CH 19: Enterobacteriaceae - Primary pathogens

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Last updated 7:49 PM on 10/16/26
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8 Terms

1
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Hektoenn Enteric (HE) agar

  • selective: bile salts and acids

    • select for enterobacteriaceae

  • differential: lactose, sucrose, and ferric iron

    • differentiates based on sugar fermentation AND ability form hydrogen sulfide

  • results

    • normal coliforms: yellow to orange

    • salmonella: clear colonies w/ black center (H2S)

    • shigella: green colonies


<ul><li><p>selective: bile salts and acids</p><ul><li><p>select for enterobacteriaceae</p></li></ul></li><li><p>differential: lactose, sucrose, and ferric iron</p><ul><li><p>differentiates based on sugar fermentation AND ability form hydrogen sulfide</p></li></ul></li><li><p>results</p><ul><li><p>normal coliforms: yellow to orange</p></li><li><p>salmonella: clear colonies w/ black center (H2S)</p></li><li><p>shigella: green colonies </p></li></ul></li></ul><p></p>
2
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Xylose-Lysine-Deoxycholate (XLD) agar

  • selective: sodium deoxycholate

    • select for enterobacteriaceae

  • differential: xylose and ferric iron

    • differentiates based on sugar fermentation AND ability form hydrogen sulfide

  • results

    • normal coliforms: yellow

    • salmonella: red colonies w/ black center

    • shigella: red/pink colonies

    • Proteus and Citrobacter: yellow halo w/ black center

      • look like salmonella


3
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Salmonella spp.

  • food poisoning (acute gastroenteritis) or enteric fever

    • spread thru fecal oral route from contaminated food or water

    • most associated w/ undercooked poultry, raw eggs, and dairy products

  • often results in carrier state after infx (ex. typhoid mary)

  • testing

    • lactose (=), PAD (=)

    • TSI: K/A, H2S

    • IMViC

      • S. typhi: =, +, =, =

      • S. enterica: =, +, =, +


4
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S. typhi - enteric fever

  • typhoid fever

    • caused by Salmonella typhi

    • infects liver, spleen, intestines, and gallbladder

  • symptoms

    • high, sustained fever

    • diarrhea or constipation

    • tummy pain

    • necrosis and perforation of bowel

    • bacteremia and sepsis


5
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Shigella spp.

  • bacillary dysentery

    • low ID50 - highly communicable

    • passed thru fecal-oral route

      • person-to-person and contaminated food/water

    • toxins cause inflammation in intestinal epithelium

  • symptoms

    • watery stools w/ blood, mucous, and pus

    • severe tummy pain + poops

    • HUS

  • testing

    • (=) most biochemicals

    • TSI: K/A (NO H2S)

    • IMViC: Variable, +, =, =

    • S. sonnei: ODC (+)


6
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Yersinia enterocolitica

  • GI illness

    • zoonotic infx thru pig products

  • characteristics

    • bipolar safety pin staining w/ methylene blue

    • preferential growth at 25C

    • CIN agar: ‘Bulls-eye’ colonies

  • testing

    • lactose (=), PAD (=)

    • TSI: K/A, NO H2S

    • motile at 25C


7
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Yersinia pestis

  • Black Death

  • can successfully treat w/ anti.

  • three major types

    • bubonic - spread thru tick bites and infected rodents

      • swollen/painful lymph nodes

      • acral necrosis

      • most common

    • pneumonic

      • respiratory

    • septicemic

      • bacteremia


8
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Plesiomonas shigelloides

  • GI illness

    • passed thru fresh and marine water + consumption seafood

  • morphology

    • similar to shigella on HE plate

  • testing

    • only one oxidase (+), glucose (+)

    • lactose (=)

    • TSI: K/A (NO H2S)

    • vibriostat 0/129: sensitive

    • string test (=), TCBS agar (=)