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microbiology > december revision > Flashcards

december revision Flashcards

1
Q

outline taxonomic (science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups) groups of life

A
  • eubacteria (bacteria)/prokaryotes
  • eukaryotes (eukaryia)
  • archae
  • viruses
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2
Q

differences between eukaryotic and prokaryotic cell

A
  • eukaryote is larger than prokaryote
  • eukaryote is complex whereas prokaryote is relatively simple
  • eukaryote has linear chromosomes and histomes, prokaryote has single circular chromosome
  • eukaryote is frequently multi-cellular, prokaryote
  • eukaryote has introns/exons, prokaryote gene structure (introns are rare)
  • eukaryote has 80S ribosomes, prokaryote has 70S ribosomes
  • eukaryote has no cell wall or has a flexible cell wall, prokaryote has a rigid cell wall
  • eukaryote cell cycle (mitosis/meosis), prokaryote has rapid cell cycle
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3
Q

main features of prokaryotes that provide targets for antibiotics

A

Antibiotics work by acting on 4 target locations on prokaryotic cells:
1. The cell wall (as eukaryotic cellls lack a cell wall, these have no effect on eukaryotes)
2. The cytoplasmic membrane - the structure of the prokaryotic cell membrane differs from that of eukaryotes
3. Protein synthesis - the process & the ribosomes involved(70s in prokaryotes, 80s in eukaryotes) are different on the two types of cells
4. On nucleic acid metabolism - bacterial DNA replication, synthesis & RNA transcription all involve different enzymes than those in eukaryotes
In all the above target locations, antibiotics act specifically on prokaryotes

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4
Q

cell structure of eukaryotes

A
  • cell membrane
  • nucleus
  • centriole/centrosome
  • nucleolus/ribosome
  • ER
  • cytosol
  • mitochondrion
  • golgi
  • cytoskeleton
  • secretory vesicles, lysosome
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5
Q

cell structure of prokaryotes

A
  • plasma membrane
  • cell wall
  • nucleoid (DNA and associated proteins)
  • ribosomes
  • cytoplasm
  • capsule, flagellar/flagellum, pili
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6
Q

the structure of the prokaryotic cell membrane/cytoplasmic membrane that makes it target site of antibiotics

A
  • lipid bilayer
  • retains cytoplasm
  • selective barrier
  • transports material across
  • reaction surface (respiration and lipid synthesis)
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7
Q

cell wall of prokaryotes

A
  • rigid layer
  • barrier
  • repeated polysaccharide structure
  • can be present in gram +ve or gram -ve bacteria
  • target of penicillin
  • cell wall contains peptidoglycan (peptidoglycan cell wall made up of NAM and NAG, and is slightly variable in gram +ve and gram -ve bacteria)
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8
Q

Lipopolysaccharide (LPS)

A
  • outer layer of gram -ve bacteria
  • glycolipid
  • has structural role
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9
Q

flagella

A
  • component of gram -ve and gram +ve bacteria

- has role in arrangement and development of bacteria

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10
Q

fimbriae/pilus

A
  • component of gram -ve bacteria

- involved in adherence and sex

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11
Q

eg’s of gram -ve bacteria

A
  • Type I pili (eg. Escherichia coli, shape = rigid rod with flexible tip)
  • type IV pili (eg. Escherichia coli, Neisseria app and pseudomonas spp, shape = flexible rod some form bundles)
  • curli pili (eg. some strains of Escherichia coli, shape = coiled/aggregative filament)
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12
Q

eg.’s of gram +ve bacteria

A
  • fibrils (eg. streptococcus salivarius K+, shape = short thin rod)
  • pili (eg. streptococcus spp and corynebacterium spp, shape =flexible rod)
  • bacillus subtilis (gram +ve rod)
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13
Q

steps involved in prokaryotic protein synthesis (target of several classes of antibiotic)

A
  • transcription =gene (DNA) -> mRNA (DNA dependent RNA polymerase)
  • translation = mRNA -> ribosome (tRNA)
  • tRNA then -> protein -> 2nd,3rd, 4th structure ->export/assembly/processing
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14
Q

prokaryotic growth requirements

A
  • food
  • temperature
  • hydrogen ion conc (pH)
  • osmotic protection
  • oxygen
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15
Q

method of prokaryotic growth

A
  • biniary fission
  • 1 divides into 2 then 2 divide into two (to give 4), then 4 divide into 2 each (to give 8) and so on
  • microorganisms grow and divide in variety of ways
  • > most divide by binary fission (2 identical daughter cells, eg. E.coli, S.typhimurium)
  • > in some cases cell division is asymmetric (non identical daughter cells, eg. caulobacter spp.)
  • > in some cases the microorganism has a filamentous habit with growth at the tips of the filament (eg.streptomyces spp.)
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16
Q

