# Inhibitory Effect ofEnterococcus faecium WB2000 on Volatile Sulfur Compound Production byPorphyromonas gingivalis

Authors: Nao Suzuki; Takuya Higuchi; Masato Nakajima; Akie Fujimoto; Hiromitsu Morita; Masahiro Yoneda; Takashi Hanioka; Takao Hirofuji
Journal: International Journal of Dentistry
 (2016)

---

## Abstract

Volatile sulfur compounds (VSCs) produced by oral anaerobes are the major compounds responsible for oral malodor.Enterococcus faecium WB2000 is recognized as an antiplaque probiotic bacterium. In this study, the effect ofE. faeciumWB2000 on VSC production byPorphyromonas gingivalis was evaluated, and the mechanism of inhibition of oral malodor was investigated.P. gingivalis ATCC 33277 was cultured in the presence of four lactic acid bacteria, includingE. faecium WB2000. Subsequently,P. gingivalis ATCC 33277, W50, W83, and two clinical isolates were cultured in the presence or absence ofE. faecium WB2000, and the emission of VSCs from spent culture medium was measured by gas chromatography. The number ofP. gingivalis ATCC 33277 in mixed culture withE. faecium WB2000 decreased at 6 h, and the rate of decrease was higher than that in mixed cultures with the other lactic acid bacteria. The numbers of fiveP. gingivalis strains decreased at similar rates in mixed culture withE. faecium WB2000. The concentration of methyl mercaptan was lower in spent culture medium fromP. gingivalis andE. faecium WB2000 cultures compared with that fromP. gingivalis alone. Therefore,E. faecium WB2000 may reduce oral malodor by inhibiting the growth ofP. gingivalis and neutralizing methyl mercaptan.


---

## Body

## 1. Introduction

Oral malodor is caused mainly by the metabolism of sulfur amino acids by anaerobic bacteria inhabiting the oral cavity [1]. The main compounds responsible for oral malodor are volatile sulfur compounds (VSCs), such as hydrogen sulfide (H2S), methyl mercaptan (CH3SH), and dimethyl sulfide; these compounds are produced by some periodontopathic bacteria. Indeed,Porphyromonas gingivalis,Treponema denticola,Tannerella forsythia, andPrevotella intermedia generate considerable amounts of H2S and CH3SH [2].Probiotic bacteria, defined as live microorganisms that benefit the health of the host when administered in adequate amounts (FAO/WHO 2001), are thought to play a role in the maintenance of oral health [3]. Enterococci are facultatively anaerobic, Gram-positive cocci that form a part of the normal flora of the gastrointestinal tract of animals and humans. They are also frequently found in fermented food, such as cheese and meat [4].Enterococcus faecium andEnterococcus faecalis are the most clinically relevant members of the genusEnterococcus. Traditionally, they are regarded as low-grade pathogens but have emerged as important causes of nosocomial infections [5]. Clinical use ofE. faecium andE. faecalis during food fermentation and as probiotics requires a careful safety evaluation [6].E. faecium strains have been reported to inhibit biofilm formation by cariogenic bacteriain vitro [7, 8]. In addition, a previous double-blind randomized trial in which the subjects cleaned their teeth using a dentifrice containingE. faecium WB2000 or placebo for 4 weeks revealed improvements in salivary flow, salivary buffering capacity, and plaque accumulation [9]. This study aimed to investigate the effect ofE. faecium WB2000 on VSC production byP. gingivalis and the mechanism of inhibition of oral malodor byE. faecium WB2000.


