tabular content spilling over right column margin. What's going on here? How can I fix it?

\documentclass[a4paper,12pt]{article} \author{Peter Cao} \date{} \usepackage[font=small,labelfont=bf,tableposition=top]{caption} %apparently needs to come first or options clash with other packages will occur \usepackage[x11names,dvipsnames]{xcolor} %for use in color links \usepackage[hyphens]{url} \usepackage[colorlinks=true,linkcolor=Blue4,citecolor=blue]{hyperref} \usepackage[hyphenbreaks]{breakurl} \usepackage{a4wide} \usepackage{graphicx} \usepackage[version=3]{mhchem} \usepackage[T1]{fontenc} %for > and < in text mode \usepackage{tikz} \mhchemoptions{arrows=pgf-filled} \usepackage{booktabs} %for top, middle and bottomline \usepackage{multirow} %multi column and row spanning \usepackage{amsmath} \usepackage{cite} \usepackage{multirow} \usepackage{tabularx} \usepackage{siunitx} \usepackage{fancyhdr} %\usepackage{fancyheadings} seems to be obsoleted by fancyhdr \usepackage{comment} \usepackage{multicol} \usepackage{lastpage} \newcommand{\ignore}[1]{} %a null macro which gobbles up comments, and thus acts as a tool for in-line commenting. \usepackage{blindtext} \begin{document} \begin{multicols}{2} \subsection*{Results} {\small \begin{tabularx}{\columnwidth}{l | c | c} \toprule Characteristic & \multicolumn{2}{c}{Result}\\ \cmidrule(l){2-3} & Seaweed isolate & Coral isolate \\ \cmidrule(r){1-1} \cmidrule(l){2-3} Cell shape & Rod & Rod\\ Gram stain & $-$ & $-$\\ Oxidase & $+$ & $-$\\ Catalase & $+$ & $-$\\ MSA & Growth & No growth\\ Anaerobic & Growth (weak) & No growth\\ Motility & & \\ Indole production & & \\ Hugh \& Leifsons & & \\ \bottomrule \end{tabularx} } \blindtext \end{multicols} \end{document} Updated version demonstrating shrinkage issues:
\documentclass[a4paper,12pt]{article} \usepackage{booktabs} %for top, middle and bottomline \usepackage{multirow} %multi column and row spanning \usepackage{multicol} \usepackage{graphicx} \begin{document} \begin{multicols}{2} \subsection*{Results} {\noindent \resizebox{\columnwidth}{!}{% \begin{tabular}{@{} l c c @{}} \toprule Characteristic & \multicolumn{2}{c}{Result}\\ \cmidrule{2-3} & Seaweed isolate & Coral isolate \\ \midrule Cell shape & Rod & Rod\\ Gram stain & $-$ & $-$\\ Oxidase & $+$ & $-$\\ Catalase & $+$ & $-$\\ Anaerobic & Growth (weak) & No growth\\ Motility & & \\ Indole production & & \\ Hugh \& Leifsons & & \\ MSA & Growth & No growth\\ Growth in absence of salt & & \\ Colony pigmentation & White & White \\ \bottomrule \end{tabular} } } \end{multicols} \end{document} 


