<unk>  is when something develops resistance to several substances that have a similar mechanism of action. For example, say a certain type of bacteria develops resistance to one antibiotic. That bacteria then also has resistance to several other antibiotics that target the same protein or use the same route to get into the bacterium. A real example of<unk>  occurred for nalidixic acid and ciprofloxacin, which are both quinolone antibiotics. When bacteria developed resistance to ciprofloxacin, they also developed resistance to nalidixic acid because both drugs work by inhibiting topoisomerase, a key enzyme in DNA replication. Due to<unk> , antimicrobial treatments like phage therapy can quickly lose their efficacy against bacteria. This makes<unk>  an important consideration in designing evolutionary therapies.
Cross-resistance
Drug resistance
Resistance 
Antigenic variation
Seroconversion
Cross-reactivity
Microbial synergy
Antibiotic synergy