**4. Conclusion**

The removal efficiency of antibiotics in wastewater sludge was enhanced using the bacterial strains isolated in this study. Batch experiments indicated that the combination of two bacterial strains enhanced the biodegradation of antibiotics in sludge to a greater extent than the application of a single bacterial strain under both aerobic and anaerobic conditions. The efficiency was comparable between the aerobic and anaerobic settings. However, anaerobic biodegradation required a longer incubation time (by 2-fold) than aerobic biodegradation. The results of repeated addition experiments indicated that the efficiency of the biodegradation of antibiotics using bacterial strains could be maintained for at least three degradation runs. The added antibiotic-degrading bacteria not only degraded antibiotics directly but also changed the composition of the microbial community in the sludge. As a consequence, the composition of the xenobiotic degradation pathways and the antibiotic degradation capacity were changed.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2073-4441/12/8/2147/s1, Table S1: Chemicals structures of target compounds, Table S2: five groups of major microbial genera in the five experimental conditions, Table S3: The PubMed ID, title and abstract of iterature reported antibiotics-degrading bacterial genera.

**Author Contributions:** Formal analysis, C.L.; Funding acquisition, B.-V.C.; Methodology, C.-W.Y. and C.L.; Project administration, B.-V.C.; Visualization, C.-W.Y.; Writing—original draft, C.-W.Y. and B.-V.C.; Writing—review and editing, C.-W.Y. and B.-V.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Ministry of Science and Technology, Taiwan (grant no. MOST 107-2313-B-031-002).

**Conflicts of Interest:** The authors declare that they have no conflict of interest.
