Microbiology Flashcards
What is the main difference betwen S Mutans and S Sobrinus
S Sobrinus is sensitive to bacitracin
Why would being able to produce intracellular polysaccharides important for S Mutans
Being able to store glycogen allows S Mutans to exist with only transient environments of sugar
Where is S Salivarius most commonly found?
Oral Mucosa, mainly the Tongue
T/F: S. vertibularis produces EPS
False
Why would S. vertibularis be important in maintaining oral ecosystem balance?
- Ability to produce Hydrogen Peroxide
- Produces Urease: which increases oral pH
What is the most opportunistic Strep that is involved with appendicitis, peritonitis and endocarditis?
S. Anginosus group
How do Mitis Group Strep evade host defenses
By producing IgA protease
Why would binding amalyse be beneficial for bacteria?
- Able to cloak from host as Amalyse would appear as self
- Amalyse on local surface would provide access to nutrition by breaking down polysaccharides closest to itself
Peptostreptococci mainly metabolise what?
They are asaccharolytic - obtain energy from amino acid fermentation
Why is the presence of Methicillin-resistant Staphylococcus aureus (MRSA) in a hospital situation particularly dangerous?
The possibility of passing antibiotic resistance to other staphylococcus strains through horizontal gene transfer
What is the antibiotic of last resort for Methicillin-resistant Staphylococcus aureus (MRSA)
Vancomyacin
What is the most dominant gram positive rod in plaque?
Actinomyces
What is the significance of Actinomyces Naeslunidii’s ability to create extracellular polymers from sucrose?
Enables attachment to biofilm - important as a pioneer plaque organism
A. Israelii can result in what opportunistic infection that results in multiple yellow sulphurous abscesses?
Actinomycosis (Lumpy Jaw)
Actinomyces is what sort of bacteria?
Facultative Anaerobic Gram Positive Rod
Where in the mouth do Actinomyces typically reside?
Gingival crevice and interproximal areas
What conditions do microaerophiles require?
Presence of some oxygen because they can not ferment or respire anaerobically. However, they are poisoned by high concentrations of oxygen
Why is homofermentative bacteria more dangerous for caries?
Homofermentative bacteria’s main by-product is lactic acid, which as a lower pKa (3.7) which inherently creates are more acidic environment for demineralisation.
Heterofermentation produces less lactic acid and acetic acid which has a higher pKa, hence is less acidic.
T/F: Lactobacilli is an early coloniser
False, it constitutes less than 1% in healthy plaque due to poor attachment mechanisms. It prefers acidogenic and aciduric conditions
Where is Propionibacterium typically found?
In root caries - adhesion to cementum is different to enamel by virtue of composition
T/F Rothia Dentocariosa is an important gram positive bacteria for caries
False, whilst it is isolated in dental caries, it is largely benign to teeth.
It is however an infective agent that during dental procedures can heighten the risk of Infective Endocarditits
What are Asaccharolytic bacteria?
Bacteria that do not metabolise carbohydrates
Why would Eubacterium be an ideal bacteria for periodontal loss?
It is asaccharolytic - digest amino acids found in PDL
It produces Hydrogen as a byproduct of metabolism, which interacts with sub-gingival oxygen creating water, thus making the environment more anaerobic, favouring itself
What is the significance of large amount of extracellular polysaccharides (EPS) produced by Stomatococcus?
EPS is formed via dietary sucrose and bacterial enzymes. It makes biofilm thicker and stickier - giving carious plaque a better environment to metabolise.
What Catalase Positive Gram Positive Cocci is associated with peri-implantitis?
S. aureus
What is the significance of S mutans being able to metabolise mannitol and sorbitol?
S. mutans has an alternative metabolism pathway in PEP-PTS in transient sucrose environments.
What are 2 ways S vestibularis is protective against oral pathogens
- Produces Urase: increasing pH making it hard for aciduric bacteria like S. mutans
- Produces hydrogen peroxide: antimicrobial
Why is the anginosus group of strep not involved in caries
Doesn’t produce EPS from sucrose
What 2 benefits does binding amylase to the cell surface have for S. gordonii?
