Effect of Seed Sludge on Survival of Antibiotic-Resistant Bacteria and Fate of Bacteria Resistant to Different Classes of Antibiotics during Anaerobic Digestion of Dairy Manure

Abstract

Livestock manure is one of main pollution reservoirs of antibiotic-resistant bacteria (ARBs) due to excessive use of veterinary antibiotics. For preventing the environmental spread, an efficient process is required to reduce ARBs in livestock manure. In this work, we investigated the survival of ARB during mesophilic anaerobic digestion of dairy cattle manure. Effects of seed sludge and the antibiotic class were investigated for reduction of ARBs by batch digestion tests. The numbers of all ARBs were 6.34×10 4 to 2.08×10 6 before anaerobic digestion. The numbers of oxytetracycline, chlortetracycline, gentamicin and kanamycin -resistant bacteria decreased close to the detection limit after 20-day anaerobic digestion. However, reduction effects of cefazolin and streptomycin -resistant bacteria were small. The seed sludge had little influence on the survival of ARBs during the anaerobic digestion. The results showed that the ARB reduction effect was influenced by the types of antibiotics, and mostly not by seed sludge.