## 2. Materials and Methods

### 2.1. Bacterial Strains and Culture Conditions

The bacterial strains used in the study are listed in Table1.Enterococcus faecium WB2000, previously classified asStreptococcus faecalis [10], was provided by Wakamoto Pharmaceutical. The selective medium forP. gingivalis consisted of Brucella agar (Becton Dickinson, Le Pont de Claix, France) supplemented with 5% horse blood, hemin (5 μg/mL), vitamin K (1 μg/mL), and gentamicin (50 μg/mL). Lactic acid bacteria were cultivated on BL agar (Nissui, Tokyo, Japan). Bacterial strains were cultivated at 37°C anaerobically for 40 h and suspended in sterile physiological saline to an optical density at 560 nm (OD560) of 1.0 forP. gingivalis and an OD560 of 0.02 for lactic acid bacteria.Table 1
Bacterial strains used in the study.
Species
Strain
Porphyromonas gingivalis
ATCC 33277
ATCC 53978 (W50)
ATCC BAA-308 (W83)
2-1 (clinical isolate)
7-1 (clinical isolate)
Enterococcus faecium
WB2000
Lactobacillus salivarius
CIP 103140
Lactobacillus reuteri
JCM 1112
Streptococcus salivarius
JCM 5707


### 2.2. Cocultivation ofP. gingivalis and Lactic Acid Bacteria

Bacterial cocultivation was carried out using 100μL ofP. gingivalis suspension, 100 μL of lactic acid bacterial suspension, and 10 mL fresh GAM broth (Nissui, Tokyo, Japan) supplemented with 0.7% glucose, hemin (5 μg/mL), and vitamin K (1 μg/mL) at 37°C anaerobically. Viable bacterial counts in the culture medium were determined at 6, 12, 24, and 48 h on the appropriate agar medium at 37°C anaerobically for 48 h.


### 2.3. Measurement of Volatile Sulfur Compounds

The VSC concentration in spent medium fromP. gingivalis cultured in the presence or absence ofE. faecium WB2000 was measured after 24 and 48 h. Aliquots (0.2 mL) of spent culture medium were added to 5 mL conical tubes, which were sealed and incubated at room temperature for 5 min. Then, 0.5 mL of the gas phase was collected and measured by gas chromatography (model GC2014, Shimadzu Works, Kyoto, Japan).


## 2.1. Bacterial Strains and Culture Conditions

The bacterial strains used in the study are listed in Table1.Enterococcus faecium WB2000, previously classified asStreptococcus faecalis [10], was provided by Wakamoto Pharmaceutical. The selective medium forP. gingivalis consisted of Brucella agar (Becton Dickinson, Le Pont de Claix, France) supplemented with 5% horse blood, hemin (5 μg/mL), vitamin K (1 μg/mL), and gentamicin (50 μg/mL). Lactic acid bacteria were cultivated on BL agar (Nissui, Tokyo, Japan). Bacterial strains were cultivated at 37°C anaerobically for 40 h and suspended in sterile physiological saline to an optical density at 560 nm (OD560) of 1.0 forP. gingivalis and an OD560 of 0.02 for lactic acid bacteria.Table 1
Bacterial strains used in the study.
Species
Strain
Porphyromonas gingivalis
ATCC 33277
ATCC 53978 (W50)
ATCC BAA-308 (W83)
2-1 (clinical isolate)
7-1 (clinical isolate)
Enterococcus faecium
WB2000
Lactobacillus salivarius
CIP 103140
Lactobacillus reuteri
JCM 1112
Streptococcus salivarius
JCM 5707


## 2.2. Cocultivation ofP. gingivalis and Lactic Acid Bacteria

Bacterial cocultivation was carried out using 100μL ofP. gingivalis suspension, 100 μL of lactic acid bacterial suspension, and 10 mL fresh GAM broth (Nissui, Tokyo, Japan) supplemented with 0.7% glucose, hemin (5 μg/mL), and vitamin K (1 μg/mL) at 37°C anaerobically. Viable bacterial counts in the culture medium were determined at 6, 12, 24, and 48 h on the appropriate agar medium at 37°C anaerobically for 48 h.


## 2.3. Measurement of Volatile Sulfur Compounds

The VSC concentration in spent medium fromP. gingivalis cultured in the presence or absence ofE. faecium WB2000 was measured after 24 and 48 h. Aliquots (0.2 mL) of spent culture medium were added to 5 mL conical tubes, which were sealed and incubated at room temperature for 5 min. Then, 0.5 mL of the gas phase was collected and measured by gas chromatography (model GC2014, Shimadzu Works, Kyoto, Japan).


