microbio Flashcards
major groups of life (3) inc. eg’s
- eukaryotes (protozoa/fungi)
- prokaryotes (bacteria)
- non-living (viruses)
components of cell structure (4)
- plasma membrane
- cell wall
- ribosomes
- capsule/flagellar/pili
is the cell wall gram +ve or -ve
can be both (LPS= component of gram -ve outer membrane)
importance of cell wall
target of penicillin
what is the gram -ve outer membrane layer composed of
lipopolysaccharide (LPS)
are fimbriae gram -ve or +ve
gram -ve
role of fimbriae
adherence and sex
steps involved in prokaryotic protein synthesis (3)
- gene (DNA) -> mRNA (DNA dependent RNA polymerase) = transcription
- mRNA -> ribosome (tRNA)
- ribosome (tRNA) -> protein (translation)
importance of prokaryotic protein syntheses
target for antibiotics
where does prokaryotic protein synthesis take place
cytoplasmic membrane
what food source is required for prokaryotic growth (4)
- C source (organic e.g. proteins/sugars, and inorganic e.g. fix CO2)
- oxygen and hydrogen
- N source (amino acid ammonia)
- inorganic salts (P, S, K, Mg, Ca, Fe)
what is the most important requirement for prokaryotic growth
oxygen
prokaryotic growth requirements
- nutrition (food)
- environment (temp., hydrogen ion conc/pH, osmotic protection, oxygen)
bacteria involved in dental caries and classification (2)
- cocci (streptococci)
- bacilli (lactobacilli)
- > both facultative anaerobes
- > GRAM POSITIVE
bacteria involved in periodontal diseases and classification
- bacilli (GNABS)
- > anaerobic
- > GRAM NEGATIVE
tb
bacteria in lungs
DNA evidence techniques involved in molecular analysis of bacteria (2)
- 16s RNA
- metagenomics
classification/taxonomy of the animalia kingdom:
- kingdom
- phylum
- class
- order
- family
- genus
- species
- kingdom = animalia
- phylum = chordata
- class = mammalia
- order =primates
- family = hominoidea
- genus = homo
- species = sapiens
classification/taxonomy of the bacteria kingdom:
- kingdom
- phylum
- class
- order
- family
- genus
- species
- kingdom = bacteria
- phylum = firmicutes
- class = bacilli
- order = bacillales
- family = bacillaceae
- genus = bacillus
- species = subtilis
important ways of classifying bacteria (3)
- shape (coccus, bacillus, etc)
- cell wall (grams stain)
- metabolism (growth in oxygen- aerobic, anaerobic, facultative)
why is classifying bacteria and identifying the organism involved in infection so important
it is the first step in treatment
bacteria shapes (3)
- cocci (spheres)
- bacilli (rods)
- spiral shaped
eg. of rigid spiral bacterium
spirillum
eg. of flexible spiral bacterium
spirochaete
difference in gram -ve and gram +ve cell wall
gram -ve:
- > cytoplasmic membrane
- > peptidoglycan
- > outer membrane
- > lipopolysaccharide
gram +ve:
- > cytoplasmic membrane
- > peptidoglycan
- > teichoic acid
aerobic bacteria definition
grow in oxygen
obligate aerobe bacteria definition
require oxygen
obligate anaerobe bacteria definition
killed by oxygen
facultative anaerobic bacteria definition
tolerate oxygen
how do most bacteria divide during the bacterial cell cycle
binary fission (into 2 identical daughter cells)
bacterial chromosome of most prokaryotes
single circular chromosome
chromosome replication steps (3)
- initiation site = the origin oriC
- two replication forks proceed bidirectionally
- termination = in a 100Kb region opposite the origin
steps involved in prokaryotic cell cycle eg. escherichia/E. coli (2)
- C period (40 minutes) = period of initiation of chromosome replication to completion of replication
- D period (20 minutes) = division
what determines the rate of E.coli growth
no. of chromosome replication origin sites
division of 35 minute bacterial cell cycle (2)
- 15 minutes for replication/C period
- 20 minutes for D period
what regulates chromosome replication
availability of DnaA protein (DnaA-ATP binds to DnaA boxes within origin)
central event of bacterial cell division
assembly of FtsZ ring
what controls bacterial cell division
regulation of FtsZ
key proteins involved in bacterial cell division (2)
- FtsZ
- PBP3 (penicillin binding protein, encoded by ftsI)
role of penicillin binding protein
target of penicillin (cross links peptide side chains/transpeptidation)