- Protection: having amylase on surface makes it look like “self”
- Nutrient Sequestration: by having the enzyme on the cell surface, it has first dibs on simple sugars when polysaccarides are broken down by amylase in its local environment
What 3 factors leads to a change in microbiota equilibrium?
- Alterations in host defense
2. Changes in microbiota in a specific microenvironment
What is a key feature of the oral microbial habitat in the lips/cheek/palate?
Biomass is restricted due to high turnover (desquamation) of epithelium
What is a key feature of the oral microbial habitat in the tongue?
Highly papillated creating a reservoir for anaerobes
What is a key feature of the oral microbial habitat on teeth
Non-shedding protected surface after formation of biofilm
Allows large number of microbes to colonise and not get washed away
When is S mutans found in children?
Newborn’s mouths are sterile at birth. S mutans appears on average around 26 months.
If there is heavy usage of broad spectrum antibiotics, what is the first coloniser in the mouth?
C albicans
T/F Smooth Tooth surfaces have low number of microbes with high diversity
F: low number of microbes, with low diversity
T/F: IV fed individuals don’t need their teeth cleaned
F: bacteria still can live within the saliva, PEP-PTS pathways can metabolise sorbitol, mannitol in the absence of sucrose
What are the roles of Langerhans Cells in the mouth?
Prevents adhesion / metabolism
What is the role of Complement in the mouth?
Activates Neutrophils
Bactericidal
What is the role of PMNs and Macrophages in the mouth
Phagocytosis
What is the role of IgG, IgA & IgM in the mouth?
Prevents adhesion
Opsonise
Complement pathways
What is the role of saliva flow in the mouth?
Physical clearance of organisms
What is the role of mucins and agglutinins in the mouth?
Physical clearance of organisms
What is the role of Lysozyme-Protease-Anion System in the mouth?
Cell Lysis of microbes by breaking down NAM-NAG bonds
What is the role of Lactoferrin in the mouth?
Iron sequestration, decreases metabolic pathways for microbes
What are the main two categories of oral gram negative rods?
Anaerobes vs Facultative
Oral Facultative Gram Negative Rods are grouped in 3 categories based on metabolism. What are these categories
- Saccharolytic (can break down sugars)
- Asaccharolytic
- Formate/Fumarate Metabolism
How does P gingivalis derive energy?
Amino Acid Fermentation
Prevotella are typically found where?
Subgingival plaque. May have a role in periodontal disease
T/F: P. gingivalis is saccharolytic
False. It metabolises via amino acid fermentation
Fusobacterium is typically known to cause what?
Extra-oral infections
A. actinomycetemcomitans is commonly associated with what?
Periodontitis due to LPS (toxins) and leukotoxins (evading white blood cells)
How does Capnocytophaga evade host defences?
By producing IgA protease
Eikenella corrodens utilised what as a form of asaccharolytic metabolism?
Ferments amino acids for energy by using NO3 as an electron acceptor for the Electron Transport Chain. This is not as efficient as oxygen
What are 2 examples of facultative gram negative rods that utilise formate/fumarate metabolism?
Wollinella
Campylobacter
Why is T. denticola pathogenic for periodontitis?
- Trypsin-like activity: highly proteolytic
2. Proline amino-peptidase: degrades hydroxyproline in collagen (PDL), gelatin
Where do humans obtain the majority of microbiota from at birth
Mother > Child
Angular Cheilitis is typically caused by what bacteria?
C. albicans
Bacteria in saliva is primarily derived from where?
From the tongue
Would you expect to see high concentrations of S. mutans outside of the teeth
No, S. mutans prefers a biofilm environment with adhesion to teeth
What salivary components aid in Buffering?
Carbonic Anhydrase
Histatins
What salivary components aid in Digestion?
Amylase
Mucins
Lipase
What salivary components aid in mineralisation?
Cystatins
Histatins
Proline rich proteins
Statherins
What salivary components aid in Lubrication + Visco-elasticity?
