The purpose of this study is to investigate the effect of administration of CAZ-AVI and CXL on the intestinal flora of male and female healthy volunteers after multiple administrations over 7 days. An assessment of the effect on intestinal flora is an important aspect to understand for the safe clinical use of the investigational products and is expected by regulatory agencies.

Inclusion Criteria:

1. Provision of signed and dated, written informed consent prior to any study specific procedures

2. Healthy male and female volunteers aged 18 to 45 years (inclusive) with suitable veins for cannulation or repeated venepuncture.

   Females: Female healthy volunteers are authorised to participate in this study if both of the following criteria are met:

   1. A negative serum pregnancy test BOTH at screening AND at admission to the study centre.
   2. Agrees not to attempt pregnancy while receiving investigational product and for a period of 7 days after last investigational product administration, and agrees to the use of acceptable methods of contraception (according to instructions) prior to, during, and for 7 days after the last investigational product administration.

3. Have a body mass index (BMI) between 19 and 30 kg/m2.

Exclusion Criteria:

1. History or presence of gastrointestinal, hepatic, or renal disease or any other condition known to interfere with the absorption, distribution, metabolism, or excretion of drugs.
2. Any clinically significant abnormalities in physical examination, ECG, clinical chemistry, haematology, coagulation, or urinalysis results, as judged by the investigator.
3. Pregnant or breastfeeding female healthy volunteers.
4. History of any clinically significant disease or disorder which, in the opinion of the investigator, may either put the healthy volunteer at risk because of participation in the study, or influence the results or the healthy volunteer's ability to participate in the study.
5. Known history of Clostridium difficile infection in last 3 months.