## 3. Results

### 3.1. Effect of Lactic Acid Bacteria on the Growth ofP. gingivalis ATCC 33277

The number of viableP. gingivalis ATCC 33277 decreased to less than the detection limit after 6 h in mixed culture withE. faecium WB2000 (Figure 1(a)). In mixed cultures with the other three lactic acid bacteria (S. salivarius JCM 5707,L. salivariusCIP 103140, andL. reuteri JCM 1112), the number of viableP. gingivalis ATCC 33277 decreased to less than the detection limit at 12 h. In mixed culture withP. gingivalis ATCC 33277,E. faecium WB2000 grew more rapidly than it did in mixed cultures with the other three lactic acid bacteria, and its growth plateaued at 6 h (Figure 1(b)).Figure 1
Viable counts ofP. gingivalis ATCC 33277 in the presence or absence of each of the four lactic acid bacteria (a) and viable counts of lactic acid bacteria in mixed culture withP. gingivalis ATCC 33277 (b). ●: number ofP. gingivalis ATCC 33277 in monoculture, ○: number ofP. gingivalis ATCC 33277 orE. faecium WB2000 in mixed cultures, △: number ofP. gingivalis ATCC 33277 orL. salivarius CIP 103140 in mixed cultures, □: number ofP. gingivalis ATCC 33277 orL. reuteri JCM 1112 in mixed cultures, and ⋄: number ofP. gingivalis ATCC 33277 orS. salivarius JCM 5707 in mixed cultures.
(a)
(b)


### 3.2. Effect ofE. faecium WB2000 on the Growth of VariousP. gingivalis Strains

The effect ofE. faecium WB2000 on the growth of fiveP. gingivalis strains (ATCC 33277, ATCC 53978, ATCC BAA-308, 2-1, and 7-1) was evaluated. The numbers of allP. gingivalis strains decreased to less than the detection limit at 24 and 48 h in mixed cultures withE. faecium WB2000 (Figure 2). In contrast, the number ofE. faecium WB2000 reached a plateau at 24 h.Figure 2
Viable counts of five strains ofP. gingivalis (ATCC 33277, ATCC 53978, ATCC BAA-308, 2-1, and 7-1) andE. faecium WB2000 in mixed cultures. ●: number ofP. gingivalis in monoculture, ○: number ofP. gingivalis in mixed cultures withE. faecium WB2000, and △: number ofE. faecium WB2000 in mixed cultures withP. gingivalis.


### 3.3. Effect ofE. faecium WB2000 on VSC Production byP. gingivalis Strains

The concentrations of VSCs in spent culture medium were measured by gas chromatography (Table2). The levels of H2S produced byP. gingivalis strains were lower than those of CH3SH. The concentrations of H2S in mixed culture media were higher than that in medium in which onlyP. gingivalis was cultured, with the exception of medium from mixed cultures of twoP. gingivalis clinical isolates (2-1 and 7-1) andE. faecium WB2000 after 48 h. In contrast, the CH3SH concentration in mixed culture medium was lower than that in medium from culture ofP. gingivalis alone, with the exception of medium from mixed cultures of twoP. gingivalis strains (W50 and 2-1) andE. faecium WB2000 after 24 h. The levels of CH3SH in spent medium fromP. gingivalis cultured for 48 h in the presence or absence ofE. faecium WB2000 are shown in Figure 3. Although CH3SH production byP. gingivalis was strain dependent, the CH3SH concentration was markedly lower in spent medium from mixed cultures of allP. gingivalis strains andE. faecium WB2000 than in medium from culture of the latter microorganism only.Table 2
The hydrogen sulfide and methyl mercaptan concentrations in spent culture medium (ng/mL).
Pg strain
Culture medium
⁢Hydrogen sulfide
⁢Methyl mercaptan
24 h
48 h
24 h
48 h
ATCC 33277
Pg
0.45
0.86
11.45
87.34
Pg + Ef WB2000
0.94
1.49
2.38
1.53
ATCC 53978 (W50)
Pg
0.87
2.20
3.40
507.27
Pg + Ef WB2000
1.44
2.91
4.36
2.92
ATCC BAA-308 (W83)
Pg
0.68
2.46
62.53
558.22
Pg + Ef WB2000
1.75
2.83
6.61
4.32
2-1
Pg
0.43
2.18
1.70
164.44
Pg + Ef WB2000
1.11
2.03
3.26
2.81
7-1
Pg
0.86
9.24
58.18
799.95
Pg + Ef WB2000
2.06
2.44
6.03
4.05
Pg:Porphyromonas gingivalis; Ef: Enterococcus faecium.Figure 3
The levels of CH3SH in spent medium fromP. gingivalis cultured for 48 h in the presence or absence ofE. faecium WB2000 (ng/mL). Grey bars: single culture; white bars: dual culture withE. faecium WB2000.


