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Microorganisms
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Oral Microbiota: Diseases, Health, and Beyond
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Oral Microbiota: Diseases, Health, and Beyond

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Medical Microbiology".

Deadline for manuscript submissions: closed (30 April 2026) | Viewed by 10629

Special Issue Editors

Dr. Federica Di Spirito

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Guest Editor
Department of Medicine, Surgery and Dentistry, Scuola Medica Salernitana, University of Salerno, 84126 Salerno, Italy
Interests: oral medicine and interconnected systemic disorders; oral microbiome, dysbiosis and interconnected systemic disorders; periodontology and implantology; applied technologies (disease prevention, teledentistry)
Special Issues, Collections and Topics in MDPI journals
Dr. Maria Pia Di Palo

E-Mail Website
Guest Editor
Department of Medicine, Surgery and Dentistry, University of Salerno, 84084 Baronissi, Italy
Interests: implant dentistry; periodontology; oral surgery; oral medicine
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Oral microbiota’ refers to the microorganisms that reside in the oral cavity, including bacteria, viruses, fungi, and protozoa. These microorganisms play a crucial role in maintaining oral health and preventing diseases. Indeed, both dental and periodontal biofilm are associated with specific oral diseases; for example, Streptococcus mutans is a key contributor to dental caries (tooth decay), while Porphyromonas gingivalis is linked to periodontitis (gum disease). Moreover, certain oral microorganisms are the causative pathogens of primary or secondary oral mucosal lesions.

The composition of the oral microbiota can be influenced by various factors, such as diet, hygiene practices, medication use, and systemic health conditions. Accordingly, some oral microorganisms have been implied in focal infections, as well as in systemic inflammatory disorders and benign and malignant neoplasms.

In adults and children, an early healthy balance of oral microbiota may aid in preventing and managing both dental and general health dysbiosis and related diseases and disorders. Accordingly, there has been growing interest in using probiotics (beneficial bacteria) to support oral health in recent years.

For this Special Issue, we invite you to send contributions related to aspects of oral microorganisms, both in health and disease, in adults and children.

Dr. Federica Di Spirito
Dr. Maria Pia Di Palo
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Microorganisms is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • oral microbiota
  • oral bacteria
  • oral viruses
  • oral fungi
  • oral protozoa
  • oral health
  • oral disease

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Published Papers (5 papers)

