Oral Microbiology Final

courtesy of alexis' quizlet

what is the 16S ribosomal gene

universal gene for bacteria; essential and highly conserved; humans have 18S gene

why is the 16S ribosomal gene targeted

targeted due to its slow evolution, easy to extract and sequence, and its variable regions reflect evolution

why is 16S used and how is it useful

provides a way to group microorganisms to identify them based on prior knowledge built from decades of culturing

what is the definition of species with respect to 16S sequence identity

97% identity in 16S indicated that they belong to the same species

describe the central dogma DNA transcription

DNA —> mRNA —> protein —> metabolites

what are metagenomics/whole genome shotgun

term used for sequencing 100s of species; this process tells us what species are present and the gene functions

describe which "omic" technique is used to investigate each phase of the central dogma

DNA: genomics (whole genome)

mRNA: transcriptomics

protein: proteomics

metabolites: metabolomics

describe the 3 roles of mutation in bacterial genetics

1) increases genetic variation in a population

2) greatly impacts virulence factors

3) the genetic variation is distributed through recombination

mutations in bacteria can be good or bad?

depends on what genes it affects; ex: if there is mutation in F1F0 ATPase that allows it to pump out H+ with less energy, this is good for Smutans

what is the average saliva production in adults

0.5-1.5L of saliva everyday

what is the average saliva production in kids

0.5-2L of saliva everyday

what are the 3 relevant antimicrobial components of saliva

1. lysozymes

2. lactoferrin

3. secretory IgA

what is the function of lysozymes to inhibit bacteria

digest the cell walls of gram positive bacteria by breaking the beta(1,4) bond between N-acetylmuramic acid and N-acetylglucosamine (NAM-NAG) in peptidoglycan

what is the function of lactoferrin to inhibit bacteria

inhibits bacterial growth by binding and sequestering Fe2+ ions and in the apo (iron free) state can be toxic to bacteria and interfere with bacterial adhesion; affects microbial metabolism

what is the function of secretory IgA to inhibit bacteria

agglutination

what is agglutination

the clumping of particles (ex: antigen/antibody or mucin/surface protein)

what are the 2 relevant salivary agglutinins

1. sIgA

2. salivary mucins

describe the structure of salivary mucins

oligosaccharide chains that bind to amino acid rich domains on the polypeptide backbone

what are the 3 characteristics of sIgA

1. dimeric

2. joining (J) chain

3. secretory component that facilitates trans-cellular transportation

what is the difference between salivary pellicle and acquired pellicle

salivary pellicle (protective film) usually coats tissue and mucosa, but when it coats a hard surfaces such as teeth, it is referred to as an acquired pellicle

what are the 3 virulence factors of Streptococcus mutans

1)adhesion

2) acidogenicitiy: ability to generate acid

3) aciduricity: able to survive with acid

describe the extracellular polysaccharide matrix (EPS) role in adhesion

bacteria forms an external polysaccharide matrix that serves as energy storage and can contribute to recruitment of secondary and tertiary colonizers (other bacteria want free lunch from the sugars in the EPS!)

emphasized role of glucosyltransferase and its interaction with EGCG

1. stores energy outside of the cell in the form of glucan and dextrans

2. EGCG blocks GTF genes from building the dextran chains outside of the cell; antagonistic to S mutans as a result

what are the major components that contribute to acidogenicity in Smutans and what are their functions

Smutans uses glycolytic fermentation - converts glucose or sucrose into pyruvate via glycolysis, and also ultimately produces acid - acid is pushed out of cell and contributes to decreasing external pH - pyruvate can be shuttled into various metabolic pathways in which organic acids are generated and ATP is produced for the cell

what are the major components that contribute to aciduricity in Smutans and what are their functions

• decreasing external pH: Smutans modifies membrane composition which will decrease proton permeability

• decreasing internal pH: pumps out the protons (translocation)

what gene contributes to Smutans modifying their membrane composition to deal with decreasing external pH

fabM: increases saturation of cell membrane phospholipids

what contributes to Smutans regulating its internal pH

F1F0 ATPase; costs energy bc pushing protons out against gradient

what is the critical pH for hydroxyapatite (HA)

5.5; threshold for when you start to see demineralization

what is the critical pH for fluorapatite (FA)

4.5

what are the roles of HA and FA in enamel equilibrium in the presence of acids and saliva

HA: above pH of 5.5 enamel will remineralize, and below pH of 5.5 enamel will demineralize; essential for protecting teeth

