Effect of Biofilm Formation on the Escherichia coli Drug Resistance of Isolates from Pigs in Central China

Background: Multi-drug resistant Escherichia coli (E. coli) can cause a variety of diseases that lead to considerable economic losses in the swine industry. In the past, the mainstream view believed that most bacterial resistance was caused by planktonic bacteria, but the ability of bacteria to form biofilms was ignored. Here, we isolated and identified 185 strains of E. coli from pigs in central China and analyzed the relationship between their genetics, antibiotic sensitivity and biofilm formation ability.Methods: First, the isolates were classified according to biofilm formation ability by semi-quantitative staining of crystal violet. Then, Phylogenetic group analysis of isolates by polymerase chain reaction. In addition, E. coli with different biofilm-forming abilities were evaluated for antimicrobial susceptibility in its planktonic and biofilm state. Finally, the drug resistance pattern of the isolates with different biofilm formation capabilities were compared.Result: most of the collected strains showed biofilm formation ability (87.57%, 162/185). The isolated E. coli with biofilm formation ability were classified into the following groups: A (16.05%, 26/162), B1 (10.49%, 17/162), B2 (33.33%, 54/162) and D (40.12%, 65/162). Simultaneously, the isolated E. coli were classified into the following groups according to the biofilm formation ability: Strong (34.57%, 56/162), Moderate (33.33%, 54/162), Weak (32.10%, 52/162) and Absent (12.43%, 23/162). Compared with the planktonic cells, the isolates showed a significant increase in the resistance rate in the biofilm form. And the isolates of the strong biofilm-forming ability group had a high drug resistance pattern. This study provides data of the drug resistance of pig-derived E. coli with different biofilm-forming abilities and provides a scientific basis for guiding veterinary clinical treatment and disease prevention.