The effect of streptococcus mutans on the growth and virulence expression of candida albicans in a mixed-species biofilm

Wang, XueLing (2024) The effect of streptococcus mutans on the growth and virulence expression of candida albicans in a mixed-species biofilm. Master dissertation/thesis, UTAR.

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Abstract

Candida albicans is a type of fungus commonly found in the oral cavity and various other parts of the human body. While it generally coexists peacefully with the host, under certain circumstances, such as immunosuppression or treatments like chemotherapy and radiotherapy, it can cause invasive lesions and infections. In individuals with weakened immune systems, C. albicans has the potential to become pathogenic and penetrate the body's defenses. This can occur due to conditions like HIV/AIDS, organ transplantation, or prolonged use of immunosuppressive medications. Similarly, cancer patients undergoing chemotherapy or radiation therapy often experience a compromised immune system, making them susceptible to Candida-related complications. In the oral cavity, C. albicans naturally reside in harmony with other microorganisms, forming part of the normal oral flora. However, when the balance is disrupted, such as through a decrease in saliva production, poor oral hygiene, or the use of certain medications (such as broad-spectrum antibiotics), C. albicans can overgrow and lead to oral candidiasis, also known as thrush. This condition manifests as white patches or sores on the tongue, inner cheeks, or the back of the throat, causing discomfort, pain, and difficulty in swallowing. Invasive Candida infections can extend beyond the oral cavity and affect other areas of the body as well. For individuals with weakened immune systems, Candida can invade the bloodstream, leading to a serious condition known as candidemia. This can result in widespread systemic infections, affecting vital organs such as the heart, kidneys, liver, and brain. If left untreated, candidemia can be life�threatening. Streptococcus mutans is a significant pathogenic bacterium known for its ability to cause dental caries, commonly referred to as tooth decay. In the oral cavity, it forms biofilms, which are complex microbial communities that adhere to various surfaces. Interestingly, C. albicans is another prominent member of the oral microbiota that coexists with S. mutans within these biofilms. The coexistence of C. albicans and S. mutans in oral biofilms is of great importance. These biofilms provide a favorable environment for the growth and survival of both microorganisms, enabling them to thrive and contribute to the development of oral diseases. S. mutans is particularly adept at utilizing dietary sugars and producing acids as metabolic byproducts. These acids can demineralize the tooth enamel, leading to the formation of cavities. Moreover, S. mutans possess unique adhesive properties, allowing them to adhere to the tooth surfaces and facilitate the establishment of biofilms. The presence of this bacterium in the biofilm community greatly enhances its cariogenic potential. C. albicans, on the other hand, can form hyphae, which are long, filamentous structures that aid in its attachment to oral surfaces. Within biofilms, C. albicans can interact with S. mutans and other microorganisms through complex interactions. These interactions can influence the overall structure and composition of the biofilm community, potentially impacting its pathogenicity. The primary objective of this research endeavor was to investigate the potential influence of S. mutans on the virulence and growth patterns of C. albicans within mixed-species biofilms, where both organisms coexist. By conducting this study, valuable insights could be gained regarding the potential correlation between caries caused by S. mutans and an increased susceptibility to C. albicans infections. Understanding such a relationship could have significant implications for patient care and treatment strategies in dental medicine. Six-well tissue culture plates were utilized to culture both single-species biofilms of Candida albicans and mixed-species biofilms consisting of C. albicans and Streptococcus mutans for a period of 24 hours. The viability of these biofilms was measured by determining the colony-forming units (CFU) per milliliter in single biofilms of C. albicans and mixed-species biofilms of C. albicans and S. mutans with different ratios (C. albicans: S. mutans = 1:10 and 1:3), while the expression of virulence genes was quantified using RT-qPCR assays. The target genes include four virulence genes: HWP1, EFG1, ALS3, and ACT1, as well as two quorum sensing genes, CHK1 and PBS2. To investigate the impact of different ratios of C. albicans and S. mutans on biofilm formation, the CFU counts were compared among the mixed and single-species biofilms grown with varying concentrations of S. mutans. The findings of the study indicated that the presence of S. mutans did not have a detrimental impact on the expression of specific virulence and quorum sensing genes in C. albicans. However, intriguingly, it was observed that the replication of C. albicans within a biofilm was significantly enhanced in the presence of S. mutans, specifically at a 1:3 ratio of C albicans to S mutan (p-value <0.05). However, at a 1:10 ratio of C albicans to S mutans, there was no statistically significant difference in the colony-forming units (CFU) between single C. albicans biofilms and mixed-species biofilms. These results suggest a potential interaction between the two species that promotes the growth of C. albicans within a biofilm environment. To gain a more comprehensive understanding of this phenomenon, further investigations are warranted. It is important to delve deeper into the intricate dynamics of virulence expression in mixed-species biofilms, considering diverse ratios of C. albicans and S. mutans, as well as varying durations of incubation. By examining these factors, we can shed more light on the interplay between these two species and the influence of their interactions on biofilm formation and pathogenicity. Additional studies will provide valuable insights into the complex relationship between C. albicans and S. mutans, potentially uncovering novel mechanisms of biofilm development and pathogenicity. Such knowledge could pave the way for targeted therapeutic strategies aimed at disrupting or controlling the growth and virulence of these microorganisms in biofilm-associated infections.

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