FA: above pH of 4.5 enamel will remineralize, and below pH of 4.5 enamel will demineralize; requires more acidic challenge to demineralize

what would happen to HA and FA at a pH of 4.7

HA would demineralize and nothing would happen to FA; remineralization would only really happen above pH of 5.5 bc HA and FA are interweaved in tooth etc

what is the major action of fluoride

inhibits F1F0 ATPase pump (major action! pH inside bacteria gets very low and kills it) must be in a super acidic environment for fluoride to be released from demineralizing FA

why is FA's critical pH lower than HA's critical pH

fluoride is more electronegative so it will hold onto electrons better

what is the function of SDF

antimicrobial properties from silver: disrupt peptidoglycan cell walls, lyse cell membranes, denature ribosomes, bind DNA; protective effect from fluoride

bacteria that are killed by SDF further act as what

carrier for silver ions; this is beneficial to kill bacteria that try to pick up the free DNA from already wiped out bacteria

what is the "zombie effect"

the process in which SDF can kill other living bacteria nearby by binding DNA directly bc no nucleus —> bacteria cannot do transcription —> bacteria dies

what is DexA

plays a role in normal activity of glucosyltransferases and glucosyltransferase efficiency; breaks down dextrans (complex class of branched glucans)

what is the target of xylitol

directly inhibits DexA

what is xylitol's mechanism in Smutans

1. causes poor biofilm formation by Smutans

2. reduces acid production

what are catechins and where are they found

epigallocatechin gallate (EGCG); found abundantly in tea

what does epigallocatechin gallate (EGCG) do

inhibits normal function of glucosyltransferases

what is the mechanism of EGCG in Smutans

1. competes for binding on salivary pellicle

2. alters bacterial cell walls and/or cell membrane

what is the chain of infection starting with the source

pathogenic organism —> reservoir or source —> mode of transmission —> portal of entry —> susceptible host

which blood borne virus has the highest risk of infection resulting from a needle stick from an infected patient

HBV (1-62%); highest risk bc it can be persistent outside of the body

at what concentration of alcohol does an alcohol-based hand rub need to be in order to be considered an effective disinfectant

most effective in aqueous solution of 70%

what is the composition of dental plaque (3)

1. salivary components like mucin

2. desquamated epithelial cells

3. microorganisms

what is alpha and beta diversity

alpha diversity reports how many species there are within a sample (ie: one person)

beta diversity reports how many species there are between samples (ie: between people)

how related are samples/sites in beta diversity

a single oral site of different individuals is more similar to each other than the oral sites within one individual

example of beta diversity

ex: bacteria in your supragingival plaque is more similar to another persons supragingivial plaque than it is to your own tongue

result of 21 city study

fluoride is optimal at the concentration of 1.0-1.2 ppm; has best protective effect without fluorosis effects

what is a major virulence factor of P. gingivalis?

FimA

what is fimA and why is it a virulence factor?

gene that encodes fimbriae which tricks hosts epithelial cells to uptake the bacteria into them, survival tactic

what is P. gingivalis antagonism?

P. gingivalis Lipid A in LPS can be modified to adjust the signal response as determined by TLR4 - it tricks TLR4

how do socransky’s microbial complexes progress from health to disease?

yellow (health) orange (gingivitis) red (periodontitis)

what are the three red complex bacteria?

Porphyromonas gingivalis

Tannerella forsythia

Treponema denticola

what is an important orange complex bacteria to know?

Fusobacterium nucleatum

what are the major differences between gingivitis and periodontitis (3)?

ginigivitis is reversible, has NO bone loss, has NO clinical attachment loss

how are diabetes and periodontitis related?

inherently lined via inflammation, one exacerbates the other

what is the keystone pathogen hypothesis? what is an example?

low abundant species can disproportionately affect the host response; P. gingivalis is a keystone pathogen for periodontitis

ecological plaque hypothesis

dysbiosis + environment

koch’s postulates purpose

to determine a key etiological agent

what are the four koch postulates?

1. suspected agent in all diseased and absent in healthy organisms

2. isolate and grow

3. cause same disease when inoculated

4. isolation again

what are the three main reasons which periodontitis does not conform to koch’s postulates?

1. some perio pathogens are present in healthy individuals

2. oral diseases are polymicrobial

3. oral species are difficult to isolate and cultivate

what is a concern for the epidemiology of periodontitis and gingivitis?

there is severely deficient and underrepresented epidemiological data

what types of microbes emerge during gingivitis compared to health?

gram negative facultative rod bacteria

what is a limitation of the DNA-DNA checkerboard hybridization by socransky?

only probes 43 taxa, there are 800-1000 oral species we know of

what is the concept of synergy in dysbiosis

sum of 2+ organisms has a greater effect than individually eg. T. forsythia and F. nucleatum with bone loss

what are the two big takeaways from Bamashamous et al. 2021?

1. first time slow responders were recognized

2. shows slow responders as the dominant phenotype

what is the big takeaway from Kerns et al. 2023?

clinically healthy teeth are directly influenced by inflammation