Microbiology for dentists theme 3 Flashcards
What is a bacteriostatic mode of action ?
holds bacterial cells in steady state of growth- stopped from increasing further
total number of cells stays in a straight line
What is a bacteriocidal mode of action ?
rupture and burst cell wall so bacteria degrade
host immunity recognises this and removes it
total number of cells doesnt chage but virulent decreases
What is a bacteriolyitc mode of action ?
agent allows the body to recognise the invading organism- removes cells and total cells drop
Which antibiotic class targets cell wall ?
penicillin
Which antibiotic class targets protein synthesis ?
macrolides and tetracycline
Which antibiotic targets DNA synthesis >
fluoroquolines
Which antibiotic targets folate metabolism ?
sulphonamides
What is the structure of penicillins ?
beta lactam ring
heteroatomic ring with 3C and 1N
lactam is cyclic amide
What is benzylpenicillin ?
penicillin with benzene ring
What are the characteristics of benzylpenicillin ?
not very active against gram negatives
easily altered in the stomach- acid - changes the chemical structure
doesnt get to GI tract either
What does benzylpenicllin work against ?
narrow spectrum
works mainly against gram positives and a few gram negatives
What is amoxicillin ?
penicillin was altered to include an amino group
facilitates penetration of the outer membrane of gram negative
broad spectrum and more absorbed
What are beta lactamse resistant antibiotics ?
some forms of penicllin are resistant against beta lactamase
What is beta lactamase ?
bacteria produce beta lactamase
destroys Beta lactam ring of penicllin
some penicillins are resistant against
What is extended spectrum penicllin ?
effective against pseudomonas species
What are reverse spectrum penicillins ?
greater activity against gram negatives
than gram positives
What does transpeptidase do ?
catalyses formation of cell wall
cross links in peptidoglycan- pentaglycines
bacterial cell wall looses rigidity
cells swell and rupture
What do beta lactam antibiotics do to transpeptidase ?
they inhibit transpeptidase
What is the gram positive cell envelope like ?
thick peptidoglycan cell wall and cytoplasmic membrane
What is the gram negative cell envelope like ?
cytoplasmic membrane
periplasm
outer membrane
What is a peptidoglycan monomer made of ?
N-acetylmuranic acid
N-acetlyglucosamine
side chain of 4 amino acids
How do side chains of amino acids join together in peptidoglycan ?
via pentaglycines
cross links between amino acid side chains
glyceine with lysine
What is penicillin absorption like ?
vary when given orally
delayed release preparations can be given
What is penicillin distribution like ?
widely distributed
doesnt enter CSF- not good for meningitis
What is penicllin metabolism like ?
short half lives- need many doses
What is penicillin excretion like ?
90% kidney tubualr secretion
clearance reduced in neonates
What are adverse reactions to penicillin ?
rashes
fever
altered gut flora
blood clotting
What do sulphonamides target ?
folate metabolism and hence DNA synthesis
What is the folate pathway ?
pABA Folate tetrahydrofolate synthesis of thymidylate DNA
Which enzymes work on the folate pathway ?
dihydroptrtoate synthetase from pABA to folate
dihydrofolate reductase from folate to tetrahydrofolate
Where do sulphonamides work ?
at dihydropteroate synthetase
What do fluoroquinolones target ?
broad spectrum- affecting gram positive and negative bacteria
targrt DNA replication - type II topoisomerases
What is DNA gyrase ?
regulates amount of torsional stress in DNA
facilitates movement of transcription and replication mechanisms through DNA helix
How is DNA gyrase targeted ?
quinolones inhibit in gram negatives
What does DNA topoisomerase IV do ?
homologue of gyrase
separates topologically linked daughter chromosomes
during terminal stage of DNA replication
How is DNA topoisomerase IV targeted ?
quinolones inhibit DNA topoisomerase IV in gram positives
What is the mechanism of action of sulphonamides?
act as false substrates - like P-aminobenzen will act on enzyme that makes folate- stop pABA binding
mimic pABA
inhibit production at dihydropteroate synthetase
Why are sulphonamides selective ?
human cells take up b9 and produce folic acid internally
bacterial cells cant take up folate so must make internally which is where sulphonamides act to stop cellular folate production
What is sulphonamide absorption like ?
