Quinolone resistant Escherichia coli from broiler in Norway - characterization, comparison to human isolates and molecular risk assessment

Background: The usage of fluoroquinolones (FQ) in the Norwegian livestock production is nearly negligible and findings of quinolone resistant Escherichia coli (QREC) in the Norwegian monitoring program for antimicrobial resistance in the veterinary sector (NORM-VET) has been rare. However, in NORM-VET 2014 a selective method was implemented for screening of QREC in poultry and QREC was found in 89.5% of caecal samples and in 70.7% of meat samples. It is unknown if humans have acquired QREC from a poultry reservoir. In this study we aimed to characterize QREC from poultry and humans in Norway. Furthermore comparison studies were carried out in order to investigate possible overlap between isolates of the two reservoirs. Material/methods: Isolates from poultry meat and caecal samples defined as resistant to nalidixic acid and/or ciprofloxacin in NORM-VET 2014 were included in the present study. These isolates (n=336) were subjected to PCR-based phylotyping and a subset were screened for gyrA mutations by PCR and sequencing. Isolates from human origin resistant to fluoroquinolones were collected via the Norwegian monitoring program for human pathogens (NORM) from urinary tract infections and sepsis, and from a study screening of healthy carriers of QREC. Resistance data was extracted from the monitoring programs (NORM-VET and NORM) and compared between isolates of poultry and human origin. A subset of 192 isolates, 96 from each category will be subjected to whole-genome-sequencing (WGS) using Nextera XT library prep and a HiSeq 250 bp PE rapid run on a HiSeq 2500. Results: Resistance data from NORM-VET 2014 showed that the majority of the broiler isolates exhibit high level resistance to nalidixic acid (> 128 mg/L), but low level tolerance to ciprofloxacin (MICs 0.12-0.5). Mutation in the gyrA gene was identified at position Ser83→Leu in a subset of relevant isolates. Furthermore the isolates grouped in the following phylogroups; 44.1% B2, 23.7% D, 18% B, 13% A, and 1.2% were non-typeable. Data from the NORM program showed that the human isolates had a different MIC distribution with the largest proportion of isolates exhibiting high level ciprofloxacin resistance (MICs > 0.25), indicative of more mutations in the gyrA/parC genes. However, a considerable proportion of human isolates exhibited a quinolone resistance MIC profile corresponding to the most common profile found among the broiler isolates. Half of the selected poultry isolates (n=48), from both poultry meat and poultry caecal samples has been subjected to WGS. These isolates were chosen on the background of their MIC profiles. Conclusions: The preliminary data indicates that the main mechanism behind quinolone resistance in the broiler isolates is somewhat different than the mechanism responsible in the majority of human isolates. Human isolates with a typical “broiler MIC profile” was detected; genetic relationship among the isolates will be investigated.