First detection of plasmid-mediated quinolone resistance (qnrA and qnrS) in Escherichia coli strains isolated from humans in Scandinavia.

strain with no parC mutations. This is consistent with previous findings that gyrA mutations are necessary for quinolone resistance, whereas parC mutations appear to be complementary, as resistant strains do not carry parC mutations alone. – 6 Some studies further suggest that additional parC mutations facilitate increasing levels of resistance, but our study did not support this. For example, one isolate with an MIC of 4 mg/L had two gyrA mutations only, whereas another isolate with an MIC of 1 mg/L had two gyrA mutations and one parC mutation. Other studies have also found no correlation between increasing QRDR mutations and MICs, suggesting that, in some populations, other mechanisms contribute towards quinolone resistance. One isolate had a novel mutation in gyrA (Ala-92 ! Ser), along with mutations at positions 91 and 95. Isolates with triple gyrA mutations have been rarely described. Previous reports of mutation at position 92 in gyrA have resulted in a different substituted amino acid (Ala-92 ! Pro). With the increasing use of non-culture molecular methods for the diagnosis of gonorrhoea, detailed knowledge of the range of mutations seen globally is essential to accurately detect antimicrobial resistance. The commonest combination of mutations, seen in 11 (61%) strains, involved two mutations in gyrA (Ser-91 ! Phe and Asp-95 ! Gly) and one mutation in parC (Asp-86 ! Asn); of these, 9 had an additional silent mutation at codon 131 of parC. Reported patterns of QRDR mutations vary between countries. This pattern of mutation positions, involving gyrA positions 91 and 95 and parC position 86, was also predominant in Austria, Philippines, Thailand, Denmark and Hawaii, but was not seen in India and Japan. The geographic variations may be due to clonal or polyclonal spread of different local or imported strains. Typing methods such as PFGE may help elucidate the molecular epidemiology and transmission networks of quinolone-resistant N. gonorrhoeae. In conclusion, quinolone-resistant N. gonorrhoeae at our hospital have mutation patterns similar to some countries yet distinct from others and demonstrate no correlation between MICs and number of mutations. We also describe a novel gyrA mutation. Although limited by the small number of isolates, this study enhances the existing knowledge of quinolone-resistant N. gonorrhoeae.