PRINCIPLES MICROBIOLOGY Flashcards
what is the genus and what is the species:
Staphylococcus Aureus
genus - staphylococcus
species - aureus
do prion proteins have DNA or RNA
neither
what disease are prion proteins known to cause
mad cow disease - Creutzfeldt-Jacob disease
incurable
Why must surgical equipment used with prion proteins be destroyed
prion proteins not killed by sterilisation or disinfection
how is DNA stored in a bacterial cell (prokaryote)
contained within a tightly coiled double stranded chromosome (nucleoid)
+ extra circular rings of DNA in cytosol (plasmids)
what is the purpose of flagellae of bacterial cells
aid movement
what is the purpose of pili (fimbriae) of bacterial cell
adhesion
what are spirillum
tufts at each end of a bacterial cell to aid movement (flagellae)
what are spirochaete
spirals within periplasm that cause cork screw motion
what shape are coccus bacteria
round
what shape are bacillus bacteria
rod shaped
where does a gram stain stain
the cell wall
what colour does gram negative stain
pink
Negative stains piNk
what colour does gram positive stain
purple
describe the gram positive cell wall
thick layer of peptidoglycan
cytoplasmic phospholipid membrane
describe the gram negative cell wall
outer cytoplasmic membrane
middle thin layer of peptidoglycan cell wall
inner cytoplasmic membrane
Larger periplasmic space
why does mycobacterium tuberculosis not stain well
waxy coat
what does virulence mean
degree of pathogenicity - how easily organism can cause disease
how do bacteria replicate
binary fission
what do bacteria need to grow
food
moisture
correct temp and pH
what is the typical temperature and pH of a human pathogen
37 degrees
pH 7.4
what are the 4 phases of bacterial growth
Lag phase
log phase
stationary phase
death phase
describe the BR/DR in the 4 phases
lag phase - BR > DR
log phase - BR > DR
stationary phase - BR = DR
death phase - BR < DR
what is meant by the term microaerophilic
decreased oxygen and increased carbon dioxide
do gram positive produce exotoxins or endotoxins
exotoxins - propelled
do gram negative produce exotoxins or endotoxins
Negative produce eNdotoxins - attached to cell wall
why is gram negative sepsis slightly worse
endotoxins can be released from cell walls when they die
are gram negative or gram positive more susceptible to antibiotics?
gram positive - outside peptidoglycan layer acts as a target
what is the effect of bacterial toxins
cause release of cytokines from immune cells damage red and white blood cells make BVs leaky reduced clotting ability reduced BP sepsis and septic shock
what do gram positive bacilli (C. Diff, bacillus anthracis) form
spores
what occurs if fusiform bacteria cross the placenta
still births / cancer
describe the 3 steps in spore formation
1) chromosome condensation
2) septum formation
3) calcium dipicolinate accumulation in core
what does a spore consist of
cytoplasm + contents + cytoplasmic membrane - surrounded by exosporium
give 5 times when hand washing is necessary
before patient contact before aseptic task after bodily fluid exposure after patient contact after contact with patient surroundings
what are the 2 types on fungi
moulds and yeasts
how do yeasts reproduce
budding
how do moulds reproduce
spores spread by air current
hyphae spread by invading organic tissue
when is asperigillus sp. mainly seen (mould)
immunocompromised patients (opportunistic)
what is the most common fungal infection in humans
candida spp. (yeast)
what do yeasts look like in a gram stain
large gram positive oval structures
do moulds stain?
no
what are protozoa
single celled parasites
Streptococci spp is …
How is it subdivided?
a gram positive cocci in strips
strep sounds like strip
haemolyisis
staphylococci app. is …
how is it subdivided?
