Objectives To determine the antibiotic phenotype and MAST-genotype distribution of Neisseria gonorrhoeae isolates in Portugal between 2004 and 2009, and to evaluate specific associations between MAST-genotypes and sexual orientation, age and antibiotic resistance.

Methods A total of 236 N gonorrhoeae isolates were typed through N gonorrhoeae multiantigen sequence typing (NG-MAST). The degree of polymorphism and the phylogenetic relatedness among NG-MAST sequence types (STs) were evaluated with MEGA4 software on concatenated sequences of por and tbpb alleles. Etest was used to determine the susceptibility to ceftriaxone, ciprofloxacin, penicillin and spectinomycin.

Results No isolates displayed resistance to spectinomycin and ceftriaxone, whereas 79.1% and 37.4% were resistant to penicillin and ciprofloxacin, respectively. A total of 104 different STs (one per 2.3 isolates) were found; the most common were ST210 (8.1%) and ST225 (7.6%). STs formed two major groups separated by 159.8 (SE 8.9) nucleotide differences, yielding several subgroups, one of them including the worldwide-prevalent ST225. The probability of ciprofloxacin resistance among isolates within this subgroup was 73.5-fold higher than for the remaining isolates. Indeed, for the genetically closest subgroup, which includes the most prevalent ST (ST210), only 8.0% of isolates were resistant to ciprofloxacin. There was a non-homogeneous distribution per year for ST225 (p<0.001), ST210 (p=0.011) and ST2 (p=0.007).

Conclusions The heterogeneous ST scenario may represent the ‘tip of the iceberg’, reflecting a high number of undiagnosed and unreported gonorrhoea cases. A laboratory-based national surveillance of N gonorrhoeae infections is necessary to provide a broader spectrum of isolates that will allow the sexual network situation in Portugal to be established.