Oral Microbiology: Bacteria, Protozoa, Fungi & Clinical Relevance
Bacterial Cell Wall Differences: Gram-Positive vs. Gram-Negative
Gram-positive bacteria have a thick murein layer, varying among species. They possess teichoic acids and a low protein content. Gram-negative bacteria have a single murein layer and lack teichoic acids. Both types share a peptidoglycan cell wall for shape and protection.
Bacterial Grouping and Staining
Bacteria group as diplococci (pairs), streptococci (chains), or staphylococci (clusters). Gram staining uses gentian violet, iodine, alcohol, and fuchsin. Gram-positive bacteria retain violet, while Gram-negative appear pink.
Oral Protozoa Characteristics
Oral protozoa, part of the endogenous flora, can cause diseases. They feed via phagocytosis or pinocytosis and reproduce sexually or asexually. Entamoeba gingivalis and Trichomonas tenax are found in periodontal diseases.
Streptococcus in Dentistry
Streptococcus are Gram-positive cocci, notably the viridans group. They colonize oral surfaces and contribute to dental caries, gingivitis, and abscesses. Streptococcus mutans is highly cariogenic.
Oral Gram-Negative Anaerobes
These capnophilic bacteria require CO2.
- Eikenella corrodens causes endocarditis and inhabits dental plaque.
- Capnocytophaga species are linked to periodontitis.
- Actinobacillus actinomycetemcomitans is a periodontal pathogen with adhesive and evasive properties.
Oral Gram-Positive Facultative Anaerobes
Actinomyces are pleomorphic and found in dental plaque. Actinomyces facial is associated with poor oral hygiene. Lactobacillus species are cariogenic and inhabit the oral mucosa.
Fungi of Oral Interest: Candida
Candida, particularly Candida albicans, is a common yeast. It colonizes oral mucosa, especially in immunocompromised individuals. Predisposing factors include poor hygiene, xerostomia, and systemic conditions.
Oral Candidiasis: Clinical Manifestations
Clinical presentations include:
- Pseudomembranous candidiasis (thrush)
- Erythematous candidiasis
- Rhomboid glossitis
- Angular cheilitis
- Denture stomatitis
- Hyperplastic candidiasis
Diagnosis involves microscopy, staining, cultures, and biochemical/molecular tests.