sources of food for prokaryotic growth

A
  • C source (organic eg. proteins/sugars, inorganic eg. fix CO2)
  • oxygen and hydrogen
  • N source (eg. amino acid ammonia)
  • inorganic salts (P,S,K,Mg,Ca,Fe)
  • trace elements (Zn, Cu, Mn, Ni, Mo)
  • vitamins (small organic cofactors) eg. biotin folic acid, niacin
  • inorganic phosphate (uptake phosphorus)
  • sulphur (reduce sulfate)
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17
Q

key features of bacterial cell wall

A
  • key features of gram -ve cell wall:
  • > lipopolysaccharide
  • > outer membrane
  • > peptidoglycan
  • > cytoplasmic membrane
  • key features of gram +ve cell wall:
  • > teichoic acid
  • > peptidoglycan
  • > cytoplasmic membrane
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18
Q

the gram stain

A
  • gram positive bacteria stains dark violet

- gram negative bacteria stains pink

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19
Q

significance of gram stain

A
  • used as a tool for the differentiation of Gram-positive and Gram-negative bacteria, as a first step to determine the identity of a particular bacterial sample
  • this is significant as identifying the organism causing an infection is the first step in treatment!
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20
Q

important ways of classifying bacteria

A
  • shape (coccus, bacillus, spiral shaped etc)
  • cell wall (grams stain) -> gram +ve, gram -ve, acid fast, no cell wall
  • metabolism (growth in oxygen) -> aerobic, anaerobic, facultative
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21
Q

most common shapes of bacteria

A
  • cocci/coccus-spheres
  • bacilli/bacillus (rod shaped, chains of bacilli)
  • spiral-shaped
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22
Q

diplococcus (shape)

A

-cocus that divide in one plane to produce 2 cocci

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23
Q

streptococcus(shape)

A

-cocci that divid in one plane to produce 4-20 cocci

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24
Q

staphylococcus (shape)

A

-division of cocci in 3 planes

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25
Q

vibrio (shape)

A
  • slightly curved rod
  • gram -ve
  • there are 34 species of vibrio (one eg. = vibrio cholera)
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26
Q

spirillum (shape)

A

-rigid spiral shaped bacterium

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27
Q

spirochaete (shape)

A

-flexible spiral shaped bacterium

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28
Q

aerobic bacteria

A

grow in oxygen/air

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29
Q

obligate aerobes

A

bacteria that require oxygen

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30
Q

obligate anaerobes

A

bacteria that are killed by oxygen

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31
Q

facultative anaerobes

A

bacteria that tolerate oxygen

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32
Q

bacteria involved in dental caries

A
  • gram +ve, facultative cocci = streptococci

- gram +ve, facultative bacilli = lactobacilli

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33
Q

bacteria involved in periodontal diseases

A

-gram -ve anaerobic bacilli = GNABs

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34
Q

prokaryotic/bacterial cell cycle

A

= C period (synthesis/chromosome replication) -> D period (mitosis/cell division) -> growth

  • process by which a newborn cell grows in size and divides to form 2 cells
  • microorganisms grow and divide in variety of ways
  • > the initiation of replication/C period depends on DnaA-ATP binding to origin
  • partition/division/segregation of chromosomes is determined by dedicated proteins (dynamic par proteins segregate chromosomes and plasmids) as the chromosome has to be organized before replication can take place
  • > once segregation has been ordered/organized, chromosome replication is terminated (chromosomes have to be separated, and D period/division begins)
  • > bacterial cell division depends upon presence of FtsZ ring
  • chromosome replication depends on DnaA-ATP levels -> segregation (ordered/partition proteins) depends on actin like proteins - actin gives diff shape to cell and and ensures segregation of chromosome -> elongation (by MreB/actin like helix) -> cell division (FtsZ determines first event, Fts1 encodes PBP3/penicillin binding protein which cross links peptide chains during cell division) (tubulin gives dimension and FtsZ’s evolutionary origin = tubulin?)
  • prokaryotic growth requirements (food, temperature, hydrogen ion conc (pH), osmotic protection, oxygen)
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35
Q

basic events in the growth and division of a model prokaryote (E.coli = model prokaryote)

A
  • E.coli = single circular chromosome (most common type of bacterial chromosome)
  • C period (synthesis/ chromosome replication) = 40 minutes, C period initiates at a specific site called oriC (the origin) -> bidirectional replication occurs -> ends in a termination region which is not a specific point due to the bidirectional replication that takes place
  • D period (mitosis/cell division) = 20 minutes
  • C+D= 40 minutes but fast growing E.coli divide every 18 minutes (this is due to there being more than one origin site) -> key thing to remember about 35 min cycle = how frequently the origin of replication fires determines how fast a bacteria grows, at time 10 more origins are fired even though replication hasn’t finished, and at time 15, replication is complete (and cell/termination initiates 20 min D period)
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36
Q

