gram pos + neg Flashcards
gram neg vs pos cell wall
gram neg
- have inner + outer membrane
- thin layer of peptidoglycan between which cannot take up the gram stain
gram pos
- lack outer layer
- thick peptidoglycan cell wall which turns purple with a gram stain
catalase positive vs negative gram positive cocci
catalase +
- staphylococcus
(catalase positive need particular nutrients, require complex media, preferably supplemented with blood)
catalase -
- streptococcus
- enterococccus
which staphylococci is coagulase + vs - ?
coaguase + = staph aureus, staph intermedius
coagulase neg = staph epidermidis
alpha haemolytic strep vs beta haemolytic
alpha (green discolouration around colonies)
- strep viridians
- strep pneumoniae
beta (complete clearing around colonies)
- group A-H
- strep pyogenes
staph aureus antibiotic in sepsis
flucloxacillin IV
- vancomycin IV in allergy or MRSA
coagulase neg staph
(staph epidermidis)
many are flucloxacillin resistant
not as virulent as staph aureus
major pathogen in bacterial meningitis
strep pneumoniae
where are streptococci commensals?
GI tract - dont cause infection here
- viridans strep live in mouth
- enterococci in bowel
name a bacteria that has gamma haemolysis
enterococci
(no-haemolysis)
faculative anaerobes
grow aerobically + anaerobically
- do not use oxygen in metabolism
- some capnophilic, some prefer anaerobic conditions for growth
haemolysis of strep pyogenes
beta
(Group A beta haemolytic strep)
- pharyngitis, skin
bacillia examples
listeria monocytogenes
clostridia (c.diff)
corynebacterium (diphtheroids)
- corynebacterium diphtheriae
drug of choice for enterococci
amoxicillin
- vancomycin if amoxicillin resistant
vancomycin resistant enterococcus (VRE)
- linezolid
- daptomycin
- tigecycline
gram pos bacillia
C.diff
C.tetani (tetanus)
corynebacterium
bacillus cereus
listeria monocytogenes
modes of antibiotic resistance
active efflux - bacteria pushes antibiotic out of the cell
target replication (making Abx less effective)
modified drug target - Abx now ineffective
decreased permeability - alters cell wall structure so cant penetrate
drug inactivating enzymes - bacteria produce enzymes to inactivate the antibiotics
mean inhibitory concentration (MIC)
concentration of drug required for kill of 99.9% of organism during 18-24hrs
- conc of drug that allows tube with pathogen to remain clear by visual examination after 18-24hrs
beta lactams
Arguably most important drug class
- Allergy is due to a degradation product of beta lactams
Class includes –
o Penicillin
o Flucloxacillin
o Cephalosporins
o Piperacillin/tazobactam
o Carbapenems
important causes of gram negative sepsis
E.coli
klebsiella
enterobacter (NOT enterococcus)
pseudomonas aeruginosa
neisseria meningitidis
neisseria gonorrhoea
Pathogens that can’t really be seen on gram
myobacterium tuberculosis
chlamydophilia sp
trepnonema pallidum
mycoplasma
lipopolysaccharide - gram neg cell wall
- Gram neg cell envelope contains an additional outer membrane composed by phospholipids + lipopolysaccharides which face the external environment
- Highly charged nature of lipopolysaccharides confer an overall negative charge to thegram neg cell wall
- Chemical structure of outer membrane lipopolysaccharides can be unique to specific strains
*Pathogenicity often assoc with lipopolysaccharide layer of gram neg cell envelope
coliforms
gram neg, non-spore forming bacilli that are lactose fermenting
e.coli
klebsiella sp
proteus sp
enterobacter sp
upper GI organisms vs lower
upper GI - aerobic organsims
lower - anaerobic
gentamicin protocol
limit duration
- 72hr duration then IDrequired (24hr if concern re renal function
monitor renal function
prescribe in once only section
haemophilus influenza
gram neg coccobacillus
- generally aerobic but can grow as a facultative anaerobe
in vitro growth, requires accessory growth factors
- X factor (hemin)
- V factor (NAD)
-> grows on chocolate agar BUT NOT blood
active agent against haemophilus influenza
amoxicillin also doxycycline
atypical causes of pneumonia
“non-strep” pneumonia
mycoplasma pneumonia
coxiella burnetti
chlamydophilia psittaci
legionella pneumophillia
atypical pneumonia therapy
most respond to doxycycline (tetracycline)
- NOT so much legionella
clarithromycin also works
- quinolones (levofloxacin) if penicillin allergic in severe pneumonia
legionella pneumophilia
gram neg bacilli
Lukewarm aerolised water (shower, air conditioning, taps)
o Multiplies within amoebae + ciliated protozoa – small one-celled organisms
->These provide nutrients + shelter from adverse environmental conditions, such as extreme temperatures + chemicals like chlorine
o Human immune cells called alveolar macrophages look very similar to protozoa
->Legionella invades + grows within alveolar macrophages, mistaking them for their natural host + causing disease
who/where is legionella pneumophilia more common
smokers, COPD
Males
immunosuppressed, malignancy
diabetes
dialysis
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