Mucins
Statherins
What salivary components aid in Tissue Coating?
Amylases Cystatins Mucins Proline rich proteins Statherins
What salivary components are anti-fungal?
Histatins
What salivary components are anti-viral?
Cystatins
Mucins
What salivary components are anti-bacterial?
Amylases Cystatins Histatins Mucins Peroxidases
What groups of bacteria are predominant in the palate
Streptococcus (52%)
Actinomyces (15%)
What group of bacteria are predominant in soft tissue mucosa (lip and cheeks)
Streptococci mitis group
What are the main bacterial ecosystems on teeth?
1) Fissure
2) Interproximal
3) Subgingival Gingival Crevice
4) Supragingival Gingival Crevice
5) Smooth Surface
What is the predominant bacterial group on the tongue?
Actinomyces
What group of bacteria are predominant in fissure plaque?
Streps
What group of bacteria are predominant in interproximal plaque?
Increase in actinomyces and obligate anaerobes
S. mutans and S. mitis less dominant
What are 7 clinically significant factors of biofilms that allow them to thrive in the oral ecosystem?
1) Protection from host defenses / predators
2) Protection from desiccation
3) Protection from antimicrobial agents
4) Novel gene expression and phenotype
5) Persistence in flowing systems
6) Touch Sensors in Cells (aids attachment)
7) Quorum Sensing (modulation of growth rates via communication with other bacteria)
What feature allows S mitis to be predominant in the oral ecosystem?
Ability to adhere on a range of different host tissues
How can biofilms provide resistance to antibiotics
1) Expression of different phenotypes - to hide
3) Growing slow - action of AB attacks cells during cell division
3) EPS barrier - chemical and sieving
4) Biofilm can concentrate β-lactamase => resistant to penicillin β-lactam
What are 2 ways that microbes can adhere to a tooth surface
1) Adhesion to acquired pellicle
2) Adhesion via co-aggregation to microbes already attached
What attractive forces initially allow bacterial adhesion to pellicle?
Short range attractional forces at 20nm via Van der Waal’s Forces
What forces provide full adhesion to the pellicle?
Hydrogen bonding via a shared electron bond with phosphate group on the bacterial cells wall
T/F: Increase hydrophobicity of a bacterial cell will lead to increased cohesion to plaque
True: ↑ cellular hydrophobicitiy = ↑ cohesion
What are the main pioneer organisms in plaque biofilm?
Neisseria + S mitis groups (S. sanguis, S. oralis, S. mitis)
How do pioneer organisms help other bacteria thrive?
Due to production of IgA proteases to evade host antibodies
How does the diversity change in the transition to mature plaque?
Reduction of Streptococci
Anaerobic Rods and Filaments dominate
What is the role of a Bacterial adhesin?
Part of the extracellular membrane of the bacteria that bind to a receptor that is either part of the pellicle or a molecule (host/bacterial) that can bind to the pellicle
What are Cryptitopes?
They are hidden adhesins that are only activated other some partial destruction of the cell surface via the host’s enzymic action
Why is fusobacterium a good transition bacteria between early colonisers and late colonisers in dental plaque?
1) Facultative anaerobic: so ideal as the biofilm starts transitioning to obligate anerobic
2) Metabolism is variable
3) Can survive in variable pH
4) Fusobacteria is also very big and has lots of attachment sites to both early/late colonisers
How are plaque water channels formed?
Extracellular Polysaccharides mostly through α1-6 Linkages
Why are water channels in plaque important?
Act like the roads in and out of the plaque colony - allows penetration of water and nutrients via pH, Eh, nutrient and end-product gradients
What are the 4 requirements for life?
1) Suitable pH
2) Environment to attach
3) Water
4) Atmosphere: O2 / CO2
Why is biomass restricted on the lips, cheek and palate?
Desquamation of epithelium means that colonies are constantly lost
What is the tongue a highly conducive environment for microbes?
Surface is highly papillated, increasing surface area and being preferential for anaerobes
What microbes are predominantly found in the lips/cheeks/tongue?