explain how prokaryotes can alter their growth rate

A
  • > availability of DNA protein regulates chromosome replication (to initiate a new round of DNA replication, sufficient DnaA-ATP has to bind to specific DNA sequences called DnaA boxes within the origin, DnaA-ATP tells you, as a cell, when you can begin to copy a chromosome
  • Ftz = key protein entirely in cytoplasm that is the central event of bacterial cell division assembly on, it is conserved in nearly all prokaryotes , you don’t have division
  • > it is a homologous (having the same relation, relative position, or structure, in particular) ring in chloroplasts
  • > regulation of FtZ controls cell division
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37
Q

types of bacterial/prokaryotic cell division

A
  • microorganisms grow and divide in variety of ways
  • > most divide by binary fission (2 identical daughter cells, eg. E.coli, S.typhimurium)
  • > in some cases cell division is asymmetric (non identical daughter cells, eg. caulobacter spp.)
  • > in some cases the microorganism has a filamentous habit with growth at the tips of the filament (eg.streptomyces spp.)
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38
Q

key proteins involved in bacterial cell division

A
  • FtsZ (required for division, FtsZ ring is the site of bacterial cell division)
  • FtsI (encodes PBP3)
  • PBP3 (recruited by FtsZ, PBP3 cross links peptide chains/transpeptidation during bacterial cell division and is a target of penicillin)
39
Q

examples of viruses that cause disease in humans

A
  • adenovirus (human respiratory and GI, dsDNA, icosahedral)
  • papillomavirus (human STD, icosahedral)
  • rotavirus (human GI, ds DNA, icosahedral)
  • influenza virus (humans/mammals/birds, helical symmetry, ssRNA)
  • Ebola virus (humans, zoonotic/fruit bat, hemorrhagic fever, ssRNA)
  • parainfluenza virus (human, ssRNA)
  • > icosahedral = 20 identical equilateral trianglular faces
  • > virus particle/genome (the complete set of genes or genetic material present in a cell or organism) can be DNA or RNA
40
Q

explain why viruses are different from other microbes

A

-fundamental difference = other organisms divide, viruses assemble from other components

41
Q

different routes of infection and spread that viruses can take

A
  • how viruses enter the host:
  • > respiratory tract (inhalation or touch)
  • > gastro-intestinal tract (ingestion, inhalation)
  • > urogenitary tract (sexual transmission)
  • > blood (blood products, needles, mother-child spread, insect bites)
  • mechanisms of spread within the host:
  • > some viruses remain at the site of infection (eg. rhinovirus, molluscum)
  • > some viruses can spread from the site of infection to other sites in the body, there are two mechanisms of spread, 1 = neural spread (eg. herpes simplex virus) and 2 = hematogenous spread ie. in the blood (eg. HIV)
42
Q

methods of controlling virus infection

A
  • vaccines (can prevent a person from getting a virus infection, useful for controlling infections within a population, eg.’s = measles, polio, influenza virus)
  • antiviral drugs (not very many have been discovered, eg.’s = anti - retroviral therapy for HIV, acyclovir for herpes simplex virus, Relenza for influenza virus)
43
Q

basic virus structures

A
  • viruses = very small, non cellular microbe/obligate intracellular parasite
  • virus particle is made up of nucleic acid genome (DNA or RNA), protein shell (capsid) and sometimes a lipid layer too (envelope/lipid envelope containing virus proteins)
  • > the genomes are either made up of DNA or RNA and can be diff structures (single stranded, double stranded, linear, circular) and can vary in size
  • > the protein capsid protects the genome from the environment and delivers the genome to the cell
  • > the virus envelope, envelopes the protein capsid, the envelope consists of a lipid bilayer (derived from the host cell) containing viral proteins, eg. of enveloped virus’s = influenza virus and herpes simplex virus
44
Q

mechanisms involved in virus replication

A
  • attachment (attachment proteins on the surface of the virus particle bind to the receptors on the host cell surface)
  • entry/absorption (by one of two mechanisms - direct fusion or endocytosis)
  • gene expression and genome replication (different genomes equal different strategies:
  • > gene expression (genome is transcribed to virus mRNA then translated to virus protein which is modified to a mature protein)
  • > genome replication (genome is replicated to another genome)
  • assembly (virion components/ proteins and genomes are assembled into virus particles)
  • release (non enveloped viruses are released by cell lysis, enveloped viruses can be released by budding/enveloped viruses acquire their envelopes by budding)
45
Q

ways in which viruses inflict damage on their hosts

A
  • note that it is not often in the virus’s interest to damage the host
  • mechanisms by which viruses can cause damage:
  • > viral factors (cell lysis, cell-cell fusion, inhibition of host cell transcription/translation, alteration of host cell cycle)
  • > host factors (apoptosis/cell ‘suicide’, lysis of infected cells by immune cells, inflammation)
46
Q

bacteriophage

A

a virus that parasitizes a bacterium by infecting it and reproducing inside it

47
Q

ebola virus disease (EBD) (haemorrhagic fever)

