one hundred forty - seven clinical isolates of m. tuberculosis were obtained from the molecular mycobacteriology laboratory , department of microbiology , faculty of medicine , siriraj hospital , mahidol university , thailand , and the t-2 project from 1997 to 2001 ( table ) .
these strains were isolated from 74 cerebrospinal fluid ( csf ) samples and 73 sputum samples from 147 different patients .
dna from these isolates was isolated by an enzymatic method and submitted for genotyping by performing the is6110 restriction fragment length polymorphism with the standard method ( 12 ) and for sequencing the pks15/1 region ( 8) .
* csf , cerebrospinal fluid . using the genotyping results , we categorized m. tuberculosis isolates into beijing , single - banded , few - banded ( 25 bands ) , nonthaburi , and heterogeneous with > 5 bands ( table and figure 1 ) , as recently reported ( 13,14 ) .
all m. tuberculosis genotypes were sequenced around the junction of pks15 and pks1 ( corresponding to the m. tuberculosis h37rv sequence ) to determine whether they contained an intact pks15/1 or separated pks15 and pks1 .
unexpectedly , the results showed that the 7-bp insertion of pks15 that causes a frameshift mutation resulting in an intact pks15/1 was found in most strains of all genotypes , except the heterogeneous group with > 5 bands ( table and figure 2 ) .
r indicates the m. tuberculosis mt 14323 strain used as the positive control for is6110 typing .
sequence alignment of region corresponding to the 3  portion of pks15 and 5  portion of pks1 in various mycobacterium tuberculosis genotypes .
b ) m. tuberculosis strains isolated from sputum . letters in brackets refer to is6110 restriction fragment length polymorphism patterns : bj , beijing ; sb , single banded ; fb , 25 bands ; nb , nonthaburi ; h , heterogeneous .
the 7-bp insertion is shown in boldface , and the start codon of the pks1 gene is underlined .
the intact pks15/1 has been shown to be responsible for the production of phenolic glycolipids and is seemingly found in m. tuberculosis w - beijing family , but it was not found in m. tuberculosis cdc1551 and h37rv ( 8) .
previous studies suggested that pgls produced by the m. tuberculosis w - beijing family were associated with the hypervirulent phenotype by inhibiting the innate immune response ( 6,7 ) .
the intact pks15/1 has also been shown to be nonpolymorphic in the w - beijing family ; it was found in all 102 w - beijing strains tested ( 15 ) . from this observation
, we hypothesized that if the ability to produce pgls is among the factors that make this family more virulent than others , the intact pks15/1 should be absent in strains other than the w - beijing family .
our results showed that the 7-bp insertion of the pks15/1 was not only present in the w - beijing family but also in other m. tuberculosis genotypes .
although almost all beijing strains contain the intact pks15/1 ( 97% ) , 38.5%100% of strains of other genotypes also contain it .
these strains could , therefore , produce pgls and cause both pulmonary and disseminated diseases as the w - beijing strains do .
our results showed no significant difference in the percentage of m. tuberculosis isolates with an intact pks15/1 gene between csf isolates ( 65 [ 87.8% ] of 74 ) and sputum isolates ( 62 [ 84.9% ] of 73 ) .
the hypothesis that the hypervirulence of the w - beijing family is solely attributable to pks15/1 is still inconclusive .
this family may have only recently been transmitted globally and may have had more chances to cause infections and disease than other families .
although pgls are involved in the hypervirulence of the pgl - producing strains , they are not a unique characteristic of the w - beijing family
. if w - beijing strains are more virulent than others , other virulence determinants besides pgls must be responsible for the hypervirulent phenotype .
 to determine whether intact pks15/1 is unique to the w - beijing family , we investigated 147 mycobacterium tuberculosis strains with different is6110 genotypes . 
 intact pks15/1 was found in 87.8% of cerebrospinal fluid and 84.9% of sputum isolates . 
 it was found not only in w - beijing strains ( 97% ) but also in other genotypes ( 38.5%100% ) . 