Indian Journal of Dental Research

: 2022  |  Volume : 33  |  Issue : 1  |  Page : 90--93

Evaluation of antimicrobial activity of chlorhexidine-containing oral gels against aspiration pneumonia-inducing bacteria: An In Vitro study

Sun-Young Han1, Jiyeon Roh2, Yun-Sook Jung3, Ki-Rim Kim3,  
1 Department of Dental Hygiene, College of Software and Digital Healthcare Convergence, Yonsei University, Wonju, Korea
2 Forensic Science Training and R&D Center, National Forensic Service, Wonju, Korea
3 Department of Dental Hygiene, Kyungpook National University, Sangju, Korea

Correspondence Address:
Prof. Ki-Rim Kim
Department of Dental Hygiene, Kyungpook National University, 2559, Gyeongsang-daero, Sangju, 37224


Aim: Hospitalised patients have a high risk of developing aspiration pneumonia because of poor oral care and oral microbial flora changes. Chlorhexidine (CHX) solution has been used to reduce inflammation and prevent infections in oral cavity, but it is difficult to use in inpatients. Gel-type antimicrobial agents rather than the liquid form may be effective for the oral management of hospitalised patients. Therefore, we evaluated the in vitro antimicrobial effects of CHX-containing oral gels on aspiration pneumonia-inducing bacteria compared to the CHX solution. Materials and Methods: The experimental products of two oral gel types containing 1% and 0.1% CHX, respectively, were selected. Hexamedine, a 0.12% CHX solution, was used as a positive control. The antimicrobial activity of CHX agents against six pneumonia-causing bacteria and Streptococcus mutans, one of the most common oral bacteria, was comparatively analysed using the agar disk diffusion method. Results: In the disk diffusion assay, the 1% CHX gels showed the highest inhibitory effect on all bacteria. All CHX agents including gels and solution had the highest antibacterial activity against Staphylococcus aureus compared with other bacteria. Conclusions: We confirmed the significant antimicrobial effects of the 1% CHX oral gels on aspiration pneumonia-inducing bacteria. These results suggest that CHX gels may be an effective oral care method for preventing infection in inpatients who have difficulty using the solution.

How to cite this article:
Han SY, Roh J, Jung YS, Kim KR. Evaluation of antimicrobial activity of chlorhexidine-containing oral gels against aspiration pneumonia-inducing bacteria: An In Vitro study.Indian J Dent Res 2022;33:90-93

How to cite this URL:
Han SY, Roh J, Jung YS, Kim KR. Evaluation of antimicrobial activity of chlorhexidine-containing oral gels against aspiration pneumonia-inducing bacteria: An In Vitro study. Indian J Dent Res [serial online] 2022 [cited 2022 Nov 26 ];33:90-93
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The oral cavity provides a suitable environment for various microorganisms to thrive, as it is moist and rich in nutrients. Many oral microorganisms cause various oral diseases such as dental caries and periodontitis and increase the risk of systemic diseases.[1] Several systemic diseases cause changes in oral microbial flora and reproduction of certain bacteria.[2],[3] Therefore, it is important to control these oral bacteria for oral health. Oral hygiene methods include general plaque control such as tooth brushing, flossing, and mouth rinsing, and professional oral healthcare such as tooth scaling and polishing, root planning, and fluoride varnish application. However, oral hygiene management is difficult for inpatients. In particular, unconscious intubation patients have a high risk of developing aspiration pneumonia due to oral bacteria changes and proliferation because oral care is rarely performed.[3] Tooth brushing with toothpaste requires rinsing the mouth, but there is a risk of aspiration to unconscious patients; hence, other oral care methods should be sought. Therefore, for critically ill patients, oral management using the mouthwash solution is performed rather than toothpaste.

Chlorhexidine (CHX), a broad-spectrum antibiotic, has been widely used in dentistry since 1970.[4] Because CHX reduces plaque and gingival inflammation, it is used to prevent infection before and after surgical procedures such as tooth extraction, periodontal or implant surgery.[5] Studies have reported that CHX decreases the growth of various oral bacterial species associated with dental caries, periodontitis or halitosis.[6],[7] It is recommended to use the CHX solution for inpatients who have difficulty in oral care, but it is difficult to apply a liquid-type gargle solution for lying patients. Research results have been reported confirming the effect of gel-type CHX application as an endodontic irrigant and for the prevention of alveolar osteitis after tooth extraction.[8],[9] It has also shown a positive effect on systemic disease prevention.[10] However, it has not been evaluated whether the aspiration pneumonia-inducing bacteria that can inhabit the oral cavity can be effectively managed using CHX.

For oral care of hospitalised patients who have difficulty lifting their upper body, gel-type antibacterial agents may be more effective than liquid ones. Therefore, we evaluated the antibacterial effect of an oral gel containing CHX against aspiration pneumonia-causing bacteria including Staphylococcus aureus, Streptococcus mutans, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae by comparing it with the CHX solution in vitro. Our results suggest a more effective oral care method for inpatients at high risk of aspiration pneumonia and may be used as basic data for practical use in hospitals.

 Materials and Methods


The oral gel products containing 1% CHX (CHoralGEL1%, HANALL Biopharma Co., Ltd, Seoul, Korea) and 0.1% CHX (ConCool Mouth Gel, Weltec, Osaka, Japan) were used. A solution of hexamedine (HXM) (0.12% Chlorhexidine Gluconate Solution, Bukwang Co., Seoul, Korea) was used as a positive control.


