Mim Lecture 21

Front 1

21.1

Enterobacteriaceae

Back 1

- family that most enteric bacteria belong to
- escherichia, salmonella and shigella
- transmission of these bacteria -> fecal-oral route

Front 2

21.2

salmonella and shigella

Back 2

- both primary pathogens
0 unequivocally asociated with disease when found in a host organism
-- not found in our normal flora

Front 3

21.3

escherichia

Back 3

- some strains are primary pathogens while some are opportunistic pathogens and can cause infections of the host becomes debilitated
- opportunistic strains of escherichia are found in our normal flora
- shigella is non-motile

Front 4

21.4

general physical features of enterobacteriaceae

Back 4

- gram negative rods (.5 x 2u)
- most are motile and peritrichous (have mutliple flagella)

Front 5

21.5

general biochemical/metabolic features

Back 5

- facultative anaerobes
- ferment glucose, oxidase negative
1. these two features distinguish Enterobacteriaceae from other enteric bacteria such as vibrio cholera
2. API strip: positive or negative tests. distinct biochemical and commercial tests that can be used to ID individual enterobacteriacea species.

Front 6

21.6

subtryping of Enterobacteriaceae species based on serotyping:

Back 6

O-antigen: outer cell wall lipopolysaccharide unique to G- organisms

H-antigen: flagellum

K-antigen: also known as Vi-antigen (for VIrulence) in salmonella. capsule

Front 7

21.7

media for selective isolation and differentiation of Enterobacteriaceae from stool

medium:selective agent: differentiation

Back 7

MacConkey:Bile salts:Lactose
EMB:Dyes:Lactose
Hektoen Enteric:Bile salts:Lactose, sucrose, salacin, H2S
SS Agar:Bile salts:lactose, H2S

enteric bacteria are resistant to high bile salt concentrations, and that commensal bacteria utilize lactose

Front 8

21.8

Escherichia coli

Back 8

- most abundant facultative anaerobe found in the gut, though not the most abundant species
- Gi and urinary infections, neonatal meningitis, and septicemia
- gram negative rod
- size 0.5 - 2 u
- motile: peritichous flagella
- fimbriae/pili: many types adhesins

Front 9

21.9

Escherichia Coli associated infections

Back 9

- Urinary tract: uropathogenic
- GI tract:
Enterotoxigenic E. coli (ETEC)
Enteropathogenic E. coli (EPEC)
Enterohemorrhagic E. coli (EHEC)
enteroaggregative E. coli (EAEC)
diffuse aggregative E. coli (DAEC)
- Neonatal meningitis: K1 encapsulated

Front 10

21.10

Enterohemorrhagic E. coli (EHEC)

Back 10

- O157H7
- causes hemorrhagic colitis - very bloody diarrhea

Front 11

21.11

Enterohemorrhagic escherichia coli (EHEC) transmission vehicle

Back 11

- feces
- beef
- unpasteurized milk
- apple cider
- water

Front 12

21.12

enterohemorrhagic E. coli mechanism of pathogenesis:

attachment and effacement

Back 12

1. loose attachment to microvilli on gut epithelium -> host cell formation of a pedestal on which the bacteria can grow
2. tight attachment results in destruction (effacement) of remaining microvilli, decreasing epithelial absorption of nutrients and water anc causing diarrhea
3. release of Shiga toxin(s) Stx1 and Stx2 which are cytotoxic to capillary endothelial cells and results in hemorrhagic blood loss

Front 13

21.13

how long does the EHEC infection last?

Back 13

- usually 5-7 days, majority of ppl recover
- can result in hemlytic uremic syndrome (HUS)

Front 14

21.14

Hemolytic Uremic Syndrome (HUS)

Back 14

- death in 10% of children < 10 years

1. blood/toxin disseminates, gets into kidneys
2. renal failure results from destruction of glomerular endothelial cells by toxin

Front 15

21.15

selection and differentiation of EHEC

Back 15

- MacConkey-Sorbitol (v. MacConkey-Lactose) agar because O157H7 cannot metabolize sorbitol while commensal bacteria can

Front 16

21.16

Salmonella

Back 16

- member of enterobacteriaceae
- lactose negative
- motile
- H2S producer

Front 17

21.17

species of salmonella

Back 17

- traditional: speciation based on O and H antigens. thousands of species,

- modern: based on DNA typing. 2 types: Salmonella enterica, Salmonella bongori

Front 18

21.18

salmonella enteritidis

Back 18

- characteristic of majority of species
- cause of bacterial gastroenteritis (diarrhea, cramping, mild fever0
- reservoir: GI tract of domesticated animals, birds, reptiles
- transmission: poultry, eggs, contaminated foods

Front 19

21.19

salmonella typhi

Back 19

- mostly just a problem in the developing world
- cause of typhoid fever that last 3-4 weeks
- reservoir: humans
- transmissionL contaminated food/water, exacerabated by 'carrier state' in which the gallbladder gets chronically infected and secretes the bacteria into the intestine

Front 20

21.20

salmonella mechanism of pathogenesis:

Back 20

- invasion of intestinal epithelium
- passage through intestinal epithelium into submucosal tissues
- phagocytosis by neutrophils and macrophages (macrophages can kill S. enteriditis but not S. typhi -> S. typhi results in a disseminated infection

Front 21

21..21

shigella

Back 21

- enterobacteriacea family
- lactose negative
- nonmotile
- cause dysentery

Front 22

21.22

shigella species

Back 22

- shigella dysenteriae (classic bacillary dysentery, produces shiga toxin, most severe infections)
- shigella sonnei
- shigella flexneri
- shigella boydii

Front 23

21.23
what is and causes of:
bacillary dysentery (vs. amoebic dysentery) aka Shigellosis

Back 23

- frequent, small volume diarrhea associated with blood mucus in the feces, abdominal cramping and tenesmus (inability or difficulty to completely empty the bowl at defecation - can be painful)

1. reservoir: humans
2. transmission vehicles: contaminated food and water. low infectious dose (200 bacteria)

Front 24

21.24

mechanism of pathogenesis for shigella

Back 24

- invasion of intestinal epithelium
- lateral cell-to-cell spread via commandeering of host ell cytoskeleton. replication kills cells, casuing epithelium to get sloughed off (mucoid stool)

Front 25

21.25

campulobacter jejuni

Back 25

- not a member of enterobacteriacea
- Gram - helical rod. 0.4-0.5 u, single polar flagellum
- microaerophilic
- 42C

reservoir: wild and domestic animals, birds, (42C body temp)

Transmission: contaminated water (most common bacterial infection in the US - 2.5 million cases/year

Front 26

21.26

mechanism of pathogenesis

campulobacter jejuni

Back 26

i. invasion of intestinal epithelium
ii. passage through intestinal epithelium into submucosal tissues
iii. phagocytosis by neutrophils and macrophages (GBS)

Front 27

21.27

Guillain-Barre syndrome (GBS)

Back 27

- immune system attacks GM1 gangliosides of the peripheral nervous system that resemble oligosaccharides made by C. jejuni (molecular mimicry)

Front 28

21.28

relative incidences of enteric infections

Back 28

- camphylobacter infections > salmonella > shigella > E. coli
- most infections in summer months
- male: female = 3:1
- age: higher in babies and the elderly, highest in males 20-29