Volatile sulfide compounds and oral microorganisms on the inner surface of masks in individuals with halitosis during COVID-19 pandemic

Abstract

Mask-wearing is still recommended owing to the continuing impact of the COVID-19 pandemic. Within the closed chamber created by the mask, people are increasingly self-aware of their oral malodor. In this prospective and cross-sectional study, we aimed to measure volatile sulfide compound (VSC) levels in patients with halitosis and investigate the oral microbiome profile on the inner surface of their KF94 masks. We also investigated which oral microbiota increases VSC levels and whether the oral microbiomes of oral saliva and mask are correlated. A total of 50 subjects (41 women, average age 38.12 ± 12.58 years old) were included in the study, 25 healthy subjects and 25 patients with halitosis who wore masks for more than 3 h. The dominant bacterial species, bacterial profile, and Shannon diversity index of whole unstimulated saliva and the inner surface of the mask were investigated. The bacterial 16S ribosomal RNA genes of the major oral bacterial species were analyzed using real-time PCR. Gas chromatography was used to measure hydrogen sulfide (H2S) and methyl mercaptan (CH3SH), which are representative VSCs. The total bacterial DNA copy number was significantly higher in the saliva sample than in the mask sample (p < 0.001), and the average value was 276 times greater. Shannon diversity index was also significantly higher in saliva than in the inner surface of the mask (2.62 ± 0.81 vs. 1.15 ± 1.52, p < 0.001). The most common Gram-negative and Gram-positive species in the masks were Porphyromonas gingivalis (Pg) and Lactobacillus casei (Lc), respectively. The bacterial species with significant positive correlations between saliva and mask samples were Prevotella intermedia (Pi) (r = 0.324, p = 0.022), Eikenella corrodens (r = 0.309, p = 0.029), Lc (r = 0.293, p = 0.039), and Parvimonas micra (Pm) (r = 0.366, p = 0.009). The mean value of CH3SH was significantly higher in the halitosis group than in the non-halitosis group (17.84 ± 29.00 vs. 3.84 ± 10.57 ppb, p = 0.031). In the halitosis group, the DNA copy numbers and VSC levels showed highly positive correlation coefficients in the order Pg, Treponema denticola (Td), Tannerella forsythia (Tf), Pi, and Prevotella nigrescens (Pn) (all p < 0.05). Regarding bacterial profiles of the mask, Td was strongly correlated with CH3SH (r = 0.414, p = 0.040) and total VSCs (r = 0.374, p = 0.033) only in halitosis group. Mask-wearing time was strongly correlated with total VSCs, H2S, and CH3SH (all r > 0.8, p < 0.001). Oral bacteria, whose association with halitosis has been identified, increased VSC levels in mask-wearing subjects during the COVID-19 pandemic, particularly the number of Gram-negative anaerobes such as Pg and Td. Mask-wearing time was a major factor in increasing VSC levels. The study results suggest that people with halitosis could control these Gram-negative bacteria by improving oral hygiene and regularly changing masks.

The Bacterial Burden of Worn Face Masks – Observational Research and Literature Review

“…Put simply: (i) the mask act as a filter trap with bacteria accumulating on its external and internal surfaces; (ii) the mask then acts as a "microbiological incubator" at the entrance of the airways; (iii) microorganisms may grow within the mask, nourished by skin debris, mucus and "exhaled breath condensate" [17,39,40,42,46,[105][106][107]. These trapped organisms/pathogens then may be inhaled, promoting infection of the respiratory tract [18,38] or, when distributed via air streams [108][109][110]117,135,136,168,169] the eye [79][80][81][82]116,135].…”

“…Masks are a good matrix for microbial accumulation and potentially, growth, retaining an aboveambient temperature [100][101][102][103][104], moisture, and nutrient-rich debris [39][40][41][42]46,105]. Besides substances sucked in from the outside, nutrients comprise exhaled proteins and other debris, exfoliated and dead epithelial cells.…”

“…This organic richness was visualised in our Bengal Rose staining. Growth, rather than mere survival [39,40,42,46,105,107] of bacterial and fungal colonies is revealed by scanning electron microscopy of face masks (FFP2) worn for several hours [41].…”

A structural color hydrogel for diagnosis of halitosis and screening of periodontitis

“…14,16,17 Especially, H 2 S can contribute to as high as 95% of halitosis. 8,18 As a symptom of periodontitis, the severity of halitosis is closely related to the population of these oral pathogens. A larger population of the pathogens leads to severe halitosis and a higher risk of periodontitis.…”

Preliminary investigation of a combined herbal extract of Aruncus dioicus, Cirsium nipponicum, and Ocimum basilicum for halitosis

“…Among individuals with halitosis, elevated VSC levels are associated with an increase in oral microorganisms, particularly Gram-negative anaerobes like Porphyromonas gingivalis and Treponema denticola , observed on the inner surface of their masks. [ 9 ] This closed environment around the oral cavity not only fosters the growth of oral microorganisms but also raises awareness of halitosis. [ 10 ] The 2 primary factors implicated in bad breath are tongue coating and periodontal health, both associated with specific oral bacterial species.…”