The fibronectin-binding protein SfbI is expressed by
approximately 50 % of invasive isolates of S. pyogenes and
is regarded as one of the major adhesins and invasins
(Medina et al., 2000). Sof is regarded as a major virulence
factor that is known to contribute to pathogenesis of
streptococcal infection in animal models (Courtney &
Pownall, 2010). The sof gene was first sequenced over
15 years ago (Rakonjac et al., 1995) and its product was
found to be a surface bound protein of over 100 kDa, with a
C-terminal domain comprised of numerous repeating
peptides that bound to both fibronectin and fibrinogen
(Courtney et al., 2003; Courtney & Pownall, 2010). End
point RT-PCR found that the genes encoding both of these
proteins were differentially expressed in response to
treatment with a sublethal dose of manuka honey. In both
instances, reduced expression was noticeable, with levels of
sof below the threshold of detection. The primary end point
for determining the RNA extraction efficiency prior to RTPCR
was total bacterial DNA, quantified using a NanoDrop.
The half-life of bacterial mRNA is estimated to be between
0.5 and 20 min, but different RNA transcripts degrade at
different rates. Studies with S. pyogenes have shown that degradation of transcripts can be broadly grouped into two
classes (Bugrysheva & Scott, 2010). Information concerning
the half-life of the transcripts used in this study was not
available; however, all RNA samples were handled and
maintained in a manner designed to minimize degradation,
as recommended (Promega). With this in mind, we feel
confident that while the effect of the half-life of the RNA
transcripts on the observed levels of RT-PCR product
cannot be ignored, it is unlikely to be the sole reason for the
differential levels of PCR product observed here.