summary of prokaryotic (bacterial) cell cycle (4)
- chromosome replication
- chromosome segregation
- elongation
- cell division
virus definition
obligate intracellular parasite
components of virus structure
- nucleic acid genome
- protein capsid, protecting/delivering genome
- sometimes a lipid envelope consisting of lipid bilayer and containing viral proteins
why are viruses unique
other organisms divide, viruses assemble from components
steps involved in virus replication cycle (5)
- attachment (attachment proteins on surface of virus particle bind to receptors on host cell surface)
- entry (via 2 mechanisms = direct fusion or endocytosis)
- gene expression (transcription of genome into virus mRNA, translation into virus proteins and modification into mature proteins) and genome replication once inside host cell
- assembly of proteins and genomes into virus particles
- release from host cell (via cell lysis for non enveloped viruses, and via budding for enveloped viruses)
what is a bacteriophage and what is lysogeny
- a virus which parasitizes a bacterium by infecting it and reproducing inside it
- > an obligate intracellular parasite/virus that multiplies inside bacteria
- > lysogeny is a way of a virus entering its host cell, incorporating its DNA into its host chromosome, so that it replicates, then synthesising viral proteins in order for cell lysis and large numbers of viruses to be released
how do viruses enter the host (4)
- resp tract by inhalation/touch
- GI tract by ingestion/inhalation
- urogenitary tract by sexual transmission
- blood via blood products, needles, mother-child spread, insect bites
mechanisms of spread of viruses within host (2)
- neural spread
- hematogenous spread/ in the blood
mechanisms by which viruses cause damage (2)
- viral factors (cell lysis, cell-cell function, inhibition of host cell transcription/translation, alteration of host cell cycle)
- host factors (apoptosis/cell suicide, lysis of infected cells by immune cells, inflammation)
methods of controlling virus infection (2)
- vaccines
- antiviral drugs
explain the ‘germ theory’ of infection control
idea that microbes could cause disease
who was joseph lister
first person to keep his instruments clean from start to finish of an operation
routes of cross infection in dental surgery
- direct contact (patient, staff, droplets)
- indirect contact (contaminated instrument/surface, aerosols)
steps involved in cleaning of reusable dental appliances
- cleaning
- disinfection
- sterilization
definition of disinfection
process by which the number of microorganisms are reduced to a level that is considered safe
steps involved in disinfection of materials (4)
- cleaning (reduces bioburden)
- heat (63 degrees for 30 min or 72 degrees for 20 secs, boiling water for 10 mins, washing/rinsing at 70-90degrees)
- ultrasound
- chemicals (disinfectants for inanimate objects and antiseptics for living tissue)
definition of sterilisation
the process by which ALL microorganisms are killed or removed to render the object incapable of causing infection
what are prions
bacterial spores resistant to sterilisation
methods of sterilisation (4)
- heat
- chemical
- radiation
- filtration
- > based on purpose, nature of material, nature of contamination and convenience/time
conditions within autoclave used for sterilisation
134 degrees for 3 mins
what is meant by standard infection control
the same standard cross-infection control measures must be applied to each patient (each patient poses a threat)
infection control procedures taken to prevent cross-infection within dental surgery (11)
- medical history
- instrument preparation
- instrument sterilisation
- disposable items (mouth rinse beakers, impression trays etc)
- decontaminating surfaces
- protective clothing (long sleeves, gloves, eye protection, mask)
- good practice (avoid sharps injuries etc)
- immunizing staff (hepB, tb, tetanus, poliomyelitis, rubella)
- aspiration and ventilation
- waste disposal
- training (effective, regular, written procedures)
occupational acquired infections
- blood borne viruses (HIV, HepB, HepC)
- other major sources (herpes, resp. viruses, mycobacterium tuberculosis)