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Research

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18 pages, 1207 KB  
Article
Marine-Derived Bacillus Biosurfactants as Potential Antibacterial and Antibiofilm Agents Against Oral Pathogens
by Thangaraj Vaishnavi and Elangovan Elavarashi
Microorganisms 2026, 14(3), 573; https://doi.org/10.3390/microorganisms14030573 - 3 Mar 2026
Viewed by 652
Abstract
The growing antimicrobial resistance (AMR) is threatening traditional treatments for oral diseases like dental caries and periodontitis, which constitute a significant global health burden. The study aimed to isolate Bacillus species from marine samples, to assess their biosurfactant-producing capabilities, and to evaluate their [...] Read more.
The growing antimicrobial resistance (AMR) is threatening traditional treatments for oral diseases like dental caries and periodontitis, which constitute a significant global health burden. The study aimed to isolate Bacillus species from marine samples, to assess their biosurfactant-producing capabilities, and to evaluate their antibacterial activity against oral pathogens. Bacillus strains were isolated from marine water and sediment samples, identified by phenotypic and genotypic methods, and screened for their biosurfactant-producing ability by drop collapse, hemolytic activity, bacterial adhesion to hydrocarbons (BATH), oil displacement, and emulsification assays. Ethyl acetate extracts of these Bacillus strains were tested for antibacterial efficacy against four oral pathogens (MTCC strains) by the agar-well diffusion method. Among 81 bacterial isolates, 13 were confirmed as Bacillus species by phenotypic and 16S rRNA gene sequencing. Six Bacillus isolates displayed significant antibacterial activity, and the majority were beta-hemolytic. Bacillus strain TVD12 (50 mg/mL) exhibited superior performance by inhibiting S. mutans (31 mm ± 0), S. anginosus (30.5 mm ± 0.7), S. aureus (20 mm ± 1.4), and E. faecalis (29 mm ± 4.24). Bacillus strain TVW12 (500 μg/mL) performs better in antibiofilm activity by inhibiting E. faecalis 90%, S. aureus 87.4%, and S. mutans 76.8%. Statistical analysis revealed a distinct dual-activity profile, characterized by consistent broad-spectrum antimicrobial efficacy (p = 0.809) alongside specialized, pathogen-specific antibiofilm inhibition (p = 0.004). Marine-derived Bacillus strains, such as TVW12, and TVD12 demonstrated effective antibacterial and antibiofilm properties, offering a feasible approach to combat oral pathogens, contributing to sustainable development goals (SDGs) by addressing the challenges of antimicrobial resistance (SDG 3) through sustainable marine bioprospecting (SDG 14). These findings suggest their possibility in developing novel antibacterial agents against oral pathogens in future therapeutic applications. Full article
(This article belongs to the Special Issue Oral Microbiota: Diseases, Health, and Beyond)
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17 pages, 4044 KB  
Article
Impact of Chemotherapy Alone and in Combination with Immunotherapy on Oral Microbiota in Cancer Patients—A Pilot Study
by Adriana Padure, Ioana Cristina Talpos-Niculescu, Paula Diana Ciordas, Mirabela Romanescu, Aimee Rodica Chis, Laura-Cristina Rusu and Ioan Ovidiu Sirbu
Microorganisms 2025, 13(7), 1565; https://doi.org/10.3390/microorganisms13071565 - 3 Jul 2025
Cited by 1 | Viewed by 1494
Abstract
The oral cavity harbors a highly intricate and dynamic microbial ecosystem of multiple microhabitats supporting diverse microbial populations. As the second most complex microbiome in the human body, surpassed only by the gut, the oral microbiome comprises over 1000 species. Disruptions in the [...] Read more.
The oral cavity harbors a highly intricate and dynamic microbial ecosystem of multiple microhabitats supporting diverse microbial populations. As the second most complex microbiome in the human body, surpassed only by the gut, the oral microbiome comprises over 1000 species. Disruptions in the microbial balance have been associated with an increased risk of both oral diseases (dental caries and periodontitis) and systemic conditions, including inflammatory diseases and certain types of cancers. In our pilot study, we purified bacterial DNA from pre-treated, saponin-based, host-depleted saliva samples and performed 16S amplicon sequencing, using Oxford Nanopore Technologies, to identify bacterial composition and investigate changes in the oral microbiota of patients with solid tumors in response to chemotherapy, either alone or in combination with immunotherapy. We found significant reductions in microbial diversity of the oral microbiota following cancer treatment, which may contribute to post-therapeutic complications such as oral mucositis. Moreover, our findings indicate that on the one hand, following chemotherapy treatment the microbial profile is characterized by an increased abundance of Streptococcus, Gemella, and Granulicatella and a decrease in the abundance of Neisseria and Veillonella. On the other hand, post combined treatment, only Streptococcus relative abundance increased, Veillonella exhibited a slight decline, and Haemophilus and Neisseria displayed a marked decrease, whilst Granulicatella and Gemella remained relatively stable. Our findings underline the impact of cancer therapy on the oral microbiome, highlighting the potential for precision-based strategies to restore microbial balance and minimize treatment-related complications. Full article
(This article belongs to the Special Issue Oral Microbiota: Diseases, Health, and Beyond)
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18 pages, 3452 KB  
Article
Effects of Long-Term Heavy Metal Exposure on the Species Diversity, Functional Diversity, and Network Structure of Oral Mycobiome
by Jia Li, Shuwei Pei, Lu Feng, Jiangyun Liu, Qiwen Zheng, Xingrong Liu, Ye Ruan, Weigang Hu, Li Zhang, Jingping Niu and Tian Tian
Microorganisms 2025, 13(3), 622; https://doi.org/10.3390/microorganisms13030622 - 7 Mar 2025
Cited by 3 | Viewed by 1659
Abstract
Oral fungal homeostasis is closely related to the state of human health, and its composition is influenced by various factors. At present, the effects of long-term soil heavy metal exposure on the oral fungi of local populations have not been adequately studied. In [...] Read more.
Oral fungal homeostasis is closely related to the state of human health, and its composition is influenced by various factors. At present, the effects of long-term soil heavy metal exposure on the oral fungi of local populations have not been adequately studied. In this study, we used inductively coupled plasma–mass spectrometry (ICP-MS) to detect heavy metals in agricultural soils from two areas in Gansu Province, northwestern China. ITS amplicon sequencing was used to analyze the community composition of oral buccal mucosa fungi from local village residents. Simultaneously, the functional annotation of fungi was performed using FUNGuild, and co-occurrence networks were constructed to analyze the interactions of different functional fungi. The results showed that the species diversity of the oral fungi of local populations in the soil heavy metal exposure group was lower than that of the control population. The relative abundance of Apiotrichum and Cutaneotrichosporon was higher in the exposure group than in the control group. In addition, Cutaneotrichosporon is an Animal Pathogen, which may lead to an increased probability of disease in the exposure group. Meanwhile, there were significant differences in the co-occurrence network structure between the two groups. The control group had a larger and more stable network than the exposure group. Eight keystone taxa were observed in the network of the control group, while none were observed in that of the exposure group. In conclusion, heavy metal exposure may increase the risk of diseases associated with Apiotrichum and Cutaneotrichosporon infection in the local populations. It can also lead to the loss of keystone taxa and the reduced stability of the oral fungal network. The above results illustrated that heavy metal exposure impairs oral fungal interactions in the population. This study extends our understanding of the biodiversity of oral fungi in the population and provides new insights for further studies on the factors influencing oral fungal homeostasis. Full article
(This article belongs to the Special Issue Oral Microbiota: Diseases, Health, and Beyond)
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Review

