lectures 8-13 Flashcards
define what is meant by an antiseptic
a product that destroys or inhibits growth of microorganisms in or on living tissues
define what is meant by sterilisation
a physical or chemical process that completely destroys or removes all microbial life including spores
define what is meant by an antibiotic
a low molecular substance often produced by a microorganisms that at a low concentration inhibits or kills other bacteria
define what is meant by an antimicrobial
any substance of natural, semi-synthetic, or synthetic origin that kills or inhibits the growth of microorganisms but causes little or no damage to the host
what are some sources of antimicrobials?
- plants
- metal based
- nanotechnology based
- animal
- microbe
what plant derivatives are used in the modern day?
- alkaloids
- aldehydes
- alcohols
- terpenes
- steroids
- tannins
- phenotic compounds
how can essential oils be encapsulated for use?
- polymer-based nanocarriers
- lipid based nanocarriers
- molecular complexes
what is curcumin used for?
- anti-tumour
- anti-inflammatory
- antimicrobial
what metal ions are used as antimicrobials?
- copper
- silver
- gold
- platinum
- palladium
- zinc
what animal based compounds can be used as antimicrobials?
- escapin from sea hares
- snake venom (C-amino acid oxidase)
- chitosan from crustacean shells
what is biofilm?
an assembly of microbial cells associated with a surface and enclosed in an extracellular matrix
what is biofilm primarily made up of?
polysaccharides
what are the principle functions of biofilm?
- provides stability
- contains pores and channels
- fills spaces between cells
- contains localised gradients
- contains synergistic micro-consortia
Is antibiotic resistance in Gram negative bacteria intrinsic or acquired?
intrinsic and acquired
how are Gram negative bacteria intrinsically resistant to antibiotics?
they have a double membrane structure that makes up a cellular envelope
alterations can occur to envelope structure (such as porin loss) which reduces permeability to antibiotics
are porin and efflux pump alterations specific or non-specific antibiotic resistance mechanisms?
they are non specific
how do porins and efflux pumps confer antibiotic resistance to a bacterium?
- porins can be lost or reduced in number via mutation
- efflux pumps can mutate so they efflux antibiotics at a high rate
what are the 2 main classes of antibiotic action?
- cell wall synthesis inhibition
- nucleic acid synthesis and protein synthesis inhibition
what antibiotics use cell wall synthesis inhibition and how is it carried out?
- beta lactam antibiotics utilise this
- binding to DD-transpeptidases inhibits crosslinking of the cell wall
what 4 methods can lead to the resistance of beta lactam antibiotics?
- mutation of PBP, lowering its affinity for penicillin
- downregulation of porins
- acquisition of beta-lactamase
- up-regulation of efflux pumps
which antibiotics inhibit nucleic acid synthesis and how do they do this?
- quinolone antibiotics do it
- they bind to topoisomerases and convert them to enzymes that fragment the bacterial chromosomes
how do some bacteria confer resistance to quinolones?
1 - mutations in gyrase and topo IV weaken quinolone action
2 - plasmid-encoded Qnr proteins decrease topoisomerase-DNA binding
3 - a plasmid-encoded enzyme acetylates ciprofloxacin, decreasing effectiveness
4 - plasmid-encoded efflux pumps decrease quinolone concentrations in the cell
how do antibiotics inhibit protein synthesis?
- chloramphenicol binds to the 50S ribosomal subunits and inhibits the formation of peptide bonds
- tetracycline binds to the 30S subunit and interferes with the binding of tRNA to the ribosomal complex
- aminoglycosides bind to the 30S subunits and cause codon misreading
how do some bacteria confer resistance to aminoglycosides?
- aminoglycosides can be modified by acetyltransferases
- methylation of the 16s tRNA by ribosomal methyltransferase prevent aminoglycosides from binding to this target
what is a nosocomial infection?
an infection developing in a patient as a result of healthcare contact, and had no signs of infection within the first 48hrs of admission
what is a non-nosocomial infection?
an infection acquired outside the healthcare setting
- when in hospitals this includes those diagnosed within 48hrs of admission
what are the 5 main types of nosocomial infection?
- central line associated bloodstream infections
- catheter associated UTIs
- nosocomial pneumonia
- surgical site infection
- gastrointestinal infections
what are the risk factors for nosocomial infection regarding the environment?
poor hygienic conditions and inadequate waste disposal from healthcare settings
what are the risk factors for nosocomial infection regarding susceptibility?
- immunosuppression
- underlying health problems
- age
- use of medical devices
- drug treatment
- pain management
- length of stay
what are the risk factors for nosocomial infection regarding unawareness?