a gram positive cocci in clusters
aerobic but facultative
in the STAPH room the teachers stand in clusters
coagulase test
enterococci sp is …
a gram positive cocci
aerobic but facultative
what is alpha haemolysis
What colour is it
partial haemolysis
caused by enzymes that denature haemoglobin inside RBCs causing a GREEN decolorisation around colony
what is beta haemolysis
What colour is it
complete haemolysis
caused by enzymes that lyse the RBC completely causing CLEAR/YELLOW around the colony
what is gamma haemolysis
give an example
no haemolysis (red appearance) enterococci
what are the most pathogenic strep species
Beta haemolytic
give 2 examples of alpha-haemolytic strep
strep pneumonia (pneumococcus) strep viridans
Streptococcus pneumoniae is …
alpha haemolytic gram positive cocci in short chains or pairs (diplococci) most common cause of pneumonia
strep viridians is …
alpha haemolytic
gram positive
cocci
in chains
what are the 2 groups of beta haemolytic strep
group A (strep. progenies) - most infectious group B
give 3 things caused by strep pyogenes
strep throat ( tonsillitis or scarlet fever if rash also present)
skin and soft tissue infection - necrotising fascitis
puerperal sepsis - fatal infection in pregnant and recently post natal women
give 2 examples of enterococcus
enterococcus faecalis
enterococcus faecium
normal bowel commensals
what type of enterococcus can cause outbreaks in hospitals
enterococcus faecium - VRE (vancomycin resistant enterococci)
what is the most common cause of skin, soft tissue, bone, joint and wound infections
staph aureus
what causes toxic shock
staph aureus
how is staphylococci divided/identified
coagulase positive - staph aureus (golden)
coagulase negative - all others (white) e.g. staph epidermidis
what does MSSA stand for
methicillin sensitive staph aureus
sensitive to flucloxacillin
what does MRSA stand for
methicillin resistance staph aureus
resistant to all penicillins, flucloxacillin and all cephalosporins
alteration of PBP2 (penicillin binding protein 2)
how does staph epidermidis stick to plastic and other artificial material in body
produces a surface polysaccharide slime
infection of prosthetic joint/valve/IV catheter
normal commensal of skin
what is Panton-Valentine leukocidin
toxin produced by some strains of staph. aureus which causes damage to WBCs
associated with necrolytic skin infection
how do endotoxins work
interact with macrophages to stimulate immune response and cytokine release
cytokines cause adverse effects of sepsis and travel to hypothalamus
what is released in response to cytokines and from where
prostaglandin E - hypothalamus
what does prostaglandin E do
increases the body’s thermal set point - shivering stimulated
what goes in the black bin bags
domestic waste
what goes in the orange bin bags
clinical waste
what is an FFP3 mask and when is it used
filter mask
airborne precaution
what is another airborne infection precaution
negative pressure room
what occurs in sepsis
leaky blood vessels loss of fluid into tissues hypotension / hypovolaemia tachycardia poor tissue perfusion
why is haemorrhage more likely in sepsis
clotting factors activated - blood clotting in tiny vessels
uses up clotting factors
what kind of symmetry do adenoviruses show
icosahedral symmetry
how many subunits in icosahedral symmetry
3
1 for apex
1 for centre of face
1 for edges
how many subunits in helical symmetry
1 repeated unit
give the 6 steps in the replicated of a virus
1) attachment to cell
2) entry into cell
3) uncoating of viral nucleic acid
4) nucleic acid and protein synthesis
5) assembly
6) release - budding / cell lysis
what is the Varicella - zoster virus
remains latent before reactivating in dorsal root ganglia (shingles)
Neisseria spp. are …
aerobic
gram negative
cocci in pairs
e.g. neisseira meningitides - most common cause of bacterial meningitis
coliform are…
rod shaped aerobic but facultative gram negative large bacilli non-spore forming
what are the 2 types of coliform
O antigens (cell wall) H antigens (flagella)
give 6 types of coliform
E. Coli Klebsiella Enterobacter Proteus Salmonella Shigella
what is the first line treatment for coliforms
gentamicin
Pseudomonas aeruginois
legionella pneumophila
are …
gram negative
bacilli
strict aerobes
haemophillus influenza is …
small
gram negative
bacillus
aerobes
H. Pylori is …
gram negative
small
curved bacilli
microaerophilic
campylobacter spp is…
gram negative
spiral
bacilli
microaerophilic
clostridium spp are…
gram positive
bacilli
produces spores
strict anaerobe
bacteriodes spp. are …
gram negative
bacilli
strict anaerobes
what is the first line treatment for anaerobes?