80% of drug id given orally and absorbed from the stomach
What is sulphonamide distribution like ?
widely distributed including CNS
What is sulphonamide excretion like ?
in urine
What are some adverse reactions to sulphonamides ?
photosensitivity
stevens johnson syndrome
haemopoietic disturbances
What is the most effective administration of fluoroquinolones ?
oral
What is quinolone distribution like ?
well absorbed by GI tract
What is quinolone metabolism like ?
potent inhibitor of CYP1A2
taking quinolones will effect drugs that are metabolised by the same enzyme
What are adverse reactions to quinolones ?
hypersensitivity and GIT disturbance
What are macrolides ?
target bacterial ribsomes and protein synthesis
What size are eukaroyitc ribsomes ?
80S
What size are prokaryotic ribosomes ?
70S
What are the subunits in 70S ribsomes ?
50s and 30s
Where is the main site of protein synthesis in prokaryotes ?
50s sub unit of the 70s ribosome
Which part of protein synthesis do macrolides target ?
translocation part
What is translocation ?
forming the new peptide bond
ribsome will move along to form new peptide bonds
What do macrolides do ?
bind to site near RNA exit tunnel and cause peptidyl transferase to drop off
What does oral administration of macrolides require?
protected tablets to avoid inactivation by gastric juice
What is macrolide distribution like ?
diffuses to most tissues bit not BBB
crosses placenta
How are macrolides metabolised ?
by demethylation via the CYP3A4 drug
potentiate effects of other drugs
How are macrolides excreted ?
in the bile
What are adverse reactions to macrolides ?
GIT disturbances
auditory imapirment
cholestatic hepatits after erythromycin estolate
What are tetracyclines ?
target bacterial ribsomes
and protein synthesis
What do tetracyclines do ?
interrupt elongation phase
stop tRNA binding to ribosome
What is tetracycline absorption like ?
greater in fasting state
absorption inhibited by digestion of dairy products
What is tetracycline distribution like ?
distributed widely
What is tetracycline metabolism like ?
excreted via bile and kidneys by glomerular filtration
What is tetracycline excretion like ?
long half live
What is antibiotic resistance ?
ability of a microbe to resist effects of medication that could have previously been used to eradicate the microbe
How does antibiotic resistance occur ?
- population of bacterial cells that show variation- some are more resistant than others
- antibiotics used will kill bacteria but resistant strains will remain - antibiotics select for resistant strains
- Resistant bacteria multiply and resistance spreads
What is intrinsic resistance ?
innate property of bacteria seen in all strains
Why are gram negatives more resistant to B lactams ?
cell envelope is different
Why are gram positives resistant to vancomycin ?
too large to cross cell membranes
What is acquired resistance ?
drug resistance is selected for by antibiotics
use of drug leads to genes encoding resistance
What is cross resistance ?
resistance to 1 antibiotic leads to resistance to another
antibiotics often in the same class
What is multi resistance ?
resistance to several via independent mechanims
What were the FAA plates with vancomycin and neomycin selecting for ?
fusobacterium - it is resistant to vancomycin and neomycin
Why is fusobacterium resistant to vancomycin and neomycin ?
intrinsically resistant
Why is fusobacterium resistant to vancomycin ?
vancomycin is a large glycopeptide
cant cross gram negative membrane
Why is fusobacterium resistant to neomycin ?
an aminoglycoside
targets ribosomes
requires an electron transport chain to be taken up
anaerobic bacteria like aminoglycosdies dont have an electron transport chain- cant take up neomycin
What is VISA ?
vancomycin insensitive S aureus
What is CA MRSA ?
community acquired MRSA
How does acquired resistance spread ?
through genetic transfer
What is vertical gene transfer ?
between generations in binary fission
resistant strains passed on to next generation
What is horizontal gene transfer ?
between cells
one strain gets resistance and passes on to others via transformation, transduction and conjugation
How does acquired resistance start ?
through mutations
What does a chromosomal mutation do ?
results in genetically altered population
DNA is altered and provides an evolutionary advantage
What is transformation ?
DNA taken up into bacterial cell from the environmrtn
free DNA from lysis - released into environment (ECM)
genetically similar bacteria take up DNA
What is transduction ?
DNA transmitted via bacteriophages
DNA picked up by virus and transferred to another cell
What is conjugation ?
between a donor cell with a conjunctive plasmid and a recipient without
via a pilus - only donor has a pilus
What are the 3 mechanisms of antibiotic resistance ?
