The effect of smokeless-tobacco extracts on the growth of oral bacteria of the genus Streptococcus

Smokeless Tobacco Harbors Bacteria Involved in Biofilm Formation as Well as Salt and Heavy Metal Tolerance Activity

In our previous culture-independent study on smokeless tobacco products, we have observed a strong positive correlation between several bacteria and genes involved in nitrate/nitrite reduction, biofilm formation, and pro-inflammation. Therefore, the present investigation was carried out to analyze the inhabitant bacterial population of the Indian ST products for assessing the health-associated risk attributes using culture-dependent approach. Traditional cultivation approaches recovered several bacterial isolates from commercial ST products on different culture media. A high colony formation unit (CFU) count was observed that ranged from 173 × 104 to 630.4 × 105 per gram of ST products. Of the 74 randomly selected and distinct bacterial isolates, 17 isolates showed a significantly enhanced growth (p-value < 0.05) in the presence of the aqueous tobacco extract. On biochemical characterization, these bacteria were identified as the member of Bacillus, Enterobacter, Micrococcus, Providencia, Serratia, Pantoea, Proteus, and Pseudomonas. Most of these bacteria also exhibited biofilm-forming activity, where eight bacterial isolates were identified for strong biofilm-forming action. 16S rRNA-based molecular characterization of these bacteria identified them as Bacillus subtilis, Bacillus paralicheniformis, Enterobacter sp., Serratia marcescens, Pantoea anthophila, and Enterobacter cloacae. Moreover, these bacteria also exhibited the potential to withstand high salt and heavy metal concentrations. The findings demonstrate that Indian ST products are heavily populated with wide bacterial species exhibiting potential in biofilm formation, heavy metal resistance, and salt tolerance.

Microorganisms: crucial players of smokeless tobacco for several health attributes

Global consumption of smokeless tobacco (SLT) reached 300 million users worldwide majorly from middle-income countries. More than 4000 chemical compounds represent it as one of the noxious consumable products by humans. Besides toxicants/carcinogens, the heavy microbial load on smokeless tobacco further keeps human health at higher risk. Several of these inhabitant microbes participate in biofilm formation and secrete endotoxin/mycotoxins and proinflammatory-like molecules, leading to several oral diseases. Tobacco-associated bacteria exhibit their role in tobacco-specific nitrosamines (TSNAs) formation and acetaldehyde production; both are well-documented carcinogens. Moreover, tobacco exhibits the potential to alter the oral microbiome and induce dysbiotic conditions that lead to the onset of several oral and systemic diseases. Traditional cultivation approaches of microbiology provide partial information of microbial communities of a habitat; therefore, microbiomics has now been employed to study the metagenomes of entire microbial communities. In the past 5 years, few NGS-based investigations have revealed that SLT harbors four dominant phyla (Firmicutes, Proteobacteria, Actinobacteria, and Bacteroidetes) dominating Bacillus spp. and/or Pseudomonas spp. However, functional characterization of their genetic elements will be a more informative attribute to understand the correlation between inhabitant microbial diversity and their relatedness concerning abundance and diseases. This review provides an update on the microbial diversity of SLT and its associated attributes in human health. KEY POINTS: • Heavy microbial load on smokeless tobacco alarms for poor oral hygiene. • Inhabitant microorganisms of SLT participate in TSNA and biofilm formation. • SLTs alter the oral microbiome and causes oral dysbiosis.

Impact of smokeless tobacco-associated bacteriome in oral carcinogenesis

Smokeless tobacco products possess a complex community of microorganisms. The microbial community ferment compounds present in the smokeless tobacco products and convert them into carcinogens like tobacco-associated nitrosamines. However, the potential of smokeless tobacco products associated bacteriome to manipulate systemic inflammation and other signaling pathways involved in the etiology of oral cancer will be a risk factor for oral cancer. Further, damage to oral epithelial cells causes a leaky oral layer that leads to increased infiltration of bacterial components like lipopolysaccharide, flagellin, and toxins, etc. The consumption of smokeless tobacco products can cause damage to the oral layer and dysbiosis of oral microbiota. Hence, the enrichment of harmful microbes due to dysbiosis in the oral cavity can produce high levels of bacterial metabolites and provoke inflammation as well as carcinogenesis. Understanding the complex and dynamic interrelation between the smokeless tobacco-linked bacteriome and host oral microbiome may help to unravel the mechanism of oral carcinogenesis stimulated by smokeless tobacco products. This review provides an insight into smokeless tobacco product-associated bacteriome and their potential in the progression of oral cancer. In the future, this will guide in the evolution of prevention and treatment strategies against smokeless tobacco products-induced oral cancer. Besides, it will assist the government organizations for better management and cessation policy building for the worldwide problem of smokeless tobacco addiction.

