% arara: pdflatex
% arara: makeglossaries
% arara: pdflatex
\documentclass[12pt]{article}

\usepackage[colorlinks]{hyperref}
\usepackage[style=tree]{glossaries-extra}

\makeglossaries

\newcommand{\latinname}[1]{\emph{#1}}
\glssetcategoriesattributes{genus,species}{textformat,glossnamefont}{latinname}

\setabbreviationstyle[genus]{long-only-short-only-desc}
\newabbreviation[category=genus,description={}]{clostridium}{C.}{Clostridium}

\newglossaryentry{botulinum}{name=botulinum,category=species,
  description={},parent=clostridium}
\newglossaryentry{perfringens}{name=perfringens,category=species,
  description={},parent=clostridium}
\newglossaryentry{tetani}{name=tetani,category=species,
  description={},parent=clostridium}

\multiglossaryentrysetup{indexothers=false,hyper=mainonly}

\multiglossaryentry
 [firstsuffix=botulism]% suffix on first use of multi-entry set
 {cbot}{clostridium,botulinum}
\multiglossaryentry
 [firstsuffix={gas gangrene}]
 {cperf}{clostridium,perfringens}
\multiglossaryentry
 [% default options for this multi-entry set
  firstsuffix=tetanus,% suffix on first use of multi-entry set
  textformat=textbf% default formatting in \mgls-like commands
 ]
 {ctet}{clostridium,tetani}

% custom separator that checks the pre-separator element's category
\renewcommand*{\glscombinedsep}[2]{%
 \glsifcategory{#1}{genus}%
 {\ifglshasshort{#1}{\ifglshasshort{#2}{\space}{~}}{\space}}%
 {\space}%
}

\begin{document}
\section{Regular Use}
First use: \mgls{cbot}.

Next use: \mgls{cbot}.

First use: \mgls{ctet}.

\section{Unset/Reset}

Unset all elements (not multi-entry) initially: \mgls[unsetall]{cperf}.

Reset all elements (not multi-entry) initially: \mgls[resetall]{cperf}.

Next use: \mgls{cperf}.

Reset multi-entry (not individual elements): \mglsreset{cperf}\mgls{cperf}.

\section{Formatting}
Change default text format to \texttt{underline}.

\subsection{One hyperlink over all}

Reset multi-entry and override entire textformat:
\mglsreset{ctet}\mgls[setup={hyper=allmain,textformat=underline}]{ctet}.

Override entire textformat: \mgls[setup={hyper=allmain,textformat=underline}]{ctet}.

Override main textformat: \mgls[setup={hyper=allmain},main={textformat=underline}]{ctet}.

Override other textformat: \mgls[setup={hyper=allmain},others={textformat=underline}]{ctet}.

\subsection{Individual hyperlinks}

Override entire textformat: \mgls[setup={hyper=individual,textformat=underline}]{ctet}.

Override main textformat: \mgls[setup={hyper=individual},main={textformat=underline}]{ctet}.

Override other textformat: \mgls[setup={hyper=individual},others={textformat=underline}]{ctet}.

\subsection{Only hyperlink main}

Override entire textformat: \mgls[setup={hyper=mainonly,textformat=underline}]{ctet}.

Override main textformat: \mgls[setup={hyper=mainonly},main={textformat=underline}]{ctet}.

Override other textformat: \mgls[setup={hyper=mainonly},others={textformat=underline}]{ctet}.

\printglossaries
\end{document}