Streptococci (Neisseria, Veillonella)
What microbes are predominantly found in the tongue?
Streptococci (Actinomyces, Veillonella)
Obligate Anaerobes
P gingivalis
What bacteria are first transmitted to infants and when does this happen?
Lactobacilli and Candida in the birth canal
What bacteria can grow in the with the high dosage of broad spectrum antibiotics?
C albicans can grow in the absence of competing commensals
T/F: People in comas that are IV/Gastric fed can’t get caries
False: plaque can still grow without sucrose, as they metabolise off contents of saliva and dead cells
T/F: Interproximal tooth surfaces have more microbes and more diversity
True
What are the 4 protected teeth surfaces?
Interproximal
Gingival Crevice
Pits
Fissures
Why is the junctional epithelium a preferred environment for p gingivalis?
Due to the availability of heme in gingival crevicular fluid
What is the pH of a diseased perio pocket?
pH 8: p gingivalis metabolises protein, releasing ammonia and increasing pH
Which environment in the mouth are you most likely to find the lowest redox potential (Eh)
Gingival Crevice, since this is an environment for obligate anaerobes, this not requiring redox reactions to take place
What is meant by Anaerobiosis?
Sustained survival in the absence of oxygen
What is a Capnophilic bacteria?
Able to thrive under high concentrations of CO2
What is a Microaerophilic bacteria?
Bacteria that only require small concentrations of oxygen for growth, and are highly sensitive to atmospheric conditions
What are Facultative Anaerobes?
Bacteria that grow in both environments with/out oxygen, by switching between aerobic respiration to fermentation/anaerobic respiration
What nutrient sources are available to bacteria in saliva?
Amino Acids
Peptides
Glycoproteins
Vitamins
What nutrient sources are available to bacteria in GCF?
Proteins
Hemin
What is the role of Glycoside hydrolase?
Glycoside hydrolase is an enzyme that bacteria can use to help break down oligosaccharides to liberate nutrients. Microbes can work together to liberate and break down nutrients to metabolise when other sources of energy are not readily available
What is the primary physico-chemical barrier in a human host?
Epithelial Mucosa layers that constantly shed
What anti-plaque agent removes and prevents plaque adhesion to tooth surfaces?
Cetylpyridinium chloride (CPC) 0.3% in Colgate Total
A high pH environment would be indicative of what sort of bacterial metabolism?
Gram Negative Bacteria that have proteolytic enzymes to digest proteins: eg p Gingivalis in gingival pockets
A low pH environment would be indicative of what sort of bacterial metabolism?
Gram Positive Bacteria that metabolise sugars and are located in areas with poor plaque removal: eg S mutans
C. albicans is an oral fungi mos commonly found where?
The tongue
What conditions are most likely to result in large numbers of C. albicans
Immunosuppression (AIDS / medication)
Antibiotic Therapy
Veillonella are Gram-negative anaerobic cocci that can metabolise lactic acid. Why isn’t this a possible therapy for protecting against caries?
The presence of lactic acid already indicates that a proton is available to push the balance towards demineralisation. Metabolism will result in more proton release, keeping the environment acidic. As a result it does not result in remineralisation
What 2 virulence factors make the Gram Negative Spirochete T denticola part of the periodontal red complex?
1) Trypsin-like activity: highly proteolytic
2) Proline amino-peptidase: degrades hydroxyproline residues in collagen, gelatin
A. actinomycetemcomitans is typically associated with what form of periodontitis?
Localised juvenile Periodontitis via LPS and Leukotoxin virulence factors
P. endodonticalis can be found where?
Infected Root Canals and Periodontal Pockets
What microbes are predominant between the lower lip and gum?
S. vestibularis
What microbes are predominant in the corner of the mouth?
C. albicans (cause of angular cheilitis)
What microbes are predominant in cheek?
Streptococci Mitis group
What microbes are predominant in the palate
Streptococcus (52%)
Actinomyces (15%)
What microbes are predominant in the tongue
More Actinomyces than Steptococcus
What microbes are predominant in fissure plaque?