Effect of smokeless tobacco products on human oral bacteria growth and viability

To evaluate the toxicity of smokeless tobacco products (STPs) on oral bacteria, seven smokeless tobacco aqueous extracts (STAEs) from major brands of STPs and three tobacco-specific N-nitrosamines (TSNAs) were used in a growth and viability test against 38 oral bacterial species or subspecies. All seven STAEs showed concentration-dependent effects on the growth and viability of tested oral bacteria under anaerobic culture conditions, although there were strain-to-strain variations. In the presence of 1 mg/ml STAEs, the growth of 4 strains decreased over 0.32-2.14 log₁₀ fold, while 14 strains demonstrated enhanced growth of 0.3-1.76 log₁₀ fold, and the growth of 21 strains was not significantly affected. In the presence of 10 mg/ml STAEs, the growth of 17 strains was inhibited 0.3-2.11 log₁₀ fold, 18 strains showed enhanced growth of 0.3-0.97 log₁₀ fold, and 4 strains were not significantly affected. In the presence of 50 mg/ml STAEs, the growth of 32 strains was inhibited 0.3-2.96 log₁₀ fold, 8 strains showed enhanced growth of 0.3-1.0 log₁₀ fold, and 2 strains were not significantly affected. All seven STAEs could promote the growth of 4 bacterial strains, including Eubacterium nodatum, Peptostreptococcus micros, Streptococcus anginosus, and Streptococcus constellatus. Exposure to STAEs modulated the viability of some bacterial strains, with 21.1-66.5% decrease for 4 strains at 1 mg/ml, 20.3-85.7% decrease for 10 strains at 10 mg/ml, 20.0-93.3% decrease for 27 strains at 50 mg/ml, and no significant effect for 11 strains at up to 50 mg/ml. STAEs from snuffs inhibited more tested bacterial strains than those from snus indicating that the snuffs may be more toxic to the oral bacteria than snus. For TSNAs, cell growth and viability of 34 tested strains were not significantly affected at up to 100 μg/ml; while the growth of P. micros was enhanced 0.31-0.54 log₁₀ fold; the growth of Veillonella parvula was repressed 0.33-0.36 log₁₀ fold; and the cell viabilities of 2 strains decreased 56.6-69.9%. The results demonstrate that STAEs affected the growth of some types of oral bacteria, which may affect the healthy ecological balance of oral bacteria in humans. On the other hand, TSNAs did not significantly affect the growth of the oral bacteria.

Effect of nicotine on growth and metabolism of Streptococcus mutans

Streptococcus mutans is a key contributor to dental caries. Smokers have a higher number of caries-affected teeth than do nonsmokers, but the association among tobacco, nicotine, caries, and S. mutans growth has not been investigated in detail. Seven S. mutans strains--UA159, UA130, 10449, A32-2, NG8, LM7, and OMZ175--were used in the present study. The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC), planktonic cell growth, biofilm formation, metabolism, and structure (determined using scanning electron microscopy) of the seven strains treated with different concentrations of nicotine (0-32 mg ml(-1)) were investigated. The MIC, MBC, and MBIC were 16 mg ml(-1) (0.1 M), 32 mg ml(-1) (0.2 M), and 16 mg ml(-1) (0.1 M), respectively, for most of the S. mutans strains. Growth of planktonic S. mutans cells was significantly repressed by 2.0-8.0 mg ml(-1) of nicotine. Biofilm formation and metabolic activity of S. mutans was increased in a nicotine-dependent manner up to 16.0 mg ml(-1) of nicotine. Scanning electron microscopy revealed that S. mutans treated with a high concentration of nicotine a had thicker biofilm and more spherical bacterial cells. In summary, nicotine enhances S. mutans biofilm formation and biofilm metabolic activity. These results suggest that smoking can increase the development of caries by fostering increased formation of S. mutans biofilm on tooth surfaces.

