Doesn't add spaces between symbols

Given the mathml

<math xmlns="http://www.w3.org/1998/Math/MathML">
 <apply>
  <times />
  <ci>k1</ci>
  <ci>k2</ci>
  <ci>S1</ci>
 </apply>
</math>

the latex conversion is

'$\mathrm{k1}\mathrm{k2}\mathrm{S1}$'

this renders to 

k1k2S1 

ie there is no spacing between the symbols.