Inclusion Criteria:

1. Diagnosis of Autism Spectrum Disorder

2. Parent or Legally Authorized Representative willing and able to provide informed
consent

3. A reliable caregiver who can report side effects and communicate effectively with
the research team

4. Stable medications in the two months prior to enrollment

5. Currently receiving interventions in the community/school for ASD

6. If female and of childbearing potential, must be willing to utilize at least one
highly effective method of birth control for the duration of the study. This
includes condoms with spermicide, oral birth control pills, contraceptive implants,
intra-uterine devices, or diaphragms. Subjects not of reproductive potential will be
exempt (e.g. post-menopausal, surgically sterilized)

7. If male, and partner is of childbearing potential, must be willing to utilize at
least one highly effective method of birth control for the duration of the study.
This includes condoms with spermicide, oral birth control pills, contraceptive
implants, intra-uterine devices, or diaphragms. Subjects not of reproductive
potential will be exempt (surgically sterilized)

Exclusion Criteria:

1. Female subjects who are pregnant, nursing, or intend to become pregnant during the
study period.

2. Subjects whose caregivers are unable/unwilling to cooperate with the protocol
requirements.

3. Subject will be excluded who are suffering with Rett syndrome and Childhood
Disintegrative Disorder.

4. Other serious co-morbid medical disorders affecting brain function and behaviour,
including uncontrolled seizures.

5. Subjects unable to refrain from taking non-study antibiotics for the period of the
study.

6. Subjects diagnosed with cancer, except small localized basal cell carcinoma.

7. Subjects known to abuse alcohol or drugs.

8. Subjects who have undergone gastric bypass or total colectomy, or who are scheduled
for these procedures.

9. Infection with HIV.

10. Infection with Hepatitis B or C.

11. Allergy to benzodiazepine.

12. Inability to stop loperamide, diphenoxylate/atropine, or cholestyramine before the
study

13. Unable to stop opiate treatment unless on a stable dose including PRN dosing, and no
dose increase planned for the duration of the study

14. Known positive stool cultures for enteropathogens including, but not limited to
Shigella, Salmonella, and Campylobacter within 30 days before enrollment.

15. Known stool studies positive for ova and/or parasites in 30 days prior to
enrollment.

16. Planned travel outside United States during study period.

17. Hypersensitivity to vancomycin

18. Renal insufficiency

19. Colitis