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Enterobacteriaceae

Enterobacteriaceae. A. General characteristics 1. Pathogenic genera: human colonizers or pathogens 2. Non-pathogenic genera: human colonizers or environmentals 3. Oxidase negative, glucose fermenters, grow on MAC. B. Epidemiology 1. Reservoirs a. Inhabit human GI tract

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Enterobacteriaceae

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  1. Enterobacteriaceae A. General characteristics 1. Pathogenic genera: human colonizers or pathogens 2. Non-pathogenic genera: human colonizers or environmentals 3. Oxidase negative, glucose fermenters, grow on MAC

  2. B. Epidemiology • 1. Reservoirs • a. Inhabit human GI tract • b. Inhabit GI tract of other animals • c. Environmental organisms • d. Zoonotic pathogens (cause disease in animals) • e. Only present during disease • 2. Transmission • a. Endogenous infections from patient’s own strain • b. Person to person • c. Ingestion of contaminated food or water • d. Vector-borne

  3. C. Pathogenesis and spectrum of disease • 1. Overt pathogens • a. Salmonella spp.: GI, bacteremia and extraintestinal infections, enteric fever (typhoid fever) • b. Shigella spp.: dysentery • c. Yersinia pestis: “black” plague • 2. Opportunistic pathogens • a. Citrobacter spp., Enterobacter spp., Klebsiella spp., Proteus spp., and Serratia spp. • b. can be very pathogenic, but usually only in immunocompromised • 3. Eschericia coli • a. more pathogenic than opportunists; some strains are overt pathogens • TABLE 25-2

  4. D. Laboratory diagnosis • 1. Specimen collection, transport, processing • a. No special considerations for these organisms • 2. Direct detection methods • a. No specific procedures for routine enterics • 3. Culture and identification • a. Media • i. BAP, CAP, Mac all support growth • large gray smooth on BAP, CAP • TABLE 25-3 • ii. CIN agar for selection of Yersinia • iii. Hektoen for Salmonella/Shigella • iv. MacConkey-Sorbitol: E. coli O157 can’t ferment sorbitol

  5. Gram stain of enteric Gram-negative rods http://www.nirgal.net/life_nano.html

  6. D. Laboratory diagnosis • 3. Culture and identification • b. Colony appearance • i. Swarming of Proteus • indole + P. vulgaris, indole – P. mirabilis • ii. Mucoid Klebsiella • iii. H2S positive Salmonella on Hektoen • iv. Serratia makes a red pigment • v. Yersinia red center with clear border on CIN • c. Identification • i. API strips, automated systems • ii. TSI slants • iii. Salmonella antisera

  7. Enteric gram-negative rods on BAP E. coli Klebsiella sp. http://www.vetmed.wisc.edu/pbs/courses/bact/labmanual/c4klebsiella.html

  8. Enteric gram-negative rods on BAP Proteus sp. http://www.vetmed.wisc.edu/pbs/courses/bact/labmanual/c4klebsiella.html

  9. Identification of Salmonella and Shigella TSI slant Hektoen agar http://www.msu.edu/course/fsc/441/resulex14.html

  10. CIN agar for the recovery of Yersinia sp. http://www.troybio.com/images/Product_Images_BBL/BBL.htm

  11. D. Laboratory diagnosis • 4. Antimicrobial susceptibility testing and therapy • a. Susceptibility is unpredictable, so testing is warranted for extra-intestinal infections • b. Treatment of GI disease with antibiotics is controversial

  12. Vibrio, Aeromonas, Plesiomonas • A. General characteristics • 1. Different from enterics: Oxidase-positive, glucose-ferm, grow on Mac • B. Epidemiology • 1. Reservoirs • a. Vibrio: brackish or salt water • b. Aeromonas: various aquatic environments • c. Plesiomonas: fresh water • 2. Transmission • a. Vibrio: fecal-oral, exposure to contaminated seafood or water • b. Aeromonas: exp. to contam food or water; traumatic injury (fish hooks) • c. Plesiomonas: exp to contam food or water; exp to reptiles

  13. C. Pathogenesis and spectrum of disease • 1. V. cholerae • a. cholera toxin causes mucosal cells to hypersecrete water and electrolytes • b. profuse watery diarrhea, fluid loss, dehydration (rice-water stools: fluid and mucous flecks) • c. somatic O1 and O139 are markers for epidemic/pandemic strains; non O1 or O139 do not produce toxin • 2. Non-cholerae vibrio • a. specific virulence factors undefined • b. gastroenteritis from seafood, wound infections, septicemia • 3. Aeromonas and Plesiomonas • a. virulence factors unclear • b. gastroenteritis, wound infections, septicemia

  14. D. Laboratory diagnosis • 1. Specimen collection, transport, processing • a. no unique requirements except that suspected Vibrio should only be transported in Cary-Blair, because glycerol in buffered glycerol saline is toxic to vibrios • 2. Direct detection methods • a. Vibrios: gnr, slightly curved • b. Aeromonas: gnr, straight • c. Plesiomonas: gnr, single, pairs, short chains, or long filaments

  15. Gram stain of Vibrio sp. http://www2.mf.uni-lj.si/~mil/bakt2/bakt2.htm

  16. D. Laboratory diagnosis • 3. Culture and identification • a. Media • i. all grow on blood and Mac • ii. may be LFs or NLFs • iii. Thiosulfate citrate bile salts sucrose (TCBS); selective media for vibrio: ferments sucrose and makes yellow colonies on blue-green plate. • b. Colony appearance • i. look like gnrs, Aeromonas may be beta-heme • ii. all are OXIDASE-POSITIVE; we look for ox+ positive that are not Pseudomonas • c. Identification • i. API strips or similar

  17. TCBS agar for the recovery of Vibrio sp. http://idsc.nih.go.jp/idwr/kansen/k01_g1/k01_12/k01_12.html

  18. D. Laboratory diagnosis • 4. Antimicrobial susceptibility testing and therapy • a. Tetracycline or doxy are first line drugs for cholera, but fluid management for this and other orgs in main therapy • b. no standardized testing methods for any of these

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