Asymptomatic bacteriuria (AB) is the isolation of a bacterium in a sample of urine appropriately collected from a person who does not have signs or symptoms of urinary infection. It is common in diabetic women, in pregnant women, in men over 60 years and in patients with spinal cord injury.

There is clinical evidence that AB should be treated in patients who will be operated on with urologic surgery because of the risk of presenting infectious complications; however, the timing of initiating antibiotic therapy has not been established, even in some studies the prophylaxis has been considered from one to seven days prior to the procedure, without determining the differences in the outcome for each one of the interventions and causing an undue and risky use of antibiotics.

A randomized, parallel-design, single-masked clinical trial will be performed to compare and analysis the bloodstream infections, surgical site infections, readmissions and hospital stay in three intervention groups, 1) those receiving antibiotics during the previous 5 days to the procedure; 2) 3 days prior to the procedure; and 3) those who receive only a single dose of antibiotic on the day of the procedure.

The main expected result is to identify the timing of initiation of antibiotic prophylaxis in urological procedures in patients with asymptomatic bacteriuria, with the purpose of diminishing the bloodstream and of the surgical site infections. If it is scientifically demonstrated that those patients who receive a single dose of antibiotic on the same day of the procedure, have the same safety and effectiveness compared to the other two groups, would reduce hospital stay, surgical waiting time and indiscriminate use of antibiotics that generate multidrug-resistant microorganisms, thus generating an impact on Public Health and on the quality of care.

Inclusion Criteria:

• Age ≥ 18 years
• Patients with asymptomatic bacteriuria identified with a urine culture prior to the surgical procedure and with a microorganism that meets the following criteria: 1) gram-negative bacteria in the enterobacterial family and non-fermenting bacilli; 2) Bacteria with resistance profile has a therapeutic option that reaches therapeutic concentration in urine.
• Patients scheduled for urological procedures, such as: transurethral resection of the prostate, open prostatectomy, cystoscopy, extracorporeal lithotripsy and flexible ureterorenoscopy.
• Informed consent

Exclusion Criteria:

• Patients with chronic renal failure; with immunosuppressive status secondary to glucocorticoid consumption, haematological or solid organ neoplasms undergoing chemotherapy or radiation therapy or neutropenia.
• Patients with active infection or clinical criteria of urinary infection.
• Patients who voluntarily do not want to participate in the study.
• Patients who can not give informed consent under reasonable or vulnerable conditions.
• Patients who present type I allergy to penicillin.
• Patients who have scheduled surgeries combined with a discipline different to urology.

A single blinding will be performed. To the database will be categorized the variable "duration of prophylaxis" so that the person in charge of analysing the data, does not know the true allocation of each of the participants. At the end of the tabulation and analysis of the data, the true allocation will be known.