Strep (45%), Actinomyces (18%) Staph (9%). Mostly S. mutans
What microbes are predominant in interproximal plaque
Increase in actinomyces and obligate anaerobes - less oxygen available in this environment
Why is salivary bacteria a poor indicator of oral health
They are simply representative of what microbes are coming off surfaces, not what is happening at the site of disease
What forms the scaffolding for biofilm
Polysaccharides
Some glycoproteins + nucleic acids
What 7 properties make microbes growing in biofilms unique?
- Protection from host defenses / predators
- Protection from desiccation
- Protection/Resistance from antimicrobial agents
- Novel gene expression and phenotype
- Persistence in flowing systems
- Touch Sensors in Cells
- Quorum Sensing
How can biofilms increase resistance to antibiotics?
By concentrating β-lactamase: prevents the effective action of penicillin based Antibiotics
Other than the oral ecosystem, what other ecosystem should dentists be concerned with respect to biofilms?
Dental Unit Water Lines - build up of bacteria in dental chairs
Can Koch’s Postulates be applied to plaque derived diseases?
Generally no, due to the chronic and long term nature of the disease. The postulates can be modified to fit this category of chronic disease:
- The microbe should be present in sufficient numbers to initiate the disease
- The microbe should generate increased levels of specific antibodies
- The microbe should possess relevant virulence factors
- The microbe should cause disease in an appropriate animal model
- Elimination of the microbe should result in clinical improvement
Why is Non-specific + Specific plaque hypothesis no longer the accepted dogma for dental caries?
Disease causing pathogens (eg S mutans) still exist in healthy individuals.
Disease often occurs when environmental and host factors are modified.
Therefore, disease occurs when there is a shift in the balance of resident plaque microflora
What are the 4 factors that can cause tooth caries from an imbalance in the oral environment?
- Plaque Bacteria
- Host Factors (Saliva, Oral Hygiene, Enamel)
- Diet (Simple Carbohydrates)
- Time
Explain the Ecological plaque hypothesis
Disease results from shifts in the balance of the resident plaque microflora
Potentially cariogenic bacteria can be present in health, but at levels that are not clinically relevant
Disease could be controlled not only by targeting pathogens but also by interfering with the environmental factors responsible for driving the deleterious shifts in the microflora
What are the bacterial species involved with Caries?
S mutans Mitis-group Strep Anginosus- group Strep S. salivarius E. faecalis A. naeslundii Lactobacilli
T/F. S Mutans is always involved in early interproximial caries
False: Lesions can develop in the absence of S mutans, but it typically seen in later lesion development
What is the 5 main reasons for rampant caries?
- Epidemiology: Population subgroups prone to extensive decay
- Xerostomia (via radiation, medication)
- Sjogren’s Syndrome
- Medication
- High Sucrose Diets
T/F: Lactobacilli are involved in early sub-surface demin
False, they are typically associated with cavitated lesions as they don’t attach well to biofilm.
What are the 5 pathogenic determinants (Virulence factors) for caries?
- Sugar Transport
- Acid Production
- Aciduricity
- EPS Production
- IPS Production
What are the 3 sucrose uptake pathways in S Mutans?
Sucrose-PTS
Trehalose-PTS
Multiple Sugar TS
Glucosotransferase in S Mutans can result in what two products
Mutan α 1-6 (water insoluble) - used a supplementary food source and aids attachment to teeth
Glucan: α 1-6 (water soluble) - adds to plaque bulk and cell aggregation
How does S Mutans maintain pH osmolarity during a low pH environment
- Low pH envrionment indicative of high sugar environment
2. Excess of ATP allows ATPase pumps to expel H+ protons extracellularly
Is the PTS Sugar Transport system utilised in an aciduric environment?
No - low pH is indicative of high sugar, additional high affinity transport systems are not needs as there excess sucrose in the environment.
If we could create a S mutans mutant that couldn’t produce Glucosyltransferase, what would be the effect on cariogenicity?
Reduced caries - decreased colonisation + plaque formatino
If we could create a S mutans mutant that couldn’t produce IPS , what would be the effect on cariogenicity?