1- modification of the antibiotic to inactivate it
2- Modification of the target so the antibiotic doesnt work
3- Sequester the antibtiotic from the target to prevent it reaching the target
How were gram negative bacteria intrinsically resistant to early penicillin ?
penicllin not permeable through membrane
efflux pumps- sequester
Beta lactamases encoded which break beta lactam ring
How did acquired resistance come about in S. Aureues ?
plasmid boune beta lactamases- modify antibiotic
modification of the mecA gene- encodes for pencillin binding protein- reduced binding to beta lactams
What are beta lactamases ?
they are modified pencillin binding proteins
bind to beta lactam ring
and hydrolyse it
How can some beta lactamases be inhibited ?
by clavulanic acid
augmetnin- amoxicillin and clavulanic acid
What are carbopneomes ?
potent beta lactams
What is NDM1 ?
new delhi metallo beta lactamase
break down carbaponemes
gene that encodes it is present on a plasmid which can be transferred between bacteria like E.coli in dental tourism
How can there be a reduced concentration of antibiotic in the periplasm or cytoplasma ?
reduced import due to outer mebrane
increased export via efflux pumps
Why can their be increased export of a drug ?
antibiotic specific drugs
multidrug efflux pumps
What are oral biofilm antibiotic resistance mechanisms ?
antibiotic reaction with ECM- modifes antibiotic
slow growth rate in plaque
exclusion of drug by matrix
up regulation of efflux pumps
What are the 3 mechanisms of biofilm resistance ?
slow penetration
resistant phenotype
altered microenvironment
What does slow penetration mean ?
antibiotic cant penetrate surface layers
antibiotic deactivated by beta lactamase on membranes
What are persisters ?
some bacteria differentiate into protected phenotype
these are persisters
How can altered microenvironment lead to resistance ?
microscale gradient of nutrietns and waste can antagonise antibiotics
What are some factors that have lead to spread of antibiotic resistance ?
excessive and prolonged use in chronic illnesses
over counter availability
animal feeds
medical tourism
What are the most common antibiotics used ?
penicillins
tetracyclines
macrolides
Why do dentists over prescribe antibiotics ?
time pressure lack of up to date knowledge miscocneption demand poor training patient pressure
What are common errors in prescrbing antibiotics ?
unecessary use
inappropriate dose
incorrect length of treatment
failure to check MH
How can we treat bacterial dental infections ?
local measures - before anything else drain pus tooth extraction access and drain root canals debride perio pockets
What is the carriage of Staphylococcus aureus ?
30 %
anterior nares, throat and groin
Where does each CFU originate from ?
from 1 cell
Why is the number of CFU not the same as the number of cells ?
dead cells in CFU
each cell divides
What type of antibiotic is methicillin ?
broad spectrum
How did MRSA become resistant ?
acquird the mecA gene that encodes the PBP2a
What does PB2A do ?
allows transpeptidase activity in the presence of methicillin
Why are gram negative bacteiria resistant to vancomycin ?
intrinsic resistance through LPS
vancomycin is a large molecule
What is amoxicillin ?
moderate spectrum
effective against gram positve
limited effectiveness agaisnt gram negative
What is metronidazole ?
active against gram positive and gram negative
What is clavulanic acid ?
binds to beta lactamase enzyme that makes bacteria resistant - stops it hydrolysing the beta lactam
mixed with amoxicillin to make augmentin
How do you work out the MIC and the MBC ?
broth culture of bacteria
make dilutions of antibiotics
add bacteria
incubate overnight
What is the MIC ?
minimum inhibitory concentration
min conc needed to inhibit growth of bacteria
What is MBC ?
minimum bacteriocidal concentration
concentration needed to kill bacteria
difficult to distinguish between killing and inhibiting
What are MIC and MBC useful for ?
drug efficacy
resistance
What is the zone of inhibition ?
diameter relates to the sensitivity of the bacteria to the antibiotic
What are bacteria in the ZOI known as ?
breakout colonies
they have resistance to the antibiotic
What makes staph aureus produce golden colonies ?
has a pigment called staphloxanthin
protects cells from oxidate stress
How can we distinguish between staph aureus and epidermidis ?
epidermidis makes white colonies
aureus has postive catalase and DNase test
In what form does fluoride enter cells ?
