Abstract
Background
Food animal AMR surveillance programs assess only small numbers of Escherichia coli (from 100 to 600 per animal class) nationally each year, severely limiting the evaluation of public health risk(s). Here we demonstrate an affordable approach for early detection of emerging resistance on a broad scale that can also accurately characterize spatial and temporal changes in resistance.
Methods
Caecal samples (n = 295) obtained from 10 meat poultry were screened using high-throughput robotics. Initial screening via agar dilution (5310 plates) quantified AMR carriage (cfu/g) for each sample. Ciprofloxacin-resistant isolates (n = 91) proceeded to downstream broth microdilution susceptibility testing. A subset of 28 ciprofloxacin-resistant isolates underwent WGS and phylogenetic analysis.
Results
Intra- and inter-flock carriage of resistance varied with drug class. Ampicillin and tetracycline resistance was ubiquitous to most birds in all flocks with an average carriage rate of 5.8 log10 cfu/g. Gentamicin and ciprofloxacin-resistant E. coli colonized fewer birds, and had an average carriage rate of 1.2 log10 cfu/g and 1.0 log10 cfu/g of faeces, respectively. Resistance to extended-spectrum cephalosporins was absent. ST354 was the dominant ST among the WGS isolates, but they demonstrated markedly lower resistance gene carriage than their international counterparts.
Conclusions
These data amply demonstrate the ineffectiveness of commonly relied-on approaches to AMR surveillance for achieving early detection of emergence, or for measuring spatial and temporal resistance trends. Genetic analysis suggested there has been transnational flow of a ciprofloxacin-resistant strain into Australian poultry flocks, explaining their detection in a nation that prohibits fluoroquinolone use in poultry.