when are health care workers allowed to carry out practice with infections (3)
- if HBsAg +ve (present in every infective individual) but not HBeAg +ve (present in highly infectious individuals), dentist/dental nurse can continue to work with appropriate procedures
- cannot undertake clinical practice if HBeAg +ve
- cannot undertake exposure prone procedures if HIV +ve
cleanliness champions
- programme put in order to help prevent healthcare acquired infections (HAI)
- modules include:
- > chain of infection
- > hand hygiene
- > personal protective equipment
- > waste disposal etc etc
how do bacteria develop in a baby with no teeth (3)
- maternal transmission
- acquisition and colonisation
- succession and diversity
bacteria present from mucosal surfaces of babies (gram positive and gram negative)
- s.oralis = majority 1-3 days then decreases as
- s.salivarius takes over
- > streptococci = gram +ve
- > GNABs (0-7 species present after a few months)
bacteria present after tooth eruption (12 months)
- S.mutans dominates (gram +ve)
- >greater diversity of GNABs around gingival margin
what happens to oral environment after patient loses teeth (edentulous)
- returns to toothless state
- bacteria become opportunist organisms which lie dormant until patients immune system is compromised and they attack
bacteria present in patient with dentures
- dentures = complex oral environment
- staphylococci, strep and actinomyces spp. (staphylococci has 100% isolation**)
factors affecting the space that bacteria occupy and for how long they occupy that area (spatial and temporal variation) (4)
- temp (35-36 degrees = favourable)
- redox potential (Eh)
- pH
- nutrients
effect of redox potential on bacteria growth in oral env.
- high Eh/aerobic env. inhibits growth of anaerobic bacteria and vice versa
- low Eh favours growth of anaerobes/spirochaetes which survive at base of periodontal pockets
pH of oral env. (3)
- normal salivary pH = 6.75-7.25
- > lowe in carious lesions (streptococci and lactobacilli cause dental caries, growth encouraged by lower pH as acidic)
- > pH less acidic in inflamed gingival crevices (promotes growth of GNABs)
what are endogenous nutrients
=provided by host
- most imp. for oral bacteria
- saliva (amino acids, peptides, proteins, vitamins, growth factors etc) and GCF (contains host defences and albumen,serum/plasma components/ haeme etc)
- > GCF =imp. for bacteria in ging. crevice and periodontal pocket
what are exogenous nutrients
- sugars in diet which promote growth/acid production
- > cause increase in S.mutans and lactobacillus
- > decrease in S.sanguinis
where does S.salivarius typically adhere to
the dorsum of tongue (not the teeth)
where does S.mutans and S.sanguinis typically adhere
tooth surfaces due to sticky polysaccharide coat
where does porphyromonas gingivalis typically adhere
not to teeth but attaches readily to bacteria of dental plaque
most common microbes on tongue (2)
- S.salivarius
- S.mitis
most common microbes in saliva (3)
- S.oralis
- S.mitis
- S.salivarius
most common microbes in oral gingivae (3)
- S.mitis
- S.sanguinis
- Actinomyces
most common microbes present on lips
mainly streptococci (eg. S.vestibularis)
most common microbes present on palate (2)
- relatively few
- mainly streptococci and actinomyces
most common bacteria colonising on teeth (3)
- S.sanguinis
- S.mitis
- actinomyces
most common microbes present on cheek surface
-S.mitis
gram +ve oral bacteria
streptococci spp. (facultative and obligate anaerobes)
- > facultative = tolerate oxygen
- > obligate = killed by oxygen
gram +ve oral bacteria present on tooth surface/fissures
Strep.mutans (mutans group)
gram +ve oral bacteria present on tooth biofilm/plaque
Strep.sanguinis (oralis group)
bacteria causing tooth decay/dental caries
S.mutans (acidogenic and aciduric)
-after streptococci, lactobacilli are most important group of bacteria involved (gram +ve, acidogenic and acidic)
definition of acidogenic
produce acid at a higher rate from sugar
definition of acidic
tolerate high concentrations of acid
bacteria causing bacterial endocarditis
- Strep. sanguinis (oralis group), enter blood after oral trauma
- may interfere with colonisation by S.mutans
location of actinomyces
