This document summarizes an outbreak investigation of E. coli infections in multiple U.S. states. 67 cases were reported with many patients hospitalized. Initial evidence pointed to chopped onions from Taco Bell as the source, but testing ruled this out. Gram staining and culture on MacConkey agar identified the causative agent as E. coli. Antibiotic susceptibility testing showed tetracycline as the best treatment.

1. LOS TACOS
Olabade and Urma

2. Debriefing
 67 cases in NJ, NY, PA, DE, and SC
 Bloody diarrhea and severe abdominal cramps
 of 67, 51 hospitalized and 8 kidney failures (hemolytic-uremic
syndrome)
 November 20 - December 5
 Peak in the last week of November
 Had all eaten at a Taco Bell
 Chopped yellow onions tested positive for a pathogen; DNA
fingerprinting confirms onions were not source of the infection

3. Possible Culprits
 Escherichia coli
 Pseudomonas aeruginosa
 Salmonella enterica
 Staphylococcus aureus
 Streptococcus pyogenes
 Haemophilus influenzae

4. Gram Stain
 E. coli = gram –
 S. aureus = gram +
 Sample = ?

5. Gram Stain

6. Gram Stain

7. Gram Stain

8. Gram Stain

9. Gram Stain

10. Gram Stain

11. Gram Stain

12. Gram Stain

13. Microscopic
E. coli
S. aureus
Sample

14. First Elimination
 Escherichia coli (Gram-) Rod Shaped
 Pseudomonas aeruginosa (Gram-) Rod Shaped
 Salmonella enterica (Gram-) Rod Shaped
 Staphylococcus aureus (Gram+) Spherical
 Streptococcus pyogenes (Gram+)Spherical
 Haemophilus influenzae (Gram-) Rod Shaped

15. Selective/Differential

Media
MacConkey Agar
 Salt bile is selective aspect
 Lactic acid is differential aspect
 Grows Gram- bacteria and stains for lactose fermentation
 Lac+  CO2, acid, and alcohol
 agar will become a bright pink/red color when lactose is
fermented because the acid lowers the pH
 Lac-  cannot ferment the lactose
 colorless
 Gram+ can’t ferment lactose because the bile salts do not
allow for them to grow, therefore not allowing them to ferment
the lactose

16. MacConkey Agar

17. Second Elimination
 Escherichia coli (Gram-) Rod Shaped (Lac +)
 Pseudomonas aeruginosa (Gram-) Rod Shaped
(Lac-)
 Salmonella enterica (Gram-) Rod Shaped (Lac-)
 Haemophilus influenzae (Gram-) Rod Shaped
(Lac +)

18. Escherichia coli or
Haemophilus
Haemophilus
influenzae?
Escherichia coli influenzae
 Can cause:  Can cause:
 Food poisoning  Bacteremia
 Diarrhea  Pneumonia
 Gastroenteritis  Acute Bacterial
Meningitis
 Urinary Tract
Infection
 Usually in kids

19. It’s… E. coli!!
 Gram –
 Rod shaped
 Generally aerobic
 Most strains are opportunistic pathogens
 Capsulated and Non-Capsulated

20. Cell Wall/Shape/
Arrangement
 Outer membrane of cell wall is lipopolysaccharide that functions
as endotoxin
 can lead to inflammation, high fever, hypotension, capillary damage,
intravascular coagulation, tissue degradation, and irreversible shock
 Some pili let bacterium adhere to epithelial cells of the mucous
membranes
 Some cell wall adhesions let bacterium make more intimate
contact with the mucous membranes
 Some strains secrete enterotoxins that cause the loss of sodium
ions and water from the small intestines  watery diarrhea
 Some strains secrete a toxin that kills epithelial cells of the large
intestines  bloody diarrhea

21. Metabolism
 Facultative Anaerobe
 Metabolizes glucose in both the presence and
absence of oxygen

22. Location in Nature
 Lower intestine of warm-blooded organisms
 Can be found in:
 Unpasteurized milk and apple cider
 Ham, turkey, chicken, roast beef, sandwich meats
 Raw vegetables, cheese
 Contaminated water

23. Damaging Human Host
 Can severely damage lining of intestines
 Resulting in

24. Epidemiology
 Consumption of contaminated foods
 Hand- mouth
 Human-human

25. Antimicrobial
Susceptibility Test

26. Antimicrobial
Susceptibility Test

27. Antimicrobial
Susceptibility Test
E. Coli (mm) Staph (mm)
Gentamycin 21 (S) 10 (R)
Penicillin 0 (R) 27 (R)
Vancomycin 0 (R) 12 (S)
Chloramphenicol 25 (S) 17 (I)
Streptomycin 13 (I) 12 (I)
Tetracycline 22 (S) 19 (S)

28. Tetracycline
 Generally used in fighting infections of urinary tract
and intestines
 Protein Synthesis Inhibitor
 Kills bacterial cells by inhibiting their translation
 Binds to 30S ribosomal subunit
 Prevents tRNA from binding to ribosome

29. Conclusion
 Patients ingested raw or undercooked meat with E.
coli from Taco Bell
 Caused an infection
 Tetracycline is the best antibiotic to give them
 Will halt the protein synthesis in the E. coli