Introduction: High-level AmpC beta-lactamase-production in Escherichia coli and Klebsiella pneumoniae (HL-AmpC-Ec/Kp) is emerging as antimicrobial resistance mechanism and is based on mutations in the promoter/attenuator of the chromosomal AmpC gene (cAmpC) or plasmid-located AmpC genes (pAmpC). This study aimed to determine the prevalence of HL-AmpC-Ec/Kp among patients in Dutch hospitals and in livestock farms.
Methods: Between September 2017 and April 2018, HL-AmpC-Ec/Kp prevalence surveys were performed in 2 hospitals, 16 pig farms and 14 broiler farms in the South of the Netherlands. Perianal or gastrointestinal stoma swabs (human) or fecal swabs (livestock) (FecalSwab, Copan Italy) were pre-enriched in a non-selective tryptic soy broth (Copan Italy) and subsequently cultured on an AmpC screening agar plate (McC, cefoxitin 8mg/L, cefotaxime or ceftazidime 1mg/L, Mediaproducts). MastDiscs (D68C, Mast Group) were used to confirm AmpC-production. Whole-genome sequencing of all phenotypic AmpC-producing Ec/Kp was performed on a MiSeq (Illumina), followed by de novo assembly with SPAdes v3.9.1 and whole-genome multilocus sequence typing (wgMLST) with Ridom SeqSphere (Ridom). ResFinder v3.1 (CGE) was used to detect acquired resistance genes and chromosomal mutations.
Results: A total number of 370 patients were cultured. Of those, 12 (3%) were rectal carrier of HL-AmpC-Ec/Kp. Mutations in the cAmpC promoter were identified in 7 Ec isolates and pAmpC (blaCMY-4,blaDHA-1) in 3 Ec and 2 Kp isolates. All HL-AmpC-Ec/Kp isolates from patients were clonally unrelated. For pig and broiler farms, 128 and 119 cultures were obtained, respectively. HL-AmpC-Ec was detected in 2 of 16 pig farms and 6 of 15 broiler farms with the prevalence of HL-AmpC-Ec-positive samples varying from 10% to 90%. Mutations in the cAmpC promoter were present in all 10 HL-AmpC-Ec isolates from pig farms and in 2 (10%) of 21 HL-AmpC-Ec isolates from broiler farms. The other 19 (90%) broiler Ec isolates all carried pAmpC (blaCMY-2). Five within-farm wgMLST clusters of 2 to 8 HL-AmpC-Ec isolates were identified in two pig farms and one broiler farm (Figure).
Conclusions: Rectal carriage of HL-AmpC-Ec/Kp was low among patients in Dutch hospitals without evidence for transmission. The prevalence of HL-AmpC-Ec/Kp in livestock farms varied between farms, and within-farm clustering was common.