## 3.1. Effect of Lactic Acid Bacteria on the Growth ofP. gingivalis ATCC 33277

The number of viableP. gingivalis ATCC 33277 decreased to less than the detection limit after 6 h in mixed culture withE. faecium WB2000 (Figure 1(a)). In mixed cultures with the other three lactic acid bacteria (S. salivarius JCM 5707,L. salivariusCIP 103140, andL. reuteri JCM 1112), the number of viableP. gingivalis ATCC 33277 decreased to less than the detection limit at 12 h. In mixed culture withP. gingivalis ATCC 33277,E. faecium WB2000 grew more rapidly than it did in mixed cultures with the other three lactic acid bacteria, and its growth plateaued at 6 h (Figure 1(b)).Figure 1
Viable counts ofP. gingivalis ATCC 33277 in the presence or absence of each of the four lactic acid bacteria (a) and viable counts of lactic acid bacteria in mixed culture withP. gingivalis ATCC 33277 (b). ●: number ofP. gingivalis ATCC 33277 in monoculture, ○: number ofP. gingivalis ATCC 33277 orE. faecium WB2000 in mixed cultures, △: number ofP. gingivalis ATCC 33277 orL. salivarius CIP 103140 in mixed cultures, □: number ofP. gingivalis ATCC 33277 orL. reuteri JCM 1112 in mixed cultures, and ⋄: number ofP. gingivalis ATCC 33277 orS. salivarius JCM 5707 in mixed cultures.
(a)
(b)


## 3.2. Effect ofE. faecium WB2000 on the Growth of VariousP. gingivalis Strains

The effect ofE. faecium WB2000 on the growth of fiveP. gingivalis strains (ATCC 33277, ATCC 53978, ATCC BAA-308, 2-1, and 7-1) was evaluated. The numbers of allP. gingivalis strains decreased to less than the detection limit at 24 and 48 h in mixed cultures withE. faecium WB2000 (Figure 2). In contrast, the number ofE. faecium WB2000 reached a plateau at 24 h.Figure 2
Viable counts of five strains ofP. gingivalis (ATCC 33277, ATCC 53978, ATCC BAA-308, 2-1, and 7-1) andE. faecium WB2000 in mixed cultures. ●: number ofP. gingivalis in monoculture, ○: number ofP. gingivalis in mixed cultures withE. faecium WB2000, and △: number ofE. faecium WB2000 in mixed cultures withP. gingivalis.