The species of microorganisms used in this study were Staphylococcus aureus (KCTC 3881), Streptococcus mutans (KCTC 5365), Escherichia coli (KCTC 2571), Pseudomonas aeruginosa (KCTC 2153), Acinetobacter baumannii (KCTC 2508) and Klebsiella pneumoniae (KCTC 2208). All bacteria were provided from the Korean Collection for Type Cultures, (KCTC). S. aureus, E. coli, P. aeruginosa, A. baumannii and K pneumoniae were cultured in trypticase soy broth. S. mutans was cultured in brain heart infusion broth. Aliquots of S. aureus, E. coli, P. aeruginosa and A. baumannii were plated on tryticase soy agar, while aliquots of S. mutans and K. pneumonia were plated on brain heart infusion and MacConkey agar, respectively. All broth and agar were purchased from BD Difco (Trenton, NJ, USA).

Disk diffusion test

Antimicrobial activity of the samples, including gels and solution of CHX, was investigated against the six bacterial strains. Approximately 15 mL agar suitable for each bacterial species was poured onto sterile Petri dishes and allowed to solidify at room temperature. Each bacterial strain was grown in a suitable broth at 37°C, and the suspension (105–7 CFU/mL) was prepared. A 0.1 mL aliquot of each microbial suspension was spread on the agar plates separately. Filter paper disks (6 mm in diameter) were immersed in 0.1 mL of various samples and put on the agar plates' surface. The plates were incubated for 24 h at 37°C. The diameter of the inhibition zones of each group was measured using a vernier caliper.

Statistical analysis

All experiments were repeated at least three times independently. Data are expressed as the mean ± standard deviation. One-way analysis of variance was performed to detect the significant effects of variables, followed by Tukey's hoc test (SPSS Statistics v. 23.0; IBM Inc., Chicago, IL, USA). The differences were considered significant at P < 0.05.


The in vitro antimicrobial activity of CHX gels and solution was performed against aspiration pneumonia-inducing bacteria, including S. aureus, S. mutans, E. coli, P. aeruginosa, A. baumannii and K. pneumoniae [Table 1]. P. aeruginosa and A. baumannii are opportunistic and aerobic pathogens. In contrast, all other bacteria used are facultative anaerobic. P. aeruginosa, A. baumannii and K. pneumoniae are important pathogens associated with hospital-acquired infections and risk factors for pneumonia.[11] The size of the inhibition zone is shown in [Table 2], which indicates that CHX gels and the HXM solution had statistically significant antimicrobial activities in the pathogenic microorganisms tested [Figure 1]. Among the experimental groups, the 1% CHX gels showed the greatest inhibitory effect on all bacteria. For K. pneumoniae, only the 1% CHX group showed a slight inhibitory effect and the other groups had no inhibitory effect. Among the tested bacterial pathogens, CHX treatment in both gels and solution forms also had significantly higher antibacterial activity against S. aureus.{Table 1}{Table 2}{Figure 1}


Bacteria may grow and colonise at various oral cavity sites such as the subgingival biofilm, dental plaque and tongue. In particular, saliva contains many microorganisms. Normal healthy people can eliminate these bacteria from their lungs by aspiration, but people with weakened immunity can develop aspiration pneumonia.[12] Previous studies have reported on the relationship between aspiration pneumonia and various bacterial species in the oral cavity.[13],[14] Therefore, reducing the number of bacteria in the oral cavity through oral care can prevent aspiration pneumonia.[15]

CHX is an effective gargle solution widely used for oral care before and after dental treatment and used in hospitalised patients to prevent nosocomial infections.[4],[16] It has been proven in many studies that a daily CHX bath and twice daily 0.12% CHX oral rinse prevent ventilator-associated pneumonia in intensive care unit (ICU) patients.[17],[18] Currently, these protocols are applied as standard guidelines in many ICUs.[16] However, in lying patients, liquid CHX is not easy to apply. Although gel-form CHX has been developed as a product, it is not commonly used in hospitals or clinics. Gel-type antimicrobial agents rather than liquid solutions may be effective for oral management of inpatients, especially for lying patients. Therefore, we compared the antimicrobial effect of HXM, the most commonly used CHX gargle solution, and a gel-type CHX product. As for the gel form, two products containing 0.1% and 1% CHX as the main component were selected.

Here, among the six aspiration pneumonia-inducing bacteria, all CHX groups showed the highest antibacterial activity on S. aureus. In a study of aspiration pneumonia, S. aureus was one of the main bacteria isolated from patients in the ICU.[19] Instead of mouthwash, the use of CHX oral gels alone could significantly reduce the risk of pneumonia in patients. The gels containing 1% CHX showed the highest inhibitory effect against all bacteria. However, all groups of CHX hardly inhibited K. pneumoniae, one of the highly drug-resistant strains. Studies have reported that K. pneumoniae may cause persistent nosocomial infections due to decreased susceptibility to CHX.[20] Therefore, other antibiotics should be applied to CHX-resistant bacteria. The combination of antibiotics should be considered for interaction.

Based on these outcomes, CHX gels can be helpful in preventing infection in hospitalised patients, who have difficulty in oral care with a solution because it is difficult to raise the upper body. However, further studies are needed on the properties of the gel and the specific method of use before clinical use of antibacterial gels in hospitals.


1% CHX-containing oral gels showed inhibitory activity against aspiration pneumonia-inducing bacteria, and this antibacterial effect was higher than that of the CHX solution commonly used in dentistry and hospitals. In oral hygiene care of inpatients at risk of aspiration pneumonia, the use of the CHX gels rather than solutions can reduce patient's discomfort and risk of aspiration pneumonia. Taken together, we suggest that CHX oral gels could help prevent infection in patients who are unconscious or unable to gargle.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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