Upquotes for code

I am using dblatex to generate pdf content from docbook source files.

I was able to make programlisting (listings in Latex) to produce
straight quotes by passing a file named 'textstyle.sty' whose contents
is as follows
------------------------
%%
%% This style is derived from the manual
%% http://dblatex.sourceforge.net/doc/manual/sec-custom-latex.html
%%
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{texstyle}[2017/04/25 PostGIS DocBook Style]

%% Just use the original package and pass the options
\RequirePackageWithOptions{docbook}

%% Make regular quotes within programlisting tags (#3726)
\usepackage{upquote}
\usepackage{listings}
\lstset{upquote=true}
------------------------

However this does not work with inline code (texttt in Latex). When
compiling with the debug flag

$dblatex -s texstyle.sty -d mobilitydb-berlinmod.xml

and analyze the generated file I can see that there is NO

\usepackage{upquote}

and the content where the problem is looks as follows

.... with one of the values \texttt{'minimal'} (the default),
\texttt{'medium'}, ....

Any idea how to solve this ?

Thanks for your answer !