Molecular characterization of Neisseria gonorrhoeae identifies transmission and resistance of one ciprofloxacin-resistant strain

Abstract

A highly discriminative and objective genetic characterization of N. gonorrhoeae, which increases our knowledge of strain populations in different geographic areas, is crucial for the development of improved control measures. In the present study, conventional phenotypic characterization and genetic characterization by means of pulsed-field gel electrophoresis (PFGE), sequencing of the entire porB gene, N. gonorrhoeae multiantigen sequence typing (NG-MAST), and pyrosequencing of a quinolone resistance determining region (QRDR) of the gyrA gene of Swedish ciprofloxacin-resistant N. gonorrhoeae serovar IB-10 isolates (n=45) were performed. The genetic characterization identified one widely spread ciprofloxacin-resistant N. gonorrhoeae ST147 strain. In addition, isolates with slightly different genetic characteristics, which presumably reflect the ongoing evolution only, were also identified. All the isolates contained single nucleotide polymorphisms in QRDR of the gyrA gene that are highly correlated with ciprofloxacin resistance. Consequently, comprehensive characterization identified the first confirmed large domestic transmission, mainly among young heterosexuals, of one ciprofloxacin-resistant N. gonorrhoeae strain in Swedish society during 2002-2003. In conclusion, a precise, i.e. genetic, characterization for identification of individual strains is a very valuable support to the crucial active surveillance of the epidemiological characteristics and the antibiotic susceptibility of N. gonorrhoeae in the effective treatment of gonorrhoea.

Fig. 1

Neighbor-joining phylogenetic tree describing the evolutionary relationship of porB1b gene sequences (993 unambiguously aligned nucleotides) coding for the mature PorB (10) of clinical Neisseria gonorrhoeae serovar IB-10 isolates (n=47). The porB1b sequence of the N. gonorrhoeae IB-9 reference strain (CCUG 15821), which represents an outgroup, was used to root the tree. The length of the branches leading to the outgroup has been reduced by a factor of four. The N. gonorrhoeae multiantigen sequence typing (NG-MAST) sequence types (STs) are denoted. The pulsed-field gel electrophoresis (PFGE) types (no band difference, e.g. A) and variants (e.g. A1), i.e. less than seven bands difference in both the SpeI and the BglII fingerprints, are shown. The serovars of the isolates using Pharmacia (Ph) MAbs are indicated in italics. The designation of each isolate (laboratory number/year of isolation) and the susceptibility to ciprofloxacin (CipS, susceptible; CipR, resistant) are also shown. The isolates that originated in the domestic core group in a Swedish county in 2003 are shaded. *, indicates not previously identified ST.