HF - uncharged so passes membrane
How is vancomycin absorbed and why is this significant in treamtent of clostridium dificile ?
vancomycin is poorly absorbed in the gut - keeps the drug at site of infection of the enteric bacterium
How does fluoride prevent caries ?
reduces demineralisation
promotes remineralisation
inhibit cariogenic bacteria
What is the mineral component of dentine and enamel ?
impure calcium hydroxyapatitte
biological apatite
How does fluoride make enamel less soluble ?
fluoride replaces the hydroxyl groups in the centre of the crystals making it less soluble
also fills gaps left by hydroxyl groups
What is the structure of the unit cell ?
calcium forms columns
and makes calcium triangles stabilised by phosphate
OH ions are very large and polar so are displaced
dispalced are exposed and can be exchanged
Replacing the hydroxide ions in enamel with fluoride ions creates what ?
calcium fluorapatite
Where does fluoride incorporate in the tooth ?
in the outer layers
pits and fissures
fluoride distribution is uneven
Why do pits and fissures hold more fluoride ?
pits and fissures have more plaque so theplaque is able to hold the fluoride close to the tooth
these areas have more dissolution leaving only fluorapatite which remineralises
What happens with age to the fluoride distribution in teeth ?
fluoride in different areas of the tooth changes
What is the process of enamel remienralisation ?
apatite dissolves in acidified plaque liquid raising the local concentration of Ca P and F
CFA forms
CFA has a lower solubility
What are the practical applications of fluoride ?
fluoride toothpastes increase local F
Acidulated phosphate fluoride - makes acidic conditions where HFA will remineralise - more stable
When is fluoride uptake by bacteira the highest ?
in acidic pH -pKa is 3.45
How does fluoride enter bacteria ?
as HF which is small and uncharged
pass through membranes
What happens to the pH of plaque fluid in a cariogenic challenge
pH lowered
What happens when HF is taken up by bacteria ?
bacterial cytoplasm is neutral so it favours the dissociation of HF- release fluoride ions
What does fluoride to do S mutans ?
inhibits growth and acidogenicity
What effect does fluoride have on enzymes ?
fluoride binds to specifc sites on enzymes and inhibits them
Give some examples of enzymes that fluoride inhibits ?
urease arginase dehydrolase enolase F ATPasse Pyruvate kinase catalase
What is the role of enolase ?
bacterial glycolysis
glucose uptake
What is the role of F ATPase ?
removes H from the cell
What is the role of pyruvate kinase ?
glycolysis
What does inhibting catalase do ?
limits the ability of the organism to deal with the oxidate stress from Hydrogen peroxide
What does fluoride do with metals ?
fluoride ions bind to metals to make complexes
complexes bind to enzymes to stimulate/inhibit them
enzymes require metal co factros but they have now been removed
How does fluoride act as a transmemebrane proton carrier ?
reduced uptake of key nutrients and export of macromolecules
Is fluoride resistance seen ?
not clinically
in some strains in labs
When is fluorie binding to enzymes enhanced ?
in acidification
What is the effect of inhibiting F ATPase ?
protons arent removed from the cell
reduced acudurcity
What are some characteristics of fluoride resistant species ?
higher F ATPase activity
stronger enolase activity and higher glucose uptake
fluoride exporters
What are standard infection control procedures in dentistry ?
hand hygeine PPE sharps safety sterilisation and disinfection waste management screening and vaccines
What are examples of infectious agents ?
blood bourne virus - HIV and HepB
respiratory virus - infleuenza and cold
bacteria- mycobacterium TB, MRSA, Legionella
prions
Which types of species have a greater resistance to destruction ?
prions
spores
mycobacterium
Which species have a low resistance to destruction ?
enveloped virus (HepB) gram positive bacteria - strep, staph and enterococcus
What are the 3 types of transmission ?
nosocomial- hospital- MRA
iatrogenic- due to physician/therapy- chemotherapy
idiopathic- unknown cause
What does transmission require ?
source of infection - person, contaminated instrument
vehicle - blood,saliva
route -
What are the sources of infection ?
overtly infected people
people incubating a disease- prodromal stage - like measles
health carriers- convalescent carriers are reservoirs of infection or asymptomatic carriers
environmental microorganisms- legionella
normal commensal flora- staph aureus and epidermidis
Who are more prone to infections ?
immunocompromised patients
What are the vehicles of transmission ?
blood- HIV and hepB
saliva- epstein barr - also if blood is in saliva
direct skin contact- stpah
objects- crubs and instrumenrs
What are the routes of transmission ?
in utero inhalation ingestion injection implantation inunction
What is in utero transmission ?
placenta is a barrier for most microbes except cytomegalovirus and rubella
What is inhalation ?
aerosol droplets
inhale strep pyogenes and TB
What is ingestion ?
food drink become infected
instruments in mouth can introduce
strep pyogenes and TB
What is implantation ?
trauma to mucosa can implant microorganisms into tissues
stap epidermidis and aureus
What is inunction ?
microbes driven into tissue by open wounds and rubbing
What is injection ?
biting - plasmodoum-malaria
needle stick
Which pathogens cane be inhaled ?
pneumonic plague- yersinia pestis TB- can be resistant to antibiotics infleunza- coughing legionnaires disease- SARS
Where can you find legionnella penumophilia ?
