三种生物膜的耐氟化钠水平一般如下：UAFR>UF35>UA159。总之，UAFR确实存在适应性后果，但令人惊讶的是，在所述条件下，这种耐氟菌株的表现优于UF35和UA159。此外，UF35未表现出适应性降低；其表现与野生型氟敏感菌株一样好。