- improper use of injection techniques
- poor knowledge of infection control
- inappropriate use of invasive devices
- lack of control points
describe the features of the Clostridium difficile bacteria
- Gram positive
- toxin producing
- anaerobic bacillus
what does Clostridium difficile cause?
responsible for a variety of GI manifestations ranging from asymptomatic damage to mild diarrhoea, and rarely bowel perforations and death
how is C. diff transmitted?
faeco-oral
what are the risk factors for C. diff transmission?
- antibiotics
- co-morbidities
- gastric acid suppressants
what are the features of Klebsiella spp.
Gram negative
rod shaped
facultative anaerobe
what is Klebsiella spp. resistant to?
carbapenem last line antibiotics
does Klebsiella spp. have a high or low mortality rate?
high
what are the symptoms of Klebsiella spp.?
- high fever
- pleuritic chest pain
what is the therapy used to treat Klebsiella spp.?
antibiotics
what are the features of Streptococcus pneumoniae bacteria?
- Gram positive
- facultative anaerobe
- haemolytic
- more than 90 different strains
what are the causes of Streptococcus pneumoniae infection in non invasive and invasive infections?
non-invasive: bronchitis, otis media, sinusitis
invasive: bacteraemia, septicaemia, meningitis, pneumonia
what control is used to limit the spread of Streptococcus pneumoniae?
- there are 3 licensed vaccines
- masks, distancing, isolation
what is a superbug?
any strain of bacteria that has become resistant to the antibiotics that are used to treat it
what are some anthropogenic drivers of antibiotic resistance?>
- farming practises
- horticultural practises - spraying crops with tetracycline
- veterinary practises
- healthcare practises
what classes can bacteria be typed by?
- Gram stain
- biochemical typing
- antibiotyping
- phage-typing
- serotyping
describe the features of Pseudomonas aeruginosa
- Gram negative rods
- found in water samples
what does Pseudomonas aeruginosa cause?
- pneumonia
- septic shock
- UTIs
- GI infections
what does RFLP stand for?
restriction fragment length polymorphism
how is RFLP carried out?
1 - A DNA sample is prepared
2 - the DNA is digested with one or more restriction enzymes that recognise and cut DNA at specific sites
3 - a loading buffer with a blue dye is added and the samples are applied to the gel
4 - a current is applied, and the DNA fragments are separated on the basis of size
why is RFLP carried out?
to detect differences in homologous DNA sequences
what is pulsed field gel electrophoresis?
- a variation of gel electrophoresis in which a voltage is periodically switched among 3 directions equally
- this results in a net forwards migration of the DNA
what is the drawback of using pulsed field gel electrophoresis?
it is very hard to reproduce
what does MLST stand for?
multilocus sequence typing
what is MLST used for?
used for the typing of multiple gene loci
how is MLST carried out
- relatively small fragments are amplified using specific PCR primers
- for each gene, the different sequences present within a bacterial species are assigned as distinct alleles, and for each isolate the alleles at each loci define the allelic profile or sequence type
how can bacteria resist the action of carbapenem?
1 - downregulate porins
2 - reduce porin number
3 - acquisition of carbapenemases
4 - up-regulation of efflux pumps
how can streptococcus and staphylococcus be differentiated?
1 - by growth habits
2 - by a catalase assay - staphylococcus contains catalase, streptococcus does not
when was the first recorded case of MRSA
1961
how have cases of MRSA been reduced in europe?
- improved hospital screening
- better infection control
- better barrier precautions
- increasing knowledge of environmental reservoirs
- introduction of the antibiotic vancomycin
what are the 4 main types of MRSA reservoirs?
- healthcare associated
- livestock associated
- community associated
- fomite associated
why is MRSA difficult to eradicate in hospitals?
- it is carried by patients, staff, and on surfaces
- it can survive on sterile goods packaging for more than 38 weeks
- it is resistant to ethanol hand washes
what makes a person at higher risk of catching community acquired MRSA?
- sports participants
- msm
- crowded conditions
- sharing personal items
- touching contaminated surfaces
- being HIV +
what does SCCmec stand for?
staphylococcal cassette chromosome mec
what proportion of MRSA isolates had SCCmec type IV and the PVL toxin gene?
98%
what is the significance of MRSA possessing SCCmec?
it carries the mecA gene which codes for methicillin resistance
what is the significance of MRSA possessing PVL toxin gene?
it produces Panton-Valentine leukocidin
- an exotoxin that stimulates apoptosis of monocytes
and secretres alpha-toxin
