In a catheter-associated urinary tract infection scenario, the organism shows resistance to cephalosporins. Which antibiotic class is most likely to be ineffective?

• A. Cephalosporins
• B. Macrolides
• C. Aminoglycosides
• D. Tetracyclines

Answer: (A)

When an organism causing a catheter-associated UTI is resistant to cephalosporins, that antibiotic class is not reliable for treatment. Cephalosporins are beta-lactam antibiotics, and resistance often arises from mechanisms like beta-lactamase production (including ESBLs or AmpC enzymes) or changes in targets that blunt the whole class of cephalosporins. Because these mechanisms typically affect multiple drugs within that class, you wouldn’t rely on cephalosporins to clear the infection.

The other classes listed are distinct families with different mechanisms of action, so cephalosin resistance doesn’t automatically imply they’re ineffective. Macrolides generally have limited activity against the common urinary pathogens, and while aminoglycosides and tetracyclines can be active against some CAUTI pathogens, their use depends on the specific organism’s susceptibility and tissue penetration. In practice, you’d choose an alternative class based on susceptibility data rather than assume those will be ineffective simply because cephalosporins failed.