Neisseria adhesin A (NadA), involved in the adhesion and invasion of Neisseria 
meningitidis into host tissues, is one of the major components of Bexsero, a 
novel multicomponent vaccine licensed for protection against meningococcal 
serogroup B in Europe, Australia, and Canada. NadA has been identified in 
approximately 30% of clinical isolates and in a much lower proportion of carrier 
isolates. Three protein variants were originally identified in invasive 
meningococci and named NadA-1, NadA-2, and NadA-3, whereas most carrier isolates 
either lacked the gene or harbored a different variant, NadA-4. Further analysis 
of isolates belonging to the sequence type 213 (ST-213) clonal complex 
identified NadA-5, which was structurally similar to NadA-4, but more distantly 
related to NadA-1, -2, and -3. At the time of this writing, more than 89 
distinct nadA allele sequences and 43 distinct peptides have been described. 
Here, we present a revised nomenclature system, taking into account the complete 
data set, which is compatible with previous classification schemes and is 
expandable. The main features of this new scheme include (i) the grouping of the 
previously named NadA-2 and NadA-3 variants into a single NadA-2/3 variant, (ii) 
the grouping of the previously assigned NadA-4 and NadA-5 variants into a single 
NadA-4/5 variant, (iii) the introduction of an additional variant (NadA-6), and 
(iv) the classification of the variants into two main groups, named groups I and 
II. To facilitate querying of the sequences and submission of new allele 
sequences, the nucleotide and amino acid sequences are available at 
http://pubmlst.org/neisseria/NadA/.