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17 pages, 1115 KB  
Review
Oral Microbiota and Type 2 Diabetes: Interactions, Potential Mechanisms, and Preventive Strategies
by Zifu Ni, Zihan Ni, Yining Wang, Qi Wu, Zhenxi Yang and Yuqi Guo
Microorganisms 2026, 14(2), 336; https://doi.org/10.3390/microorganisms14020336 - 2 Feb 2026
Viewed by 950
Abstract
The oral cavity harbors the second-largest and one of the most diverse microbial communities in the human body, playing a critical role in maintaining local and systemic health. Type 2 diabetes mellitus (T2DM), a chronic metabolic disease accounting for nearly 90% of all [...] Read more.
The oral cavity harbors the second-largest and one of the most diverse microbial communities in the human body, playing a critical role in maintaining local and systemic health. Type 2 diabetes mellitus (T2DM), a chronic metabolic disease accounting for nearly 90% of all diabetes cases, has shown rapidly increasing global prevalence. Growing clinical and experimental evidence indicates a strong bidirectional relationship between oral microbiota dysbiosis and T2DM. Imbalanced oral microbial communities can contribute to systemic inflammation, insulin resistance, and metabolic dysregulation, while hyperglycemia and impaired immunity in T2DM promote oral diseases such as periodontitis, xerostomia, and mucosal infections. This review summarizes current research on the interactions between oral microbiota and T2DM, highlighting their clinical correlations, underlying mechanisms, and mutual influences on inflammation, microbial composition, and metabolic pathways. We also discuss emerging strategies for T2DM prevention and management through oral microbiota modulation. These insights may provide new perspectives for early diagnosis, targeted intervention, and integrative management of T2DM. Full article
(This article belongs to the Special Issue Oral Microbiota: Diseases, Health, and Beyond)
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16 pages, 2136 KB  
Review
Crossing the Barrier: Eikenella corrodens Bacteremia Following CNS Infection in a Patient Treated with Nivolumab—A Case Report and Literature Review
by Terenzio Cosio, Cataldo Maria Mannavola, Barbara Fiori, Matteo Zelinotti, Francesco Taccari, Brunella Posteraro, Tiziana D'Inzeo and Maurizio Sanguinetti
Microorganisms 2025, 13(9), 2135; https://doi.org/10.3390/microorganisms13092135 - 12 Sep 2025
Viewed by 2534
Abstract
Eikenella corrodens is a facultative anaerobic Gram-negative bacillus, part of the normal oropharyngeal flora, with opportunistic pathogenic potential particularly in immunocompromised hosts. The progression from localized intracranial infections such as cerebritis and subdural empyema to secondary bloodstream infection represents a rare but clinically [...] Read more.
Eikenella corrodens is a facultative anaerobic Gram-negative bacillus, part of the normal oropharyngeal flora, with opportunistic pathogenic potential particularly in immunocompromised hosts. The progression from localized intracranial infections such as cerebritis and subdural empyema to secondary bloodstream infection represents a rare but clinically significant pathway, especially in immuno-compromised patients. Here, we report a case of secondary E. corrodens bacteremia following left temporal cerebritis and ipsilateral subdural empyema in a 50-year-old man with advanced nasopharyngeal carcinoma treated with nivolumab. The patient presented neurological deficits and systemic inflammatory response, suggesting for a bacterial infection. Neuroimaging confirmed the intracranial infectious foci and blood cultures identified E. corrodens via MALDI-TOF MS and 16S rRNA gene sequencing. We discuss how cancer-associated immune dysregulation and immune checkpoint inhibition could modulate host susceptibility and clinical presentation of infection, potentially facilitating microbial dissemination across compromised blood–brain barriers. Additionally, we examine the cases of E. corrodens bacteremia secondary to CNS and head and neck infections. This case underscores the importance of heightened clinical vigilance for secondary bacteremia in oncologic patients with CNS infections and highlights the need for integrated microbiological and radiological assessment to optimize outcomes. Full article
(This article belongs to the Special Issue Oral Microbiota: Diseases, Health, and Beyond)
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