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microb > enterobacteriae: gram negative rods > Flashcards

enterobacteriae: gram negative rods Flashcards

1
Q

name the lactose fermenter gram negative rods

A

escherichia coli

klebsiella spp.

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2
Q

name the non lactose fermenter gram negative rods

A

shigella spp.
proteus spp.
salmonella spp.

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3
Q

name the 2 groups of salmonella

A

enteric (typhoid) fever group: s. typhi, s. paratyphi
acute gastroenteritis group:
s. typhimurium, s. enteritidis

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4
Q

name the bactera of shigella spp.

A

sh. dysenteriae, sh. boydii, sh. flexneri, sh. sonnei

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5
Q

how to differentiate between lactose fermenters and non-lactose fermenters

A

lactose fermenters show pink/red colonies (produce acid)

non lactose fermenters show yellow/pale colourless colonies

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6
Q

enterobacteriae culture medium

A

macconkey agar:

contains bile salts the inhibit the growth of unwanted bacteria

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7
Q

enterobacteriae are oxidase __

A

negative

gram negative cocci are oxidase positive

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8
Q

escherichia coli: character

A

oxidase negative lactose fermenting gram negative rods

normal gut flora

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9
Q

escherichia coli: virulence factors

A

exotoxins produced by certain strains

EPEC, ETEC, EHEC, EIEC

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10
Q

escherichia coli: clinical presentations

A

urinary tract infections
neonatal infections (meningitis, septicaemia)
sepsis associated with the gut (either due to GIT lining damage or due to blockage that prevents bacterial drainage)
nocosomial disease

diarrhoeal disease:

  • e. coli (enteropathogenic e. coli): infantile gastroenteritis
  • etec (enterotoxigenic e. coli): diarrhoeal disease in developing world and travellers
  • eiec (enteroinvasive e. coli): invades colonic wall, produces similar disease to shigella dysentry
  • ehec (verocytotoxin producing/ enterohaemorrhagic e. coli): causes haemorrhagic colitis with bloody diarrhoea, complicated by renal failure
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11
Q

what does epec cause

A

infantile gastroenteritis

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12
Q

what does etec cause

A

adult diarrhoeal disease

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13
Q

what does eiec cause

A

invades colonic wall, produces similar disease to shigella dystentry

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14
Q

what does ehec cause

A

haemorrhagic colitic with bloody diarrhoea, complicated by renal failure

shigatoxins produced by ehec lead to haemolytic uraemic syndrome

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15
Q

escherichia coli: diagnosis

A

difficult: virulent strains closely resemble normal e. coli strains

PCR: detect genes encoding specific toxins
serology: impt e. coli serotype O157H7 surface antigens
urine microscopy (UTI must contain white blood cells)
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16
Q

important e. coli serotype

A

O157 H7

o represents the somatic bacterial cell wall antigen, h represents the flagellar antigen

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17
Q

klebsiella spp.: character

A

oxidase negative lactose fermenter gram negative rod

normal gut flora

18
Q

klebsiella spp.: clinical presentations

A

urinary tract infection
friedlander’s pneumonia (severe form of community-acquired pneumonia with abscess formation)
nocosomial infections
community acquired liver abscess

frequently seen in alcoholics/ diabetic patients

19
Q

enterobacteriae is a common cause of __

A

nocosomial infections

20
Q

explain why enterobacteriae is a common cause of nocosomial infections

A
  1. due to git surgery - release of bacteria, causing wound infections, peritonitis, abdominal and pelvic abscesses
  2. due to neurosurgery or head trauma that causes meningitis
  3. due to prolonged hospitalisation as broad spectrum antibiotic used select for survival of resistant strains of coliforms
21
Q

enterobacteriae treatment

A 
most strains produce beta lactamases:
ceftriaxone
co-amoxiclav/piptazo
ciprofloxacin
aminoglycosides like gentamicin and amikacin (requires therapeutic drug monitoring)
22
Q

shigella spp.: character

A

oxidase negative non lactose fermenting gram negative rods

NOT normal flora

23
Q

shigella spp.: transmission

A

faecal-oral transmission, flies

24
Q

shigella spp.: clinical presentations

A

sh. dysenteriae: dysentery (intestinal inflammation) that leads to blood stained mucopurulent stools, may be complicated by HUS from shiga toxin)
sh. sonnei: common cause of mild diarrhoeal disease (outbreaks in institutions)

