Final answer:
Carbapenem-resistant Enterobacteriaceae (CRE) have acquired genes that code for enzymes, which provide resistance to carbapenem antibiotics. Therefore, the correct option is a.
Step-by-step explanation:
Carbapenem-resistant Enterobacteriaceae (CRE) have acquired one of three genes that code for enzymes, which provide resistance to carbapenem antibiotics. These enzymes, called carbapenemases, are broad-spectrum β-lactamases that inactivate all β-lactams, including carbapenems.
For example, one type of carbapenemase gene is the KPC (Klebsiella pneumoniae carbapenemase) gene, which is commonly found in Enterobacteriaceae and confers resistance to multiple classes of antibiotics including carbapenems.