Spread of Extended Spectrum Cephalosporinase-Producing Escherichia coli Clones and Plasmids from Parent Animals to Broilers and to Broiler Meat in a Production Without Use of Cephalosporins

Abstract

Objectives:

This study investigated the occurrence of extended spectrum cephalosporinase (ESC)–producing Escherichia coli in a broiler production with no cephalosporin use and a low use of antimicrobials in general. Furthermore, it investigated whether the current consumption of aminopenicillins selects for ESC-producing E. coli and whether certain clones or plasmids spread from imported parent flocks to the meat.

Materials and Methods:

ESC-producing E. coli was isolated using MacConkey broth with 1 mg/L of ceftriaxone. ESC genes were identified using polymerase chain reaction and sequencing. Isolates with bla _CMY-2 were subtyped by pulsed-field gel electrophoresis (PFGE), phylotyping, and antimicrobial susceptibility testing. Selected isolates were used as donors in filter-mating experiments, multilocus sequence typing (MLST), and plasmid replicons were typed. Aminopenicillin use at the farm (not flock) level was obtained from VetStat, a database for mandatory registration of veterinary prescriptions in Denmark.

Results:

ESC-producing E. coli occurred in 93% (27/29) of broiler parent farms in 2011, 27% (53/197) of broiler flocks in 2010, and 3.3% (4/121) of Danish retail broiler meat in 2009 and 8.6% (16/187) in 2010. The ESC producing E. coli contained bla _CMY-2, bla _SHV-2 or bla _CTX-M-1. Isolates with bla _CMY-2 represented 35 PFGE groups. One group dominated (39 isolates) and included isolates with indistinguishable PFGE patterns from parents, broilers, and meat. Most bla _CMY-2 isolates were susceptible to non-β-lactams, and bla _CMY-2 was mostly present on horizontally transferable incI1 or incK plasmids. Phylogroup D was most common and E. coli MLST types previously found in humans were observed. Broiler farms with registered aminopenicillin use had significantly higher occurrence of ESC E. coli.

Conclusions:

ESC-producing E. coli from flocks of imported broiler parents spread clonally and horizontally to broiler meat (including potentially human pathogenic types) even in a country with no cephalosporin use. Use of aminopenicillins may influence the persistence of ESC-producing E. coli in the broiler production, but other factors should be investigated.