V DONÀ¹, S KASRAIAN¹, R ZBINDEN², B SAVIC³, F IMERI³, H FURRER⁴, N LOW⁵, A ENDIMIANI<sup>1

1</sup>Institute for Infectious Diseases, University of Bern, Bern, Switzerland, ²Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland, ³Laborgemeinschaft 1, Zurich, Switzerland, ⁴Department of Infectious Diseases, Bern University Hospital, University of Bern, Bern, Switzerland, ⁵Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland

Background: Antimicrobial resistance in Neisseria gonorrhoeae is a major public health concern, requiring continuous surveillance to identify emerging resistance and monitor susceptibility trends.

Methods: Overall, 270 N. gonorrhoeae isolates collected between 1989 and 2015 (of which: 1989-91, n=57; 1999-2003, n=71; and 2011-2015, n=99) in Bern (n=86) and Zurich (n=184) were included in our study. Antimicrobial susceptibility tests for cefixime, ceftriaxone, ciprofloxacin, azithromycin and spectinomycin were assessed using the Etest method on GC agar to obtain MIC values. Results were interpreted according to the EUCAST 2015 criteria. Sequence type (ST) was obtained from NG multi-antigen sequence typing (NG-MAST) for 105 (38.9%) representative isolates (of which: 1989-91, n=12; 2001-2005, n=32; and 2011-2015, n=61).

Results: The following MIC_50/90 (µg/ml) and % of susceptible isolates were recorded: cefixime (1989-1991: ≤0.016/0.023, 100%; 1999-2003: ≤0.016/,≤0.016, 100%; 2011-2015: ≤0.016/0.094, 96%), ceftriaxone (1989-1991: ≤0.016/≤0.016, 100%; 1999-2003: ≤0.016/0.023, 100%; 2011-2015: ≤0.016/0.032, 100%), ciprofloxacin (1989-1991: ≤0.016/≤0.016, 98%; 1999-2003: ≤0.016/4, 79%; 2011-2015: ≤0.016/≥32, 53%), and azithromycin (1989-1991: 0.125/0.38, 67%; 1999-2003: 0.19/0.38, 69%; 2011-2015: 0.19/0.38, 75%). All N. gonorrhoeae isolates were fully susceptible to spectinomycin. The most common STs in each period were: 1989-91 (ST10856, 3/12); 1999-2003 (ST8672, 3/32); 2011-2015 (ST2992, 8/61; ST1407, 3/61).

Conclusions: In Switzerland, MIC creep for extended-spectrum cephalosporins is occurring (4/99, 4.0% cefixime resistant isolates in 2011-2015). Ciprofloxacin resistance rose from 2% (1989-1991) to 47% (2011-2015) over the study period; the highest prevalence (89%) was in 2012. Around 30% of isolates in all periods were non-susceptible to azithromycin. The presence of international hyperepidemic clones (ST2992 and ST1407) was observed. Our results are consistent with those globally observed.

This study was funded by the SwissTransMed (Rapid Diagnosis of Antibiotic Resistance in Gonorrhoea, RaDAR-Go).