PipEracillin Tazobactam Versus mERoPENem for Treatment of Bloodstream Infections Caused by Cephalosporin-resistant Enterobacteriaceae (PETERPEN)

Inclusion Criteria:

1. Adults (age ≥ 18 years)

2. New onset BSI due to E. coli or Klebsiella spp. in one or more blood culturesassociated with evidence of infection.

3. The microorganism will have to be non-susceptible to third generation cephalosporins (ceftriaxone and ceftazidime) and susceptible to both PTZ and meropenem (seemicrobiological methods).

4. Both community and hospital-acquired bacteremias will be included.

5. We will permit the inclusion of bacteremias due to E. coli or Klebsiella spp. withconcomitant growth in blood of skin commensals considered as contaminants.

Exclusion Criteria:

1. More than 72 hr. elapsed since initial blood culture taken, regardless of the timecovering antibiotics were started (up to 72 hrs.).

2. Polymicrobial bacteremia. Polymicrobial bacteremia will be defined as either growthof two or more different species of microorganisms in the same blood culture, orgrowth of different species in two or more separate blood cultures within the sameepisode.

3. Patients with prior bacteremia or infection that have not completed antimicrobialtherapy for the previous infectious episode.

4. Patients with septic shock at the time of enrollment and randomization, defined asat least 2 measurements of systolic blood pressure < 90 mmHg and/or use ofvasopressors (dopamine>15μg/kg/min, adrenalin>0.1μg/kg/min,noradrenalin>0.1μg/kg/min, vasopressin any dose) in the 12 hours prior torandomization. In the absence of the use of vasopressors, a systolic blood pressure <90 would need to represent a deviation for the patient's known normal bloodpressure.

5. BSI due to specific infections known at the time of randomization:

6. Endocarditis / endovascular infections

7. Osteomyelitis (not resected)

8. Central nervous system infections

9. Allergy to any of the study drugs confirmed by history taken by the investigator

10. Previous enrollment in this trial

11. Concurrent participation in another interventional clinical trial

12. Imminent death (researcher's assessment of expected death within 48 hrs. ofrecruitment)