2011 Postgraduate Research Competition - UNSW Science - The ...

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Variation of pertussis toxin promoter (ptxP) and the
re-emergence of Bordetella pertussis
Connie Lam and Ruiting Lan
School of Biotechnology & Biomolecular Sciences
Abstract
Variation of pertussis toxin promoter (ptxP) and the re-emergence of Bordetella pertussis
Vaccines against pertussis, caused by the bacterium Bordetella pertussis, were developed in
the 1950s, but due to side effects were replaced by acellular vaccines in the 1990s. Despite
high vaccination rates, epidemic cycles of pertussis continue to occur, with the most recent
Australian epidemic in 2008.
Isolates of B. pertussis have been characterised by changes in genes encoding antigenic
components of acellular vaccines, including pertussis toxin. The production of pertussis toxin is
controlled by the gene ptxP. In this study, the ptxP of 313 global B. pertussis isolates were
sequenced. There were 2 predominant ptxP types: ptxP1 and ptxP3 which differed by a
single base change. ptxP3 has been shown to be capable of inducing the organism to
produce a higher level of toxin.
We found 73% of isolates carried ptxP1, and were largely older isolates collected prior to the
introduction of the acellular vaccine. More interesting however, is the fact that the most
recent group of isolates all carried ptxP3. Based on epidemiological data, we have shown
that the ptxP3 emerged only after the introduction of the acellular vaccine in the 1990s.
Together with other antigenic gene variations observed previously, our results suggest the
change in ptxP allows current isolates to evade vaccine induced selection pressure and
cause more severe disease.
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