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

Na-Hye Park,Seung-Jin Lee,Biruk Tesfaye Birhanu,Eon-Bee Lee,Seung-Chun Park

doi:10.3390/pathogens10111525

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 (<2 μg/mL) was confirmed in all isolates. Hence, a mutant selection window (MSW) was determined to obtain colistin-induced resistant bacteria. The minimum inhibitory concentration (MIC) of colistin against the colistin-induced resistant APEC strains ranged from 8 to 16 μg/mL. To identify the inhibitory activity of colistin against the resistant strains, the mutant prevention concentration (MPC) was investigated for 72 h, and the single and multi-dose colistin activities were determined through the time-kill curve against APEC strains. Bacterial regrowth occurred after 12 h at a double MIC50 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.

Highlights

Antibiotics are used to treat bacterial infections and to prevent further spreading of disease in humans and livestock
The indefinite application of antimicrobials in poultry farms is the main cause of the emergence of drug-resistant pathogens, such as Escherichia coli (E. coli) [2]
The expression of various genes of the avian pathogenic Escherichia coli (APEC) strains is presented in Table S1 and Figure S1

Summary

Introduction

Antibiotics are used to treat bacterial infections and to prevent further spreading of disease in humans and livestock. The emergence of antimicrobial resistance in several bacterial agents poses a threat for the future treatment and control of infections [1]. Poultry farms, which are an important source of eggs and meat for human consumption, are alarmingly affected by drug resistant gram-negative bacteria. The indefinite application of antimicrobials in poultry farms is the main cause of the emergence of drug-resistant pathogens, such as Escherichia coli (E. coli) [2]. APEC is a major pathogen of the Enterobacteriaceae family that causes colibacillosis, an acute and mostly systemic disease with respiratory symptoms [4,5,6,7]

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Results