Update 1.abortive-infection.md

Add title in general concept and change titles size

content/2.general-concepts/1.abortive-infection.md

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   - doi: 10.1038/s41579-023-00934-x
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+# Abortive Infection
 
 The term abortive infection was coined in the 1950s :ref{doi=10.1128/jb.68.1.36-42.1954} 
 to describe the observations that a fraction of the bacterial population did not support phage replication.