Final answer:
An organism that is resistant to three or more different antimicrobial agents is known as a multidrug-resistant (MDR) organism or superbug. These pathogens have multiple resistance mechanisms and pose a significant challenge to healthcare treatments.
Step-by-step explanation:
The term that best describes an organism that is resistant to three or more different antimicrobial agents is a multidrug-resistant (MDR) organism, also known colloquially as a superbug. These superbugs harbor multiple resistance mechanisms, making them formidable foes against a range of antimicrobial agents. While cross resistance refers to a single resistance mechanism conferring resistance to several drugs, the term 'superbug' applies more broadly to microbes that are resistant to multiple antimicrobial agents due to various resistance mechanisms.
Pathogens that can resist more than one type of antimicrobial treatment pose a severe challenge to healthcare as they can escape conventional forms of antimicrobial therapy, potentially leading to higher rates of morbidity and mortality. An example of MDR pathogens is multidrug-resistant Mycobacterium tuberculosis (MDR-TB), which is resistant to the drug combination typically prescribed for tuberculosis treatment.