A
  • reservoir = fruit bats, chimpanzees, gorillas, monkeys, forest antelopes, porcupines
  • transmission = human-human
  • symtoms = occur 2-21 days after infection, sudden onset, include:fever, fatigue, muscle pain, headache, sore throat, vomiting, diarrhea, rash, kidney and liver function failure, internal and external bleeding, blood oozing from gums (symptoms increase in severity over time and can lead to death)
48
Q

why do viruses cause disease in certain tissues (and eg’s)

A
  • viruses are heavily dependent on the host cell for their replication
  • cells in different tissues have different properties
  • viruses can only replicate in cells that have the right properties for that virus
  • eg.’s:
  • > influenza virus (post translational modification of one of influenza’s virus proteins is dependent on a protein only expressed in cells of respiratory tract)
  • > HIV (can only enter cells that have CD4 and the chemokine receptor on the cell surface/cells of the immune system)
49
Q

define the meaning of sterilization

A

=the process by which all microorganisms are killed or removed to render the object incapable of causing infection

  • > if an object is sterile, it is unable to reproduce sexually, and is free from living microorganisms
  • > medical definition of sterilization = 1x10 to the power of six (one in a million instruments has one bacteria)
  • > methods of sterilization = heat, chemical, radiation, filtration
  • > method of sterilization is chosen based on (purpose, nature of material eg. withstand heat etc, nature of contamination, convenience)
  • > some viruses are very sensitive to sterilization in comparison to others therefore cleaning is emphasized before sterilization
  • viruses/bacterial cells are sensitive to sterilization, bacterial spores/ prions (prions are responsible for mad cow disease) are resistant to sterilization, fungal spores are mid way between being sensitive and resistant to sterilization
50
Q

define the meaning of disinfection

A

=the process by which the number of organisms are reduced to a level that is considered safe

  • note that some bacteria, spores and viruses remain
  • methods of disinfection:
  • > cleaning (reduces the bioburden, can be manual or automated, using hot water and detergent then rinsing to remove chemical traces thoroughly before drying via disposable towels or automatically)
  • > heat (pasteuration at 63 degrees for 30mins or 72 degrees for 20 secs -> boiling water for 10 mins -> washing and rinsing 70-90 degrees)
  • > ultrasound (high frequency sound waves, plastic absorbs sound waves, removes dirt and also disrupts cells/membranes, used in preparation of material prior to autoclaving eg tooth burs)
  • > chemicals (disinfectants for inanimate objects, antiseptics for living tissue/antimicrobial agent that can be applied safely to the surface of the body or exposed tissues eg. when blood is being taken/injection given)
51
Q

diff between disinfection and sterilization

A
  • instruments are sterile before packaged if they are new

- instruments are disinfected if they are able to be reused on more than one patient

52
Q

what is meant by standard/universal infection control

A

-the same (standard or universal) cross-infection control measures must be applied to each patient (this is because wide variety of pathogens pose a problem, there are many often unknown sources of infection and every patient is a significant source of infection whether they are a carrier or their blood is potentially infectious)

53
Q

procedures used to prevent cross infection in a dental surgery

A
  • infection control procedures:
  • > medical history (must be accurate/identify immune-compromised patients/ identify complicating factors, patients in prodromal phase of infection do not present with symptoms eg. measles, mumps and chickenpox, patients can be carriers eg. HIV, HepB, HepC, herpes, myco)
  • > instrument preparation
  • > instrument sterilization
  • > disposable items (mouth rinse beakers, saliva injectors, impression trains -> there is a symbol for single use objects that is a circle with a number two inside and a big cross right through it)
  • > decontaminating surfaces (disposable surfaces)
  • > protective clothing (long sleeved jackets, operating gloves, eye protection, surgical mask -> protects both dentist and patient from infection, injured/broken skin and mucous membranes/eyes/mouth exposure can cause transmission therefore they are covered)
  • > good practice
  • > immunizing staff (HepB is the most common blood borne virus, can also be immunized against tuberculosis, tetanus, poliomyelitis and rubella)
  • > aspiration and ventilation
  • > waste disposal
  • > training (effective, regular, written procedures)
54
Q

time taken to kill all bacteria and make the material safe using autoclave

A

134 degrees for 3 minutes

55
Q

methods of cross-infection

A
  • direct (patient, staff, droplets)

- indirect (contaminated instrument, contaminated surface, aerosols)

56
Q

occupational acquired infections

A
  • blood borne -> HIV, HepB, HepC
  • other major sources -> herpes, respiratory viruses, mycobacterium tuberculosis
  • > can be acquired due to sharps injury, splash of blood/saliva to mucous membranes/eyes/cut to skin/respiratory
  • > dentists/dental hygienists that are HIV positive can not undertake exposure prone procedures (exposure prone = if you cant see finger tips, therefore in the mouth)
57
Q

how can physical and chemical conditions in the mouth effect the growth of plaque bacteria

