Colistin Induces Resistance through Biofilm Formation, via Increased <i>phoQ</i> Expression, in Avian Pathogenic <i>Escherichia coli</i>

Abstract

This study aimed to optimize the colistin-based antibacterial therapy to prevent antimicrobial resistance related to biofilm formation in avian pathogenic Escherichia coli (APEC) in chicken. Of all the bacterial isolates (n = 136), 69 were identified as APEC by polymerase chain reaction (PCR). Through a series of antibiotic susceptibility tests, susceptibility to colistin (50 concentration (1.00 μg/mL), and regrowth was not inhibited even during multiple exposures. However, upon exposure to 8 μg/mL—a concentration that was close to the MPC—the growth of APEC was inhibited, including in the resistant strains. Additionally, colistin-induced resistant strains showed a slower growth compared with the susceptible ones. Colistin-induced resistant APEC strains did not show colistin resistance gene (mcr-1). However, the expression of higher mgrB and phoQ levels was observed in the resistant strains. Furthermore, these strains showed increased formation of biofilm. Hence, the present study indicated that colistin could induce resistance through the increased formation of biofilm in APEC strains by enhancing the expression of phoQ.

Keywords

• antibacterial therapy
• colistin
• Avian Pathogenic <i>Escherichia coli</i> (APEC)
• antibiotic resistance
• biofilm formation