- supra and sub gingival plaque
- >historically associated with root surface caries
location of gingival crevice
groove between tooth and gum
what is gingivitis
gingival inflammation caused by accumulation of plaque bacteria on surface of teeth
what causes formation of periodontal pocket
in periodontal disease where the whole support tissue around the tooth becomes inflamed (periodontitis) when dental plaque bacteria grow between the tooth and the gum
bacteria present in healthy gingival crevice
mostly gram +ve cocci
periodontal pocket environment
- more anaerobic conditions
- nutrients come from GCF rather than food and saliva
GNABS present in periodontal pocket/red complex
- the 3 bacteria that are frequently found together when disease occurs and classified as the red complex:
- > tannerella forsythia (GNAB)
- > porphyromonas gingival (GNAB)
- > treponema denticola (spirochaete)
bacteria involved in caries and endocarditis
gram positive
groups of streptococcus and eg’s
- mutans (S.mutans)
- oralis (S.sanguinis)
- salivarius
- anginosus
biofilm definition
=microbial communities attached to a surface
->typical qualities = 3D structure, enclosed in ECM, increases habitat range of indiv. bacteria
what is the acquired pelicle
- layer of material acquired by a cleaned tooth
- >mucins, salivary glycoproteins, minerals and immunoglobins
how can acquired pelicle be removed
by vigorous brushing with abrasive dentrifice
how does dental plaque develop
- ordered accumulation of bacteria
- adhesion/attachment
- bacteria do not attach/adhere directly to the enamel they attach to the pellicle
- > attachment to extracellular polymers (extracellular polysaccharides and sucrose)
- > adhesins recognise ligands/receptors on tooth surf. (associated with fimbriae)
- > lectins recognise carb. groups and bind them (associated with fimbriae)
- > fimbriae are involved in adhesion to enamel/pellicle and to other bacteria
- colonisation and biofilm formation
what changes in environment occur when bacteria adheres to the pellicle
- aerobic -> anaerobic
- pH, nutrients, ions, metabolic products
- new attachment sites, co-aggregation
bacteria present in plaque development (within 2 hours, after 24hours and within first week)
- within 2 hours = gram +ve and -ve cocci (gram +ve = S.oralis group, gram -ve = neisseria, haemophilus)
- > biofilm develops
- after 24 hours streptococci predominate (S.sanguinis = most common)
- increased diversity of gram +ve bacteria within first week (Eh is reduced and anaerobes survive and multiply -> actinomyces increase, streptococci decrease)
succession of bacteria present during plaque development (3)
1-streptococcus attach to acquired pellicle
2-streps are joined/replaced (actinomyces)
3-gram -ve species develop (eg.fusobacterium)
location of supra gingival plaque (3)
- smooth tooth surfaces
- interproximal surfaces
- pits and fissures
arrangement of supra gingival plaque organisms
- highly organised
- filaments at right angles to tooth
- streptococci at right angle to enamel
- coagreggation complexes (corn cobs of S.sanguinis attached to corynebacterium and test tube brushes of gram -ve bacilli attached to filamentous bacterium)
supragingival plaque conditions
- influenced by saliva and diet
- conditions are aerobic and variable
subgingival plaque conditions
- influenced by gingival fluid
- conditions are aerobic and constant
subgingival plaque bacteria
- GNABs
- spirochaetes
calculus/tartar
-calcium and phosphate ions (crystals form and coalesce)
how do viruses proliferate/multiply
virus directs synthesis of viral protein to the cells nucleus and uses the cells machinery
2 features of gingival crevice/periodontal pocket that can affect development of dental plaque
- deeper sulcus (more anaerobic)
- inflammatory exudate (rich in nutrients) -> nutrients come from gingival tissues rather than food and saliva
key differences in gram +ve and gram -ve bacteria
- gram +ve:
- > no outer cell membrane
- > retains cell staining
- > (cause dental caries)
- gram -ve:
- > has outer cell membrane
- > doesn’t retain cell staining
- > (cause periodontal disease)
definition of plaque
general term for microbial community found on the tooth surface