A
  • different surfaces in the mouth have characteristic oral floras
  • this is because of the different physical and chemical conditions at the different sites in the mouth
  • as the environment changes, the distribution of microorganisms changes
  • effect of physical conditions:
  • > tooth eruption (approx 12 months) has significant ecological impact as it creates a new non shedding surface for new bacteria to appear ( eg. S mutans, there is a greater diversity of GNABS around the gingival margin - porphyromonas gingivalis, tannerella forsythia and aggretibacter actinoycetemconitns found in 10% of 18-36 month olds)
  • > edentulousness (all teeth are removed, in old age/elderly) = simple environment therefore few bacteria spp, oppertunist organisms are present (klebseila, E.coli, pseudomonas aeruginosa)
  • > dentures are a complex oral environment as there is a higher carriage of yeast therefore many bacterial spp. (streptococci, staphylococci, actinomyces spp.)
  • effect of chemical factors:
  • > factors promoting microbial growth (warmth/stable temperature between 35-36 degrees as it is the favourable conditions for the growth of a wide range of saliva/plaque organisms, moisture, and nutrients eg. food, saliva and GCF/gingival crevicular fluid as there are principally large numbers of protein present in it)
  • > factors inhibiting growth (availability of nutrients, antibacterial factors in saliva, shedding of epithelial cells, swallowing of saliva)
58
Q

distribution of oral bacteria

A
  • oral flora = bacteria and other microorganisms that normally inhabit the oral cavity
  • there are many different sites in the mouth including lips, palate, cheek, tongue, gingiva, tooth etc
  • each site has its own characteristic oral flora because each site is a separate environment with different physical and chemical conditions for bacterial growth therefore a different build up of microorganisms
59
Q

oral flora (bacteria and other microbes) present on the tongue

A
  • this has a large surface area
  • S salivarius and S. mitis is the most common bacteria
  • > S.salivarius adheres to the dorsum of the tongue not to the teeth (ability of diff bacteria to adhere to diff surfaces is due to the chemical nature of their cell walls or polysaccharide coats)
60
Q

oral flora (bacteria and other microbes) present in saliva

A
  • the salivary flora originates from the tongue
  • the most common microbes are S.oralis, S. mitis and S. salivarius
  • > mutans streptococci and lactobacilli numbers are raised in patients consuming high sugar diets
61
Q

oral flora (bacteria and other microbes) present on healthy gingivae

A

-thin bacterial layer of S. mitis, S. sanguinis, and actinomyces

62
Q

oral flora (bacteria and other microbes) present on the lips

A
  • border between the skin flora and the oral flora

- mainly streptococci (eg. S. vestibularis) present

63
Q

oral flora (bacteria and other microbes) present on the palate

A
  • relatively few bacteria colonize the palate, (approx 5-25 bacteria per epithelial cell)
  • mainly streptococci and actinomyces
64
Q

oral flora (bacteria and other microbes) present on teeth in ‘clean’ mouths

A

-S.sanguinis, S. mitis and actinomyces are the largest group of bacteria
->mutans streptococci and S.sanguinis adhere strongly to tooth surfaces because of their sticky polysaccharide coats
->porphyromonas gingivalis does not stick to teeth but attaches readily to bacteria of dental plaque
(ability of diff bacteria to adhere to diff surfaces is due to the chemical nature of their cell walls or polysaccharide coats)

65
Q

oral flora (bacteria and other microbes) present on cheek surface

A

-S. mitis is the most common species (about 30% of buccal mucosa bacteria)

66
Q

oral flora during a lifetime

A
  • 24 hours after birth mouth is colonized by pioneer species/organisms (Streptococcus salivarius, S.mitis and S.oralis)
  • pioneer microbial community quickly establishes (major acquisition and colonization comes from the mother/maternal transmission and streptococci, staphylococci, lactbacilli and neisseria become important, especially oral streptococci as it sticks to pelicle as it develops on tooth surface and not directly on epithelia)
  • tooth eruption (12months) introduces climax community as there is a new non shedding surface (S.mutans) and there is a greater diversity of GNABs around the gingival margin of 18-36month olds (porphyromonas gingivalis, tannerela forsythia, and aggretibacter actinoycetemcomitans)
  • after all teeth fall out (edentulousness) oral flora remains as climax community as oppertunist organisms are present (klebseilla, E.coli and pseudomonas aeruginosa)
67
Q

development of streptococci in babies

A
  • S. oralis (41% at 1-3 days, 24% at 14 days and 20% at 30days)
  • S.salivarius (10% at 1-3 days, 30% at 14 days and 28% at 30 days)
  • S. sanguinis only increases after 12 months
  • > 0-7 species of GNABs (gram negative anaerobic bacteria) present after a few months
68
Q

factors which affect adherence to surfaces in oral cavity

A

-ability of diff bacteria to adhere to diff surfaces is due to the chemical nature of their cell walls or polysaccharide coats