Reduced caries - decreased intracellular glycogen
If we could create a S mutans mutant that couldn’t produce lactate dehydrogenase, what would be the effect on cariogenicity?
Reduced cares - no lactic acid production
If we could create a S mutans mutant that was less aciduric, what would be the effect on cariogenicity?
Reduced caries, population decreases towards critical pH threshold for hydroxyapetite
If we could create a S mutans mutant that couldn’t produce Fructosyltransferase, what would be the effect on cariogenicity?
No effect, this is a secondary metabolism pathway
Why do Down’s Syndrome people have lower caries risks?
Increased production of Salivary Secretory IgA
Does overall amount of plaque increase caries risk?
Yes, there is evidence that total plaque population weight is higher in high caries risk patients even if S mutans populations are the same
How is fluoride bacteriostatic?
- Reduces Glycolysis by inhibiting enolase
- PEP/PTS System inhibited
- Acidifises Internal pH > resulting in inhibition of intracellular enzymes
- Interferes with membrane function
- Reduces IPS Synthesis
How is Chlorhexidine Bacteriostatic?
- Blocks adherence: blocks binding of S mutans to dextran-coated Hydroxyapatite
- Inhibits PEP/PTS System
- Interferes intracellular pH (blocks ATPase ion channels)
How long is the bacteriostatic action of Chlorhexidine?
5 hours
What is the action of triclosan on cariogenic bacteria?
Substantive effect = reduces acid production
What are the broad categories of anti-microbials that can be used against carious bacteria?
- Fluoride
- Bisbiguanide: Chlorhexidine, Alexidine
- Enzymes: Mutanase, Glucanase
- Essential Oils: Thymol, Eucalyptol
- Metal Ions: Copper, Zinc, Tin (Stannous)
- Plant Extracts: Sanguinarine
- Phenols: Triclosan
- Quaternary Ammonium Compounds: Cetylpyridinium Chloride
- Surfactants: Sodium Lauryl Sulphate
- Sugar Substitutes: Xylitol, Mannitol, Sorbitol
How are metal ions bacteriostatic?
They inhibit sugar transport, protease activity and acid production
How are sugar substitutes bacteriostatic?
- Product futile metabolism cycle in S mutans
- Interfere with protein synthesis
- Reduce surface adhesion
What are examples of bacteriostatic sugar substitutes?
Xylitol
Mannitol
Sorbitol
What are examples of metal ions that are bacteriostatic?
Copper
Tin (Stannous)
Zinc Citrate
What are 2 caries bacteria prevention strategies that work directly on bacteria?
- Replacement Therapy: varnish that replaces native S mutans strains with strain that doesn’t produce lactate (lower acid production)
- Vaccination: Whole Cell/Surface Protein Vaccination, which they allows for antibodies to be produced against S mutans
What are 3 methods of directly assessing bacterial caries risk?
- Past Caries experience (what we use clinically)
- Stimulated Saliva Microbial Testing
- S mutans antibody test (still in development)
What is the optimal fluoride concentration in water for a bacteriostatic effect?
1 ppm
What are the only 2 recommended agents that can control caries apart from mechanical brushing?
Chlorhexidine Essential Oils (Listerine)
How does Zinc Citrate work as an anti-microbial?
Inhibits Sugar Transport, Protease Activity, Acid Production
Where can phenols like triclosan be found?
Toothpaste
How does triclosan work as an antimicrobial?
Broad spectrum substantive effect to reduce S Mutans acid production
What is the mechanism of action of Xylitol?
- Bacteriostatic
- Produces futile metabolism cycle in S mutans
- Interferes with protein synthesis
- Reduces surface adhesion
- Helps retain neutral pH
What are disadvantages of Xylitol?
Expensive compared to sugar
GIT side effects in large quantities
What Saliva Flow Rate would indicate a high caries risk?
Saliva Flow Rate < 0.7ml/min
If Stimulated Saliva microbial testing notes high levels of lactobacilli what is this indicative of?
Indicative of active lesions
