1. Klebsiella oxytoca as a Causative Organism of Antibiotic-Associated Hemorrhagic Colitis N Engl J Med 2006;355:2418-26 N Engl J Med 2006;355:2418-26

2. Background Colitis a complication of treatment with antibiotic agents overgrowth of toxin-producing Clostridium difficile in the colon Antibiotic-associated hemorrhagic colitis a distinct form of antibiotic-associated colitis without C. difficile. Usually reported after antibiotic therapy with penicillins spontaneously resolved after cessation of antibiotics The cause is unknown : allergic reaction, mucosal ischemia, and infection with Klebsiella oxytoca

3. Background Klebsiella oxytoca gram-negative bacterium Found in patients with antibiotic-associated hemorrhagic colitis But, it was also found in healthy subjects. K. oxytoca strains isolated from patients with antibiotic- associated hemorrhagic colitis and half of the strains isolated from healthy subjects → produce a cytotoxin inducing cell death There is no in vivo animal model for antibiotic-associated hemorrhagic colitis

4. Background It is uncertain whether K. oxytoca causes antibiotic- associated hemorrhagic colitis, since Koch’s postulates have not been fulfilled. A K. oxytoca strain isolated from patients with antibiotic-associated hemorrhagic colitis was used in an animal model of antibiotic-associated hemorrhagic colitis, which allowed us to fulfill Koch’s postulates.

5. Methods Patients 22 patients who had antibiotic- associated colitis but were negative for C. difficile. Diagnostic colonoscopy, March 2001~ April 2004 Diagnosis Clinical history : use of antibiotics before the onset of diarrhea Endoscopic finding : typical of segmental hemorrhagic colitis

6. Methods Stool exam C. difficile, campylobacter, salmonella, yersinia, shigella, Escherichia coli O157, and C. difficile toxin A K. oxytoca using MacConkey agar plates Prevalence of K. oxytoca in normal bowel flora : stool samples from 385 healthy subjects

7. Methods Controls Negative control two strains of K. oxytoca (American Type Culture Collection [ATCC] 13182 and 8724) nontoxigenic Positive control cytotoxin-producing strain of K. oxytoca (MH 43-1)

8. Methods Cytotoxin Assay Filtered supernatant from the culture of K. oxytoca strains was added to the culture plates Cytotoxicity : cell rounding and cell death Antibiotic susceptibility testing isolated K. oxytoca strains use of Etest (AB Biodisk)

9. Methods Experiments in Animals Female Sprague-Dawley rats that weighed 180 to 200 g The K. oxytoca strain AHC (antibiotic hemorrhagic colitis) 1, isolated from the stool of Patient 1 The experiments lasted for 5 days. Amoxicillin–clavulanate : intraperitoneally twice daily on days 1 through 5 at a dose of 20 mg Indomethacin : subcutaneously once daily on days 3 and 4 at a dose of 1 mg On day 5 of the experiment, the intestines of animals removed for histologic examination. Stool samples (cecum, distal colon) : bacterial culture and test for C. difficile toxin A.

10. GroupNumberAmoxicillin- clavulanate AHC 1Indomethacin 111++- 28+-- 310-+- 418+++ 511+-+ 612--+

11. Methods Scoring system for histologic change of bowel specimen 1. 1. Mucosal inflammation 2. 2. Epithelial alteration 3. 3. Mucosal hemorrhage 4. 4. Mucosal erosion 0 : none 1 : infiltration of the mucosal stroma by neutrophils 2 : infiltration of the epithelial layer by neutrophils 3 : formation of crypt abscess 0 : none 1 : mild 2 : moderate 3 : severe

12. Results

13. Table 1. Characteristics of the Five Patients with Antibiotic-Associated Hemorrhagic Colitis (AAHC) Who Were Positive for K. oxytoca. Healthy subjects : K. oxytoca was founded in 6 of the 385 (1.6%)

14. Table 1. Characteristics of the Five Patients with Antibiotic-Associated Hemorrhagic Colitis (AAHC) Who Were Positive for K. oxytoca (cant’).

15. Figure 1. Colonoscopic Images in Two Patients with Antibiotic-Associated Hemorrhagic Colitis

16. Table 2. Characteristics of K. oxytoca Isolates.

17. Experiments in animals Treatment with amoxicillin–clavulanate reduced the total number of bacteria and changed the bacterial spectrum in rat stool. → Disappearance of lactobacillus after treatment. K. oxytoca AHC 1 colonized the colon of rats receiving amoxicillin–clavulanate in addition to K. oxytoca (groups 1 and 4) Isolated K. oxytoca strains had a pattern of biochemical and antibiotic resistance (ESBL) that was identical to that of the inoculated AHC 1 strain The left and small bowel were not affected.

18. Figure 2. Morphologic Changes in the Cecum of Rats, as Compared with Pathological Findings on Colonic Biopsy in Patients, According to the Histologic Score.

20. Conclusions Infection with K. oxytoca should be considered in patients with antibiotic- associated colitis who are negative for C. difficile. It will probably suffice to discontinue antibiotics and NSAIDs and to begin symptomatic therapy.