The resident oral Microbiota (detailed version)

What does microbial classification involve?

The arrangement of organisms into groups based on similarities and differences.

What is identification in microbiology?

The process of determining where a new isolate belongs within a taxon or group, such as genus or species.

What is taxonomy?

The nomenclature and identification of microorganisms.

What is the main purpose of microbial classification?

To develop a logical arrangement of organisms based on similarities and differences.

What is modern microbial classification based on?

Genetic relatedness among strains, especially 16S rRNA genes.

What does morphological classification refer to?

The shape of the cell.

What does physiological classification refer to?

The pattern of fermentation of simple sugars.

What does chemotaxonomy focus on?

The chemical composition of the cell wall, cell membrane, and whole protein profiles.

What does serology study in classification?

Antigenic characteristics, such as antibodies used to detect specific cell surface antigens.

What advances have impacted microbial classification?

Whole Genome Sequencing (WGS), Next Generation Sequencing (NGS), and Metagenomics.

What does metagenomics determine?

The composition of microbial communities.

What is a type strain?

The primary strain nominated that represents the species’ properties.

What are biotypes?

Strains with special biochemical or physiologic properties.

What are serotypes?

Strains with distinctive antigenic composition.

Where are microbial strains held for reference?

In National Collections like the American Type Culture Collection (ATCC).

What are common conventional microbial identification methods?

Gram staining, determination of cellular morphology, monoclonal antibodies, and nucleic acid probes.

Why are some species considered unculturable?

Because they require essential nutrients or specific growth conditions not easily replicated in labs.

What problems arise from recent advances in microbial classification?

Reclassification issues, difficulty interpreting older literature, and challenges comparing data.

What genus represents Gram-positive cocci found throughout the mouth?

Streptococcus.

How are Streptococcus species distinguished from Staphylococci and Micrococci?

By lacking the enzyme catalase.

What are the four major groups of Streptococcus?

Mutans, Salivarius, Anginosus, and Mitis.

What is Streptococcus mutans also known as?

The Mutans group.

How many serotypes exist for Streptococcus mutans?

Nine (a-h, and k).

Why is Streptococcus mutans important in dentistry?

It plays a major role in the etiology of dental caries.

When was Streptococcus mutans first isolated?

In 1924.

What medical condition can Streptococcus mutans cause outside the mouth?

Infective endocarditis on damaged heart valves.

What do Streptococcus mutans produce from sucrose?

Extracellular soluble and insoluble polysaccharides that help in plaque maturation.

Why are Streptococcus mutans highly cariogenic?

They efficiently scavenge dietary sugars and survive in acidic environments.

Where are Streptococcus salivarius group species found?

Most areas of the mouth, especially mucosal tissue and the tongue.

Which species belong to the Salivarius group?

S. salivarius and S. vestibularis.

Where is S. vestibularis mainly isolated from?

Vestibular mucosa.

What do members of the Salivarius group produce?

Urease and hydrogen ammonia.

How does the Salivarius group inhibit other bacteria?

They generate ammonia, raising local pH to inhibit competing bacteria.

Where are members of the Anginosus group commonly found?

Dental plaque and mucosal surfaces.

What type of diseases does the Anginosus group cause?

Purulent diseases and maxillofacial infections.

Where else are Anginosus group bacteria found?

Abscesses in internal organs such as the brain, liver, appendix, and heart.

Which species belong to the Anginosus group?

S. constellatus, S. anginosus, and S. intermedius.

Where is S. intermedius primarily found?

Liver and brain.

What cytotoxin does S. intermedius produce?

Intermedilysin, which interferes with neutrophil function and helps evade host defenses.

What are characteristics of the Mitis group?

Early tooth surface colonizers that form biofilm and are opportunistic pathogens.

Which species are most common in the Mitis group?

S. mitis and S. oralis.

What other members are part of the Mitis group?

S. gordonii and S. pneumoniae.

What does S. gordonii bind to?