## 3.3. Effect ofE. faecium WB2000 on VSC Production byP. gingivalis Strains

The concentrations of VSCs in spent culture medium were measured by gas chromatography (Table2). The levels of H2S produced byP. gingivalis strains were lower than those of CH3SH. The concentrations of H2S in mixed culture media were higher than that in medium in which onlyP. gingivalis was cultured, with the exception of medium from mixed cultures of twoP. gingivalis clinical isolates (2-1 and 7-1) andE. faecium WB2000 after 48 h. In contrast, the CH3SH concentration in mixed culture medium was lower than that in medium from culture ofP. gingivalis alone, with the exception of medium from mixed cultures of twoP. gingivalis strains (W50 and 2-1) andE. faecium WB2000 after 24 h. The levels of CH3SH in spent medium fromP. gingivalis cultured for 48 h in the presence or absence ofE. faecium WB2000 are shown in Figure 3. Although CH3SH production byP. gingivalis was strain dependent, the CH3SH concentration was markedly lower in spent medium from mixed cultures of allP. gingivalis strains andE. faecium WB2000 than in medium from culture of the latter microorganism only.Table 2
The hydrogen sulfide and methyl mercaptan concentrations in spent culture medium (ng/mL).
Pg strain
Culture medium
⁢Hydrogen sulfide
⁢Methyl mercaptan
24 h
48 h
24 h
48 h
ATCC 33277
Pg
0.45
0.86
11.45
87.34
Pg + Ef WB2000
0.94
1.49
2.38
1.53
ATCC 53978 (W50)
Pg
0.87
2.20
3.40
507.27
Pg + Ef WB2000
1.44
2.91
4.36
2.92
ATCC BAA-308 (W83)
Pg
0.68
2.46
62.53
558.22
Pg + Ef WB2000
1.75
2.83
6.61
4.32
2-1
Pg
0.43
2.18
1.70
164.44
Pg + Ef WB2000
1.11
2.03
3.26
2.81
7-1
Pg
0.86
9.24
58.18
799.95
Pg + Ef WB2000
2.06
2.44
6.03
4.05
Pg:Porphyromonas gingivalis; Ef: Enterococcus faecium.Figure 3
The levels of CH3SH in spent medium fromP. gingivalis cultured for 48 h in the presence or absence ofE. faecium WB2000 (ng/mL). Grey bars: single culture; white bars: dual culture withE. faecium WB2000.


## 4. Discussion

The hypothetical mechanisms of probiotic action in the oral cavity are (1) involvement in binding of oral microorganisms to proteins, (2) effects on plaque formation and its complex ecosystem by competing and interfering with interbacterial attachment, (3) involvement in the metabolism of substrates, and (4) production of compounds that inhibit oral bacteria [11].E. faecium has been reported to inhibit biofilm formation by cariogenic bacteria [7, 8]. Kumada et al. [8] reported a protein that inhibited biofilm formation by streptococci. In addition, our previous study suggested thatE. faecium inhibits the growth of some mutans streptococci [7]. In this study,E. faecium WB2000 inhibited the growth of, as well as reduced CH3SH production by,P. gingivalis. A study onL. salivarius TI 2711 reported that a low pH (≤6.0) and the presence of lactic acid (40–50 mmol/L) inducedP. gingivalis death [12]. The pH ofE. faecium WB2000 culture medium was 4.4 after 24 h of incubation (data not shown). The growth rate ofE. faecium WB2000 was higher than that of the other lactic acid bacteria, suggesting that this organism rapidly inhibited the growth ofP. gingivalis.P. gingivalis strains produced CH3SH and a low level of H2S, as reported previously [13].E. faecium WB2000 suppressed CH3SH production byP. gingivalis but did not inhibit production of H2S in the current study. Some probiotic bacteria produce VSCs in the presence of cysteine or methionine [14]. The GAM broth used in the current study contains cysteine, and thusE. faecium WB2000 might have produced H2S.Streptococcus thermophilus inhibited the growth and H2S, CH3SH, and CH3SCH3 production ofP. gingivalis [13]. To determine whetherE. faecium WB2000 specifically inhibits production of CH3SH, different media and culture conditions should be used. Furthermore, future studies are needed to evaluate otherP. gingivalis strains producing high levels of H2S.In addition toE. faecium andS. thermophilus, other organisms have been reported to inhibit oral malodor.Streptococcus salivarius K12 suppressed the growth ofSolobacterium moorei, which produces H2S and is involved in halitosis [15, 16].Lactobacillus salivarius WB21 andL. reuteri have been reported to inhibit oral malodor in clinical trials [17–19].L. salivarius WB21 reduced the number ofFusobacterium nucleatum and ubiquitous bacteria in saliva [19].E. faecium WB2000 has been used in traditional Japanese medicine (Strong Wakamoto®) to treat gastrointestinal discomfort, and its effect on dry eye was reported recently [20]. Moreover, the effect of dentifrice containingE. faecium WB2000 on plaque control has been investigated [9]. The findings of this study suggest thatE. faecium WB2000 may reduce oral malodor by inhibiting the growth ofP. gingivalis and neutralizing CH3SH. The effect ofE. faecium WB2000 on oral malodor will be investigated in a future clinical trial involving the use of dentifrice.



---

*Source: 8241681-2016-10-09.xml*