Alterations in the Oral Microbiome in HIV Infection: Causes, Effects and Potential Interventions
Introduction
Human immunodeficiency virus (HIV) infection is a global health concern, with approximately 38 million people living with HIV worldwide as of 2019. While antiretroviral therapy (ART) has improved the prognosis for many, oral diseases like oropharyngeal candidiasis (OPC) and periodontitis remain common. Additionally, the risk of HIV – associated non – AIDS comorbidities such as cardiovascular disease is increasing. Just as gut microbiome alterations in HIV infection have been studied, the oral microbiome also plays a crucial role.
The Human Oral Microbiome
The oral microbiome is a diverse community of bacteria, fungi, viruses, mycoplasma, and protozoa. Bacteria are the most abundant, with around 700 species identified. The Human Oral Microbiome Database lists 775 microbial species, of which 57% are cultivated and named, 13% can be cultivated but not named, and 30% are uncultivated. The oral bacterial microbiome mainly consists of six phyla: Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Spirochaetes, and Fusobacteria. In healthy individuals, the most abundant bacterial genus is Streptococcus, followed by Haemophilus, Neisseria, Prevotella, Veillonella, and Rothia. Fungi also colonize the oral cavity, with Candida being a common genus in both healthy and immunocompromised individuals.
Alterations in the Oral Microbiome in HIV Infection
HIV infection disrupts the homeostasis of the oral microbiome. Changes in salivary composition and function are key. Saliva contains secretory components like immunoglobulin A (IgA), lysozyme, and host defense peptides that are essential for oral mucosal immunity. In HIV – infected individuals, decreased levels of these components (such as IgA, defensins, and cytokines) can convert commensal microorganisms to more pathogenic ones, leading to dysbiosis. For example, HIV – infected individuals have a higher frequency and load of opportunistic microorganisms in their saliva compared to controls. Innate immune components in the oral cavity, such as macrophages, natural killer cells, and dendritic cells, recognize pathogens through pattern recognition receptors (PRRs). However, in HIV infection, innate immune responses are impaired, which can lead to dysbiosis. Adaptive immune responses are also affected. Th17 cells, for instance, are crucial for controlling fungal infections in the oral mucosa. Their deficiency in HIV infection can contribute to oral microbiota dysbiosis. Different studies have shown varying results regarding the diversity of the oral microbiome in HIV – infected individuals. Some studies report increased diversity due to the presence of opportunistic pathogens, while others show decreased diversity. Alterations in the oral fungal community composition have also been observed, with Candida being more prevalent in some HIV – infected individuals.
Effects of the Oral Microbiome on HIV – Associated Oral Diseases
The oral microbiome is involved in the development of various oral diseases in HIV – infected individuals. OPC, caused by Candida species, is a common oral manifestation. Its incidence is influenced by factors like immune status and bacteriome – mycobiome interaction. Periodontal diseases are also more prevalent in PLWH, and specific bacterial genera (such as Abiotrophia, Rothia, and Treponema spp.) are associated with different severities of periodontal disease. In addition, oral microbiota composition in HIV – infected individuals with oral Kaposi’s sarcoma (KS) is different from those without, indicating a role of the oral microbiome in the development of this disease.
Effects of Potential Interventions on the Oral Microbiome
ART has been shown to reduce the occurrence of opportunistic oral infections, but it cannot fully restore the oral microbiome to normal. Some studies have found that after ART, certain bacterial genera (such as Fusobacterium, Campylobacter, Prevotella, etc.) increase, while Aggregatibacter decreases. However, the oral microbiome in ART – treated HIV – infected individuals still differs from that of healthy controls. Probiotics are emerging as a potential therapeutic approach. They can regulate the immune system and control pathogen colonization. In vitro and in vivo studies have shown that probiotics like Lactobacillus can have antifungal effects against Candida species. Prebiotics, which stimulate beneficial bacteria, also have a role in promoting oral health. For example, prebiotic intervention in HIV – infected individuals has been shown to decrease the abundance of some potential pathogens in the saliva microbiome.
Conclusion
The oral microbiome is significantly affected in HIV infection. Understanding its composition and function is crucial for developing preventive and therapeutic strategies. Further research is needed to clarify the long – term effects of ART and the optimal use of probiotics and prebiotics in managing the oral microbiome in HIV – infected individuals. This knowledge can improve the oral health of PLWH and potentially reduce the risk of associated comorbidities.
doi: 10.1097/CM9.0000000000001825
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