A/C
dental water lines
water lines
How can we keep surface clean ?
disinfection of surfaces
single use instruments
What is sterilisation ?
killing/removal of viable microorganisms
What is disinfection ?
reduction in viable microorganisms to a point where infection risk is acceptable
What is the formula for efficiency ?
N=k/CT N= number of microoganims K- constant C- cocnetration T- time applied
What does K depend on ?
species
physiological state
organic material- clean before disinfection
What is accepted as sterile ?
less than 1x106 chance of a single microorganism being present
What are methods for disinfection ?
boiling water - kills bacteria not spores
pasteurisation- heat to 66/71- kills TB but not heat resistant
chemical- glutaraldehyde, chlorine , alcohol, chlorhexidine
What does the functionality of chemical disinfectants rely on ?
concentration
temperature
pH
chemicals can be toxic and corrode instruments
What are the methods of sterilisation ?
dry heat-oven moist heat- autoclave radiation-cobalt 60- for single use gases0 s02 filtration
What is the process of autoclaving ?
high pressure saturated steam
121 for 15 minutes
How do we safeguared agaisnt prion disease ?
endodontic files are single use
Do prions have a nucleic acid ?
no
What is risk ?
the probability an individual will develop a disease in a particular time period
usually expressed as a percentage
What is risk factor ?
increases the likelihood that an individual will develop a disease
can be modified or immutable
can be part of the causal pathway
What is a risk determinant ?
risk factor that cant be modified
What is a risk marker ?
associated with the disease but not in the causal pathway
What are host risk factors for periodontitis ?
age genetics host response illness local plaque retentive factors occlusion
What are environmental risk factors for periodontitis ?
smoking poor OH nutrition drugs- can impact on saliva dental attendance
What are bacterial risk factors for periodontitis ?
plaque composition- red complex bacteria
plaque amount
What are social risk factors for periodontitis ?
socio economic status
income
attitude
education
What is the odds ratio ?
represents the odds that an outcome will occur given a particular exposure compared with the odds of not having the exposure
What does it mean if the OR=1 ?
exposure doesnt affect outcome
What does it mean if OR>1 ?
exposure associated with higher odds of outcome
What does it mean if OR<1 ?
exposure associated with lower odds of outcome
What is the odds ratio used for ?
comparing if an exposure is a risk factor
comparing the magnitude of risk
How can you test the significance of the odds ratio ?
p value
What is the advantage of assessing the risk at population level ?
targeted at risk populations
What is the advantage of assessing risk at an individual level ?
treatment and preventitive strategies specific to the individual
How can we assess individual risk ?
patient history
clinical examination
biological assay
What is the validity of a test ?
test measures what it is intended to measure
What is the reliability of a test ?
test is consistent when used at different time
What is the quantifiability of a test ?
can be analysed statistically
What is the sensitivity of a test ?
true positive rate
ability of a test to pick up all individuals who have the disease
What is the specificity of a test ?
true negative rate
proportion of people who have false negatives
Which periodontal markers can be assessed ?
pathogenic bacteria host response factors tissue breakdown factors host enzymes inflammatory mediators
What does the BANA test measure ?
proteolytic enzyme activity due to
p.gingivalis
T.Forsytha
T.denticola
Give some antimicrobials used in the UK ?
iodine
chlorhexidine
SLS
triclosan
What are the characteristics of chlorhexidine ?
cationic- attracted to the negative charge of phospholipids in cell wall
has a high substantivity
What are the benefits of Chlorhexidine ?
plaque growth almost inhibited
gingivitis inhibited
What are the problems of chlorhexidine ?
tooth staining
allergy can be severe
What are the characteristics of tirclosan ?
lower substantivity than chlorhexidine
lipid soluble - penetrate skin and mucosa
reduces inflammation
How does triclosan act as a broad spectrum antimicrobial ?
targets lipid synthesis - enoyl reductase
inhibits glycolysis - pyruvate kinase and lactate dehydrogenase
inhibits Proton ATPase- cellular pH falls
