High Prevalence and Predominance of the aph(2″)-If Gene Conferring Aminoglycoside Resistance in Campylobacter

Abstract

Campylobacter is a major foodborne pathogen, and previous studies revealed that Campylobacter isolates from food-producing animals are increasingly resistant to gentamicin in China. The molecular epidemiology and genetic mechanisms responsible for gentamicin resistance in China have not been well understood. In this study, 607 Campylobacter isolates of chicken and swine origins collected in 2014 were analyzed, revealing that 15.6% (25/160) of the Campylobacter jejuni isolates and 79.9% (357/447) of the Campylobacter coli isolates were resistant to gentamicin. PCR detection of the gentamicin resistance genes indicated that aph(2″)-If was more prevalent than the previously identified aacA/aphD gene and has become the dominant gentamicin resistance determinant in Campylobacter Transformation and whole-genome sequencing as well as long-range PCR discovered that aph(2″)-If was located on a chromosomal segment inserted between two conserved genes, Cj0299 and panB Cloning of aph(2″)-If into gentamicin-susceptible C. jejuni NCTC 11168 confirmed its function in conferring high-level resistance to gentamicin and kanamycin. Molecular typing by pulsed-field gel electrophoresis suggested that both regional expansion of a particular clone and horizontal transmission were involved in the dissemination of the aph(2″)-If gene in Campylobacter To our knowledge, this is the first report describing the high prevalence of a chromosomally encoded aph(2″)-If gene in Campylobacter The high prevalence and predominance of this gene might be driven by the use of aminoglycoside antibiotics in food animal production in China and potentially compromise the usefulness of gentamicin as a therapeutic agent for Campylobacter-associated systemic infection.

Keywords: Campylobacter; aph(2″)-If; food safety; gentamicin resistance.

FIG 1

Distributions of gentamicin MICs for C. coli (n = 447) and C. jejuni (n = 160) isolates. The breakpoint for gentamicin resistance is 8 μg/ml.

FIG 2

Chromosomal organization of the aph(2″)-If-carrying segment in C. coli HS11B and C. jejuni CN9 in comparison with plasmid pCG8245, pN29710-1, the multidrug resistance genomic island of C. coli SX81, and C. jejuni NCTC 11168. Arrows indicate the positions and directions of transcription of the genes. The locations of primers panB-F and cj0299-R used to detect the unique genomic island are indicated. The gray-shaded areas represent regions sharing 99% DNA identity. Gentamicin resistance genes are colored red, while other aminoglycoside resistance genes are colored yellow. Chloramphenicol and tetracycline genes are colored pink and blue, respectively.

FIG 3

PFGE analysis of aph(2″)-If-positive C. coli (A) and C. jejuni (B) isolates. SmaI was used for digestion of the genomic DNA. Isolation sources include Guangdong (GD), Shandong (SD), Ningxia (NX), and Shanghai (SH). Hosts include chicken (C) and swine (S). Abbreviations of antimicrobial agents: C, ciprofloxacin; T, tetracycline; E, erythromycin; F, florfenicol; L, clindamycin; K, kanamycin; G, gentamicin.