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USMLE microbiology > gram negative rods > Flashcards

gram negative rods Flashcards

1
Q

after identifying that a bacteria is a gram negative rod what is the next step in lab diagnosis ?

A

find out if it is lactose fermenting or not

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2
Q

most gram negative rods are resistant to ?

A

penicillin and vancomycin

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3
Q

what type of patients are most commonly infected by klebsiella ?

A

people with impaired host defense so alcoholics, diabetics

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4
Q

what is the usual case of klebsiella infection ?

A

usually happens due to the aspiration of GI contents and causes lung abscess

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5
Q

what type of pneumonia is massociated with klebsiella ?

A

lobar pneumonia
classically makes a red currant jelly sputum

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6
Q

what are the virulence factors associated with e coli ?

A

fimrbae - which usually cause UTIs
k capsule - K1 capsular antigen which cause meningitis in babies , inhibits phagocytosis

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7
Q

what is the most likley source of Ecoli bacteremia ?

A

UTI infection by E coli

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8
Q

what are the four different E coli diarrheal illnesses ?

A

enteroinvasive
enterotoxigenic
enteropathogenic
enterohemorrhagic

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9
Q

what is the clinical picture associated with enteroinvasive E coli ?

A

clinically similar to shigella as it presents with bloody diarrhea but it doesnt produce a toxin like shigella

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10
Q

what are the two toxins associated with enterotoxigenic e coli ?

A

heat stable and heat labile exotoxin

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11
Q

which type of e coli is associated with travellers diarrhea ?

A

ETEC
shows watery diarrhea
no inflammation or invasion

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12
Q

what is the problem with enteropathogenic e coli ?

A

no toxin or inflammation
blunting of the villi decreases the absorption
this usually happens in children

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13
Q

does EHEC ferment sorbitol ?

A

no

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14
Q

what are the mechanisms of action associated with nthe toxin in EHEC ?

A

toxin mediated
doesnt invade the cell
produces shiga like toxin

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15
Q

what is the toxin effect of EHEC ?

A

endothelium swells , vessel lumen narrows
deposition of fibrin
hemolysis and inflammation

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16
Q

what is the feared complication of EHEc ?

A

HUS

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17
Q

what s the triad in HUS ?

A

hemolytic anemia
thrombocytopenia acute renal failure
Acute renal failure

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18
Q

what is the oset of HUS in relation to te diarrhea in EHEc ?

A

HUS usually happens 5-7 days later

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19
Q

what is the driving factor in gram negative sepsis ?

A

endotoxin LPS and Lipid A

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20
Q

what are the common scenarios associated with gram negative sepsis ?

A

insertion of a catheter in a
elderly patient

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21
Q

what are the features of diarrhea in
invasive infections
toxin mediated disease
protozoal infection ?

A

invasive infection - fecal leukocytes and RBCs
toxin mediated disease - mucous epithelial cells
protozoal infection - stool ova

22
Q

why is enterobacter resistant to many antibiotics ?

A

because of the presence of extended spectrum beta lactamases

23
Q

what is enterobacter usually treated with ?

A

carbapenems

24
Q

what are the two types of salmonella ?

A

salmonella typhi - cause typhoid fever
non typhoid strains - invasive gastroenteritis

25
Q

what is the classic cause of osteomyelitis in sickle cell patients ?

A

salmonella

26
Q

what is the cellular response in association with salmonella ?

A

mainly monocytes

27
Q

how is salmonella differentiated fro shigella ?

A

with a triple sugar iron test where the media turns black with salmonella but not with shigella

28
Q

what are the classic features of typhoid fever ?

A

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

29
Q

what is the treatment for typhoid fever ?

A

ceftriaxone and fluoroquinolone

30
Q

what drugs are contraindicated for diarrhea in salmonella ?

A

loperamide

31
Q

what cells are invaded by shigella ?

A

m cells in peyers patches

32
Q

what is the difference in terms of spread between salmonella and shigella ?

A

salmonella spreads in the blood stream whilst shigella spreads from one cell to the other

33
Q

what is the cellular response associated with shigella ?

A

PMN

34
Q

what are the similarities between shigella and salmonella ?

A

both are gram negative rods both cause bloody diarrhea and both are invasive

35
Q

what bis the cell to ell spread in shigella called ?

A

macropinocytosis

36
Q

what appearance does proteus have on agar ?

A

bulls eye appearance

37
Q

which bacteria is associated with struvite kidney stones ?

A

proteus

38
Q

what is the most common causative organism associated with VAP ?

A

psedomonas aeruginosa

39
Q

what pigment and odor does does pseudomonas produce ?

A

blue green pigment called pyocyanin
sweet grape like odor

40
Q

what environment is most likely associated with pseudomonas aerigonsa ?

A

water sources

41
Q

what are the toxins associated with pseudomonas ?

A

endotoxin LPS
exotoxin A which causes adp ribosylation of E2F

42
Q

what is the cause of pneumonia in patients with cystic fibrosis ?

A

pseudomonas aerigonsa

43
Q

what bacteria are burn victims more susceptible to ?

A

pseudomonas aerugonsa

44
Q

what water associated infections does pseudomonas cause ?

A

otitis externa
hot tub folliculitis

45
Q

what is the causative organism of mosteomyelitis in IV drug abusers ?

A

pseudomonas

46
Q

what are the manifestations of pseudomonas bacteremia ?

A

ecthyma gangrenosum
black necrotic ulcers on the skin

47
Q

what is the classic case associated with ecythma gangrenosum ?

A

neutropenic cancer patient that is hospitalized and develops black lesions on the chest or back

48
Q

what cancer is associated with h pylori ?

A

MALT lymphomawhat

49
Q

what stain and medium is used for legionella ?

A

silver stain
buffered charcoal yeast extract agar

50
Q

how is someone infected by legionella ?

A

inhaled bacteria
outbreaks in nursing homes hotels with contaminated water

51
Q

what are the symptoms of legionella ?

A

watery diarrhea with pneumonia
hyponatraemia ( confusion)
no bacteria on gram stain

52
Q

what is the mild form of legionella ?

A

pontiac fever , no respiratory complaints

USMLE microbiology (14 decks)

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