Incomplete recovery of the fecal flora of hematological patients with neutropenia and repeated fluoroquinolone prophylaxis Yong Chong,1 Shinji Shimoda,1 Noriko Miyake,1 Takatoshi Aoki,2 Yoshikiyo Ito,3 Tomohiko Kamimura,2 Nobuyuki Shimono4 1Department of Medicine and Biosystemic Science, Kyushu University Graduate School of Medical Sciences, 2Department of Blood and Marrow Transplantation, Hara-Sanshin Hospital, Fukuoka, 3Department of Internal Medicine, Kyushu University Beppu Hospital, Beppu, 4Center for the Study of Global Infection, Kyushu University Hospital, Fukuoka, Japan Background: Routine fluoroquinolone prophylaxis in neutropenic patients with hematological malignancies is still controversial, because of antibiotic resistance concerns. The recovery of the fecal microbiota to the initial composition in patients receiving multiple courses of quinolone prophylaxis and repeated chemotherapy has not been evaluated. Methods: We prospectively examined the changes in the fecal bacterial composition before and after levofloxacin prophylaxis. A sequential observation of bacterial resistance in patients receiving multiple prophylactic courses was also conducted. Results: In this trial, 68 cases, including (35 with the first course and 33 with the second and subsequent courses) were registered. The disappearance of quinolone-susceptible (QS) Enterobacteriaceae and dominant emergence of quinolone-resistant (QR) coagulase negative staphylococci (CNS) and QR Enterococci were observed after the first prophylaxis. The detection of QS Enterobacteriaceae was recovered before the second and subsequent courses to a level of the initial composition (28/35 samples, 80.0% before the first course vs 23/33 samples, 69.7% before the second and subsequent courses,