69
Q

effect of redox potential (Eh) on growth of bacteria in oral cavity

A
  • high Eh/aerobic environment inhibits the growth of anaerobic bacteria (high in saliva/tooth interface, relatively high in gingival crevice, however drops with caries, and low in periodontal pockets)
  • low Eh values favour the growth of anaerobes and spirochaetes, which only survive at the base of periodontal pockets
  • Eh changes during plaque development
70
Q

effect of pH on growth of bacteria in oral cavity

A
  • normally salivary pH =6.75 - 7.25 (lower in dental plaque especially after sugar intake)
  • pH is lower in carious lesions (pH = 4) ad this encourages the growth of aciduric bacteria, such as streptococci and lactobacili which cause dental caries
  • pH is probably less acidic in inflamed gingival crevices, this promotes the growth of GNABs (porphyromonas gingivalis grows at optimum ph &.5)
71
Q

effect of nutrients on growth of bacteria in the oral cavity

A
  • endogenous nutrients (provided by host:
  • > most important source of nutrients for oral bacteria
  • > saliva provides amino acids, proteins, vitamins, growth factors and gases etc
  • > GCF/gingival crevicular fluid contains host defences and other nutrients such as albumen, scrum/plasma components and haeme/iron and is important for bacteria in the gingival crevice and periodontal pocket
  • exogenous nutrients:
  • > especially important sugars in diet, sucrose in particular, which promote growth and acidic production
  • > increase in S.mutans (mutans streptococci) and lactobacillus sp.
  • > decrease in acid sensitive bacteria, eg. S. sanguinis and S. gordonii
72
Q

effect of time on growth of bacteria in oral cavity

A
  • bacteria numbers in the mouth continuously change with time
  • > time since meals and sugar intake
  • > time since toothbrushing
  • > time of day (saliva flow during sleep affects the pH and supply of nutrients to the plaque bacteria as you don’t salivate at night)
73
Q

factors affecting growth of dental bacteria

A
  • physical factors (tooth eruption etc)
  • heat
  • moisture
  • nutrients
  • redox potential (Eh)
  • pH
  • nutrients
  • factors affecting adherence
  • time
74
Q

classification of streptococcus groups (4 types)

A

1-mutans (appearance on blood agar = alpha haemolytic):

  • > S.mutans = most common species isolated/most effective and important, implicated in human caries, colonise the teeth especially in fissures)
  • > other less commonly isolated examples include S.sobrinus and S.cricetus
  1. salivarius (appearance on blood agar = alpha haemolytic):
    - >S.salivarius = prefers keratinised surfaces, commonly isolated from most areas but especially the tongue
    - >S.vestibulans = most commonly isolated on vestibular mucosa

3-oralis (appearance on blood agar = alpha haemolytic):

  • > S.oralis = an early coloniser of smooth surfaces, produce IgA protease and glucans/polymers of glucose
  • > S.sanguinis = colonises teeth and has been shown to cause caries, produces IgA protease
  • > S.mitris = may occur in plaque but has a preference for non-keratinised surfaces in the mouth
  • > S.gordonii and S. parasanguinis = found in dental plaque,
  • > all members of the oralis group may act as opportunistic pathogens and are frequently isolated from cases of infective endocarditis

4-milleri (appearance on blood agar = most are beta haemolytic):
-> S.anginosus, S. intermedius, S.constellatus (isolated from dental plaque, are common in absesses/ S.anginosus is associated with absesses)

75
Q

gram positive oral bacteria important in caries and endocarditis

A
  • streptococci spp (facultative and obligate anaerobes)
  • staphylococci spp (facultative anaerobes)
  • actinomyces spp (facultative and obligate anaerobes)
  • lactobacillus spp. (facultative anaerobes)
  • eubacterium (obligate anaerobes)
  • > facultative anaerobes = bacteria that tolerate oxygen
  • > obligate anaerobes = bacteria that are killed by oxygen
76
Q

most significant oral streptococci (4 groups)

A
  • steptococci spp (facultative and obligate anaerobes)
  • 4 groups:
  • > mutans (alpha), important eg. = S.mutans (tooth surface/fissures)
  • > salivarius (alpha)
  • > anginosus (beta)
  • > oralis/mitis (alpha), important eg. = S.sanguinis (tooth biofilm/plaque)
77
Q

bacteria involved in tooth decay/dental caries

A
  • dental caries = localised dissolution of the enamel, may advance to dentine and pulp, common in pits and fissures/stagnation sites, due to the accumulation of plaque (carb->acid->demineralize enamel)
  • S.mutans (part of mutans group of oral streptococci therefore = facultative and obligate anaerobe), leading cause of tooth decay/dental caries
  • > mutans steptococci initiate dental caries at the enamel surface by binding to and colonizing the tooth surface and produce a sticky extracellular polysaccharid
  • > S.mutans are acidogenic and aciduric
  • > S.sanguinis (oralis/mitis group of streptococcus) is an early colonizer and can compete with S.mutans to stick to the tooth surface therefore if you have alot of oralis you have a smaller chance of infection
  • > lactobacilli are the next most important group of bacteria involved in dental caries after steptococci (they dont bind early on plaque), they are gram +ve pleomorphic/variable shaped rod and are facultative anaerobes (they are also acidogenic and aciduric)
  • > eg.’s of lactobacilli = lactobaciullus casei, lactobacillus acidophilus, lactibacillus rhamnosus
78
Q

acidogenic definition

A

-produces acid at a high rate from sugar therefore drops to a lower pH (pH4)

