What characteristic distinguishes second generation cephalosporins from first generation?

Second generation cephalosporins are distinguished from first generation cephalosporins primarily by their increased activity against gram-negative bacteria. This enhanced spectrum is due to structural modifications made to the cephalosporin molecule, which allow it to penetrate the outer membrane of gram-negative bacteria more effectively. As a result, second generation cephalosporins, such as cefuroxime and cefoxitin, show better efficacy against organisms like Escherichia coli, Haemophilus influenzae, and Klebsiella species compared to their first generation counterparts.

The other choices do not accurately represent the distinguishing features of second generation cephalosporins. First generation cephalosporins, like cephalexin and cefazolin, are generally more effective against gram-positive bacteria, whereas second generation cephalosporins have a broader spectrum that includes improved activity against gram-negatives but reduced efficacy against gram-positives. Resistance to beta-lactamases can vary among these generations, and while some second generation cephalosporins may have improved stability against certain beta-lactamases, this is not a universal characteristic. Finally, while oral bioavailability can differ among various cephalosporins, it is