title: How to italicize part (one or two words) of an axis title
body: <p>Is there any way to change the style of part of an axis title while keep the rest part unchanged? In my case, How could I italicize<br>
  "bacteria X" in the y-axis title? To my knowledge, the command <code>theme(axis.title.y=element_text(face="italic"))</code> can only change the whole y-aixs title, is it?</p>
  
  <pre><code>ggplot(fig1,aes(x=cf,y=Freq,fill=Var1)) +
  geom_bar(stat="identity") +
  labs(x="Groups",y="No. of bacteria X isolates with corresponding types",fill="Var1") +
  theme(axis.title.y=element_text(face="italic"))
  </code></pre>