25
Q

proteus spp.: character

A

oxidase negative non lactose fermenting

normal gut flora

swarms on surface of blood agar in waves

26
Q

proteus spp.: clinical presentations

A

urinary tract infections
renal calculi/stones: urease produced breaks down urea to ammonia and carbon dioxise, alkalinsation of urine results in stone formation

27
Q

enteritic (typhoid) fever group: character

A

s. typhi, s. paratyphi

oxidase negative non-lactose fermenting gram negative cocci

NOT normal flora

28
Q

enteritic (typhoid) fever group: transmission

A

faecal-oral transmission

29
Q

enteritic (typhoid) fever group: clinical presentation

A

initial invasion of ileal mucosa & multiplication within mesenteric lymph nodes; entry into bloodstream and replication within macrophages of many organs (incubation period 10-14days)

second invasion of bloodstream resulting in clinical symptoms (fever, anorexia, epistaxis, cough, headache, abdominal pain, constopation or diarrhoea, bradycardia, enlarged liver and spleen, rose spots)

excretion of infected bile by gall blader into gut creates second invasion of gut wall, resulting in inflammation caused typhoid ulcers of ileal patches (can cause haemorrhage and intestinal perforations)

*some individuals become chronic carriers even after recovery due to chronicall infected gall bladder

30
Q

enteritic (typhoid) fever group: diagnosis

A

culture: blood (early), urine/stool (later)
serology: widal’s test (not reliable)

31
Q

enteritic (typhoid) fever group: prevention

A

vaccination- Ty 21a oral, Vi injectable
detect and treat carriers
clean food and water, proper sewage disposal

32
Q

acute gastroenteritis group: character

A

s. typhimurium, s. enteritidis

oxidase negative non-lactose fermenting gram negative rods

NOT normal flora, usually originates in animal faeces

33
Q

acute gastroenteritis group: transmission

A

contaminated food by animal faeces

34
Q

acute gastroenteritis group: clinical presentations

A

salmonella food poisoning (diarrhoea, vomitting, abdominal pain, fever) that is usually self limiting

invasive infections after spread through blood; atheromatous plaques in arteries, osteomyelitis, meningitis

in HIV and SLE patients, any food poisoning salmonella may produce a disseminated invasive infection

35
Q

acute gastroenteritis group: diagnosis

A

culture: stool, blood

36
Q

enteric (typhoid) fever group: explain ileal perforation

A

it targets m cells on the epithelial lining; m cells phagocytose the salmonella bacteria, and spit them out through onto the peyer’s patches which is part of the submucosal layer

necrosis of the epithelial layer results in ileal perforation; secondary infection of the peritoneum

37
Q

enteric (typhoid) fever group: main effectors

A

macrophages; phagocytose the salmonella bacteria and can travel to different sites of the body to cause systemic effects

38
Q

acute gastroenteritis group: mechanism of inflammation and diarrhoea

A

main effectors: neutrophils that induce inflammation of the colon

as immune cells travel through the mucosa to the site of infection, they damage the mucosa and cause git dysfunction; excessive loss of water hence diarrhoea

39
Q

mechanism of ehec

A

e. coli travels to the epithelial cells and release shiga toxins that cause injury to the intestinal epithelium + the underlying blood vessels -> results in inflammation

^fluids and blood leak into the intestine; bloody diarrhoea

40
Q

haemorrhagic uremic syndrome

A

after. e.coli releases shiga toxins into the bloodstream that travel to the kidneys and damage the glomerular endothelial cells through apoptosis

holes in the endothelium allow proteins and blood to enter the urine - bloody urine, proteinuria
platelets clot the holes formed and there are less platelets in the blood; thrombocytopenia

rbcs try to squeeze through these clots and microangiopathic hemolysis occurs - forms schistocytes; number of rbcs reduce and there is anemia

clots can block blood supply to the kidney and cause ischemia, non functional kidneys prevent filtration and there is uraemia

microb (12 decks)

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