Transrectal prostate biopsies carry the risk of infection. By using non-selective culture plates, instead of commonly used ciprofloxacin (CIP)-containing plates, we analyzed the association between Escherichia coli CIP minimal inhibitory concentration (MIC) and post-biopsy infectious complications. A pre-biopsy rectal swab was taken from 207 consecutive men, scheduled for transrectal 12-core prostate biopsy with CIP 750 mg as the mostly used prophylaxis. CIP MIC of rectal Gram-negative bacilli was determined from a chromogenic agar. Rectal E. coli were categorized to resistant (R) and intermediate (I) isolates together (R + I, MIC > 0.25 mg/l) and to sensitive (S, MIC ≤ 0.25 mg/l) using EUCAST clinical breakpoints. In addition, epidemiological cutoff (ECOFF R, MIC > 0.064 mg/l) was used for categorization. Eighteen (8.7%) men showed CIP R + I E. coli by the EUCAST breakpoints and 41 (19.8%) using the ECOFF R criteria. During follow-up, 15 (7.2%) men had infectious symptoms, of which 9 (4.3%) were culture-confirmed infections. Only 4 (26.7%) of these 15 patients showed R + I E. coli in the rectal swab according to EUCAST, but 10 (66.7%) using the ECOFF cutoff. Rectal E. coli CIP R + I by the EUCAST clinical breakpoints associated with infectious complications with OR 5.7 (95% CI 1.5-21.8, P = 0.005) and ECOFF R E. coli by OR 10.7 (95% CI 3.0-37.6, P < 0.001). Men carrying rectal E. coli with moderately lowered CIP susceptibility (MIC > ECOFF 0.064 mg/l) were identified and, interestingly, they showed a high risk of developing infectious symptoms after the biopsy. This explains why some men develop infectious complications despite appropriate antibiotics before prostatic biopsies.
Trial registration: NCT02140502.
Keywords: Antibiotic prophylaxis; Complication; Infection; Prostate biopsy.