Salivary α-amylase.

Why is α-amylase binding beneficial?

It helps break down starch and masks bacterial antigens, allowing evasion of host defenses.

What is significant about S. pneumoniae in the Mitis group?

It can acquire and transfer antibiotic resistance genes.

Where are anaerobic Gram-positive cocci found?

Dental biofilms, caries, infected pulp, advanced periodontal disease, and abscesses.

What are Enterococci and where are they found?

Gram-positive cocci like Enterococcus faecalis found in mouths of immunocompromised patients.

Where is Enterococcus faecalis isolated from?

Periodontal pockets and root canals that fail to respond to therapy.

Are Staphylococci and Micrococci common in the oral cavity?

No, they are uncommon.

Where might Staphylococci and Micrococci be found in the mouth?

Denture plaque and in immunocompromised individuals.

What genus represents Gram-positive rods and filaments?

Actinomyces.

Where is Actinomyces commonly found?

In dental plaque, especially interproximal areas and gingival crevices.

What diseases are associated with Actinomyces?

Gingivitis, root caries, and actinomycosis.

What species is an opportunistic pathogen among Actinomyces?

Actinomyces israelii.

What is actinomycosis?

A chronic inflammatory condition of the orofacial region.

Where else is Actinomyces found?

In cervical smears of women using intrauterine devices.

What is Eubacterium’s role in oral microbiota?

It makes up over 50% of anaerobic bacteria in periodontal pockets.

Where is Eubacterium common?

In dentoalveolar abscesses.

What are characteristics of Lactobacillus?

Acidogenic, acid-tolerant, and associated with advanced enamel and root caries.

What are the two main Gram-negative cocci genera?

Neisseria and Veillonella.

What is their role in oral health?

They contribute to plaque formation and create conditions for anaerobes to grow.

What are the two types of Gram-negative rods?

Facultatively anaerobic and obligately anaerobic genera.

What is Aggregatibacter actinomycetemcomitans implicated in?

Aggressive periodontal disease, endocarditis, brain abscesses, and osteomyelitis.

What does Aggregatibacter actinomycetemcomitans stimulate?

Bone resorption through its surface layers.

Where are obligately anaerobic genera mainly found?

Dental plaque and the tongue.

Are all obligately anaerobic genera culturable?

No, many are unculturable.

What are common culturable obligate anaerobes?

Prevotella intermedia and Porphyromonas gingivalis.

What do Porphyromonas colonies look like?

Brown or black pigments that protect them from oxygen toxicity.

Where are Mycoplasma species found?

On mucosal surfaces, in saliva, and dental plaque.

What is unique about Mycoplasma?

They lack a cell wall.

What are examples of Mycoplasma species?

M. pneumoniae, M. buccale, M. orale, and M. salivarium.

What are characteristics of Mycoplasma growth?

Slow growing, require protein and carbon dioxide, and pleomorphic.

How much of the oral microbiota do fungi make up?

A small portion.

What is the most prevalent fungus in the oral cavity?

Candida albicans.

Where is Candida albicans commonly found?

On the dorsum of the tongue, dentures, and orthodontic appliances.

In what type of patients is Candida albicans more prevalent?

Immunocompromised patients.

Where are Archaea found in the human body?

In complex microbial communities of the gut and mouth.

What is the main archaeal species in the oral cavity?

Methanobrevibacter oralis.

How do Archaea obtain energy?

By reducing CO₂ to methane.

What techniques detect viruses in the mouth?

Molecular techniques.

What are common viruses found in the oral cavity?

Herpes simplex virus (HSV-1, HSV-2), Cytomegalovirus, Human papillomavirus, and HIV.

What are protozoa?

Unicellular eukaryotic microorganisms that lack a cell wall.

What are the two most common protozoa in the mouth?

Trichomonas tenax and Entamoeba gingivalis.

What characteristics do oral protozoa share?

They are motile and ingest other microorganisms.