metronidazole
give 3 examples of clostridium spp
C. difficile - diarrhoea
C. Tetani - tetanus
C. Perfringens - gas gangrene
what do gram negative bacteria release when they die
lipopolysaccharides - form a ligand:receptor communication with toll-like receptor 4 (found on macrophage surface)
what are beta lactam antibiotics
contain beta lactam structure in their molecular structure
penicillins, co-amoxiclavs, cephalosporins
what are mycobacteria stained by
acid-alcohol fast bacilli
what is genetic variation in bacteria and what are the 3 ways it can occur
mutation and gene transfer
transformation
conjugation
transduction
what is transformation
when DNA released from dead bacteria is taken up by living bacteria and incorporated into plasmids of nucleoid
what is conjugation
sex plus is produced by one bacteria through which plasmid DNA can be transferred
what is transduction
when viruses infect bacteria and transfer bits of DNA from one bacterium to another
What would a bacteria that produces beta lactamase be resistant to
amoxicillin
What would a bacteria that produces extended spectrum beta lactamase be resistant to
all penicillins and cephalosporins
What would a bacteria that produces carbapenemase be resistant to
all penicillins
all cephalosporins
all carbapenems
how does penicillin work
ACTS ON CELL WALL
inhibit cell wall synthesis by preventing cross linking of peptidoglycan subunit
how do cephalosporins work
ACT ON CELL WALL
bactericidal
inhibit cell wall synthesis
how do glycopeptides work
e.g. vancomycin, tercoplanin
ACT ON CELL WALL
bactericidal
bind to end of growing pentapeptide chain preventing cross linking and therefore weakening cell wall
gram positive only
why can persistor cells not be targeted by antibiotics
enclosed within a biofilm so can’t be targeted in a dormant/inactive state
give examples of 3 types of penicillin
benzylpenicillin - penicillin G (IV)
phenoxymethyl penicillin - penicillin V (oral)
benzathine penicillin - IM, long acting
what is the functional group of penicillin
beta-lactam ring
what is co-amoxiclav
amoxicillin + clavulanic acid - inhibits action of beta-lactamase enzyme so that amoxicillin can work where it wouldn’t normally
how do macrolides work
e.g. erythromycin, clarithromycin, azithromycin
INHIBIT PROTEIN SYNTHESIS
bacteriostatic - protein synthesis can resume once the antibiotic is removed
taken into bacterial cell by AT, bind to 50S subunit and prevent tRNA from binding at receptor sites
how do tetracyclines work
e.g. tetracycline, doxycycline
INHIBIT PROTEIN SYNTHESIS
bacteriostatic
taken into bacterial cell by AT, bind to 30S subunit and prevent tRNA from binding at receptor sites
how do aminoglycosides work
e.g. gentamicin
INHIBIT PROTEIN SYNTHESIS
bactericidal - binding to ribosome is lethal
taken into bacterial cell by AT, bind to 30S subunit and prevent tRNA from binding at receptor sites
when should vancomycin be avoided
kidney failure
how are macrolides excreted
via liver, biliary tract and into faeces
how is gentamicin excreted
kidneys
what 2 things does gentamicin cause damage to
kidneys
vestibulocochlear nerve CN VII
how does metronidazole work
ACTS ON BACTERIAL DNA
causes DNA strand breakage
anaerobic infections and some protozoal
how does trimethoprim work
ACTS ON BACTERIAL DNA
inhibits bacterial folic acid synthesis
how is trimethoprim excreted
kidneys
what is co-trimoxazole
trimethoprim + sulphamethoxazole
how do fluoroquinolones work
e.g. ciprofloxacin
levofloxacin
ACT ON BACTERIAL DNA
prevent supercoiling of bacterial DNA
bactericidal
what is used for atypical cover
clarithromycin
Amoxicillin covers …
Gentamicin covers …
Metronidazole …
gram positive
gram negative
anaerobes
(most) enterococci sensitive to …
co-trimoxazole
(most) amoxicillin
what is pseudomonas aeruginosa treated with
ciprofloxacin
resistant to most antibiotics and gram negative