79
Q

aciduric definition

A

-tolerates high concentrations of acid

80
Q

infective endocarditis and dental bacteria involved

A
  • endocarditis = an infection of the innermost layers of the heart, it may occur in people that have congenital and valvular diseases and those who have rheumatic fever/inflammation of the joints
  • most common bacteria involved (40-50% of the cases) = S.sanguinis, S.mitis, S.ordalis, S.gordonii and S. parasanguinis)
  • > S.sanguinis is the most important, it can enter the blood following oral trauma eg.tooth extractions, subgingival scaling, toothbrushing and chewing
  • > the bacteria then settle on damaged endocardial surfaces causing bacterial vegetation
  • > at risk with patients with history of heart problems (therefore prophylaxis antibiotics were taken one hour before dental treatment, however it is now unclear whether prophylaxis actually has a detrimental effect therefore make patient aware of risks and seek medical advice as the antibiotics can be prescribed following dental treatment)
  • dentine caries are associated with deep carious lesions with low pH environment
  • > te level of lactobacilli in the saliva correlates with carbohydrate intake
81
Q

advantages and disadvantages of S.sanguinis (oralis/mitis streptococcus group)

A
  • advanatges = can out-compete S.mutans and prevent dental caries
  • disadvantages = can cross colonize to cause infective endocarditis
82
Q

gingival crevice and periodontal pocket formation

A
  • gingival crevice = the groove seen in most individuals between the tooth and the gum, accumulation of plaque bacteria on the surface of the teeth causes gingival inflammation/gingivitis
  • a periodontal pocket occurs in peiodontal disease, where the whole support around the tooth becomes inflamed/periodontitis, when dental plaque bacteria grow between the tooth and the gum
  • below the tooth margin the conditions for bacterial growth are very different to the tooth surface as they are moore anaerobic/CO2 requiring, and nutrients come from the GCF/gingival tissues rather than food and saliva
  • plaque accumulates around the neck of the tooth causing gingivitus which can be reversed -> the plaque then grows down between the tooth and gum to form periodontal pocket which is difficult to reverse at this stage -> the pocket deepens, gingiva begins to recede and bone begins to be lost (by this point it is irreversible)
83
Q

bacteria present in healthy gingival crevice

A

mostly gram +ve cocci

84
Q

bacteria present in periodontal pocket/peridontitis

A
  • peridontitis = a periodontal pocket occurs in periodontal disease, where the whole support tissue around the tooth becomes inflamed, when bacteria grow down between the tooth and the gum
  • 70-80% are GNABs (gram negative anaerobic bacteria)
  • GNAB’s produce alot of enzymes that degrade proteins
  • in addition, at the base of the pockets, many spirochaetes (a flexible spirally twisted bacterium) are found (treponema spp.)
  • > one group of bacteria frequently found together when periodontal disease occurs is the red complex:
  • > 1=tannerella forsythia (GNAB)
  • > 2=porphyromonas gingivalis (GNAB/equivalent to S.mutans)
  • > 3=treponema denticola (spirochaete)
85
Q

3 bacteria that are classed as the red complex

A

1-tannerella forsythia (GNAB)
2-porphyromonas gingivalis (GNAB/equivalent to S.mutans)
3-treponema denticola (spirochaete)

86
Q

actinomyces

A
  • gram +ve pleomorphic rods
  • arranged singly, in pairs, short chains or clumps
  • can grow as a branched network of hyphae but do not form spores
  • anaerobic or facultative anaerobes
  • some posses fimbriae which aid adherence and aggregation
  • non motile
  • mainly found in the mouth, in dental plaque and in tonsil crypts (however some are found in the female genital tract)
  • > found in supra and subgingival plaque
  • historically associated with root surface caries
  • a number of different actinomyces are found in the mouth (A.naesludi, A.viscosus)
87
Q

what is dental plaque/biofilm

A

=plaque is the general term for the microbial community found on the tooth surface (it is the microbial biofilm associated with the tooth)

  • > it is associated with hard and soft tissue
  • > contains living and dead bacteria
  • > includes extra-cellular bacterial products
  • > involves host contents
  • plaque is described as the oral biofilm, biofilm = name given to microbial communities attached to a surface (as it is a community of microorganisms associated with a surface and not just with regards to teeth)
  • properties of a typical biofilm:
  • > spatially organized in a 3D structure
  • > bacteria cells enclosed in ECM/extracellular matrix and EPS/extracellular polymeric substances
  • > increases habitat range of individual bacteria (adhesion is key at extending habitat range as it allows them to assemble and manipulate environment)
  • > sucrose supports polysaccharide synthesis and bacteria can attach to extracellular polysaccharides
88
Q

bacterial adhesion and attachment of bacteria (acquired pellicle)

