Species versus Biotype Status

I was very disappointed to see that the pointless discussion regarding the species versus biotype status of Ara⁻ and Ara⁺ strains of Burkholderia pseudomallei continues (3). My laboratory has performed a number of studies on B. pseudomallei and B. pseudomallei-like strains, and we demonstrated using well-defined criteria that these should be classified as two separate species (1). In 1998, the International Journal of Systematic Bacteriology published a manuscript, based upon peer-reviewed studies from my laboratory, indicating tht B. pseudomallei-like strains should be awarded separate species status and that this species should be named Burkholderia thailandensis (2). The awarding of species status was based upon significant differences between B. thailandensis and B. pseudomallei, including distinctive nucleotide sequence differences in 16S rRNA (15 nucleotide dissimilarities), differences in lipopolysaccharide composition [B. thailandensis synthesizes a repeating disaccharide having the structure →3)-β-d-glucopyranose-(1→3)-6-deoxy-α-l-talopyranose-(1→; B. pseudomallei strains also produce this repeating disaccharide as well as a 1,3-linked homopolymer of 2-O-acetylated 6-deoxy-β-d-manno-heptopyranosyl residues (4, 5)], differences in colonial morphology on Ashdown's selective medium (B. thailandensis colonies are smooth and glossy with a pink pigmentation, while B. pseudomallei colonies are rough and wrinkled with a dark purple pigmentation [6]), biochemical differences (B. thailandensis assimilates l-arabinose, 5-keto-gluconate, and adonitol, and it does not utilize erythritol and dulcitol as carbon sources; B. pseudomallei does not assimilate l-arabinose, 5-keto-gluconate, and adonitol, and it does utilize erythritol and dulcitol as carbon sources [6]). B. thailandensis is not associated with human disease, and B. pseudomallei is associated with human disease (6), B. thailandensis is avirulent for Syrian golden hamsters (50% lethal dose [LD₅₀] > 10⁵), and B. pseudomallei is virulent for Syrian golden hamsters (LD₅₀ < 10⁰) (2).

In November 1998, at the International Congress on Melioidosis held in Bangkok, Thailand, the authors of the article recently published in the Journal of Clinical Microbiology (3) presented data published in abstract form, showing that distinctive nucleotide sequence differences in the 16S rRNA gene of Ara⁺ and Ara⁻ B. pseudomallei could be detected by a simple PCR system and that these nucleotide diffferences appeared to be species specific (7). Additionally, the same group proposed that the species name B. siamensis be given to this new species rather than B. thailandensis, since the former more appropriately describes the geographic location where the organism was first identified. The authors also indicated that Siam is the Thai name for Thailand, and the taxon siamensis has been used to describe many indigenous species found in Thailand. As the species name B. thailandensis clearly has precedent over B. siamensis, this proposal was not accepted.

When will the madness end?