Multiple choice Which of the following is mismatched? Syphilis-Treponema pallidum Fireblight of apples-Erwinia amylovora Citrus canker-Phytomonas citri Plague-Clostridium tetani Reveal answer Fill a bubble to check yourself D Correct answer Explanation Plague is caused by the bacterium Yersinia pestis, not Clostridium tetani (which causes tetanus).