A
  • contact surface via: liquid flow, diffusion through mucosal barrier or movement
  • > bacteria do not attach/adhere directly to the enamel they attach to the pelicle/layer of material that is aquired by a cleaned tooth
  • > the pelicle contains mucins, salivary glycoproteins, minerals and immunoglobins
  • the pelicle is aquired within seconds of cleaning the teeth (90-120seconds for maximum thickness) and different pelicles form on different oral surfaces (enamel, cementum and oral mucosa)
  • > the pelicle can be removed by vigorous brushing with an abrasive dentifrice
  • constituents of enamel pellice:
  • > acidic proline-rich proteins
  • > stratherin (antibacterial)
  • > amylase (enzyme, along with lipase, that is involved in breakdown of food)
  • > lysosome (antibacterial)
  • > albumin
  • > immunoglobins (antibacterial)
  • > glucosyltransferases/GFTs (bacterial)
  • > glucans (bacterial)
  • eDNA
  • > the adhesion of bacteria to pelicle is ordered accumulation (pioneer to climax community)
  • > the frequency is specific on relative affinity of each bacterium for the pelicle
  • > adhesion/attachment -> growth -> removal
89
Q

development of plaque/ succession of bacteria involved in plaque

A
  • > gram +ve and gram -ve cocci accumulate on the pelicle within 2 hours (gram +ve = S.oralis group which is the first colnizer and gram -ve = Neisseria and Haemophilus)
  • microcolonies form and spread across the tooth surface and confluent biofilm develops
  • > after 24 hours, streptococci predominate (95%, S.sanguinis is the most common)
  • during the first week there is an increased diversity of gram +ve bacteria (actinomyces naeslundii and actinomyces isreaelii), pioneer species reduce Eh/anaerobic, and anaerobic species survive and multiply, therefore actinomyces and anaerobes increase and streptococci decrease (as a proportion)
  • succession:
  • > stage 1 (streptococcus spp attaches to pellicle) -> stage 2 (streps joined/replaced eg. actinomyces spp) -> stage 3 (gram -ve species accumulate eg. fusobacterium)
90
Q

supragingival plaque

A
  • surfaces = smooth tooth surfaces, interproximal surfaces, pits and fissures
  • arrangement of plaque = highly organised (filaments are at right angles to the tooth, palisades of streptococci at right angles to enamel, co-aggregation complexes aka ‘corn-cobs’ and ‘test-tube brushes)
  • the co-aggregation complexes are eg.’s of the heterotypic cell-cell adhesion complexes that can occur in plaque:
  • > ‘corn-cob’ complexes = streptocoryne bacteria (streptococcus sanguinis or crista adhering to corynebacterium matruchotti)
  • > ‘tes-tube brush’ complexes = gram -ve bacilli adheres to filamentous bacterium
  • mature supragingival plaque develops in 7-14 days
  • conditions are aerobic and variable and influenced by saliva and diet
91
Q

importance of adhesins in the adhesion of bacteria to the pelicle

A
  • > adhesins = specific molecules on bacterial surface, which recognize specific ligands or receptors on the tooth surface, often associated with fimbriae
  • > lectins = recognize carbohydrate groups and bind them, often associated with fimbriae
  • > fimbriae = pili/fibrils, incorporate adhesins, ‘hair-like’ proteinacous appendages involved in adhesion to enamel/pellicle and adhesion to other bacteria
92
Q

subgingival plaque

A
  • initial coloniztion of plaque develops to subgingival plaque
  • plaque formation occurs supra/border
  • inflammatory response
  • tissue swelling
  • deeper sulcus/pocket (contains more fastidious and anaerobic bacteria)
  • > increasing proportion of GNABs (porphyromonas, tannerella and treponema/ GNABs)
  • inflammatory exudate (rich in nutrients)
  • more loosely structures micobiota develops
  • highly organised (most fastidious and anaerobic bacteria is seen most apically)
  • at the base of the sulcus/pocket rows of spirochaetes form at right angles to the enamel and cementum surface
  • mature gingival plaque develops after 7-28days
  • > conditions are anaerobic and constant and influenced by gingival fluid
93
Q

calculuss (tartar)

A
  • forms due to poor oral hygiene
  • can also be linked with bacteria
  • > calcium and phosphate ions supersaturated in saiva
  • crystals form within 24-72 hours then the crystals coalesce (come together to form one mass)
  • bacteria associated with promoting calculus formation but is relatively non-specific
  • crystals form foci/centre of interest for bacteria and can act as a ‘sink’ for toxins and other potentially harmful molecules

microbiology (1 decks)

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