Introduction

The two-locus NG-MAST procedure has been developed for the characterisation of isolates of N. gonorrhoeae, the causative bacterium of gonorrhoea.

The method uses two of the most variable gonococcal genes to provide a method that is discriminatory and where the genotypes of strains are likely to diversify rapidly. This approach has been taken as the main interest in characterising gonococcal strains is to identify clusters of linked individuals by the sharing of the same gonococcal strain.

See Martin et al. (2004) J. Infect. Dis. 189: 1497-1505 for further details.

The two-digit allelic profile of a N. gonorrhoeae strain is obtained by sequencing internal regions of the genes encoding two variable outer membrane proteins, Por and TbpB.

The primers for amplification and sequencing are the same and can be obtained here.

Sequences for both strands are necessary to provide accuracy. The sequences are then trimmed to a fixed length from known conserved regions of the genes, so they can be compared to all existing alleles.

For a query isolate, the sequences for por and tbpB must be checked separately and this can be done as a single query or as a batch query from the ‘locus query’ drop down box. Paste your sequence into the box, select the gene from the drop down box, and then press the submit query button.

The software will check that the sequence(s) is/are of the correct length and does not contain any unrecognised characters. The sequence(s) are then checked against all existing alleles. The software will report if the sequence matches an existing allele (and will provide its allele number) or will assign a new allele number if the sequence has not been found previously.
The allele numbers at the two loci (in the order por-tbpB) provide a convenient two-digit identifier (e.g. 36-156) and each unique two-digit identifier is assigned a sequence type (ST).

To date, isolates of N. gonorrhoeae that have been characterised using the por and tbpB sequence data are from many sources: surveillance isolates collected in London as part of the national surveillance in England and Wales (GRASP), random isolates from diverse geographical locations, isolates from known sexual contacts, high level antibiotic resistant strains (PPNG, PP/TRNG, TRNG, QRNG, CMRNG).