Influence of tobacco use in dental caries development

This review article describes different forms of tobacco usage and its direct relationship with the prevalence of dental caries. Smoking along with co-existing factors like old age, bad oral hygiene habits, food habits, limited preventive dental visits and over all health standards, can be associated with high caries incidence. However, a direct etiological relationship is lacking. Environmental tobacco smoke (ETS) causes dental caries in children but no studies have been reported in adults. Existing findings are not sufficient and conclusive enough to confirm that ETS causes dental caries. Oral use of smokeless tobacco (ST), predominantly tobacco chewing, is presumably a positive contributing factor to higher incidence of dental caries. Unfortunately, published studies are not converging towards one single factor through which tobacco usage can have direct relationship to dental caries.

Chewing tobacco use and dental caries among U.S. men

BACKGROUND

Chewing tobacco has high levels of sugars and may be cariogenic, but few studies have investigated such an association. This study examined the relationship between chewing tobacco use and dental caries among U.S. adult men.

METHODS

Participants in the Third National Health and Nutrition Examination Survey conducted from 1988 to 1994 were interviewed about tobacco use and examined by dentists. The authors included in their analysis dentate men 18 years of age or older. They calculated the mean number of decayed or filled permanent teeth, or DFT, and decayed or filled coronal tooth surfaces, or DFS, as well as the mean number and percentage of decayed or filled root surfaces, or RDFS, and decayed root surfaces, or RDS, by tobacco-use status. They used multiple logistic regression to examine the association between chewing tobacco use and root-surface caries.

RESULTS

Men who currently used only chewing tobacco had a higher adjusted mean number of DFT than did those who currently used only snuff, only cigarettes or more than one form of tobacco or who never used tobacco. Mean DFS also was higher among chewing tobacco users than among those who used only snuff, only cigarettes or more than one form of tobacco. Chewing tobacco users had a higher mean RDFS and RDS than did the users of other forms of tobacco or nonusers. Current users of chewing tobacco were more than four times as likely as those who never used tobacco to have one or more RDFS or RDS, with a dose-response relationship between number of packages used per week and odds of having root-surface caries.

CONCLUSIONS

In addition to its established role as a carcinogen, chewing tobacco may be a risk factor in the development of root-surface caries and, to a lesser extent, coronal caries. This may be due to high sugar content, increased gingival recession and enhanced collagenase activity.

CLINICAL IMPLICATIONS

Interventions by dentists and other members of the oral health care team to prevent tobacco use and help users quit can reduce the risk of developing oral and systemic disease.

The effects of smokeless tobacco extract on bone nodule formation and mineralization by chick osteoblasts in vitro

Short-term exposure to smokeless tobacco extracts (STE) reportedly inhibits osteoblast metabolism. The objective of this study was to determine the effects of serial dilutions of a water-soluble extract of smokeless tobacco on osteoblast proliferation and their potential to form and mineralize bone nodules. STE significantly stimulated cell proliferation when diluted 10(2)-10(4) times; 10(3) and 10(4) dilutions produced the greatest effect. 10(2)-10(4) STE dilutions significantly increased alkaline phosphatase activity at day 7 but 10(6) STE dilutions significantly decreased it. 10(3) and 10(4) dilutions significantly increased bone nodule formation, but inhibited their mineralization. In contrast, 10(5) and 10(6) dilutions significantly decreased bone nodule formation, but increased their mineralization. Stimulation of in vitro bone nodule formation by STE was similar to that produced by 10(-7) M insulin-like growth factor 1 (IGF-1) in vivo. Heat and acid treatment of STE significantly reduced its beneficial effect on cell proliferation, suggesting that a peptide within STE may be responsible for enhancement of osteogenic cell proliferation. Thus, STE may contain a peptide capable of significantly stimulating osteoblast proliferation, differentiation and metabolism, similar to the effects of IGF-1. This peptide could have potential therapeutic benefits.

Effect of smokeless tobacco use in humans on mucosal immune factors

To assess the effects of smokeless tobacco on the secretory immune system and dental caries, we examined users of smokeless tobacco and non-tobacco users. There were no significant differences in the prevalence of DMFS between users and non-users. There was significantly more salivary IgA, IgA2 and J-chain in users. Levels of salivary lysozyme and lactoferrin were significantly lower in users than controls. Because there was no difference in levels of secretory component in relation to the increased IgA levels of smokeless tobacco users, this suggests an effect of smokeless tobacco on secretory epithelial cells responsible for synthesis of secretory component, lysozyme and lactoferrin, and for the packaging of secretory component on IgA. There were only slight differences in salivary or serum antibody levels to Streptococcus mutans. These findings indicate that although smokeless tobacco has a significant influence on the synthesis of secretory IgA, the numbers of DMFS were similar between smokeless tobacco users and controls.