gram negative rods Flashcards
after identifying that a bacteria is a gram negative rod what is the next step in lab diagnosis ?
find out if it is lactose fermenting or not by usingg mackonkey agar
most gram negative rods are resistant to ?
penicillin and vancomycin
what type of patients are most commonly infected by klebsiella ?
people with impaired host defense so alcoholics, diabetics
what is the usual case of klebsiella infection ?
usually happens due to the aspiration of GI contents and causes lung abscess which is anchovy coloured on aspiration
what type of pneumonia is massociated with klebsiella ?
lobar pneumonia
classically makes a red currant jelly sputum
what are the virulence factors associated with e coli ?
fimbrae - which usually cause UTIs
k capsule - K1 capsular antigen which cause meningitis in babies , inhibits phagocytosis
what is the most likley source of Ecoli bacteremia ?
UTI infection by E coli
what are the four different E coli diarrheal illnesses ?
enteroinvasive
enterotoxigenic
enteropathogenic
enterohemorrhagic
what is the clinical picture associated with enteroinvasive E coli ?
EIEC is invasive and clinically similar to shigella but no toxin is made
what are the two toxins associated with enterotoxigenic e coli ?
heat stable and heat labile exotoxin
no inflammation or necrosis
which type of e coli is associated with travellers diarrhea ?
ETEC
shows watery diarrhea
no inflammation or invasion
what is the problem with enteropathogenic e coli ?
no toxin or inflammation
just prevents absorption
blunting of the villi decreases the absorption
this usually happens in children
does EHEC ferment sorbitol ?
no
what are the mechanisms of action associated with nthe toxin in EHEC ?
toxin mediated
doesnt invade the cell
produces shiga like toxin
what is the toxin effect of EHEC ?
endothelium swells , vessel lumen narrows
deposition of fibrin
hemolysis and inflammation
what is the feared complication of EHEc ?
HUS
what s the triad in HUS ?
hemolytic anemia
thrombocytopenia acute renal failure
Acute renal failure
what is the oset of HUS in relation to te diarrhea in EHEc ?
HUS usually happens 5-7 days later
what is the driving factor in gram negative sepsis ?
endotoxin LPS and Lipid A
what are the common scenarios associated with gram negative sepsis ?
insertion of a catheter in a
elderly patient
what are the features of diarrhea in
invasive infections
toxin mediated disease
protozoal infection ?
invasive infection - fecal leukocytes and RBCs
toxin mediated disease - mucous epithelial cells
protozoal infection - stool ova
why is enterobacter resistant to many antibiotics ?
because of the presence of extended spectrum beta lactamases
what is enterobacter usually treated with ?
carbapenems
what are the two types of salmonella ?
salmonella typhi - cause typhoid fever
non typhoid strains - invasive gastroenteritis
what is the classic cause of osteomyelitis in sickle cell patients ?
salmonella
what is the cellular response in association with salmonella ?
mainly monocytes
how is salmonella differentiated fro shigella ?
with a triple sugar iron test where the media turns black with salmonella but not with shigella
what are the classic features of typhoid fever ?
1- rose spots on trunk and abdomen
2- pulse temperature dissociation ( high fever slow pulse )
3- can hide i nthe gall bladder and cause a carrier state
what is the treatment for typhoid fever ?
ceftriaxone and fluoroquinolone
what drugs are contraindicated for diarrhea in salmonella ?
loperamide
what cells are invaded by shigella ?
m cells in peyers patches
what is the difference in terms of spread between salmonella and shigella ?
salmonella spreads in the blood stream whilst shigella spreads from one cell to the other
what is the cellular response associated with shigella ?
PMN
what are the similarities between shigella and salmonella ?
both are gram negative rods both cause bloody diarrhea and both are invasive
what bis the cell to ell spread in shigella called ?
macropinocytosis
what appearance does proteus have on agar ?
bulls eye appearance
which bacteria is associated with struvite kidney stones ?
proteus
what is the most common causative organism associated with VAP ?
psedomonas aeruginosa
what pigment and odor does does pseudomonas produce ?
blue green pigment called pyocyanin
sweet grape like odor
what environment is most likely associated with pseudomonas aerigonsa ?
water sources
what are the toxins associated with pseudomonas ?
PEEP
endotoxin LPS
phospholipase C which degrades the cell membrane
exotoxin A which causes adp ribosylation of E2F
what is the cause of pneumonia in patients with cystic fibrosis ?
pseudomonas aerigonsa
and the mucoid polysacchride capsule which may contribute to the chronic pneumonia
what bacteria are burn victims more susceptible to ?
pseudomonas aerugonsa
what water associated infections does pseudomonas cause ?
otitis externa
hot tub folliculitis
what is the causative organism of mosteomyelitis in IV drug abusers ?
pseudomonas
what are the manifestations of pseudomonas bacteremia ?
ecthyma gangrenosum
black necrotic ulcers on the skin
what is the classic case associated with ecythma gangrenosum ?
neutropenic cancer patient that is hospitalized and develops black lesions on the chest or back
what cancer is associated with h pylori ?
MALT lymphoma
what stain and medium is used for legionella ?
silver stain
buffered charcoal yeast extract agar with iron and cysteine
how is someone infected by legionella ?
inhaled bacteria
outbreaks in nursing homes hotels with contaminated water
what are the symptoms of legionella ?
watery diarrhea with pneumonia
hyponatraemia ( confusion)
no bacteria on gram stain
what is the mild form of legionella ?
pontiac fever , no respiratory complaints
